- Email: [email protected]
World map of active faults (preliminary results of studies)
Quaternary International, Vol. 25, pp. 3-12, 1995. Copyright © 1994 INQUA/Elsevier Science Ltd Printed in Great Britain. All fights reserved. 1040~ 182/95 $29.00
Pergamon
1040-6182(94)00029-8
WORLD MAP OF ACTIVE FAULTS (PRELIMINARY RESULTS OF STUDIES) Vladimir G. Trifonov
Geological Institute of the Russian Academy of Sciences, 7 Pyzhevsky, Moscow 109017, Russia
The Project 'World map of major active faults' was confirmed in 1989 as a part of the International Lithosphere Program. The objectives are to compile the World map in scale 1:10,000,000, the maps of continents in scale 1:5,000,000 and the maps of some seismic regions in scale of 1:1,000,000 or 1:5,000,000 with the Explanatory Notes and the Catalogue of major active faults of continents. The maps will show location, age, sense and rate of motion and reliability of identification of faults not older, than 100,000 years, as well as Middle Pleistocene faults, contemporary folds, flexures, volcanoes and epicentres of strong earthquakes differentiated by magnitude, depth and age. The first results of the Project are discussed. One of them is predominance of the strike-slip component of motion over the vertical one for the majority of continental active faults. It has occurred because the strike-slip motion is more efficient, than the thrust, the reverse and even the normal ones. Strike-slip faults are differentiated into faults of translation, rotation and squeezing. The contribution of seismicity to faulting depends on the inpulse, the creep and the inpulse-creep regimes of recent motion in the fault-zones. Different geological techniques for estimating the motion regime, the magnitudes and the recurrence interval of strong Holocene earthquakes are discussed.
~TRODUCTION All faults with present-day and Holocene offsets or other manifestations of activity during the last 10,000 years have been defined as active faults (Allen, 1975; Trifonov, 1985). However, since it is hard in many regions to differentiate the Holocene geological features from those of the Late Pleistocene, we consider it is necessary to extend the time interval accepted as characteristic for active faults to 100,000 years, i.e. Holocene and Late Pleistocene. Studying active faults is useful for : - - estimating seismic and other geological hazards (volcanism, fluid and gas activity, hydrogeological changes, karst, landslides, catastrophic erosion and sedimentation); - - research of recent geodynamics; - - interpretation of more ancient tectonics by comparison with the recent ones. O B J E C T I V E S AND SENSE OF THE PROJECT
The importance of studying active faults led to the establishment of the Project 'World Map of Major Active Faults' as a part of the International Lithosphere Program in 1989. The objectives of the Project are to compile the World Map at a scale of 1:10,000,000, the maps of the continents at a scale 1:5,000,000 and the maps of some seismically dangerous regions at scales of 1:1,000,000 or 1:500,000. The maps will be accompanied by the Explanatory Notes and the Catalogue of major active faults of the continents. According to the legend of the maps (Fig. 1) all faults are differentiated by intensity of tectonic movements, age of the last manifestation of activity, sense of displacements and reliability of identification. Three groups of faults are differentiated by rates of motion (V): V _> 5 mm/year; 5 mm/year >V _> 1 mm/year; V < 1 mm/year. Three kinds of faults of their segments are differentiated by age of the last
manifestation of activity: (1) the historical time; (2) the Holocene and the Late Pleistocene; (3) the Middle Pleistocene (700,000-100,000 years ago). We decided to show in the maps the information about Middle Pleistocene faults because Late Quaternary displacements are very small in relatively inactive regions, and to estimate the tendency of recent motion it is necessary to use data representing a wider time span. It is reasonable to show these faults also with a view to using the maps for nuclear power plant investigations. The historical period is different in different regions. As well, the lower boundaries of the epochs (2) and (3) may vary from one region to others. All these differences will be shown in the final map legend according to the author's contributions. The faults are differentiated between the reliable and the inferred ones and into 5 kinematic types. These are: (1) thrusts and reverse faults; (2) strike-slip faults; (3) normal faults; (4) extensional faults (i.e. cracks and narrow grabens without vertical or strike-slip movements of the fault sides); (5) faults with unknown sense of slip. Deep-sited fault zones, buried by non-faulted rocks and manifested in the land surface only by indirect signs, are shown by a special symbol. Transform faults and surficial continuations of deep-sited seismofocal zones are to be shown in the oceans only. Manifestations of young folds, contemporary and Holocene volcanism and seismicity are shown in the maps as reflecting tectonic activity. Young anticlines, synclines and flexures are differentiated by the age of the last deformation in the same manner as the faults are. Epicentres of earthquakes are differentiated by hypocentre depths H (H _< 70 km; 70 km < H < 300 km; H _>300 km), magnitudes of earthquakes M (4 < M < 6, shown only in stable regions; 6 _< M < 7; 7 _ 8) and age of events (the 20th century; older than the 20th century; records of Holocene paleoseismicity).
4
V.G. Trifonov ACTIVE FAULTS, d i f f e r e n t i a t e d by: Rates of f a u l t movements V: ~ V > 5 mm/yr ~ A l l f a u l t s with unknown r a t e s can be shown only | f ]5 mm/yr>V>l mm/yr ~ by symbols of the t h i r d or the second groups ~ V < I mm/yr J Age of the l a s t m a n i f e s t a t i o n s of a c t i v i t y : ~Historical (blue) ~ The h i s t o r i c a l pe ri od i s d i f f e r e n t in ~Holocene and Late P l e i s t o c e n e , | d i f f e r e n t r e g i o n s , and the lower boundsi . e . the l a s t 100,000 y r s | r e d ) ~ r i e s of the second and the t h i r d groups ~Middle Pleistocene, i.e. [ c a n vary from one re gi on t o o t h e r s . 700,000-100,000 yrs ago (black) JThese d i f f e r e n c e s w i l l be shown in the f i n a l map legend More d e t a i l e d age d i f f e r e n t i a t i o n in some r e g i o n s : ~ L a t e P l e i s t o c e n e , i . e . 100,000-10,000 y r s ago ( a l t e r n a t i o n of blue and red s h o r t l i n e s ) ; in those r e g i o n s the f a u l t s with Holocene (t he l a s t 10,000 yrs) a c t i v i t y w i l l be shown by red l i n e s ~Reliable Middle P l e i s t o c e n e a c t i v i t y and surmised Late P l e i s t o c e n e and Holocene a c t i v i t y ( a l t e r n a t i o n of b l a c k and red s h o r t l i n e s ) Sense of d i s p l a c e m e n t s and r e l i a b i l i t y of f a u l t i d e n t i f i c a t i o n : ~Thrusts and r e v e r s e f a u l t s ~ Reliable ~Strike-slip faults [ f a u l t s a re ~Normal faults ]shown on the ~lExtensional f a u l t s , i . e . c r a c k s and narrow grabens w i t h o u t ~ l e f t and g e n e r a l v e r t i c a l or s t r i k e - s l i p o f f s e t s of t he f a u l t s i d e s ]]fsauur lmt i sse d ~ w ~ - ' ~ F a u l t s with unknown sense of s l i p are ~Transform faults ~ Jshown on the ~Surficial continuations of ~Only in the oceans right ~+deep-sited seismofocal zones ~ - ~ D e e p - s i t e d fault zones, buried by nonfaulted rocks and manifested in the land surface only by indirect signs
YOUNG FOLDS, diffirentiated by age of the last deformation t o the same groups as f a u l t s : ~Anticlines, l i n e a r on the l e f t and i s o m e t r i c on the r i g h t ~Synclines, l i n e a r on t he l e f t and i s o m e t r i c on the r i g h t ~Flexures YOUNG VOLCANISH: ~ F - ~ V o l c a n o e s , a c t i v e now on the l e f t (red) and in the Late Quaternary on the r i g h t (bla c k; the time i n t e r v a l can be d i f f e r e n t in d i f f e r e n t r e g i o n s and i t w i l l be shown in the f i n a l map legend) ~ } - ~ A r e a s of the hydrothermal a c t i v i t y , shown in t he map s c a l e on the l e f t and out of the s c a l e on the r i g h t EARTHQUAKE EPICENTRES, d i f f e r e n t i a t e d by: Depths of hypocentres H: O [{470 km ( r e d ) ; O 70 km
o
s4M<7;0 7~M,8
Ages of events: 0 of the XX c e n t u r y ; ~ o l d e r than the XX c e nt ury; @ rec ords of p a l e o s e i s m i c i t y FIG. 1. The legend of maps of major active faults of the World (1:10,000,000) and the continents (1:5,000,000).
The Explanatory Notes must contain principles and methods of active fault detection, regional description of the faults, regional and planet-scale regularities of recent tectonics. The following characteristics of active faults must be shown in the Catalogue by special symbols: (1) number and name; (2) co-ordinates (~b, ~,) of both ends of the fault and points, where its parameters change; (3) average strike; (4) dip (for points or segments of the fault with the coordinates); (5) length; (6) sense of slip; (7) faulted layers of the lithosphere; (8) age of the last manifestation of activity; (9) signs of fault activity; (10) magnitudes of vertical and lateral offsets during the indicated time interval (for points or segments of the fault with the coordinates); (1 I) rates of motion (total and of different components of motion); (12) seismic manifestations; (13) other records of activity (exogeneous, geophysical, hydrothermal, gas and hydro-
geochemical, volcanic, etc.); (14) reliability of data (A, B or C); (15) author(s) of the interpretation and references. The faults with various characteristics are shown by segments. Of course, not all characteristics can be determined for each fault and shown in the Catalogue. Records of fault activity include the following: (1) Offsets of young topographic features and deposits (channels, valleys, terraces, alluvium fans, etc.); (2) Contrast of composition and/or thickness of young deposits; (3) Seismological data (chains of hypocentres; sense and volume of displacement, found by calculation of focal parameters; recent and old seismic ruptures in the land surfaces; other signs of paleoseismicity); (4) Geophysical data testifying to recent motion in the deeper part of the Earth's crust and the lithosphere; (5) Geodetic data;
World Map of ActiveFaults L
data are available, geological and/or geomorphological correlation with dated objects can be used for the estimation. The geometry of the fault line as well as the data of the Catalogue will be presented in the computer data base. The Project led by V.G. Trifonov joins 50 scientists from 30 countries and is open for wider cooperation. The Project is supported by ICSU and UNESCO as a contribution of the International Lithosphere Program to the International Decade of Natural Disaster Reduction.
L'R m
10,000 7500
10,000
--
5OO0 4OO0 3000 2000 1500
D
1000 750
1000
-
500 400 3OO
--
200 150
:
5
oeOcV •
P R E D O M I N A N C E OF S T R I K E - S L I P F A U L T M O T I O N IN T H E C O N T I N E N T S O
The implementation of the Project is in progress now and the initial results can be presented. At first, the vertical 50 A 40 component of fault offsets within the continents appears to AO~O ~ O -• O 30 V ~v be controlled by the reverse or thrust motion, rather than by 20 T A % normal faulting. In this sense, essentially different regimes 10 -DO V O I0 seem to dominate only in some regions, such as Eastern 5 -OA ' ~ ev I I I Lo,, t t Africa (System of the Great African Faults), Eastern China, 0 6 7 g M 6 7 8 M the Baykal region (the Baykal rift system) and the Lut basin ~ " ] Strike-slipfaults ~ in Iran. It shows that the major part of the continents is under o ~ ~ - ] Normalfaults the influence of compression at present. The more important results confirming previous data [ " ~ Thrusts, reversefaults O (Pavoni, 1971; Tapponnier and Molnar, 1976; Nikonov, FIG. 2. Correlationbetweenthe magnitudesM of the strongearthquakesof 1977; Trifonov, 1978; Ding Guoyu, 1984) is the the 20th century and the lengths L (km) of seismic ruptures in the land surface (on the left) and the lengths L (km) multiplied to the maximum predominance of the strike-slip component of the motion seismic offsets R, (m) (on the fight) (Trifonov, 1991). It is seen that the over the vertical one for the majority of the continental faults. strike-slipfaultsproducethe longerL and the largerL x Rmfor the sameM, This phenomenon can be understood if it is connected with than the normal and especiallythe thrust faults. peculiarities of strike-slip sense of motion. Studying of seismic ruptures in the land surface during the 53 strong earthquakes of the 20th century (Fig. 2) shows that strike-slip faults are more energy efficient than thrust, reverse and even the normal ones. It means that for a given magnitude of (6) offsets of artificial or natural objects, discovered by earthquake, length of rupture and the length multiplied to offset mould be greater for the strike-slip faults than for using historical or archeological data. These records permit to map an active fault as a defined normal and especially thrust ones. Three types of active strike-slip faults can be identified. one. Other records permit faults to be shown only as inferred These are faults of translation, rotation and squeezing. Faults active faults. These are: of translation are typical for flank sides of moving plates and (7) Young volcanic chains and fractures; (8) Signs of present-day and Late Quaternary microplates and for the majority of intraplate regions. They are faults with one side moving as a whole relative to the hydrothermal activity; (9) Mud volcanoes and data about abnormally high layer other one. The San Andreas fault zone between the North American and the Pacific plates, the Levant and the East pressure; (10) Recent gas and hydro-geological anomalies in the Anatolian zones, and the Main recent fault of Zagros on the sides of the Arabian plate, the Chaman, the Darvaz and the fault zone; (11) Concentration of landslides and other exogeneous Pamir-Karakorum faults on the sides of the Indian plate as well as the Talas-Fergana, the Djunghar and the other major signs of geodynamic activity; (12) Active flexure or linear fold system above the intraplate faults of Asia belong to this type (Fig. 3). Strike-slip faults of rotation and squeezing are surmised buried fault; (13) Linear deformation of topography in space images characteristic of the collision regions. In the faults of rotation as well as spectrometric anomalies interpreted as the strike-slip effect is produced by rotation of rocks between two faults in front of the moving plate or large block (Fig. 4). manifestations of recent geodynamic activity. The estimation of the age of fault motion (as well as of The result of rotation is shortening of territory in crossection, other manifestations of activity) are based on 14C, K-Ar, i.e. the same as the result of thrusting or folding. This type of thermoluminescent, tephrochronological, pale•magnetic, tectonic motion took place in northern Armenia between the lichen•metric, historical and archeological and instrumental northwestern parts of the Pambak-Sevan and the Alavar (geodetic and seismological) dating of rock complexes offset faults during the Spitak earthquake of 1988, as well as in the by the fault or created by slipping along its plane. If no direct earlier stages of development of the faults (Fig. 4E). Both 100 75
m
•O
••
V V
~
aV
100
-
-
tt
j
~['~ ~"
v
6
V.G. Trifonov
;.u
~2
0
~L, --'E
1
',5
il'
,...,
z~
L.,,.
c5 ~
~ o o
0 ~
0
~P
,
Z 41
z~ 2~
~c
0
k_____
Cg m~
~,
World Map of Active Faults
I;1 :i
Iql
I,I !/
35
7
d0
45
50
--1 70
72
I "~
11
;/I
'~
,
,
I 22,,,,,0, ,,
T
5
I[[,,I
, 0
5
t
10 km "
EA " ~ ~
-~
,..~ ~
PS
Stress direction
VV~
Symbolic lines showing block deformatio.
Direetionofrockmotion
~
Former position of faults
FIG. 4. Kinematic types of strike-slip faults: (A,B) Principal schemes of formation of faults of rotation (A) and squeezing (B); (C) Squeezing of sedimentary rocks in the northeastern part of the Tadjik depression; (D) Major active faults of the Middle East (EA-the East Anatolian zone, LV-the Levant zone, MZ-the Main recent fault of Zagros, NA-the North Anatolian zone, PS-the Pambak-Sevan fault) with location of Figs 4E and 6; (E) Strike-slip faults of rotation and squeezing in the epicentral area of the Spitak earthquake of 1988 in the northern Armenia (AL-the Alavar fault, EA-the East Anatolian zone, PS-the Pambak-Sevan fault). Symbols are shown in Fig. l.
faults are dextral with magnitudes of strike-slip offsets several times larger than those of contemporary reverse components of displacements. The strike-slip faults of squeezing are produced by not only shortening rocks in cross-section in front of the moving plate or the block, but also by squeezing rocks out of the area with maximum compression. The squeezing is accompanied by non-uniform longitudinal lengthening of the squeezed zone and thrusting and folding around the moving plate. This type of motion is represented by the active structure of the Tadjik depression and the Kunluns in both sides of the Pendjab--Pamir syntaxis as well as of the Anatolian and the Iranian microplates in both sides of the Arabian syntaxis. The motion of the Anatolian rocks to the west along the North-Anatolian and the other west- and southwest-trending dextral strike-slip faults results in extension of the Aegean region and thrusting of its southern side to the African plate. It means that the recent evolution of the Cretean arc depends on the kinematics of the microplate interaction in the southern part of Eurasia rather than of the northern drift of the African plate. This interpretation is supported by determination of recent crustal movements of the region by using the GPS technique (Drewes and Geiss, 1990; Oral et al., 1991) (Fig. 5). The East Anatolian fault zone was continued by our studies to the northeast of the North Anatolian zone to Northern Armenia, and sinistral offsets were found there as well as in the southwestern part of the zone. The principal
N I cm/A 50
40
301
20
30
40
FIG. 5. Vectors of present-day deformation in the Eastern Mediterranian by the G P S data, calculated for the non-homogeneous faulted model (Drewes and Geiss, 1990). Stars show point of observation.
8
V.G. Trifonov 38
40
42
44
40 Erzurum Erzincan
o*'
/
0 g
38
50 it
100 k m !
FIG. 6. Intersection of the North Anatolian and the East Anatolian active fault zones (A) and principal scheme of evolution of these faults (B). The oldest fault branches in (A) and new fault branches in (B) are shown by dots. Other symbols are shown in Fig. 1.
site is the area of interaction of two active strike-slip faults: the North Anatolian dextral zone with a rate of recent motion of 20 mm/year and the East Anatolian sinistral zone with a rate of 5 mm/year (Fig. 6). We found several fault branches in the North Anatolian zone to the northwest of the intersection, the southern branch being the oldest one and the northern branch being the youngest. The same peculiarity was found in the East Anatolian zone to the SW of the intersection. The southeastern branch is the youngest there. We interpreted these peculiarities of both fault zones in the following way: the strike-slip movement along one of the faults offset the other fault, halting the possibility of movement along it. As a result, the new fault branch, joining the offset fault segments was formed. The subsequent movement along the fault thus restored offset the first one, and the latter had to form the new branch for the continuation of movement etc. (Fig. 6B). The distances between branches of the East Anatolian zone are larger than of the North
Anatolian zone because of the larger rate of motion along the latter. C O N T R I B U T I O N OF S E I S M I C I T Y T O F A U L T I N G AND S I G N I F I C A N C E OF A C T I V E FAULTS F O R E S T I M A T I O N OF S E I S M I C HAZARD Allen (1968) and Wallace (1970) showed dependence of recent motion regimes in different parts of the San Andreas fault on the geology of the fault zone. Three types of the regime were differentiated by comparative analysis of active faults (Trifonov, 1985). These are the impulse, the creep and the impulse-creep regimes. The impulse regime is typical for the thick sections of granitic and metamorphic hard rocks of the upper crust. The regime is characterized by large offsets during strong earthquakes after periods with the lack of essential movements for several hundreds or in some areas even several thousand years. The Khangay, the Gobi-Altay
4 0 ~ 42 44
4 26
28
30
32
34
36
38
4q
4o
1,967 1784
I 38 __
I
~
.,..
1715 1648
"°
FIG. 7. Seismic ruptures of 17th-20th centuries in the North Anatolian fault zone (Ambraseys, 1975, 1988, 1989).
World Map of Active Faults
o
o
20--
l0
-
E Z
I
I
I
I
I
10
20
30
40
50m
Left l a t e r a l offset
FIG. 8. The histogram of distribution of different sinistral strike-slip offsets of the minor landforms in the central parts of the Khangay fault in northern Mongolia (Trifonov, 1985).
and the Kobdo faults of Mongolia as well as several faults of China and in Soviet Central Asia belong to this type. The creep regime was detected in areas with unconsolidated and incompetent rocks (clays, serpentinites, etc.) as well as with very fractured and tectonically destructed rocks, often with the fluid activity and the high heat flow. The regime is characterized by slow movements with a large number of weak earthquakes and moderate earthquakes repeated every several tens of years. The active fault zones between the Pamirs and the Tien Shan with the tectonically destructed and incompetent rocks as well as in Western Turkmenia with the thick section of weakly consolidated sediments belong to this type. The impulse-creep regime is really a combination of phenomena of the first and second types. It is characteristic of island arcs, ophiolitic zones and areas with thin continental crust. In active zones with the impulse-creep regime large displacements occur during strong earthquakes repeated through several hundred years. But unlike the zones with the impulse regime, the weaker earthquakes (and the creep in some zones) occur in periods between strong earthquakes. Jackson and McKenzie (1988) tried to estimate the contribution of seismic movements to the total deformation rates in the interplate active zones by comparison of seismic deformation rates in the twentieth century with the total deformation rate in the Neogene and the Quaternary calculated from geological and geophysical data. The method gave good results for regions with small contribution of the seismic movements, i.e. with the creep regime (the Zagros, the Crete arc, the Sicily and the Tell-Atlas) because of the relatively small recurrence interval between the earthquakes, but the method did not show satisfactory results for some zones with the impulse and the impulse-creep regimes. For example, in the different parts of the North Anatolian zone the calculated contribution ranges from 80 to 250%. It obviously reflects the fact that in the 20th century the fault zone revealed growing seismic activity. Recalculated for four centuries, the seismic contribution turned out to be several times less (Fig. 7). On the other hand, the Levant zone showed a small contribution because of absence of catastrophic earthquakes in the 20th century. However, such earthquakes happened there in the previous
9
centuries. In the Damascus region they have been repeated every 200 to 300 years (Karam E1 Hakeem, 1986). Thus, it is necessary to analyze the seismic history over a longer time interval, and the data of paleoseismicity are useful for the analysis. Studying the San Andreas fault, Wallace (1968) proposed the technique for registration of strong Holocene earthquakes in the major strike-slip zones. We developed the technique by studying some Mongolian and Central Asian active faults (Trifonov, 1985). All offsets of minor landforms are measured in some representative fault segment and shown in a histogram (Fig. 8). The discrete distribution of the offset magnitudes shows that the increase of the general fault displacement was carried out mostly by the impulse movements, i.e. probably during strong earthquakes. In the histogram of Fig. 8 there are 7 or 8 maxima of offsets. The smallest maximum is 5-6 mm and corresponds to the offset during the earthquake of 1905 with magnitude of 8.3. Each larger offset is 5-6 m bigger than the smaller one. It means that every former strong earthquake produced approximately the same offset as the earthquake of 1905 and could have had the same magnitude. Different techniques were proposed to estimate the recurrence interval between the strong earthquakes in the regions. Nikonov et al. (1983) used the 14C age determinations of the landslides provoked by the Holocene earthquakes in the northern flank of the Pamirs. In Fig. 9A the land surface projection of the underground irrigational channel, built approximately 2300 years ago and later displaced dextrally along the Main Copet Dagh fault during three strong earthquakes and reconstructed after them, is shown. So, the recurrence interval was from 600 to 750 years. Sieh (1978) studied the correlation between the Late Holocene lake deposits at the Pallet Creek and fractures, created by the strong earthquakes in the San Andreas fault zone. It permitted the determination of the age of the fracture displacements and estimation of the recurrence interval of the strong earthquakes. It was 160 _+ 100 years. Depending on topography, active fault zones may display different signs of strong earthquakes. On the crossections of the mountain areas the strong earthquakes are often marked by colluvium lenses among the thinner deposits (Fig. 9B). The ~4Cdating of the deposits permitted estimation of the age of the colluvium, i.e. the age of the earthquakes (Deng Quidong and Zhang Weiqi, 1984). Another technique was used for the same estimation in the Khangay left lateral west-trending fault zone of Mongolia with more gentle topography (Trifonov, 1985). The small extensional structures (grabens and sag ponds behind the normal faults dammed streams) were formed in the local northeastern-trending segments of the fault (Fig. 9C). They were renewed during the strong earthquakes and their subsidence were marked by lacustrine or swamp deposits. During the quiet epochs between earthquakes these deposits were covered by alluvium or deluvium. Fine swamp material from different ponds marking the moments of their subsidence (i.e. earthquake) was dated by 14C (Fig. 9D). Their correlation across the fault zone showed that at least 8
10
V.G. Trifonov
SW t
0 19 20m
NE
/
" ,
I I
,
~ . ~ ~
l
~ - r
I
I
•*';;.,.,. •
..~.~." ~
....
.
.
°....
x\ ;.
i"
o
,
.
~lml~ 4
~. , •
.
•
~...*':.
'....*...-*.
o -.,.*~.**" , ,'. ,: o . .
~,.
". ". . * a ~.
•
. .;
/
.. .
o . •,"
,O*/83--600
,
[ ~
Breccia 14C date site
~
Sand
~'~
Precambrian schist and marble
~
The number of cultural relic layer
F~
a
' ~ Gravel
Eroded loess
]
. . . . .
Cnllnvian wedge produced bt earthquaake and the number of normal accumulation
h
Remains of cave
~
C
~ears 0
cm 0
7
;"~
~"
~
\, ~
1o9o±5o 40
I1~- -~17s0+200
IOO0
. I• ~
/---
li~'3STO~So it--~-
!
r •J I=~Z elOO ~-=-q I I~
2000
•l ~ :
i/t1434o
- ~ - -
~ 7 ----I~
I I f I,,,~l ~ \ - m ~ a
3
2370 ,80 t
~
"='~'~"'~ ~
,
I ~ .:11~,+2o r r - m : , / I~'~it ~'~ d • ~'t I tjl ,t ~, "r[j-~l ; I :~2i~:j 'Y~, ' I I
"~
~
I
\,
s
~"
~ -I ~"
L. . . . .
: .3280
920
80
3720
120
i:l~o " ~
~:90 /
__.-JM
''a60
160
3000
4000
~ ~
N
o___/
200
:::::::.:.1 .....
Soil
~
Fine sand
Stones
~
Silt
Gravel
~
Clay
Rough sand
i
o
I
Clay with organics
~
Peat Disconformity
F ~
D
14C d a t e , years Catastrophic earthquake in the time scale
FIG, 9. Signs of the Holocene strong earthquakes in some active fault zones: (A) Offset of the ancient irrigation channel on the Main Copet Dagh fault; the reconstructed channel segments are shown by dots. (B) Profile in the central part of the Haiyuan fault, China (Deng Quidong and Zhang Weiqi, 1990); the signs of earthquakes are represented by colluvium lenses in loess and silt, (C) Principle scheme of formation of graben and pit behind the normal fault scarp in the Khangay fault zone. (D) Correlation of the pit deposits in the Khangay fault zone (Trifonov, 1985; the ~4Cdating was made by L.D. Sulerzhitsky); the signs of earthquakes are represented by lacustrine and swamp materials.
11
World Map of Active Faults 10 8 6 4 = 0
2
o
FI
S-B Z
I
I I I I I I I I I
)~
6 4
q
I
I I
I
I
I
I
\
\
I
1
I
I
o 3 6 9
[
I
[
I
\
I
'~
I
m nh
2 o q
O
mI nI
0
n I [ 1 1 ] I I I [ [ I ] I I I I 12 15 18 21 24 27 30 33 36 39 42 45 4g 51 54m
Right lateral offset l
c
2 Gravel
0 ~3740+600yrs Clay and l o a m y soil
m
'Clay or loamy soil
with organic material
FIG. 10. Characteristics of the dextral strike-slip Holocene offsets in the southeastern part of the Talas-Fergana fault (Trifonov et al., 1990). (A) The histogram of distribution of major landform offsets in the southeastern fault segment (20 km); the thick dots mark the offset maxima that can correspond to increasing of the general displacement during strong earthquakes. (B) The histogram of distribution of minor landform offsets in the next NW fault segment (30 km); the larger distance between some adjacent maxima, than the maxima in the histogram A, shows that the earthquake epicentres were located closer to the segment B, than the segment A. (C) Two sections of the fault pit deposits, located in the southeastern parts of the segments A and B; the first pit corresponds to the ravine offset to 19 m and the second pit corresponds to the offset to 27 m; the '4C dating was made by LD. Sulerzhitsky in the Geological Institute of the Russian Academy of Sciences.
strong earthquakes had occurred during the last 4300 years. The estimated recurrence interval was determined to be 600 ± 300 years. If the signs of the individual earthquakes cannot be identified in the fault zone, a simpler way can be proposed for the preliminary estimation of the recurrence interval. The dated sag pond is correlated with strike-slip offset of the dammed stream. We can estimate using the histogram how many earthquakes are necessary to produce the offset, and calculate the recurrence interval. In this way the recurrence interval of the strong earthquakes was estimated approximately at 750 years in the southeastern part of the Talas-Fergana fault (Fig. 10). The described techniques permit estimates of location, magnitude and recurrence interval of possible strong
earthquakes. REFERENCES
Allen, C.R. (1968). The tectonic environments of seismically active and inactive areas along the San Andreas fault system. Proceedings of Conference on Geological Problems of San Andreas Fault System. Stanford University Publications in Geological Science, Palo Alto, California. Vol. 11, pp. 70-82. Allen, C.R. (1975). Geological criteria for evaluating seismicity. Bulletin of the Geological Society of America, 86, 1041-1057. Abraseys, N.N. (1975). Studies in historical seismicity and tectonics. Geodynamics Today. Royal Scottish Publications, London, pp. 7-16. Ambraseys, N.N. (1988). Engineering seismology. Earthquake Engineering and Structural Dynamics, pp. 1-105.
Ambraseys, N.N. (1989). Temporary seismic quiescence: SE Turkey. Geophysical Journal, 96, 311-331. Dend, Quidong and Zhang, Weiqi (1990). The Haiyuan Active Fault Zone. State Seismological Bureau, Beijing. 286 pp. (in Chinese). Ding, Guoyu (1984). Active Faults of China. Prediction of Earthquakes and Continental Seismicity, pp. 225-242. State Seismological Bureau, Beijing. Drewes, H. and Geiss, E. (1990) Modellirung geodynamischer Deformation in Mittelmeerraum. Satellitengeodasie, pp. 335-349, VCH Verlagsgesellschaft mbH, D-6940, Weihelm. Jackson, J and McKenzie, D. (1988). The relationship between plate motion and seismic moment tensors and the rates of active deformation in the Mediterranian and Middle East. Geophysical Journal, 93, 45-73. Karam, El Hakeem (1986). Analysis of the 1759 A.D. Damascus earthquake. Syrian Atomic Energy Commission, Damascus, 88 pp. Nikonov, A.A. (1977). Recent Crustal Movements: GeologicalGeomorphological and Seismotectonic Aspects. Print. Off. Nauka, Moscow, 240 pp. (in Russian). Nikonov, A.A., Vakov, A.V. and Veselov, I.A. (1983). Seismotectonics and Earthquakes of the Collision Zone Between the Pamirs and the Tien Shan. Print Off. Nauka, Moscow, 240 pp. (in Russian). Oral, M.B., Toksoz, M.N. and Reilinger R. (1991). GRS measurements and finite element modelling of present-day tectonic deformation in the Eastern Mediterranian. AGU chapman conf. on time dependent positioning; Modelling crustal deformation. Annapolis, MD (oral presentation). Pavoni, N. (1971). Recent and Late Cenozoic movements of the Earth's crust. Recent Crustal Movements. Bulletin of the Royal Society of New Zealand, Earth Science Section, 9, 7-17. Sieh, K.E. (1978). Prehistoric large earthquakes by slip on the San Andreas fault at Pallet Creek, California. Journal t~f Geophysical Research, 83, 3907-3939. Tapponnier, P. and Molnar, P. (1976). Slip-line theory and large-scale continental tectonics. Nature, 264, 319-324. Trifonov, V.G. (1978). Late Quaternary tectonic movements of western and
12
V.G. Trifonov
central Asia. Bulletin of the Geological Society of America, 89, 1059-1072. Trifonov, V. G. (1985). Peculiarities of active fault development. Geotectonics, 2, 16-26 (in Russian). Trifonov, V.G. (1991). General specific properties of the recent dynamics of the continent. In: Goretsky, R.G. (ed.), Geodynamics and Tectonosphere Evolution, pp. 144-160. Print. Off. Nauka, Moscow (in Russian).
Trifonov, V.G., Makarov, V.I. and Scobelev, S.F. (1990). The Talas-Fergana active fight lateral fault. Geotectonics, 5, pp. 81-92 (in Russian). Wallace, R.E. (1968). Notes on stream channels offset by the San Andreas fault, southern Coast Ranges, California. Proceedings of Conf. on Geological Problems of San Andreas Fault System, pp. 6-20. University Publications, Stanford. Wallace, R.E. (1970). Earthquake recurrence intervals on the San Andreas Faults. Geological Society of America Bulletin, 81, 2875-2890.
Pergamon
1040-6182(94)00029-8
WORLD MAP OF ACTIVE FAULTS (PRELIMINARY RESULTS OF STUDIES) Vladimir G. Trifonov
Geological Institute of the Russian Academy of Sciences, 7 Pyzhevsky, Moscow 109017, Russia
The Project 'World map of major active faults' was confirmed in 1989 as a part of the International Lithosphere Program. The objectives are to compile the World map in scale 1:10,000,000, the maps of continents in scale 1:5,000,000 and the maps of some seismic regions in scale of 1:1,000,000 or 1:5,000,000 with the Explanatory Notes and the Catalogue of major active faults of continents. The maps will show location, age, sense and rate of motion and reliability of identification of faults not older, than 100,000 years, as well as Middle Pleistocene faults, contemporary folds, flexures, volcanoes and epicentres of strong earthquakes differentiated by magnitude, depth and age. The first results of the Project are discussed. One of them is predominance of the strike-slip component of motion over the vertical one for the majority of continental active faults. It has occurred because the strike-slip motion is more efficient, than the thrust, the reverse and even the normal ones. Strike-slip faults are differentiated into faults of translation, rotation and squeezing. The contribution of seismicity to faulting depends on the inpulse, the creep and the inpulse-creep regimes of recent motion in the fault-zones. Different geological techniques for estimating the motion regime, the magnitudes and the recurrence interval of strong Holocene earthquakes are discussed.
~TRODUCTION All faults with present-day and Holocene offsets or other manifestations of activity during the last 10,000 years have been defined as active faults (Allen, 1975; Trifonov, 1985). However, since it is hard in many regions to differentiate the Holocene geological features from those of the Late Pleistocene, we consider it is necessary to extend the time interval accepted as characteristic for active faults to 100,000 years, i.e. Holocene and Late Pleistocene. Studying active faults is useful for : - - estimating seismic and other geological hazards (volcanism, fluid and gas activity, hydrogeological changes, karst, landslides, catastrophic erosion and sedimentation); - - research of recent geodynamics; - - interpretation of more ancient tectonics by comparison with the recent ones. O B J E C T I V E S AND SENSE OF THE PROJECT
The importance of studying active faults led to the establishment of the Project 'World Map of Major Active Faults' as a part of the International Lithosphere Program in 1989. The objectives of the Project are to compile the World Map at a scale of 1:10,000,000, the maps of the continents at a scale 1:5,000,000 and the maps of some seismically dangerous regions at scales of 1:1,000,000 or 1:500,000. The maps will be accompanied by the Explanatory Notes and the Catalogue of major active faults of the continents. According to the legend of the maps (Fig. 1) all faults are differentiated by intensity of tectonic movements, age of the last manifestation of activity, sense of displacements and reliability of identification. Three groups of faults are differentiated by rates of motion (V): V _> 5 mm/year; 5 mm/year >V _> 1 mm/year; V < 1 mm/year. Three kinds of faults of their segments are differentiated by age of the last
manifestation of activity: (1) the historical time; (2) the Holocene and the Late Pleistocene; (3) the Middle Pleistocene (700,000-100,000 years ago). We decided to show in the maps the information about Middle Pleistocene faults because Late Quaternary displacements are very small in relatively inactive regions, and to estimate the tendency of recent motion it is necessary to use data representing a wider time span. It is reasonable to show these faults also with a view to using the maps for nuclear power plant investigations. The historical period is different in different regions. As well, the lower boundaries of the epochs (2) and (3) may vary from one region to others. All these differences will be shown in the final map legend according to the author's contributions. The faults are differentiated between the reliable and the inferred ones and into 5 kinematic types. These are: (1) thrusts and reverse faults; (2) strike-slip faults; (3) normal faults; (4) extensional faults (i.e. cracks and narrow grabens without vertical or strike-slip movements of the fault sides); (5) faults with unknown sense of slip. Deep-sited fault zones, buried by non-faulted rocks and manifested in the land surface only by indirect signs, are shown by a special symbol. Transform faults and surficial continuations of deep-sited seismofocal zones are to be shown in the oceans only. Manifestations of young folds, contemporary and Holocene volcanism and seismicity are shown in the maps as reflecting tectonic activity. Young anticlines, synclines and flexures are differentiated by the age of the last deformation in the same manner as the faults are. Epicentres of earthquakes are differentiated by hypocentre depths H (H _< 70 km; 70 km < H < 300 km; H _>300 km), magnitudes of earthquakes M (4 < M < 6, shown only in stable regions; 6 _< M < 7; 7 _
4
V.G. Trifonov ACTIVE FAULTS, d i f f e r e n t i a t e d by: Rates of f a u l t movements V: ~ V > 5 mm/yr ~ A l l f a u l t s with unknown r a t e s can be shown only | f ]5 mm/yr>V>l mm/yr ~ by symbols of the t h i r d or the second groups ~ V < I mm/yr J Age of the l a s t m a n i f e s t a t i o n s of a c t i v i t y : ~Historical (blue) ~ The h i s t o r i c a l pe ri od i s d i f f e r e n t in ~Holocene and Late P l e i s t o c e n e , | d i f f e r e n t r e g i o n s , and the lower boundsi . e . the l a s t 100,000 y r s | r e d ) ~ r i e s of the second and the t h i r d groups ~Middle Pleistocene, i.e. [ c a n vary from one re gi on t o o t h e r s . 700,000-100,000 yrs ago (black) JThese d i f f e r e n c e s w i l l be shown in the f i n a l map legend More d e t a i l e d age d i f f e r e n t i a t i o n in some r e g i o n s : ~ L a t e P l e i s t o c e n e , i . e . 100,000-10,000 y r s ago ( a l t e r n a t i o n of blue and red s h o r t l i n e s ) ; in those r e g i o n s the f a u l t s with Holocene (t he l a s t 10,000 yrs) a c t i v i t y w i l l be shown by red l i n e s ~Reliable Middle P l e i s t o c e n e a c t i v i t y and surmised Late P l e i s t o c e n e and Holocene a c t i v i t y ( a l t e r n a t i o n of b l a c k and red s h o r t l i n e s ) Sense of d i s p l a c e m e n t s and r e l i a b i l i t y of f a u l t i d e n t i f i c a t i o n : ~Thrusts and r e v e r s e f a u l t s ~ Reliable ~Strike-slip faults [ f a u l t s a re ~Normal faults ]shown on the ~lExtensional f a u l t s , i . e . c r a c k s and narrow grabens w i t h o u t ~ l e f t and g e n e r a l v e r t i c a l or s t r i k e - s l i p o f f s e t s of t he f a u l t s i d e s ]]fsauur lmt i sse d ~ w ~ - ' ~ F a u l t s with unknown sense of s l i p are ~Transform faults ~ Jshown on the ~Surficial continuations of ~Only in the oceans right ~+deep-sited seismofocal zones ~ - ~ D e e p - s i t e d fault zones, buried by nonfaulted rocks and manifested in the land surface only by indirect signs
YOUNG FOLDS, diffirentiated by age of the last deformation t o the same groups as f a u l t s : ~Anticlines, l i n e a r on the l e f t and i s o m e t r i c on the r i g h t ~Synclines, l i n e a r on t he l e f t and i s o m e t r i c on the r i g h t ~Flexures YOUNG VOLCANISH: ~ F - ~ V o l c a n o e s , a c t i v e now on the l e f t (red) and in the Late Quaternary on the r i g h t (bla c k; the time i n t e r v a l can be d i f f e r e n t in d i f f e r e n t r e g i o n s and i t w i l l be shown in the f i n a l map legend) ~ } - ~ A r e a s of the hydrothermal a c t i v i t y , shown in t he map s c a l e on the l e f t and out of the s c a l e on the r i g h t EARTHQUAKE EPICENTRES, d i f f e r e n t i a t e d by: Depths of hypocentres H: O [{470 km ( r e d ) ; O 70 km
o
s4M<7;0 7~M
Ages of events: 0 of the XX c e n t u r y ; ~ o l d e r than the XX c e nt ury; @ rec ords of p a l e o s e i s m i c i t y FIG. 1. The legend of maps of major active faults of the World (1:10,000,000) and the continents (1:5,000,000).
The Explanatory Notes must contain principles and methods of active fault detection, regional description of the faults, regional and planet-scale regularities of recent tectonics. The following characteristics of active faults must be shown in the Catalogue by special symbols: (1) number and name; (2) co-ordinates (~b, ~,) of both ends of the fault and points, where its parameters change; (3) average strike; (4) dip (for points or segments of the fault with the coordinates); (5) length; (6) sense of slip; (7) faulted layers of the lithosphere; (8) age of the last manifestation of activity; (9) signs of fault activity; (10) magnitudes of vertical and lateral offsets during the indicated time interval (for points or segments of the fault with the coordinates); (1 I) rates of motion (total and of different components of motion); (12) seismic manifestations; (13) other records of activity (exogeneous, geophysical, hydrothermal, gas and hydro-
geochemical, volcanic, etc.); (14) reliability of data (A, B or C); (15) author(s) of the interpretation and references. The faults with various characteristics are shown by segments. Of course, not all characteristics can be determined for each fault and shown in the Catalogue. Records of fault activity include the following: (1) Offsets of young topographic features and deposits (channels, valleys, terraces, alluvium fans, etc.); (2) Contrast of composition and/or thickness of young deposits; (3) Seismological data (chains of hypocentres; sense and volume of displacement, found by calculation of focal parameters; recent and old seismic ruptures in the land surfaces; other signs of paleoseismicity); (4) Geophysical data testifying to recent motion in the deeper part of the Earth's crust and the lithosphere; (5) Geodetic data;
World Map of ActiveFaults L
data are available, geological and/or geomorphological correlation with dated objects can be used for the estimation. The geometry of the fault line as well as the data of the Catalogue will be presented in the computer data base. The Project led by V.G. Trifonov joins 50 scientists from 30 countries and is open for wider cooperation. The Project is supported by ICSU and UNESCO as a contribution of the International Lithosphere Program to the International Decade of Natural Disaster Reduction.
L'R m
10,000 7500
10,000
--
5OO0 4OO0 3000 2000 1500
D
1000 750
1000
-
500 400 3OO
--
200 150
:
5
oeOcV •
P R E D O M I N A N C E OF S T R I K E - S L I P F A U L T M O T I O N IN T H E C O N T I N E N T S O
The implementation of the Project is in progress now and the initial results can be presented. At first, the vertical 50 A 40 component of fault offsets within the continents appears to AO~O ~ O -• O 30 V ~v be controlled by the reverse or thrust motion, rather than by 20 T A % normal faulting. In this sense, essentially different regimes 10 -DO V O I0 seem to dominate only in some regions, such as Eastern 5 -OA ' ~ ev I I I Lo,, t t Africa (System of the Great African Faults), Eastern China, 0 6 7 g M 6 7 8 M the Baykal region (the Baykal rift system) and the Lut basin ~ " ] Strike-slipfaults ~ in Iran. It shows that the major part of the continents is under o ~ ~ - ] Normalfaults the influence of compression at present. The more important results confirming previous data [ " ~ Thrusts, reversefaults O (Pavoni, 1971; Tapponnier and Molnar, 1976; Nikonov, FIG. 2. Correlationbetweenthe magnitudesM of the strongearthquakesof 1977; Trifonov, 1978; Ding Guoyu, 1984) is the the 20th century and the lengths L (km) of seismic ruptures in the land surface (on the left) and the lengths L (km) multiplied to the maximum predominance of the strike-slip component of the motion seismic offsets R, (m) (on the fight) (Trifonov, 1991). It is seen that the over the vertical one for the majority of the continental faults. strike-slipfaultsproducethe longerL and the largerL x Rmfor the sameM, This phenomenon can be understood if it is connected with than the normal and especiallythe thrust faults. peculiarities of strike-slip sense of motion. Studying of seismic ruptures in the land surface during the 53 strong earthquakes of the 20th century (Fig. 2) shows that strike-slip faults are more energy efficient than thrust, reverse and even the normal ones. It means that for a given magnitude of (6) offsets of artificial or natural objects, discovered by earthquake, length of rupture and the length multiplied to offset mould be greater for the strike-slip faults than for using historical or archeological data. These records permit to map an active fault as a defined normal and especially thrust ones. Three types of active strike-slip faults can be identified. one. Other records permit faults to be shown only as inferred These are faults of translation, rotation and squeezing. Faults active faults. These are: of translation are typical for flank sides of moving plates and (7) Young volcanic chains and fractures; (8) Signs of present-day and Late Quaternary microplates and for the majority of intraplate regions. They are faults with one side moving as a whole relative to the hydrothermal activity; (9) Mud volcanoes and data about abnormally high layer other one. The San Andreas fault zone between the North American and the Pacific plates, the Levant and the East pressure; (10) Recent gas and hydro-geological anomalies in the Anatolian zones, and the Main recent fault of Zagros on the sides of the Arabian plate, the Chaman, the Darvaz and the fault zone; (11) Concentration of landslides and other exogeneous Pamir-Karakorum faults on the sides of the Indian plate as well as the Talas-Fergana, the Djunghar and the other major signs of geodynamic activity; (12) Active flexure or linear fold system above the intraplate faults of Asia belong to this type (Fig. 3). Strike-slip faults of rotation and squeezing are surmised buried fault; (13) Linear deformation of topography in space images characteristic of the collision regions. In the faults of rotation as well as spectrometric anomalies interpreted as the strike-slip effect is produced by rotation of rocks between two faults in front of the moving plate or large block (Fig. 4). manifestations of recent geodynamic activity. The estimation of the age of fault motion (as well as of The result of rotation is shortening of territory in crossection, other manifestations of activity) are based on 14C, K-Ar, i.e. the same as the result of thrusting or folding. This type of thermoluminescent, tephrochronological, pale•magnetic, tectonic motion took place in northern Armenia between the lichen•metric, historical and archeological and instrumental northwestern parts of the Pambak-Sevan and the Alavar (geodetic and seismological) dating of rock complexes offset faults during the Spitak earthquake of 1988, as well as in the by the fault or created by slipping along its plane. If no direct earlier stages of development of the faults (Fig. 4E). Both 100 75
m
•O
••
V V
~
aV
100
-
-
tt
j
~['~ ~"
v
6
V.G. Trifonov
;.u
~2
0
~L, --'E
1
',5
il'
,...,
z~
L.,,.
c5 ~
~ o o
0 ~
0
~P
,
Z 41
z~ 2~
~c
0
k_____
Cg m~
~,
World Map of Active Faults
I;1 :i
Iql
I,I !/
35
7
d0
45
50
--1 70
72
I "~
11
;/I
'~
,
,
I 22,,,,,0, ,,
T
5
I[[,,I
, 0
5
t
10 km "
EA " ~ ~
-~
,..~ ~
PS
Stress direction
VV~
Symbolic lines showing block deformatio.
Direetionofrockmotion
~
Former position of faults
FIG. 4. Kinematic types of strike-slip faults: (A,B) Principal schemes of formation of faults of rotation (A) and squeezing (B); (C) Squeezing of sedimentary rocks in the northeastern part of the Tadjik depression; (D) Major active faults of the Middle East (EA-the East Anatolian zone, LV-the Levant zone, MZ-the Main recent fault of Zagros, NA-the North Anatolian zone, PS-the Pambak-Sevan fault) with location of Figs 4E and 6; (E) Strike-slip faults of rotation and squeezing in the epicentral area of the Spitak earthquake of 1988 in the northern Armenia (AL-the Alavar fault, EA-the East Anatolian zone, PS-the Pambak-Sevan fault). Symbols are shown in Fig. l.
faults are dextral with magnitudes of strike-slip offsets several times larger than those of contemporary reverse components of displacements. The strike-slip faults of squeezing are produced by not only shortening rocks in cross-section in front of the moving plate or the block, but also by squeezing rocks out of the area with maximum compression. The squeezing is accompanied by non-uniform longitudinal lengthening of the squeezed zone and thrusting and folding around the moving plate. This type of motion is represented by the active structure of the Tadjik depression and the Kunluns in both sides of the Pendjab--Pamir syntaxis as well as of the Anatolian and the Iranian microplates in both sides of the Arabian syntaxis. The motion of the Anatolian rocks to the west along the North-Anatolian and the other west- and southwest-trending dextral strike-slip faults results in extension of the Aegean region and thrusting of its southern side to the African plate. It means that the recent evolution of the Cretean arc depends on the kinematics of the microplate interaction in the southern part of Eurasia rather than of the northern drift of the African plate. This interpretation is supported by determination of recent crustal movements of the region by using the GPS technique (Drewes and Geiss, 1990; Oral et al., 1991) (Fig. 5). The East Anatolian fault zone was continued by our studies to the northeast of the North Anatolian zone to Northern Armenia, and sinistral offsets were found there as well as in the southwestern part of the zone. The principal
N I cm/A 50
40
301
20
30
40
FIG. 5. Vectors of present-day deformation in the Eastern Mediterranian by the G P S data, calculated for the non-homogeneous faulted model (Drewes and Geiss, 1990). Stars show point of observation.
8
V.G. Trifonov 38
40
42
44
40 Erzurum Erzincan
o*'
/
0 g
38
50 it
100 k m !
FIG. 6. Intersection of the North Anatolian and the East Anatolian active fault zones (A) and principal scheme of evolution of these faults (B). The oldest fault branches in (A) and new fault branches in (B) are shown by dots. Other symbols are shown in Fig. 1.
site is the area of interaction of two active strike-slip faults: the North Anatolian dextral zone with a rate of recent motion of 20 mm/year and the East Anatolian sinistral zone with a rate of 5 mm/year (Fig. 6). We found several fault branches in the North Anatolian zone to the northwest of the intersection, the southern branch being the oldest one and the northern branch being the youngest. The same peculiarity was found in the East Anatolian zone to the SW of the intersection. The southeastern branch is the youngest there. We interpreted these peculiarities of both fault zones in the following way: the strike-slip movement along one of the faults offset the other fault, halting the possibility of movement along it. As a result, the new fault branch, joining the offset fault segments was formed. The subsequent movement along the fault thus restored offset the first one, and the latter had to form the new branch for the continuation of movement etc. (Fig. 6B). The distances between branches of the East Anatolian zone are larger than of the North
Anatolian zone because of the larger rate of motion along the latter. C O N T R I B U T I O N OF S E I S M I C I T Y T O F A U L T I N G AND S I G N I F I C A N C E OF A C T I V E FAULTS F O R E S T I M A T I O N OF S E I S M I C HAZARD Allen (1968) and Wallace (1970) showed dependence of recent motion regimes in different parts of the San Andreas fault on the geology of the fault zone. Three types of the regime were differentiated by comparative analysis of active faults (Trifonov, 1985). These are the impulse, the creep and the impulse-creep regimes. The impulse regime is typical for the thick sections of granitic and metamorphic hard rocks of the upper crust. The regime is characterized by large offsets during strong earthquakes after periods with the lack of essential movements for several hundreds or in some areas even several thousand years. The Khangay, the Gobi-Altay
4 0 ~ 42 44
4 26
28
30
32
34
36
38
4q
4o
1,967 1784
I 38 __
I
~
.,..
1715 1648
"°
FIG. 7. Seismic ruptures of 17th-20th centuries in the North Anatolian fault zone (Ambraseys, 1975, 1988, 1989).
World Map of Active Faults
o
o
20--
l0
-
E Z
I
I
I
I
I
10
20
30
40
50m
Left l a t e r a l offset
FIG. 8. The histogram of distribution of different sinistral strike-slip offsets of the minor landforms in the central parts of the Khangay fault in northern Mongolia (Trifonov, 1985).
and the Kobdo faults of Mongolia as well as several faults of China and in Soviet Central Asia belong to this type. The creep regime was detected in areas with unconsolidated and incompetent rocks (clays, serpentinites, etc.) as well as with very fractured and tectonically destructed rocks, often with the fluid activity and the high heat flow. The regime is characterized by slow movements with a large number of weak earthquakes and moderate earthquakes repeated every several tens of years. The active fault zones between the Pamirs and the Tien Shan with the tectonically destructed and incompetent rocks as well as in Western Turkmenia with the thick section of weakly consolidated sediments belong to this type. The impulse-creep regime is really a combination of phenomena of the first and second types. It is characteristic of island arcs, ophiolitic zones and areas with thin continental crust. In active zones with the impulse-creep regime large displacements occur during strong earthquakes repeated through several hundred years. But unlike the zones with the impulse regime, the weaker earthquakes (and the creep in some zones) occur in periods between strong earthquakes. Jackson and McKenzie (1988) tried to estimate the contribution of seismic movements to the total deformation rates in the interplate active zones by comparison of seismic deformation rates in the twentieth century with the total deformation rate in the Neogene and the Quaternary calculated from geological and geophysical data. The method gave good results for regions with small contribution of the seismic movements, i.e. with the creep regime (the Zagros, the Crete arc, the Sicily and the Tell-Atlas) because of the relatively small recurrence interval between the earthquakes, but the method did not show satisfactory results for some zones with the impulse and the impulse-creep regimes. For example, in the different parts of the North Anatolian zone the calculated contribution ranges from 80 to 250%. It obviously reflects the fact that in the 20th century the fault zone revealed growing seismic activity. Recalculated for four centuries, the seismic contribution turned out to be several times less (Fig. 7). On the other hand, the Levant zone showed a small contribution because of absence of catastrophic earthquakes in the 20th century. However, such earthquakes happened there in the previous
9
centuries. In the Damascus region they have been repeated every 200 to 300 years (Karam E1 Hakeem, 1986). Thus, it is necessary to analyze the seismic history over a longer time interval, and the data of paleoseismicity are useful for the analysis. Studying the San Andreas fault, Wallace (1968) proposed the technique for registration of strong Holocene earthquakes in the major strike-slip zones. We developed the technique by studying some Mongolian and Central Asian active faults (Trifonov, 1985). All offsets of minor landforms are measured in some representative fault segment and shown in a histogram (Fig. 8). The discrete distribution of the offset magnitudes shows that the increase of the general fault displacement was carried out mostly by the impulse movements, i.e. probably during strong earthquakes. In the histogram of Fig. 8 there are 7 or 8 maxima of offsets. The smallest maximum is 5-6 mm and corresponds to the offset during the earthquake of 1905 with magnitude of 8.3. Each larger offset is 5-6 m bigger than the smaller one. It means that every former strong earthquake produced approximately the same offset as the earthquake of 1905 and could have had the same magnitude. Different techniques were proposed to estimate the recurrence interval between the strong earthquakes in the regions. Nikonov et al. (1983) used the 14C age determinations of the landslides provoked by the Holocene earthquakes in the northern flank of the Pamirs. In Fig. 9A the land surface projection of the underground irrigational channel, built approximately 2300 years ago and later displaced dextrally along the Main Copet Dagh fault during three strong earthquakes and reconstructed after them, is shown. So, the recurrence interval was from 600 to 750 years. Sieh (1978) studied the correlation between the Late Holocene lake deposits at the Pallet Creek and fractures, created by the strong earthquakes in the San Andreas fault zone. It permitted the determination of the age of the fracture displacements and estimation of the recurrence interval of the strong earthquakes. It was 160 _+ 100 years. Depending on topography, active fault zones may display different signs of strong earthquakes. On the crossections of the mountain areas the strong earthquakes are often marked by colluvium lenses among the thinner deposits (Fig. 9B). The ~4Cdating of the deposits permitted estimation of the age of the colluvium, i.e. the age of the earthquakes (Deng Quidong and Zhang Weiqi, 1984). Another technique was used for the same estimation in the Khangay left lateral west-trending fault zone of Mongolia with more gentle topography (Trifonov, 1985). The small extensional structures (grabens and sag ponds behind the normal faults dammed streams) were formed in the local northeastern-trending segments of the fault (Fig. 9C). They were renewed during the strong earthquakes and their subsidence were marked by lacustrine or swamp deposits. During the quiet epochs between earthquakes these deposits were covered by alluvium or deluvium. Fine swamp material from different ponds marking the moments of their subsidence (i.e. earthquake) was dated by 14C (Fig. 9D). Their correlation across the fault zone showed that at least 8
10
V.G. Trifonov
SW t
0 19 20m
NE
/
" ,
I I
,
~ . ~ ~
l
~ - r
I
I
•*';;.,.,. •
..~.~." ~
....
.
.
°....
x\ ;.
i"
o
,
.
~lml~ 4
~. , •
.
•
~...*':.
'....*...-*.
o -.,.*~.**" , ,'. ,: o . .
~,.
". ". . * a ~.
•
. .;
/
.. .
o . •,"
,O*/83--600
,
[ ~
Breccia 14C date site
~
Sand
~'~
Precambrian schist and marble
~
The number of cultural relic layer
F~
a
' ~ Gravel
Eroded loess
]
. . . . .
Cnllnvian wedge produced bt earthquaake and the number of normal accumulation
h
Remains of cave
~
C
~ears 0
cm 0
7
;"~
~"
~
\, ~
1o9o±5o 40
I1~- -~17s0+200
IOO0
. I• ~
/---
li~'3STO~So it--~-
!
r •J I=~Z elOO ~-=-q I I~
2000
•l ~ :
i/t1434o
- ~ - -
~ 7 ----I~
I I f I,,,~l ~ \ - m ~ a
3
2370 ,80 t
~
"='~'~"'~ ~
,
I ~ .:11~,+2o r r - m : , / I~'~it ~'~ d • ~'t I tjl ,t ~, "r[j-~l ; I :~2i~:j 'Y~, ' I I
"~
~
I
\,
s
~"
~ -I ~"
L. . . . .
: .3280
920
80
3720
120
i:l~o " ~
~:90 /
__.-JM
''a60
160
3000
4000
~ ~
N
o___/
200
:::::::.:.1 .....
Soil
~
Fine sand
Stones
~
Silt
Gravel
~
Clay
Rough sand
i
o
I
Clay with organics
~
Peat Disconformity
F ~
D
14C d a t e , years Catastrophic earthquake in the time scale
FIG, 9. Signs of the Holocene strong earthquakes in some active fault zones: (A) Offset of the ancient irrigation channel on the Main Copet Dagh fault; the reconstructed channel segments are shown by dots. (B) Profile in the central part of the Haiyuan fault, China (Deng Quidong and Zhang Weiqi, 1990); the signs of earthquakes are represented by colluvium lenses in loess and silt, (C) Principle scheme of formation of graben and pit behind the normal fault scarp in the Khangay fault zone. (D) Correlation of the pit deposits in the Khangay fault zone (Trifonov, 1985; the ~4Cdating was made by L.D. Sulerzhitsky); the signs of earthquakes are represented by lacustrine and swamp materials.
11
World Map of Active Faults 10 8 6 4 = 0
2
o
FI
S-B Z
I
I I I I I I I I I
)~
6 4
q
I
I I
I
I
I
I
\
\
I
1
I
I
o 3 6 9
[
I
[
I
\
I
'~
I
m nh
2 o q
O
mI nI
0
n I [ 1 1 ] I I I [ [ I ] I I I I 12 15 18 21 24 27 30 33 36 39 42 45 4g 51 54m
Right lateral offset l
c
2 Gravel
0 ~3740+600yrs Clay and l o a m y soil
m
'Clay or loamy soil
with organic material
FIG. 10. Characteristics of the dextral strike-slip Holocene offsets in the southeastern part of the Talas-Fergana fault (Trifonov et al., 1990). (A) The histogram of distribution of major landform offsets in the southeastern fault segment (20 km); the thick dots mark the offset maxima that can correspond to increasing of the general displacement during strong earthquakes. (B) The histogram of distribution of minor landform offsets in the next NW fault segment (30 km); the larger distance between some adjacent maxima, than the maxima in the histogram A, shows that the earthquake epicentres were located closer to the segment B, than the segment A. (C) Two sections of the fault pit deposits, located in the southeastern parts of the segments A and B; the first pit corresponds to the ravine offset to 19 m and the second pit corresponds to the offset to 27 m; the '4C dating was made by LD. Sulerzhitsky in the Geological Institute of the Russian Academy of Sciences.
strong earthquakes had occurred during the last 4300 years. The estimated recurrence interval was determined to be 600 ± 300 years. If the signs of the individual earthquakes cannot be identified in the fault zone, a simpler way can be proposed for the preliminary estimation of the recurrence interval. The dated sag pond is correlated with strike-slip offset of the dammed stream. We can estimate using the histogram how many earthquakes are necessary to produce the offset, and calculate the recurrence interval. In this way the recurrence interval of the strong earthquakes was estimated approximately at 750 years in the southeastern part of the Talas-Fergana fault (Fig. 10). The described techniques permit estimates of location, magnitude and recurrence interval of possible strong
earthquakes. REFERENCES
Allen, C.R. (1968). The tectonic environments of seismically active and inactive areas along the San Andreas fault system. Proceedings of Conference on Geological Problems of San Andreas Fault System. Stanford University Publications in Geological Science, Palo Alto, California. Vol. 11, pp. 70-82. Allen, C.R. (1975). Geological criteria for evaluating seismicity. Bulletin of the Geological Society of America, 86, 1041-1057. Abraseys, N.N. (1975). Studies in historical seismicity and tectonics. Geodynamics Today. Royal Scottish Publications, London, pp. 7-16. Ambraseys, N.N. (1988). Engineering seismology. Earthquake Engineering and Structural Dynamics, pp. 1-105.
Ambraseys, N.N. (1989). Temporary seismic quiescence: SE Turkey. Geophysical Journal, 96, 311-331. Dend, Quidong and Zhang, Weiqi (1990). The Haiyuan Active Fault Zone. State Seismological Bureau, Beijing. 286 pp. (in Chinese). Ding, Guoyu (1984). Active Faults of China. Prediction of Earthquakes and Continental Seismicity, pp. 225-242. State Seismological Bureau, Beijing. Drewes, H. and Geiss, E. (1990) Modellirung geodynamischer Deformation in Mittelmeerraum. Satellitengeodasie, pp. 335-349, VCH Verlagsgesellschaft mbH, D-6940, Weihelm. Jackson, J and McKenzie, D. (1988). The relationship between plate motion and seismic moment tensors and the rates of active deformation in the Mediterranian and Middle East. Geophysical Journal, 93, 45-73. Karam, El Hakeem (1986). Analysis of the 1759 A.D. Damascus earthquake. Syrian Atomic Energy Commission, Damascus, 88 pp. Nikonov, A.A. (1977). Recent Crustal Movements: GeologicalGeomorphological and Seismotectonic Aspects. Print. Off. Nauka, Moscow, 240 pp. (in Russian). Nikonov, A.A., Vakov, A.V. and Veselov, I.A. (1983). Seismotectonics and Earthquakes of the Collision Zone Between the Pamirs and the Tien Shan. Print Off. Nauka, Moscow, 240 pp. (in Russian). Oral, M.B., Toksoz, M.N. and Reilinger R. (1991). GRS measurements and finite element modelling of present-day tectonic deformation in the Eastern Mediterranian. AGU chapman conf. on time dependent positioning; Modelling crustal deformation. Annapolis, MD (oral presentation). Pavoni, N. (1971). Recent and Late Cenozoic movements of the Earth's crust. Recent Crustal Movements. Bulletin of the Royal Society of New Zealand, Earth Science Section, 9, 7-17. Sieh, K.E. (1978). Prehistoric large earthquakes by slip on the San Andreas fault at Pallet Creek, California. Journal t~f Geophysical Research, 83, 3907-3939. Tapponnier, P. and Molnar, P. (1976). Slip-line theory and large-scale continental tectonics. Nature, 264, 319-324. Trifonov, V.G. (1978). Late Quaternary tectonic movements of western and
12
V.G. Trifonov
central Asia. Bulletin of the Geological Society of America, 89, 1059-1072. Trifonov, V. G. (1985). Peculiarities of active fault development. Geotectonics, 2, 16-26 (in Russian). Trifonov, V.G. (1991). General specific properties of the recent dynamics of the continent. In: Goretsky, R.G. (ed.), Geodynamics and Tectonosphere Evolution, pp. 144-160. Print. Off. Nauka, Moscow (in Russian).
Trifonov, V.G., Makarov, V.I. and Scobelev, S.F. (1990). The Talas-Fergana active fight lateral fault. Geotectonics, 5, pp. 81-92 (in Russian). Wallace, R.E. (1968). Notes on stream channels offset by the San Andreas fault, southern Coast Ranges, California. Proceedings of Conf. on Geological Problems of San Andreas Fault System, pp. 6-20. University Publications, Stanford. Wallace, R.E. (1970). Earthquake recurrence intervals on the San Andreas Faults. Geological Society of America Bulletin, 81, 2875-2890.