Seismic liquefaction features in the Kashmir Karewas: Natural seismograms of the paleoearthquakes

Journal Pre-proof Seismic liquefaction features in the Kashmir Karewas: Natural seismograms of the paleoearthquakes Rais Ahmad Khan PII:

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DOI:

https://doi.org/10.1016/j.jsg.2019.103949

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SG 103949

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Journal of Structural Geology

Received Date: 17 March 2019 Revised Date:

23 November 2019

Accepted Date: 27 November 2019

Please cite this article as: Khan, R.A., Seismic liquefaction features in the Kashmir Karewas: Natural seismograms of the paleoearthquakes, Journal of Structural Geology (2019), doi: https:// doi.org/10.1016/j.jsg.2019.103949. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

1 2 3 4

Seismic liquefaction features in the Kashmir Karewas: Natural seismograms of the paleoearthquakes

5

*Corresponding author,Email:[email protected],Mobile:+919906416576

6 7

Rais Ahmad Khan

Abstract

8

Karewas occur within the seismically active Kashmir Valley. Natural seismograms in the

9

form of seismites exist within the Karewa sediments. Seismites were identified and characterized

10

to know their genesis. The magnitude of the paleoearthquakes were ranging from 6.0-7.4 with

11

paleointensity

12

63 mm. PGA computed for the paleoearthquakes were ranging from 0.18g to 0.77g using cyclic

13

stress method. PGA computed for the simulated historical and instrumental earthquakes using

14

GMPE were of the order of 1.11g, 0.86g and 0.83g. FS, and

15

sediments of the source stratum near the paleoliquefaction sites are still liquefiable and have

16

retained their liquefaction potential since Early Pleistocene. FS values of the paleoearthquakes

17

indicate that the geological conditions were appropriate to liquefy sediments as FS=1 and are still

18

susceptible to liquefaction as advocated by the FS values of the simulated historical and

19

instrumental earthquakes. Empirical relationships that account for the age of soil deposits show

20

significant influence on PGA values of the paleoearthquakes and no effect on FS values of the

21

paleoearthquakes as FS=1. However, significant influence was observed on FS values of the

22

historical and instrumental earthquakes.

23 24

Keywords: Seismites; Paleomagnitudes; Paleointensity; Liquefaction severity index; Peak

25

ground acceleration; Factor of safety.

= 8.5. LSI values computed for the paleomagnitudes were ranging from 16 to

26

1

values indicate that the

27

1. Introduction

28 29

The entire Himalayan belt is prone to earthquake hazard and has experienced infrequent

30

but damaging earthquakes in the past (Fig.1). The instrumental (NDMA, 2010), historical

31

(Bilham, 2004; Iyengar et al., 1999; Ahmad et al., 2009; Ahmad et al., 2015; Rajendran et al.,

32

2013) and paleoseismic record of earthquakes attest to how vulnerable Himalayan belt is to

33

earthquakes. The paleoseismic record of Himalayan earthquakes is preserved in the Himalayan

34

sediments in the form of seismites. During the last two decades, seismites have been reported

35

from various locales along the entire Himalayan belt by various researchers (Table.1).

36 37

Seismites are the sedimentary signatures of the paleoearthquakes. The study of seismites

38

is of great importance because they provide information regarding soft sediment deformation,

39

paleoseismicity and liquefaction hazard. The study of seismites plays an important role in

40

understanding the characteristics of paleoearthquakes and estimating seismic hazard in regions

41

that experience infrequent but damaging earthquakes (Green et al., 2005). There are two

42

approaches used in paleoseismology to determine the paleoseismicity of the region. One is the

43

direct use of faults and other is the use of paleoliquefaction features. This study was carried out

44

by use of paleoliquefaction features to determine paleoseismicity rather than the faults. Nobody

45

knows when and where the paleoearthquakes struck. The only evidence of paleoearthquakes

46

preserved in the geological record is paleoliquefaction features. So using the paleoliquefaction

47

features to determine the paleoseismicity of the region is the best approach.

48 49

The aim of this study is to identify and characterize seismites and to assess the

50

magnitudes, intensity, peak ground acceleration (PGA) and liquefaction severity index (LSI) of

51

the paleoearthquakes. This study also aims to know whether diagenetic/or pedogenic processes 2

52

(aging effects) have retained or diminished the liquefaction potential of the source stratum near

53

paleoliquefaction features.

54 55

2. Seismites: Natural seismograms of the paleoearthquakes

56 57

Seismites are the sedimentary deformational structures formed because of earthquake-

58

induced liquefaction. Seilacher (1969) introduced the term “Seismites”. The study of seismites is

59

of great importance as it is entirely a modern approach in the field of paleoseismology (Sims,

60

1973, 1975; Hempton & Dewey, 1983; Ringrose, 1989; Obermeier, 1996; Moretti and Van

61

Loon, 2014). Sand dikes preserved in the Quaternary and Holocene sediments are useful tools to

62

determine seismic parameters of the paleoearthquakes. Therefore, seismites are great concern for

63

geologist, seismologist and geotechnical engineers (Malkawi and Alawneh, 2000).

64 65

Whenever an earthquake occurs, everyone is interested to know what was its magnitude,

66

intensity, peak ground acceleration and where was its seismic source. All this information is

67

obtained

68

paleoseismologists are also interested to know these seismic parameters for paleoearthquakes. To

69

obtain this information for paleoearthquakes, liquefaction features in the form of sand dikes

70

prove potential tools. In this study, all these parameters have been obtained using

71

paleoliquefaction features. Therefore, seismic liquefaction features are the natural seismograms

72

of the paleoearthquakes.

by

the

analysis

of

seismograms

of

instrumental

earthquakes.

Similarly,

73 74

Quaternary and Holocene sediments have been studied extensively by researchers all

75

around the world for “Seismites” during the last five decades as they have potential applicability

76

in estimating;

77 3

78 79

1. Possible seismic sources of the paleoearthquakes (Tuttle, 2001; Green et al., 2005; Khan and Shah, 2016).

80 81

2. Magnitudes of the paleoearthquakes (Martin and Clough, 1994; Munson et al., 1997; Tuttle,

82

2001; Hu et al., 2002; Gonzalez de Vallejo et al., 2003; Green et al., 2005; Perucca et al.,

83

2009; Khan and Shah, 2016 ).

84 85 86 87 88

3. Peak ground acceleration of the paleoearthquakes (Martin and Clough, 1994; Hu et al., 2002; Khan and Shah, 2016).

3. Geological and stratigraphic setting of the Study Area

89 90

Karewas are the soft, unconsolidated, aeolian, glacial and fluvio-lacustrine sedimentary

91

deposits of Kashmir Valley. Karewa sediments occur in the form of terraces, plateaus, mounds

92

and vast table lands. Karewa deposits are composed of sand, silt, clay, conglomerate and lignite.

93

“Karewa” is the term, which in Kashmiri dialect means an elevated table land (Bhat, 1989).

94 95

The “Karewas” are located within the seismically active Kashmir Valley in the North-

96

West Himalayas, India (Fig. 2A). Kashmir Valley is bounded by Great Himalayan Range in the

97

east-northeast, Saribal Range in southeast, Pir Panjal Range in south-southwest and Kaznag

98

Range in northwest (Fig. 2, A1). The Valley of Kashmir lies between Panjal Thrust and Zanskar

99

Thrust (Fig. 2, A2).

100 101

Plio-Pleistocene fluvio-lacustrine Karewa deposits are scattered throughout the Kashmir

102

Valley (Fig. 3). The present study has been carried out along southwest Karewas of Kashmir

103

Valley. The study area (Subset of Karewas, Fig. 3) extends for about 50 kms in length from Koil

104

Wudder in district Pulwama and Pattan Karewas in district Baramulla with width ranging from 4

105

15-20 Kilometers. The study area comprises four lithostratigraphic units of Karewas (i.e.,

106

Methawoin Member, Shupiyan Member, Pampur Member and Dilpur Formation) covering an

107

area of approximately 800

108 109

4. Seismites in the Karewas

.

110 111

Karewa sediments contain sedimentary structures interpreted as seismites. Six variants of

112

seismites (Fig.4) were identified at nine locations (Fig.5) in the Karewas of Kashmir Valley. The

113

seismites were observed within the Pampur Member and Methawoin Member (Fig.6). The

114

observed seismites were characterized (Table. 2) to know their genesis and to determine seismic

115

parameters of the paleoearthquakes.

116 117

5. Timing of the formation of Seismites

118 119

The timing of the formation of observed seismites is estimated on the basis of occurrence

120

of seismites within the Pampur Member and Methawoin Member (Fig 6). Methawoin Member is

121

estimated to be 2.1 ± 0.2 Ma (Fig. 6). Therefore, Methawoin Member is Early Pleistocene in

122

age. Pampur Member is also Early Pleistocene in age based on the fossil record of Elephus

123

hysudricus and other vertebrate mammal fossils in the basal part of the Pampur Member (De

124

Terra and Patterson, 1939). Therefore, seismites under study are roughly estimated to be early

125

Pleistocene in age.

126 127

6. Geotechnical investigation of the paleoliquefaction sites exhibiting liquefaction features

128 129

Standard penetration tests were carried out at the paleoliquefaction sites (Pattan, Parigam

130

and Narigund) to generate geotechnical data of the source stratum (Table 3). The locations of the

131

standard penetration test boreholes are shown in (Fig.5). The obtained geotechnical data was 5

132

analysed to compute relative density, shear wave velocity, peak ground acceleration, factor of

133

safety and magnitudes of paleoearthquakes.

134 135

7. Location of the seismic source

136 137

Locating the exact seismic source of the paleoearthquakes is an impossible task. In “Back

138

Analysis” of the paleoliquefaction features size, pattern, density, systematic trend like

139

attenuation of dikes is used for estimating the seismic source of the paleoearthquakes.

140 141

In some geological settings, the occurrence of paleoliquefaction features are abundant

142

while in other geological settings they are sparse. In geological settings, where paleoliquefaction

143

features are abundant it is easy and convenient to predict systematic trends like attenuation of

144

paleoliquefaction features to locate the possible seismic source.

145 146

The geological settings where paleoliquefaction features are sparse like in this study, it is

147

difficult to predict systematic trends. The only viable tool to locate the possible seismic source is

148

to make an reasonable assumption based on the spatial pattern of dikes in planer view. The size

149

and spatial distribution of paleoliquefaction features reflect the source region of a

150

paleoearthquake and the largest liquefaction features define the epicentral area of a

151

paleoearthquake (Tuttle, 2001). In this study, the largest paleoliquefaction feature was observed

152

to be centered near Badipora (Fig. 7). Therefore, it is assumed that the Badipora was the seismic

153

source of the paleoearthquakes.

154 155 156 157 158 159 160 6

161

8. Magnitudes of the paleoearthquakes

162 163

Energy stress method and the methods based on empirical relationships given by

164

Ambraseys and Jackson (1998) and Gutenberg and Richter (1956) have been used in the present

165

study to determine the magnitude of the paleoearthquakes.

166 167

8.1. Energy stress method

168 169 170 171 172

Energy stress method has been used in this study to determine the magnitude of a paleoearthquake using the empirical equation given by Obermeier and Pond, 1999 as = × log [1.445 ×

× (

)

!."!

]

(1)

173 174

Where; “M” = Moment magnitude, “R” = Assumed hypocentral distance and (

175

Corrected SPT N-Value for field procedures to an average energy ratio of 60% of the theoretical

176

free-fall SPT hammer energy and overburden stress of the source stratum. Hue et al. (2002) also

177

used energy stress method to estimate magnitudes of paleoearthquakes in the South Carolina

178

Coastal Plain.

179 180

8.2. Magnitude of the paleoearthquake as a function of intensity and hypocentral distance

)

=

181 182

The magnitude of the paleoearthquake using intensity and hypocentral distance of the

183

paleoearthquake has been calculated using the empirical relationship given by Ambraseys and

184

Jackson (1998) as

185 186

= −1.74 + 0.66 × + 0.0015 ×

+ 2.26 × )*+

187 188 189 7

(2)

190

Where; “M”=Magnitude, “R”= hypocentral distance and = intensity.

191 192

8.3. Magnitude of the paleoearthquake as a function of the intensity of paleoearthquake

193 194 195

The magnitude of the paleoearthquake using intensity of the paleoearthquake has been calculated using the empirical relationship given by Gutenberg and Richter (1956) as

196

-

= 1 + 2 × , . /

197 198 199 200 201 202

(3)

Where; “M”=Magnitude," " = Intensity. 9. Estimated paleointensity

203 204

The paleointensity with reference to this study is defined as the effect of seismic ground

205

shaking observed in the form of paleoliquefaction features within the prehistoric liquefied field

206

as a result of paleoearthquakes. Intensity at a particular location is assessed on the basis of the

207

observed property damage by an earthquake. It is unlikely there would be any existence of

208

anthropogenic structure at the time of the pre-historic earthquake. If exist, it is impossible to be

209

preserved till date for the assessment of paleointensity. Therefore, it is not possible to assess the

210

paleointensity of the earthquakes using anthropogenic structures. Liquefaction features (dikes)

211

can preserve within the geological records for the millions of years after their formation and can

212

be used to assess the intensity of the paleoearthquakes. In this study, paleointensity has been

213

calculated using the empirical relationship given by Galli and Ferreli (1995) as

214 215

1

= 2

. 34 .

(5)

(4)

216

8

1

= Intensity (Mercalli– Cancani– Sieberg (MCS) − Scale and E = Epicentral distance

217

Where;

218

(Kms).

219 220

10. Liquefaction severity index of the paleoearthquakes

221 222

The LSI model (Youd and Perkins, 1987) relates the amplitude of ground deformations,

223

distance, and earthquake magnitude as follows:

224 225

log(LSI) = −3.49 − 1.86 ∗ )*+ + 0.98 ∗

226 227

K

(5)

Where; LSI=maximum amplitude of ground failure displacement (inches or mm), R is

228

the epicentral distance (kms), M is the earthquake moment magnitude. LSI cannot exceed 100.

229 230

11. Peak ground acceleration of the paleoearthquakes

231 232

Cyclic stress method has been used in this study to determine the peak ground

233

acceleration of the paleoearthquakes using in-situ SPT based geotechnical data (Table 3) of the

234

source stratum near the paleoliquefaction sites by the following equation

235 LMN = 236 237

0.65 ∗

O

P ,PˊQR / ∗ ,U TV/ ∗ ,W / QR X

Where; O

(6)

= Cyclic resistance ratio and is defined as the liquefaction resistance

238

(capacity) of the soils against liquefaction. In this study, CRR has been calculated using the

239

procedure given by Idriss and Boulanger (2006) as

240 241 242 9

243 244 245 246 247 248 249 250 251

CRR = exp \ (

)

cd

(]^ )!"_`

= (

(]^ )!"_`

3.

+,

)

+ ∆ (

/ −,

(]^ )!"_` .

(]^ )!"_` 3

/ +,

a.3

/ − 2.8b

)

(8)

∆ (

) =SPT-N value adjusted to an equivalent clean sand value and is given as

∆ (

)

i.j

= 2fg h1.63 + Vk4

(7)

a.j

− ,Vk 4 . / l

.

(9)

0.65=Factor used to convert the peak cyclic shear stress ratio to a cyclic stress ratio that is

252

representative of the most significant cycles over the full duration of loading, σno = Total vertical

253

stress, σˊno = Effective vertical stress, p5 = Stress reduction factor and has been calculated using

254

the equation given by (Idriss, 1999; Golesorkhi, 1989) as

255 256

qr (p5 ) = s(t) + u(t) ∗

(10a)

257

s(t) = −1.012 − 1.126 sin ,

258

u (t) = 0.106 + 0.118 sin ,

259 260 261 262 263 264 265 266 267 268 269 270 271 272

v

.j

v

. w

+ 5.133/

(10b)

+ 5.142/

(10c)

Where; Z=Depth in metres and M is the magnitude of earthquake under consideration.

MSF = Magnitude scaling factor and has been calculated in this study using empirical relationship given by (Seed and Idriss, 1982) as

xy = Where;

.a

(11)

(Uz )

is the magnitude of earthquake under consideration. P=

Overburden correction factor for cyclic stress ratios and has been calculated using

the equation given by (Boulanger and Idriss 2014) as 10

273 P

274

275

Pˊ

= 1 − OP In , { Q/ ≤ 1.1

(12a)

|

OP =

w.iz .aa ~(]^ )!"

276 277

≤ 0.3

(12b)

Where; •ˊ€ = Effective vertical stress, g• = Atmospheric pressure = 100 kpa,(

)

=

278

Corrected SPT – N value.

279 280 281 282 283

(

284

of 60% of the theoretical free-fall SPT hammer energy. In this study, N values were corrected,

285

using the equation given by (Coduto, 1994).

286 287 288 289 290

)

= O] ×

(13)

Where;

( )

=

= SPT-N values corrected for the field procedures to an average energy ratio

‚ƒ ×k„ ×k… ×k† ×]

(14)

.

Where; ‡ˆ = Hammer Efficiency correction factor, O‰ = Borehole diameter correction

291

factor, O = Sampler correction factor, OŠ = Rod length correction factor,

292

N Value.

293 294

O] = Factor to normalize N-values to a common reference effective over burden stress

295 296 297 298 299 300 301

•

‹Œ

•ˊŽ•

/ ≤ 1.7 where s = 0.784 − 0.0768~(

(

)

O] = ,

)

= Measured SPT-

(15)

& O] are interdependent as evident from equation (13) and (15). In this regard, an

iterative procedure is followed to determine (

)

302

11

and O] .

303 304 305 306 307

12. Liquefaction potential analysis of the susceptible sediments near paleoliquefaction sites Paleoliquefaction features under study were formed by the process of liquefaction within

308

the Karewa sediments. So, it is essential to know what were the appropriate ‘ˆ’“ -M

309

combination of the paleoearthquakes that generated the observed paleoliquefaction features on

310

the one hand. On the other hand, it is necessary to know whether the paleoliquefaction sites near

311

the paleoliquefaction features have retained or diminished their liquefaction potential since Early

312

Pleistocene. Therefore, it is necessary to compute the liquefaction potential of the liquefied beds

313

(source stratum) near the paleoliquefaction features. In this regard, Earthquake data of paleo,

314

historical and instrumental earthquakes were simulated to determine the liquefaction potential of

315

the source stratum near the paleoliquefaction features within the Methawoin Member and

316

Pampur Member.

317 318

The earthquake data of paleoearthquakes were simulated to know the liquefaction

319

potential of the source stratum at the time of the formation of the observed paleoliquefaction

320

features. It is evident that Kashmir Valley is seismically active region and high magnitude

321

earthquakes are expected in this region. Seismic record of Kashmir Valley reveal that the

322

magnitudes of historical and Instrumental earthquakes were ranging from (M=6.0 to M=8.5).

323

Therefore, historical earthquakes of 1555 AD (M=8.5), 1778 AD (M=7.7) and instrumental

324

earthquake of 2005 AD (M=7.6) were simulated to know whether the sediments of source

325

stratum have retained or diminished the liquefaction potential since Early Pleistocene.

326 327

The earthquake data of paleoearthquakes, historical earthquakes (1555 AD & 1778 AD

328

Kashmir Earthquakes) and instrumental earthquake (2005 AD Kashmir Earthquake) were used in

329

the present study to compute PGA,MSF and stress reduction factor (p5 ) values. The obtained 12

330

values were further incorporated with the geotechnical data (Table. 3) of the source stratum near

331

the paleoliquefaction sites to compute Factor of Safety “FS” against liquefaction at Pattan,

332

Parigam and Narigund. The liquefaction potential “LP” was determined by mean of factor of

333

safety.

334 335

yx =

kŠŠ

(16)

”•–—˜™!."š›.œ,X™^

336 337

Where; FS = Factor of safety;

K=

Moment magnitude; • = 1 = overburden pressure

338

σˊno of 1 atmosphere. Factor of safety is one of the important parameter for predicting the

339

occurrence and non-occurrence of liquefaction in soil/sediments. Liquefaction is expected to

340

occur if yx values fall within the Group 1 to 3 and unexpected to occur if yx values fall within

341

the Group 4 to 5 (Table. 4). CRR= Cyclic resistance ratio and has been computed in this study

342

using the empirical relationships (equation 7, 8 and 9) proposed by (Idriss and Boulanger, 2006).

343

CSR= Cyclic stress ratio. CSR has been computed in this study by the expression given by

344

(Idriss and Boulanger, 2006) as

345 346

CSR Už

. zw.a,Pž

= 0.65 ∗ ,

•Ž•

•ˊŽ•

/ ∗ aŸ• ∗

¡¢

£•¤

∗

(17)

¥¦

347 348

Where; except aŸ• all the other parameters (i.e., 0.65, σno ,σˊno ,p5 , MSF and

349

same and has been computed in a similar manner as the parameters computed in (equation 6).

350

The aŸ• = Peak ground acceleration in gʹs and has been calculated in this study using the

351

empirical equation given by (Kumar et al., 2017) as

352 353

log(N) = −1.497 + 0.3882

− 1.19 ∗ )*+(§ + 2

354

13

. wj ∗U

)

P)

(18)

are

355

Where; log(N) = peak ground acceleration in (g), § =hypocentral distance (km) and M=

356

magnitude of historical and instrumental earthquakes used in this study.

357 358

13. Effect of soil aging on PGA values of the Paleoearthquakes and FS values of Paleo,

359

Historical and Instrumental Earthquakes near the paleoliquefaction Features

360 361

Sedimentary deposits experience the process of aging with the passage of time since their

362

deposition. The effect of soil aging increases the strength and stiffness in sediments. Therefore,

363

decreases the liquefaction resistance of sediments. The sedimentary deposits of Pampur Member

364

and Methawoin Member are Early Pleistocene in age (Fig. 6). Based on the age of these two

365

lithostratigraphic Members of Karewas the sediments of Pampur Member and Methawoin

366

Member should have gained the strength and resistance to liquefaction. On the basis of this fact,

367

it is essential to know whether the liquefied beds have retained or diminished their liquefaction

368

potential. Therefore, it is necessary to compute the effect of soil aging on PGA and FS values of

369

the liquefied beds (source stratum) near the paleoliquefaction features.

370 371

The effects of soil aging on PGA values of the paleoearthquakes were assessed by the ¨Š )

372

substitution of CRR with deposit resistance-corrected cyclic resistance ratio (O

373

wave velocity based cyclic resistance ratio (CRR ©… ) in equation 6. The effects of soil aging on

374

FS values of the paleoearthquakes were assessed by the substitution of PGA values in equation

375

17 computed by the substitution of CRR with O

376

substitution of CRR with O

377

on FS values of simulated historical and instrumental earthquakes were assessed by the

378

substitution of CRR with O

¨Š

¨Š

¨Š

and shear

and CRR ©… in equation 6 and the

and CRR ©… in equation 16. However, the effects of soil aging

and CRR ©… in equation 16.

379 14

380

13.1. Deposit resistance-corrected cyclic resistance ratio

381 382 383

The deposit resistance-corrected cyclic resistance ratio (O

¨Š )

has been calculated in

384

this study using the empirical relationship proposed by (Hayati and Andrus, 2008) as

385 386 387 388 389

O

390

empirical relationships (equation 7, 8 and 9) proposed by (Idriss and Boulanger, 2006).

¨Š

∗

¨Š

(19)

Where; CRR= Cyclic resistance ratio and has been computed in this study using the

391 392 393

=O

¨Š =

strength gain factor for correcting influence of age, cementation and

compressibility of soils using empirical relationship given by (Hayati et al.,2008) as

394 395

¨Š

= 0.17 ∗ q*+ (ª) + 0.83

396 397

Where;

¨Š =

(20)

strength gain factor to correct for influence of age, cementation and/or

398

compressibility of soils and (t) = time since initial deposition in years.

399 400

13.2. Shear wave velocity based cyclic resistance ratio

401 402 403

The Shear wave velocity based cyclic resistance ratio (CRR©… ) is calculated using empirical relationship proposed by (Andrus et al., 2004) as

404 405 406 407 408 409

O

=

xy ∗ \ 0.022 ∗ ,

WŒ^ ∗ «…^

/ + 2.8 h

∗ z(W ∗ « ) «…^ Œ^ …^

−

∗ «…^

lb ∗

’

(21)

Where; MSF = Magnitude scaling factor and has been calculated in this study using empirical relationship (equation 11) given by (Seed and Idriss, 1982).

410

15

’ =

411

Correction factor for high

values caused by aging and its suggested average

412

value of (0.61) proposed by (Ohta and Goto, 1978) and (Rollins et al., 1998a) for Pleistocene

413

soils has been used in this study as mentioned in (Andrus et al., 2004, p, 295). The use of

414 415

’ value

assumed value for the Narigund site in this study in terms of their estimated age.

416 417 418

= 0.61 for the Pattan and Parigam sites act as best fit value but serves as an estimated

= overburden stress-corrected shear-wave velocity and has been computed in this study using empirical relationship proposed by (Kayen et al., 1992; Robertson et al., 1992) as

419

=

420 421 422 423

d

¬

∗ ,PŒ´ /

. a

Q

Where;

.a

∗ , W´ /

.

a

d

= Shear wave velocity (m/s),L’ = Atmospheric pressure = 100 kpa, •€´ = Total

Effective vertical stress in kPa,

424 425

d

(22)

"

´

= coefficient of effective earth pressure (

´

= 0.5).

= Shear wave velocity. It is one of the most widely used parameter in earthquake

426

engineering (Wang and Wang, 2016). Shear wave velocity is used for classifying soil types, site

427

characterization (Table 5), site-specific amplification factor and computing liquefaction potential

428

(Hanumantharao and Ramana, 2008; Jhinkwan and Jain, 2016; Wang and Wang, 2016). In this

429

study, shear wave velocity has been computed using the empirical relationship proposed by

430

(Hanumantharao and Ramana, 2008) as

431 432 433 434 435 436 437 438 439

d

= 79.0 ∗

.3 3

/ for (Sand),

d

= 86.0 ∗

.3

/ for (Silty sand/Sandy silt),

(23b)

d

= 82.6 ∗

.3

/ for (All Soils),

(23c)

(23a)

Where; N= Standard penetration test N-value obtained near the paleoliquefaction site. 16

∗

440 441 442 443 444 445 446 447 448 449 450

= Limiting upper value of

for occurrence of cyclic liquefaction and has been

computed in this study using the empirical relationship given by (Andrus and Stokoe, 2000) as ∗

= 215 / for y¯r2 O*rª2rª < 5%

(24a)

∗

= 215 − 0.5 ∗ (yO − 5) / for 5% < y¯r2 O*rª2rª < 35%

(24b)

∗

= 200 / for y¯r2 O*rª2rª > 35%

(24c)

’

= Correction factor for the influence of age on CRR and its value has been

451

approximately calculated (Table 6) using empirical relationship (equation 20) given by (Hayati et

452

al., 2008).

453 454

14. Relative density of the source stratum near paleoliquefaction features

455 456

The relative density is defined as the degree of compactness of the sediments (McCalpin,

457

2009). In this study, relative density of the source stratum near the paleoliquefaction sites has

458

been calculated using the equation given by (Idriss and Boulanger, 2006) as

459 460 461 462 463

Š

= ³

(]^ )!"

(25)

3

Where;

Š =Relative

Density,(

) = Corrected SPT – N-value to an average energy

ratio of 60% of the theoretical free-fall SPT hammer energy and overburden stress.

464 465 466 467 468 469 470 471 472 473 474 17

475 476 477 478

15. Results The analysis of deformational structures, geotechnical data and earthquake data reveal that:

479 480

Except an Isolated load cast, all the soft-sediment deformation structures under study

481

suggest their origin to be seismogenic. Liquefaction, hydroplastic deformation and partial loss of

482

strength and density inversions seems to be the most credible trigger mechanisms leading to the

483

development of seismites within the Karewa sediments.

484 485

To assess the magnitude of the paleoearthquakes, the Energy stress method (Obermeier

486

and Pond, 1999) and the methods based on intensity versus hypocentral distance and intensity of

487

the paleoearthquake were used in this study to compute paleomagnitudes.

488 489

Using the Energy stress method, the magnitude of the paleoearthquakes were ranging

490

from 6.0-7.4 (Table 7) when considering (N )

491

distance of 15 km.

of source stratum and assumed hypocentral

492

Using the Ambraseys and Jacksons (1998) empirical relationship, the magnitude of the

493

paleoearthquake was estimated to be Mw=6.6 (Table 7) when considering ( = 8.5 ‘rE =

494

15

495

paleoearthquake was estimated to be Mw=6.7 (Table 7) when considering ( = 8.5).

496 497

).Using the Gutenberg and Richter (1956) empirical relationship, the magnitude of

To assess the intensity of the paleoearthquakes, the relationship given by Galli and Ferreli 1

= 8.5 (Table 8, Fig.8) when considering the

498

(1995) has been used in this study. The result is

499

epicentral distance E = ~34 km between the farthest paleoliquefaction features observed at

500

Pattan and the estimated seismic source centered near Badipora (Fig.7).

18

501

To assess the liquefaction severity index (LSI) for the computed magnitudes of the

502

paleoearthquakes, the relationship given by Youd and Perkins (1987) has been used in this study.

503

Using the LSI model (Youd and Perkins, 1987), the liquefaction severity index (LSI) values of

504

the paleoearthquakes were ranging from 0.63-2.49 inches or 16-63 mm when multiplied by 25.4

505

(Table 9; Fig. 9).

506 507

To assess the stress reduction factor (p5 ) of the paleo, historical and instrumental

508

earthquakes, the relationship given by Idriss, (1999) and Golesorkhi (1989) has been used in this

509

study to obtain p5 values as a function of depth of source stratum and magnitude under

510

consideration (Table 10).

511 512

To assess the magnitude scaling factor (MSF) of the paleo, historical and instrumental

513

earthquakes, the relationship given by Seed and Idriss (1982) has been used in this study to

514

obtain MSF values as a function of the magnitude under consideration (Table 11; Fig. 10).

515 516

To assess the minimum peak ground acceleration of the source stratum near the

517

paleoliquefaction sites for the computed magnitudes of the paleoearthquakes, cyclic stress

518

method has been used in this study. Using the cyclic stress method, PGA values were ranging

519

from 0.18g – 0.77g (Table 12).

520 521

To assess the peak ground acceleration for the historical and instrumental earthquakes,

522

the ground motion prediction equation (GMPE) of the Himalayan regions given by Kumar et al

523

(2017) has been used in this study. The result is PGA = 1.11g and 0.86g for 1555 AD, 1778 AD

524

historical earthquakes and 0.83g for 2005 AD instrumental earthquakes (Table 13).

525

19

526

To assess the CRR of the paleo, historical and instrumental earthquakes, the empirical

527

relationship given by Idriss and Boulanger (2006) has been used in this study. The obtained CRR

528

were of the order of 0.18, 0.26, and 0.59 (Table 14).

529 530

To assess the CSR of the paleo, historical and instrumental earthquakes, the empirical

531

relationship given by the Idriss and Boulanger (2006) has been used in this study. The obtained

532

CSR were of the order of 0.18, 0.26 and 0.59 for the paleoearthquakes (Table 15). The CSR

533

obtained for the simulated 1555 AD,1778 AD and 2005 AD Kashmir Earthquakes were of the

534

order of (1.27, 1.28 and 1.27),(0.86, 0.87 and 0.87) and (0.82, 0.83 and 0.84) respectively (Table

535

16).

536 537

The in-situ SPT based geotechnical data was analysed in terms of factor of safety against

538

liquefaction to know whether the sediments of source stratum near the paleoliquefaction features,

539

(dikes) have retained or diminished the liquefaction potential since Early Pleistocene.

540 541

FS values of the paleoearthquakes indicate that the geological conditions were

542

appropriate to liquefy the susceptible sediments of the source stratum near the paleoliquefaction

543

sites (Table 17; Fig. 11) as the FS = 1. FS values of the simulated historical and instrumental

544

earthquakes also indicate that the liquefied sediments of source stratum near the

545

paleoliquefaction features have not diminished the liquefaction potential since Early Pleistocene

546

as the FS < 1 (Table 18; Fig. 12).

547 548

In-situ SPT based geotechnical data (Table 3,Table 6 and Table 19) of the source stratum

549

near the paleoliquefaction sites were incorporated with the empirical relationships that account

550

for the age of soil deposits like O

¨Š

and CRR ©… .The O

20

¨Š

obtained using empirical

551

relationship proposed by Hayati and Andrus, (2008) were of the order of 0.34, 0.49 and 1.12

552

(Table 14). The CRR ©… obtained using empirical relationship proposed by Andrus et al., (2004)

553

show medium range of CRR values for paleo, historical and instrumental earthquakes (Table 14).

554 555

The effects of soil aging on PGA values of the paleoearthquakes were assessed by the

556

substitution of CRR with O

557

(0.35g to 1.47g) were obtained by the substitution of CRR with O

558

PGA values (0.14g to 0.70g) were obtained by the substitution of CRR with CRR ©… (Table 12).

559

However, no effect of soil aging was observed on the FS values of the paleoearthquakes as FS=1

560

(Table 17, Fig. 11) even after the substitution of CRR with O

561

and substitution of age corrected PGA values (Table 12) in equation 17.

¨Š

and CRR ©… in the cyclic stress method. High PGA values

¨Š

¨Š

and medium range of

and CRR ©… in equation 16

562 563

CSR of the paleoearthquakes show increase in value by the substitution of high PGA

564

values in equation 17 that were of the order of 0.34, 0.49 and 1.12 (Table 15) and the medium

565

ranged CSR values were obtained by the substitution of medium ranged PGA values in equation

566

17 (Table 15).

567 568

The FS values of the simulated historical and instrumental earthquakes also advocate that

569

the sediments of source stratum near the paleoliquefaction sites are still liquefiable (Table 18).

570

The substitution of CRR with O

571

the source stratum near the paleoliquefaction features are still liquefiable as the FS < 1 except at

572

Narigund site where it is slightly above 1 for magnitude 7.7 and 7.6 but still liquefiable (Table

573

18; Fig. 13). The substitution of CRR with CRR ©… in equation 16 also indicate that the liquefied

574

sediments of the source stratum near the paleoliquefaction features are still liquefiable as the FS

575

< 1 (Table 18; Fig. 14).

¨Š

in equation 16 also indicate that the liquefied sediments of

21

The

576

values are also in favour for the liquefaction susceptibility of liquefied sediments

577

of the source stratum near the paleoliquefaction features as indicated by moderate to low range

578

of

579

medium for the paleoliquefaction sites at Pattan (51%), Parigam (63%) and dense (75%) for the

580

paleoliquefaction site at Narigund (Table 3; Fig. 16).

581 582

16. Discussion

values (Table 19; Fig. 15). Further, the relative density (

%) of sands of source stratum is

583 584

Karewas are located in the seismically active Kashmir Valley. Sedimentary processes and

585

seismic activity have affected Karewa sediments of Methawoin Member and Pampur Member

586

leading to the formation of seismites. The occurrence of seismites sandwiched between

587

undeformed beds in the presence of susceptible sediments (sands and silts) satisfies the

588

prerequisite criteria that the observed deformational structures were formed because of seismic

589

activity.

590 591

The observation of deformational structures in the form of dikes and fluid escape

592

structures (Fig. 4, 1-6; 7 and Fig. 5) suggest that they are the product of liquefaction. Dikes under

593

study show clear evidence that the liquefied sediments of the source stratum have intruded into

594

the overlying host stratum because of liquefaction (Fig. 17). Fluid escape structures under study

595

show evidence of inter-grain rearrangement of liquefied sediments by escaping fluids in response

596

to increase in pore pressure due to seismic shock in the presence of permeability barrier (Fig.

597

17).

598 599

22

600

The observation of deformational structures in the form of simple and complex convolute

601

bedding (Fig. 4, 8AB; Fig. 5 and Fig. 18) suggest that they are the product of rapid hydroplastic

602

deformation and partial liquefaction leading to the remoulding of mechanically weak layers. The

603

absence of fluid escape structures suggest that they were formed in response to partial

604

liquefaction and loss of strength in sediments associated with dewatering processes (Lowe, 1976;

605

Collinson, 1994; Bezerra et al., 2001) by seismic shock.

606 607

The observation of deformational structures in the form of Ball-and-Pillow structures,

608

Load casts associated with flame structures and Isolated load casts (Fig. 19) suggest that they are

609

the product of plastic movement whose sense of movement was dominantly vertical (Maltman,

610

1994; Selley, 2000). Such structures are formed under unstable situation where the reduction of

611

shear strength leads to foundering of the denser layer into the less dense layer (Maltman, 1994).

612 613

Ball-and-Pillow structures under study suggest complete detachment of lobes of sand

614

from the original sand bed (Fig. 4, 9; Fig. 5). The orientation of Ball-and-Pillow structures imply

615

downward movement resulted from the foundering of sandy sediments into fine grained silty

616

sediments as demonstrated by the experiments of Kuenen (1958, p.18). The deformation was

617

sudden or catastrophic probably a seismic shock.

618 619

Load casts associated with flame structures (Fig. 4, 10; Fig. 5) suggest penetration of

620

laminated silty sediments wedged in between sandy lobes. This is because of reverse density

621

gradation aided by liquefaction produced by seismic shock leading to the formation of flame

622

structures at sand-silt bed interface (Anketell et al., 1970; Collinson et al., 2006). The occurrence

623

of flame structures sandwiched between undeformed beds and their near vertical orientation

23

624

supports their origin to be seismogenic (Visher and Cunningham, 1981; Collinson and

625

Thompson, 1982; Dasgupta, 1998; Sukhija et al., 1999; Li et al., 2008).

626 627

An isolated load cast observed at Shihanpur (Fig. 4,11;Fig. 5) suggest small-scale vertical

628

readjustment of sandy and silty sediments as the load cast has not lost its original continuity and

629

is attached to its parent sand bed.

630 631

Assumptions play vital and key role in obtaining the seismic parameters (i.e., seismic

632

source, epicentral or hypocentral distance, magnitude, peak ground acceleration and LSI) of the

633

paleoearthquakes using paleoliquefaction features.

634 635

The first and the most vital assumption in the “Back Analysis” of the paleoliquefaction

636

features is the location of seismic source. As it is not possible to locate the exact seismic source

637

of the paleoearthquakes. Therefore, assuming the seismic source based on the size and pattern of

638

paleoliquefaction features is the simplest possible theoretical approach for any paleoliquefaction

639

study. The estimated seismic source of the paleoearthquakes in this study was assumed to be

640

centered near “Badipora” based on the size and pattern of observed paleoliquefaction features.

641 642

The paleoliquefaction features in the form of sand dikes are concentrated in the Budgam,

643

Parigam and Pattan Karewas of Kashmir Valley (Fig.7). Among the six-paleoliquefaction

644

features observed in this study, five were identified in the Budgam and Parigam Karewas except

645

the one paleoliquefaction feature that was observed in the Pattan Karewas. This indicates that the

646

Budgam and Parigam Karewas represents the meizoseismal zone on the basis of spatial

647

distribution of paleoliquefaction features.

648

24

649

The pattern of paleoliquefaction features in the planar view (Fig.7) supports the

650

interpretation of the present paleoliquefaction data that the seismic source of the

651

paleoearthquakes should have remained in and around Budgam and Parigam Karewas. Taking

652

the central point of the Budgam and Parigam Karewas which lies approximately at Badipora as

653

the assumed seismic source of the paleoearthquakes is a reasonable estimation. It is further

654

supported by the presence of largest sand dike within the Budgam and Parigam Karewas.

655

However, the single paleoliquefaction feature observed within Pattan Karewas at Pattan

656

represents the distal paleoliquefaction feature.

657 658

Estimating the seismic source of the paleoearthquakes is not a science based on empirical

659

or experimental evidence but simply the possible explanation based on the size and pattern of

660

paleoliquefaction features. It will be always an impossible task to know where was the seismic

661

source of the paleoearthquakes and whether there was a single or multiple seismic sources of the

662

paleoearthquakes that generated the observed paleoliquefaction features. The use of assumed

663

seismic source is a basic input parameter for computing magnitude, LSI, intensity and epicentral

664

distance of the paleoearthquakes using empirical relationships.

665

If multiple seismic sources are used in the Back Analysis of paleoliquefaction features,

666

there will be infinite number of assumption to be considered as the possible seismic source of the

667

paleoearthquakes especially in the Himalayan region, which is “High” in seismic activity. This

668

will in turn give infinite number of magnitudes, LSI, intensity and epicentral values and the back

669

analysis of paleoliquefaction features will be cumbersome task. It will eliminate the role of

670

paleoliquefaction features in estimating the possible seismic source of the paleoearthquakes.

671

However, assuming the single seismic source estimated on the basis of paleoliquefaction features

25

672

gives reasonable results for the computation of paleoearthquake parameters (i.e., M, PGA, LSI

673

and epicentral distance).

674

Paleoliquefaction features never reveal their exact seismic source of the paleoearthquakes

675

even if dated. This is because dating gives information about the timing of the formation of

676

paleoliquefaction features but not the information about seismic source. However using the size

677

and pattern of paleoliquefaction features is the best method to estimate the possible seismic

678

source of the paleoearthquakes that occurred at the centre of the liquefied field.

679

In this study, the epicentral distance of ~34 km was used as one of the input parameter in

680

empirical relationships given by (Galli and Ferreli, 1995) and (Youd and Perkin 1987) for

681

computing the intensity and LSI of the paleoearthquakes.

682 683

As it is impossible to know the seismic source of the paleoearthquakes, so it is also

684

impossible to know the hypocentral distance of the paleoearthquakes and historical earthquakes.

685

The hypocentral distance of paleoearthquakes and historical earthquakes was assumed to be the

686

15 kms. This assumption is based on the hypocentral distance of the corresponding hypocentral

687

distance

688

(https://en.wikipedia.org/wiki/2005_Kashmir_earthquake, Retrieved on 03 March 2019) and the

689

Earthquakes

690

(https://www.greaterkashmir.com/article/news.aspx?story_id=307447&catid=2&mid=53&Aspx

691

AutoDetectCookieSupport=1, Retrieved on 26 December 2018). In this study, the hypocentral

692

distance of 15 km was used as one of the input parameter in empirical relationships given by

693

(Obermeier and Pond, 1999) and (Ambraseys and Jackson 1998) for computing the magnitude of

694

the paleoearthquakes. Similarly same hypocentral distance of (i.e., 15 km) was used to compute

of

that

2005

struck

the

AD

Kashmir

26

Kashmir

Valley

on

26

Earthquake

December

2018

695

PGA values of historical earthquakes of 1555 and 1778 AD Kashmir Earthquakes (Kumar et al.,

696

2017).

697 698

The estimated paleomagnitudes using energy stress method are highly sensitive to (N )

699

and assumed hypocentral distance of paleoearthquake. It was observed that in case of the

700

“energy stress method “the higher the (N )

701

on the age (and so density) of the sediments at the time of the paleoearthquake. The (N )

702

the source stratum near the paleoliquefaction sites were obtained after the causative earthquakes

703

that induced the observed liquefaction features. In this study, it is assumed that present (N )

704

represents the back-calculated (N )

705

Pleistocene, the sediment was likely significantly less dense at the time. Furthermore, the deeper

706

the assumed hypocenter distance the higher the paleomagnitude.

value, the higher the paleomagnitude. This depends of

values. If these liquefaction features formed in early

707 708

The LSI values ranging between (16-63 mm) indicates that with the increase in

709

earthquake magnitude the amplitude of ground failure displacement also increases. The value of

710

( * = 8.5) is used as a input parameter in equation (2 and 3) for computing magnitudes of the

711

paleoearthquakes is calculated by using the empirical relationship given by (Galli and Ferreli,

712

1995) equation (4). The computation of paleoearthquake magnitudes in this study using an

713

intensity value of

714

between the assumed seismic source and distal paleoliquefaction feature using ArcGIS 10.2. The

715

intensity of the paleoearthquakes has been computed using the empirical relationship given by

716

Galli and Ferreli (1995) as a function of epicentral distance of ~ 34 Kms between the assumed

717

seismic source and distal paleoliquefaction feature observed in the study area. The seismic

718

source of the paleoearthquakes is estimated on the basis of size and pattern of observed

=8.5 is based on the epicentral distance calculated by measuring the distance

27

719

paleoliquefaction features. The paleoliquefaction feature observed at Pattan act as distal

720

paleoliquefaction features on the basis of its occurrence away from the meizoseismal zone i.e.,

721

Budgam Karewas and Parigam Karewas (Fig.7). This is the only possible approach in

722

paleoseismology to estimate epicentral distance of paleoearthquakes using paleoliquefaction

723

features and using the estimated epicentral distance to compute paleointensity.

724 725

The PGA values of the paleoearthquakes have been computed using in-situ SPT based

726

geotechnical data (Table 3) and ground motion parameters of the paleoearthquakes (i.e., p5 and

727

MSF). The PGA values of the simulated historical and instrumental earthquakes have been

728

computed using assumed hypocentral distance of historical earthquakes and exact hypocentral

729

distance of instrumental earthquake. Further, the magnitudes of historical and instrumental

730

earthquakes used in attenuation equation are estimated in case of 1555 AD and 1778 AD

731

historical earthquakes and exact in case of 2005 AD Kashmir Earthquake. The PGA values

732

increases with increasing M.

733 734

The CRR computed for the paleo, historical and instrumental earthquakes are based on

735

in-situ geotechnical data i.e., fines content and (N1)60CS. (Table 3) of the source stratum near the

736

paleoliquefaction sites. The CRR have same values for paleo, historical and instrumental

737

earthquakes. The CSR computed for paleo, historical and instrumental earthquakes are based on

738

in-situ geotechnical data (Table 3) and ground motion parameters (i.e., ‘ˆ’“ , p5 and MSF) of the

739

paleo, historical and instrumental earthquakes. The FS values obtained by simulating Paleo,

740

Historical and Instrumental earthquakes advocate that the liquefied beds of source stratum near

741

the paleoliquefaction sites are still liquefiable since Early Pleistocene.

742

28

743

Sedimentary deposits experience aging processes with the passage of time, which results

744

in the reduction of liquefaction susceptibility as they gain strength (Table 20; Fig. 20). The

745

factors, which influence the aging of sediments, are either mechanical or chemical resulting in

746

the lithification of sediments. Some sediments are lithified immediately; others may take

747

millions of years: there are sediments that never become consolidated, remaining as loose

748

material millions of years after deposition (Nichols, 2009, p292). It was observed that

749

values of lithostratigraphic members of Karewas ranges from 1.51 to 1.95 (Table 21).

750 751

¨Š

The effect of soil aging on PGA and FS values of the paleoearthquakes is computed by

752

applying age correction factor to CRR values.

753

resistance-corrected cyclic resistance ratio (O

¨Š ¨Š )

is the correction factor applied to deposit because of the effect of aging on CRR. The

754

¨Š

values are computed as a function of age of soils in years since deposition. In this study, the

755

¨Š

values computed for Pattan, Parigam and Narigund sites (Table 6) are the approximate

756

estimated representative age values considered in this study which are based on the age inferred

757

from the literature review of the Karewas of Kashmir Valley (Fig.6). The analysis reveal that

758

there is increase in PGA values of the paleoearthquakes (Table 12) and CRR values of the paleo,

759

historical and instrumental earthquakes (Table 14). It was also observed that there is increase in

760

FS values of the simulated historical and instrumental earthquakes by substitution of CRR with

761

O

762

of the effect of aging on VS1 and CRR values (Andrus et al., 2004). The analysis reveal that

763

medium range of PGA values were obtained for the computed magnitudes of paleoearthquakes

764

(Table 12) and CRR values of the paleo, historical and instrumental earthquakes (Table 14). It

765

was observed that medium range of FS values of the simulated historical and instrumental

¨Š

(Table 18).

’

and

’

are the two correction factors applied to CRR ©… values because

29

766

earthquakes were obtained by substitution of CRR with CRR ©… (Table 18). However, no effect of

767

soil aging was observed on FS values of the paleoearthquakes (Table 17).

768 769

The

versus (

d

relationships indicate increase in shear wave velocity with

770

increasing (

771

susceptible to liquefaction (McCalpin, 2009). Sediments with dense relative density are less

772

susceptible to liquefaction and require high magnitude and PGA values to liquefy. The (

773

sands of source stratum is medium (51% and 63%) for the paleoliquefaction sites at Pattan,

774

Parigam and dense (75%) for the paleoliquefaction site at Narigund. This indicates sediments of

775

source stratum near paleoliquefaction sites at Pattan and Parigam are most susceptible to

776

liquefaction and least susceptible to liquefaction in terms of relative density. However, it should

777

not be ignored that the relative density is directly related to (

778

and Parigam Site is 12 and 18 respectively which means the sediments are medium in terms of

779

)

)

values (Fig. 21). Sediments with low to moderate relative density are most

) . The value of (

% and are most susceptible to liquefaction. The value of (

)

)

%) of

at Pattan

at Narigund site is 26 which

% as the value of (

)

780

means the sediments are slightly dense in terms of

781

above the medium scale (Fig.16). It indicates that sediments at Narigund site is less susceptible

782

to liquefaction as compare to Pattan and Parigam site. In terms of FS values all the

783

paleoliquefaction sites are in the susceptible range of liquefaction (Table 17 and 18). It can be

784

interpreted from the relative density of sands at Narigund Site that high PGA values are required

785

to liquefy the sediments of source stratum. The (

786

increase in (

)

) /

Š

is just one number

versus age relationship suggest

values with increase in age of sediments/soils (Table 3; Fig. 22).

787

788

30

789 790 791 792

17. Conclusion

793

cast. The magnitudes of prehistoric earthquakes that struck the Kashmir Valley were ranging

794

from 6.0 to 7.4 and the corresponding PGA were ranging from 0.18g to 0.77g. The intensity of

795

the paleoearthquakes was of the order of 8.5. LSI values of the computed paleoearthquakes

796

indicate that the maximum amplitude of ground failure displacement was ranging from 16 to 63

797

mm for the epicentral distance of ~34 kms. High PGA values (0.35g to 1.47g) to medium

798

ranged PGA values (0.14g to 0.70g) were obtained by the substitution of CRR with O

799

CRR ©… in the cyclic stress method indicating effects of soil aging has significant influence on

800

PGA of the paleoearthquakes. FS values indicate geological conditions were appropriate for the

801

onset of liquefaction by the paleoearthquakes as FS=1. The effects of soil aging show no effects

802

on FS values of the paleoearthquakes as indicated by FS=1 even after the substitution of high to

803

medium ranged PGA values in the empirical equation to compute CSR and the substitution of

804

CRR with O

805

earthquakes are in the susceptible range of liquefaction even after the substitution of CRR with

806

O

807

0.86g and 0.83g using GMPE. Therefore, sediments of source stratum near the paleoliquefaction

808

features have retained their liquefaction potential as indicated by the values of FS since Early

809

Pleistocene. The

810

paleoliquefaction features are also susceptible to liquefaction. Seismites under study proved

811

potential tools to determine the seismic source, magnitude, intensity, peak ground acceleration

812

and LSI of the paleoearthquakes therefore act as “Natural Seismograms”.

Seismites under study are interpreted to have seismogenic origin except an isolated load

¨Š

¨Š

¨Š

and

and CRR ©… . The FS values of the simulated historical and instrumental

and CRR ©… with CSR values computed using PGA value that were of the order of 1.11g,

and

values advocate that sediments of source stratum near the

813 31

814

Acknowledgement

815 816

Financial support in the form of CSIR-UGC (NET-JRF/SRF) Fellowship was provided to

817

the author of this research paper by UGC-India. The author is highly thankful to the reviewer

818

whose constructive suggestions and recommendation led to significant improvement of this

819

research paper.

820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855

32

856

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42

S.No.

Structures Observed

Location

Reference

1

Sumdo area in the lower Spiti Valley, Tethys Himalaya, Himachal Pradesh (India).

2

Doon Valley.

Mohindra &Bagati (1996) Mohindra & Thakur (1998)

Khalsar in the Shyok Valley, northern Ladakh and eastern Karakoram, India. Chhidu Nala near Garbyang village in the Tethys zone of Kumaun Himalaya.

3 4

Lahaul-Spiti and Ladakh Himalaya (Spiti Valley, Baspa Valley and Indus Valley).

6 7 8 9 10 11 12

Seismites

5

Yamuna Basin in the Himalayan Frontal Belt. Asan reservoir in the northwestern SubHimalaya. Palaeoproterozoic Damtha Group of the Lesser Himalayan Basin. Middle-Siwalik sequence in the Darjiling Himalaya. Burfu village that is located in the Tethyan Himalaya of Uttarakhand. Permian-Triassic Boundary, Guryul Ravine, Kashmir, India. Karewas of Kashmir Valley.

Upadhyay (2001) Kotlia & Rawat (2004) Singh & Jain (2007) Joshi et al., (2009) Pandey et al., (2009) Ghosh et al.,(2010) Kundu et al., (2011) Rana et al., (2013) Brookfield et al., (2013) Khan and Shah (2016) and this Study

Table 1. Paleoseismic record of Himalayan earthquakes preserved in the Himalayan sediments within Himalayan Belt.

S.No.

1

2

3

4

5

6

Structures observed

Description

Dikes Fig.4,(1-6)

Linear vertical features characterized by upward intrusion of lower liquefied sandy and silty sediments of source stratum into the overlying nonliquefied host strata.

Structures characterized by upward projecting flow waves formed due to Fluid Escape the inter-grain rearrangement of Structures liquefied sediments by escaping fluids in response to increase in pore pressure Fig.4,(7) due to seismic shock in the presence of permeability barrier. Simple convolute bedding is Simple and characterized by broad flat synclines complex separated by sharp peaked anticlines. convolute Complex convolute bedding is bedding characterized by intensely deformed Fig.4,(8-AB) laminae having irregular inner laminates. Ball-andStructures characterized by kidney and Pillow semi-spherical bodies of sand with internal contorted lamination set in Structures silty sediments. Fig.4,(9) Load casts associated with flame structures are characterized by irregular rounded lobes of sand that Load casts descend from the parent sand bed into associated with the silt bed beneath. Flame structures flame are characterized by the crenulated structures blunt tips, which laterally exhibit sharp Fig.4,(10) anticlines and broader synclines that have risen irregularly upward into an overlying sandy layer. Structures characterized by downwardIsolated Load facing, bulbous structure formed at an Cast interface between a sandy layer and an Fig.4,(11) underlying silt layer.

Table 2. Description of Seismites.

Location (As on Fig.5) Pattan(1), Parigam(2), Narigund(3), Pakharpora(4), Badipora(5), Shihanpur(6)

Trigger Mechanism

Liquefaction Dalipora Nagum (7)

Parigam (8AB)

Hydroplastic deformation and partial liquefaction

Kunzer Khanpur (9)

Malangpur (10)

Shihanpur (11)

Partial loss of strength and density inversion

σvo (kPa)

σʹvo (kPa)

FC (%)

1 2 3

Pattan Parigam Narigund

7 7 3

183.05 182.96 79.46

114.41 114.31 50.04

86 33 33

N60

16 23 31

13 19 20

(N1)60CS

Dr

Dr %

(N1)60 / Dr

Z (m)

(N1)60

Site

SPT N-Value

S.No.

Kσ

12 18 26

17.53 23.46 31.46

0.51 0.63 0.75

51 63 75

23 29 35

0.99 0.98 1.00

Where; Z = Depth of Source Stratum in metre; σvo = Total vertical stress; σʹvo = Effective vertical stress; FC (%) = Fines Content; SPT N-Value = Total number of blows to drive splitspoon sampler the 2nd and 3rd 150 mm increments; N60 = SPT-N values corrected for field procedures as per equation (14); (N1)60 = Corrected SPT N-Value for field procedures to an average energy ratio of 60% of the theoretical free-fall SPT hammer energy and overburden stress; (N1)60CS = Clean-sand-corrected N-value; Dr = Relative density; Kσ = Overburden correction factor for cyclic stress ratios Table 3. SPT based geotechnical data of the source stratum near paleoliquefaction sites.

S.No. 1 2 3 4 5

Group 1 2 3 4 5

Range of values for Factor of Safety <1 1-2 2-3 >3 Non Liquefiable (NL)

Liquefaction Severity Index High Moderate Low Nil Nil

Table 4. Index for liquefaction potential as a function of Factor of Safety (after Sitharam et al., 2005).

1 2

Site Classification A B

>1500 760-1500

3

C

360-760

4

D

180-360

5

E

<180

S.No.

m/s

Soil Type Hard Rock Soft Rock Dense soils and cohesionless soils like sands Sandy, silty and soft, stiff to very stiff clays and some clay. Soft/Medium Stiff Clay

Table 5. Index for shear wave velocity (BSSC, 2003, Sitharam et al., 2005).

Susceptibility Rating Nil Nil Low Moderate High

Approximate age (t) KDR in (Years) 1 Pattan 7 1800000 1.89 2 Parigam 7 1800000 1.89 3 Narigund 3 2100000 1.90 The value of (t) used in equation (20) for computing KDR are the approximately estimated representative values considered in this study. S.No.

Site

Depth

Table 6. KDR values used in computing the deposit resistance-corrected cyclic resistance ratio

7 7 3

Magnitude of the paleoearthquakes based on intensity of the paleoearthquake

Pattan Parigam Narigund

(N1)60

Magnitude of the paleoearthquakes based on intensity and hypocentral distance of the paleoearthquake

Depth (metres)

1 2 3

R2

Magnitude of the paleoearthquakes using, “Energy stress method”

Site

Assumed Hypocentral distance “R” (km)

S.No.

and Vs based CRR.

15 15 15

225 225 225

12 18 26

6.0 6.7 7.4

6.6

6.7

Table 7. Magnitudes of the Paleoearthquakes.

S.No.

Epicentral distance “d” Km

Io (MCS -Scale)

1

~34

8.5

Where;

=Intensity (MCS)

Table 8. Intensity of the paleoearthquakes as a function of epicentral distance.

Epicentral distance “Re” or “d” Km for the liquefied field between estimated seismic source and distal paleoliquefaction site.

Magnitude of the paleoearthquakes

1

~34

6.0

0.63

16

Moderate

2 3

~34 ~34

6.6 6.7

1.14 1.26

29 32

High High

4

~34

7.4

2.49

63

Very High

S.No.

Effects of Liquefaction

Maximum amplitude of ground failure Displacement

Inches

(mm)

Severity

Description

Effect of liquefaction remain confined within the host stratum. Little effect of liquefaction seen on the ground surface. Effects of liquefaction seen on ground surface in the form of sand boils.

Table 9. Liquefaction severity index for the prehistoric earthquakes.

S.No.

Site

6.0

6.6

6.7

7.4

8.5

7.7

( ) Instrumental Earthquake 7.6

( ) Paleoearthquakes

Depth (m)

( ) Historical Earthquakes

1

Pattan

7

0.87

0.90

0.90

0.93

0.98

0.95

0.94

2

Parigam

7

0.87

0.90

0.90

0.93

0.98

0.95

0.94

3

Narigund

3

0.96

0.97

0.97

0.98

1.00

0.98

0.98

Where;

= Stress reduction factor; m=Metre.

Table 10. Stress reduction factor calculated for the Paleoearthquakes (M=6.0, M=6.6, M=6.7, M=7.4), Historical earthquakes 1555 AD (M=8.5) and 1778 AD (M=7.7) Kashmir Earthquakes and Instrumental earthquake of 2005 AD Kashmir Earthquake (M=7.6) as a function of the depth of source stratum and Magnitude under consideration.

S.No. Simulated Earthquakes Category 1 Paleoearthquake (M=6.0) 2 Paleoearthquake (M=6.6) Paleoearthquakes 3 Paleoearthquake (M=6.7) 4 Paleoearthquake (M=7.4) 5 1555 AD Earthquake Historical Earthquakes 6 1778 AD Earthquake 7 2005 AD Earthquake Instrumental Earthquakes Where; M=Magnitude; MSF=Magnitude scaling factor.

M 6.0 6.6 6.7 7.4 8.5 7.7 7.6

MSF 1.3 1.2 1.1 1.0 0.9 1.0 1.0

Table 11. Magnitude scaling factor computed for the Paleo, Historical and Instrumental

S.No.

earthquakes of the Kashmir Valley as a function of the Magnitude under consideration.

Site

Z (m)

1 2 3

Pattan Parigam Narigund

7 7 3

PGA computed for the Paleoearthquakes using Cyclic stress method (Equation 6)

Effects of Soil Aging on PGA values of the Paleoearthquakes PGA computed by the substitution of CRR with in the Cyclic stress method (Equation 6) 6.0 6.6 6.7 7.4

PGA computed by the substitution of CRR with CRR in the Cyclic stress method (Equation 6) 6.0 6.6 6.7 7.4

6.0

6.6

6.7

7.4

0.26g

0.23g

0.21g

0.18g

0.48g

0.43g

0.40g

0.35g

0.36g

0.29g

0.24g

0.19g

0.37g

0.33g

0.30g

0.26g

0.69g

0.62g

0.56g

0.50g

0.70g

0.58g

0.50g

0.40g

0.77g

0.71g

0.65g

0.58g

1.47g

1.34g

1.23g

1.11g

0.25g

0.20g

0.18g

0.14g

Table 12. PGA computed for the magnitudes of paleoearthquakes (M=6.0, M=6.6, M=6.7, M=7.4) using SPT based geotechnical data of the source stratum near paleoliquefaction sites.

S.No. Simulated Earthquakes Category M R 1 1555 AD Earthquake 8.5 15 Historical Earthquakes 2 1778 AD Earthquake 7.7 15 3 2005 AD Earthquake Instrumental Earthquakes 7.6 15 Where; M=Magnitude; R=Hypocentral distance, PGA=Peak ground acceleration.

PGA 1.11 g 0.86 g 0.83 g

Table 13. Peak ground acceleration calculated for the simulated Historical and Instrumental earthquakes using attenuation equation of the Himalayan region.

Site

Z (m)

Deposit resistance-Corrected CRR

S.No .

CRR

Effect of Soil Aging on CRR values of the Paleo, Historical and Instrumental Earthquakes Shear wave velocity based CRR

CRR computed for the magnitudes of Paleoearthquakes (M=6.0, M=6.6, M=6.7, M=7.4) incorporated with age correction factors in the form of and

CRR computed for the magnitudes of 1555 AD & 1778 AD Historical Earthquakes and 2005 AD Instrumental Earthquake incorporated with age correction factors in the form of and Historical Earthquakes

Instrumental Earthquake

M=6.0

M=6.6

M=6.7

M=7.4

M=8.5

M=7.7

M=7.6

1

Pattan

7

0.18

0.34

0.25

0.23

0.21

0.19

0.17

0.19

0.19

2

Parigam

7

0.26

0.49

0.50

0.46

0.43

0.39

0.35

0.39

0.39

3

Narigund

3

0.59

1.12

0.19

0.17

0.16

0.14

0.13

0.14

0.14

Where; CRR = Cyclic resistance ratio; Z=Depth in metres; M=Magnitude.

Table 14. CRR of the source stratum near paleoliquefaction sites.

S.No.

Effect of Soil Aging on CSR values of the Paleoearthquakes

Site

Z (m)

CSR computed by the substitution of PGA values in equation 17 which were computed by equation 6

CSR computed by the substitution of PGA values in equation 17 which were computed by the substitution of CRR with in equation 6

CSR computed by the substitution of PGA values in equation 17 which were computed by the substitution of CRR with in equation 6

6.0

6.6

6.7

7.4

6.0

6.6

6.7

7.4

6.0

6.6

6.7

7.4

1

Pattan

7

0.18

0.18

0.18

0.18

0.34

0.34

0.34

0.34

0.25

0.23

0.21

0.19

2

Parigam

7

0.26

0.26

0.26

0.26

0.49

0.49

0.49

0.49

0.50

0.46

0.43

0.39

3

Narigund

3

0.59

0.59

0.59

0.59

1.12

1.12

1.12

1.12

0.19

0.17

0.16

0.14

Where; CSR = cyclic stress ratio; m=Metre.

Table 15. CSR of the source stratum near paleoliquefaction sites for the computed magnitudes and PGA values of the paleoearthquakes (M=6.0, M=6.6, M=6.7, M=7.4).

CSR computed for the Historical Earthquakes 8.5 7.7

CSR computed for the Instrumental Earthquake 7.6

S.No.

Site

Depth (m)

1

Pattan

7

1.27

0.86

0.82

2

Parigam

7

1.28

0.87

0.83

3

Narigund

3

1.27

0.87

0.84

Table 16. CSR of the source stratum near the paleoliquefaction sites for the computed magnitudes and PGA values of the Historical earthquakes 1555 AD (M=8.5) and 1778 AD (M=7.7) Kashmir Earthquakes and 2005 AD Kashmir Earthquake (M=7.6).

S.No.

Effect of Soil Aging on FS Values of the Paleoearthquakes

Site

Z (m)

FS computed by using CRR computed as per equation 7,8&9 versus CSR computed as per equation 17 in which PGA values incorporated were calculated as per equation 6

6.0 6.6 1 Pattan 7 1.0 1.0 2 Parigam 7 1.0 1.0 3 Narigund 3 1.0 1.0 Where; FS = Factor of safety; m=Metre.

6.7 1.0 1.0 1.0

7.4 1.0 1.0 1.0

FS computed by the substitution of CRR with in equation 16 versus CSR computed as per equation 17 in which PGA values incorporated were calculated by substitution of CRR with in equation 6

FS computed by the substitution of CRR with in equation 16 versus CSR computed as per equation 17 in which PGA values incorporated were calculated by substitution of CRR with in equation 6

6.0 1.0 1.0 1.0

6.0 1.0 1.0 1.0

6.6 1.0 1.0 1.0

6.7 1.0 1.0 1.0

7.4 1.0 1.0 1.0

6.6 1.0 1.0 1.0

6.7 1.0 1.0 1.0

7.4 1.0 1.0 1.0

Table 17. FS values of the source stratum near the paleoliquefaction sites computed for the Paleoearthquakes (M=6.0, M=6.6, M=6.7, M=7.4) of the Kashmir Valley.

S.No.

Z Site

FS computed as per equation 16

(m)

1

Pattan

7

2

Parigam

7

3

Narigund

3

Effect of Soil Aging on FS values of Historical and Instrumental Earthquakes FS computed by the FS computed by the substitution of CRR substitution of CRR in equation in equation with with 16 versus CSR 16 versus CSR computed as per computed as per equation 17 equation 17

8.5

7.7

7.6

8.5

7.7

7.6

8.5

7.7

7.6

0.14 0.20 0.46

0.21 0.30 0.68

0.22 0.31 0.70

0.27 0.38 0.88

0.40 0.56 1.29

0.41 0.59 1.33

0.13 0.27 0.10

0.22 0.45 0.16

0.23 0.47 0.17

Table 18. FS values of the source stratum near the paleoliquefaction sites computed for the Historical 1555 AD Kashmir Earthquake (M=8.5), 1778 AD Kashmir Earthquake (M=7.7) and Instrumental earthquakes of the 2005 AD Kashmir Earthquake (M=7.6) of the Kashmir Valley. S.No. Site Depth (m) VS m/s VS1 m/s V*S1 m/s 1 Pattan 7 263 254 200 2 Parigam 7 308 298 201 3 Narigund 3 351 417 201 Where; VS m/s = Shear wave velocity per metre second; VS1 m/s = Overburden stresscorrected shear-wave velocity per metre second; V*S1 m/s = Limiting upper value of ! per metre second.

Table 19. Shear wave velocity of the source stratum computed near the paleoliquefaction sites using SPT based empirical relationships.

S.No. 1 2 3 4 5 6 7 8 9 10 11 12

T (Years) 1 10 100 1000 10000 100000 1000000 2000000 3000000 4000000 5000000 10000000

Strength Gain Factor KDR 0.83 1.00 1.17 1.34 1.51 1.68 1.85 1.90 1.93 1.95 1.97 2.02

Table 20. Generalized strength gain factor KDR for geologically aged soils.

Karewas Age (Years) Strength Gain

Pleistocene Epoch Mid to Late Pleistocene Early Pleistocene Pampur Member Methawoin Rembiara Dilpur Formation & Member Member Shupiyan Member

10 Ka

18 Ka-35 Ka

110 Ka

1.51

1.55-1.60

1.69

Pliocene Epoch Dubjan Member

1.8 Ma

2.1 Ma

2.3 Ma to 2.4 Ma

4 Ma

1.89

1.90

1.91

1.95

1.51-1.69 Note: - The age of the Pampur Member and Shupiyan Member (1.8 Ma) considered in this study is the approximately estimated representative age value. The age of Rembiara Member is estimated close to 2.4 Ma to 2.3 Ma and the age of Methawoin Member is estimated to be 2.1 Ma (Fig. 6).

Table 21. Strength gain factor of the Karewa sediments since their deposition.

Fig. 1. Google Earth map showing the Epicenters of notable Himalayan Earthquakes along the Himalayan Belt.

Fig. 2. (A) Seismotectonic map of the Himalayas (Modified after Sorkhabi & Macfarlane, 1999; Gansser, 1981; Windley, 1983) showing location of Kashmir Valley in the North-West Himalayas, India. (A1) Shaded relief image of Kashmir Valley. (A2) Cross-sectional view of Kashmir Valley (modified after Wadia, 1976).

Fig. 3. Location map of study area (modified after Bhat, 1982).

Fig.4. Soft sediment deformation structures in the Karewas of Kashmir Valley. Key: (1-6) = Paleoliquefaction features (dikes) at 1=Pattan, 2=Parigam, 3=Narigund, 4=Pakharpora, 5=Badipora and 6=Shihanpur, 7=Fluid escape structure observed at Dalipora Nagum, 8A=Simple convolute bedding at Parigam, 8B=Complex convolute bedding at Parigam, 9=Balland-Pillow structures at Kunzer Khanpur, 10=Load casts associated with flame structure at Malangpur, 11=Isolated Load cast at Shihanpur Budgam.

Fig. 5. Map of study area (modified after Bhat, 1982) showing the spatial distribution of various lithounits of Karewas, Seismites, SPT sites and estimated Seismic source. Key: (1) Pattan, (2) Parigam, (3) Narigund, (4) Pakharpora, (5) Badipora, (6) Shihanpur (7) Dalipora Nagum (8) Parigam (9) Kunzer Khanpur (10) Malangpur (11) Shihanpur.

Fig.6. Schematic simplified stratigraphic litho-column of Karewas showing seismites bearing lithostratigraphic units (i.e. Methawoin Member and Pampur Member) and age of Karewas.

Fig. 7. Map of study area (modified after Bhat, 1982) showing the spatial pattern of dikes in planar view, meizoseismal zone, estimated seismic source and dike width and height.

Fig. 8. Epicentral distance measured on the basis of estimated seismic source and distal liquefaction feature versus intensity for the liquefied field in the Karewas of Kashmir Valley.

Fig.9.

LSI for the epicentral distance of ~34 km vs magnitudes of paleoearthquake

(M=6.0,M=6.6,M=6.7 and M=7.4).

Fig.10. Magnitude scaling factor (MSF) computed for the Paleo, Historical and Instrumental earthquakes of the Kashmir Valley as a function of the Magnitude under consideration.

Fig. 11. FS values of the source stratum near the paleoliquefaction sites computed for the Paleoearthquakes (M=6.0, M=6.6, M=6.7, M=7.4) of the Kashmir Valley. The FS=1 with or without considering the effects of soil aging.

Fig. 12. FS values of the source stratum near the paleoliquefaction sites computed for the Historical 1555 AD Kashmir Earthquake (M=8.5), 1778 AD Kashmir Earthquake (M=7.7) and Instrumental earthquakes of the 2005 AD Kashmir Earthquake (M=7.6) of the Kashmir Valley.

Fig. 13. FS values of the source stratum near the paleoliquefaction sites computed for the Historical 1555 AD Kashmir Earthquake (M=8.5), 1778 AD Kashmir Earthquake (M=7.7) and Instrumental earthquakes of the 2005 AD Kashmir Earthquake (M=7.6) of the Kashmir Valley.

Fig. 14. FS values of the source stratum near the paleoliquefaction sites computed for the Historical 1555 AD Kashmir Earthquake (M=8.5), 1778 AD Kashmir Earthquake (M=7.7) and Instrumental earthquakes of the 2005 AD Kashmir Earthquake (M=7.6) of the Kashmir Valley.

Fig. 15. Shear wave velocity of the source stratum computed near the paleoliquefaction sites using SPT based empirical relationships.

Fig. 16. Correlation between (

)

and relative density (classification modified after, Terzaghi

et al., 1996).

Fig. 17. Illustration for the formation of paleoliquefaction features.

Fig. 18. Illustration for the formation of Simple and Complex Convolute Beddding.

Fig. 19. Illustration for the formation of Ball-and Pillow Structures, Load casts associated with Flame structures and Isolated Load casts.

Fig. 20. Generalized Strength Gain Factor

Fig. 21.

computed for soil of all ages.

m/s versus SPT N Value relationship near paleliquefaction sites.

Fig. 22. Effect of age on corrected SPT blowcounts and relative density.

Highlights • Seismites were identified and characterized to know their genesis • M, PGA, ,LSI & FS were computed for paleoearthquakes • Empirical relationships were used to assess the effect of soil aging on PGA & FS • Karewas exhibit natural seismograms in the form of seismites within Kashmir Himalayas

There is no conflict of interest.