Local groundwater and tidal changes induced by large earthquakes in the Taiyuan Basin, North China from well monitoring

Journal Pre-proofs Research papers Local groundwater and tidal changes induced by large earthquakes in the Taiyuan Basin, North China from well monitoring Rui Yan, Guangcai Wang, Yuchuan Ma, Zheming Shi, Jianxin Song PII: DOI: Reference:

S0022-1694(19)31214-4 https://doi.org/10.1016/j.jhydrol.2019.124479 HYDROL 124479

To appear in:

Journal of Hydrology

Received Date: Revised Date: Accepted Date:

28 June 2019 23 October 2019 16 December 2019

Please cite this article as: Yan, R., Wang, G., Ma, Y., Shi, Z., Song, J., Local groundwater and tidal changes induced by large earthquakes in the Taiyuan Basin, North China from well monitoring, Journal of Hydrology (2019), doi: https://doi.org/10.1016/j.jhydrol.2019.124479

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 B.V.

Local groundwater and tidal changes induced by large earthquakes in the Taiyuan Basin, North China from well monitoring Rui Yana, b, Guangcai Wanga, Yuchuan Maa, b, Zheming Shia, Jianxin Song c

a School

of Water Resources and Environment, China University of Geosciences, 100083 Beijing, China.

b China

c China

Earthquake Networks Center, 100045 Beijing, China.

Institute of Geo-environment Monitoring, 10081 Beijing, China

Abstract: Seismically induced water level and tidal behavior changes were analyzed in four wells (TY, QX, XY and JX) in the Taiyuan rift Basin. One of the wells (JX) with higher storativity and higher permeability mainly recorded oscillation changes, which suggests that higher seismic energy density might be required to cause sustained water level changes in such wells. The other three wells recorded sustained water level changes following multiple large earthquakes, in which two of the wells located within fault damage zone or developed fracture area showed synchronized water level and tidal behavior changes after earthquakes. Moreover, the two wells recorded different tidal behaviors (positive or negative correlation between tidal factor and phase shift), which suggested that far field earthquake caused the mixture of vertical flow and radial flow. 1

We suggest that local hydro-geological setting and fissures connected to the aquifer play an important controlling role in earthquake-induced water level and tidal behavior changes.

Key words: Water level, Earth tides, Permeability, Storativity, Taiyuan Basin.

1. Introduction Groundwater level changes caused by earthquakes have been the concern of hydrological seismologists throughout the world since the 1930s (Leggette and Taylor, 1935; Bower and Heaton, 1978; King et al., 1999; Brodsky et al., 2003; Wang et al., 2009). However, the mechanism of offset-type water level changes is uncertain. Several models have been proposed to explain these changes, including poro-elastic pressure response to the earthquake's static strain in the near field (Wakita, 1975; Quilty and Roeloffs, 1997; Jonsson et al., 2003), the compaction and/or liquefaction-induced increase in fluid pressure in sedimentary environments, removal of gas from the pore space (Steinberg et al., 1989; Linde et al., 1994; Matsumoto and Roeloffs, 2003; Wang et al., 2004; Crews and Cooper, 2014), removal of barriers clogging (Brodsky et al., 2003). Recently, the changed permeability model was promoted as the most plausible mechanism for sustained water level changes (Rojstaczer and Wolf, 1992; Rojstaczer et al., 1995; Roeloffs, 1998; Brodsky et al., 2003; Elkhoury et al., 2006; Wang et al., 2009; Geballe et al., 2011; Faoro et al., 2012). For example, Elkhoury et al. (2006) used 2

the response of well water levels to solid Earth tides as a proxy for permeability variations. Specifically, they observed co- and post-seismic phase changes of the tidal band M2 and argued that reductions of the M2 phase indicate permeability increases. The permeability increase depends almost linearly on the amplitude of the peak ground velocity (PGV) of the seismic waves, if it is above a threshold value of about 0.2 cm/s. Kocharyan et al. (2011) analyzed the water level response to remote earthquakes and explosions. It was shown that the amplitude of post-seismic water level changes scale with the square root of the amplitude of the dynamic strain which can change the number of open cracks and increase the effective permeability. On the basis of experimental laboratory data and a compilation of worldwide field observations (Wang and Manga, 2010b), Beresnev et al., (2011) and Manga et al. (2012) concluded that barriers in the fractures can be broken and the effective permeability may increase considerably during the passage of seismic waves. The latest study indicated that permeability changes caused by static or dynamic strain might explain a great number of co-seismic hydrological response (Shi and Wang, 2014; Kinoshita et al., 2015; Shi and Wang, 2015). However, most of the studies were based on single or several wells. Yan et al (2014) studied water level changes at 216 wells induced by the 2011 Tohoku MW 9.0 earthquake in mainland China. They found that earthquake-induced temporal variations in the permeability might have occurred at about 43 per cent of those wells that displayed offset water level changes. The statistical analysis did not indicate any obvious significant relationships between water level changes and any other parameter—except the tidal admittance—indicating that the processes behind 3

groundwater level changes induced by a distant great earthquake are complex. Moreover, the permeability even decrease in some wells (Yan et al., 2017; Shi et al., 2018; Shi et al., 2019). The analogous results were drawn from water level changes following four large earthquakes in mainland China (Shi et al., 2015), and from 161 wells in response to nine earthquakes in Canterbury, New Zealand (Weaver et al., 2019). The reason of earthquake-induced such water level and tidal behavior changes remains unclear.

In this work, we focus on water level and tidal changes induced by multiple large earthquakes in four wells in the Taiyuan rift Basin, North China. In order to clarify the temporal evolution of tidal behavior and further attempt to analyze the mechanism of earthquake induced water level and tidal changes, M2 and O1 tidal factor and phase shift of water level related to volume strain were calculated from May 2007 to May 2019. The results showed that tidal behavior and water level changes after earthquakes occurred in the two wells located in fault damage zones or developed fracture area, which suggested that fissures connected to the aquifer play an important controlling role in earthquake-induced water level and tidal behavior changes.

2. Tectonic background and data collection The study area is located in the middle of Shanxi Province, north of China, in a large-scale Cenozoic rift Basin of Taiyuan (Figure 1). Tectonically, Taiyuan Basin is surrounded by the Lvliang Moutains to the west and by the Taihang Mountains to the east. The surrounding mountains are high with elevation of ~3000 m and the basin is 4

quite flat with elevation from ~735 m to 830 m (Han et al., 2008; Tang et al., 2018).The basin is bounded by the Jiaocheng Fault to the northwest and Taigu Fault to the southeast. The two boundary faults control the shape, evolution history, and hydrogeological settings of the basin. The basin is about 150 km length from northeast to southwest and 40 km width from northwest to southeast, with an area of about 6000 km2 (Xie et al., 2008). In geology, the basin was characterized by thick Cenozoic strata with a depth of about 1000–2000 m. The exposed and deeply buried stratums around it were mainly comprised of Paleozoic, Ordovician, Carboniferous, Permian, and Triassic strata. The bottom of the basin was characterized by Permian and Triassic sandy shale, which was covered by loose rock groups of the Tertiary and Quaternary systems in which the Quaternary strata were deeply buried and gradually become shallower from northwest (500m) to southeast (100-200m). The climate is of a semiarid-type with a mean annual air temperature varying from 4°C to 13°C. Annual rainfall amounts is about 400-650 mm which mainly occurs between June and September (Tang et al., 2013). The Fenhe River and its tributary is the major surface water source, running through the middle section of the basin, flowing from northeast to southwest (Guo et al., 2019). Hydro-geologically, groundwater in the basin is mainly supplied by surrounding mountains through lateral recharge. The aquifers in the basin is mainly composed of the Quaternary Holocene unconfined aquifer group (0–50 m), the Quaternary Late and Middle Pleistocene confined aquifer group (50–200 m), the Quaternary Early Pleistocene lacustrine–alluvial weak aquifer group (200–400 m); and the Neogene red soil with thin layers of sandy gravel lacustrine weak confined aquifer 5

group (Guo et al., 2007). In the last few decades, increasing human activity and continuing over-exploitation of groundwater have caused groundwater-level declines accompanied by land subsidence and developed earth fissures. In this work, we examine the relationship between groundwater level and tidal behavior changes induced by farfield large earthquakes.

Four groundwater monitoring wells were constructed in Taiyuan Basin as part of the groundwater dynamic monitoring network in mainland China, for monitoring pore pressure changes in confined aquifers, which was believed to be associated with possible earthquake precursor. All four wells were drilled into consolidated rocks in 1970s or 1980s and all wells are open. Well depths range from 315 m to 765.78 m. Two of the monitoring wells, TY and QX, are located within the fault damage zone or earth fissure area. The TY well is located at the northwestern edge of the Taiyuan Basin. It is 765.78 m deep and screened at the depth interval of 480–765 m where it penetrates the damage zone of Jiaochen faults. Rock type of the aquifer is limestone with dolomite. The QX well is located in the Taigu–Qixian earth fissure area of central Taiyuan Basin (Peng et al., 2018). Depth of the borehole are 442.19 m and rock types of the aquifers are mainly Metamorphic volcaniclastic rock and bedded tuff. The other two wells, XY and JX, are located in the southern section of the Taiyuan Basin. The XY well is 502.93 m deep and screened at the depth interval of 403-502 m. The JX well is located in a groundwater depression cone of the southern Taiyuan Basin (one of the major coalproducing areas). The JX well is 315 m deep and screened at six different depths in the interval of 77.58-301.64 m. Rock types of aquifer in the open intervals of both wells 6

are mainly sandstone or consolidated sand gravel. Table 1 lists basic well construction information. Figure 1 shows locations of each well and the study area. Figure 2 shows geochronology and lithology information of the aquifer in the wells.

Water level in the four wells are recorded by an LN-3A digital piezometer sensor developed by the Institute of Earthquake Science, China Earthquake Administration (CEA) at a sampling interval of 1 min from May 2007. The digital piezometer readings are converted into groundwater level with a resolution of 1 mm in the range between 0 and 10 m; the absolute accuracy is 0.2 percent of full scale. To identify water level changes induced by earthquakes, barometric pressure and rainfall data near the wells were collected to clarify their influence on water levels in our analysis. Figure 3 shows the time series of water level changes recorded from 2007 to 2019. Additionally, in order to examine the relationship between earthquake-induced groundwater level changes and regional groundwater flow field, we further collected the data of deep groundwater level contours constructed by almost 100 hydrological well data（Figure 1，cyan dots）which were published by Shanxi Geological Environment Monitoring Center, China Geological Survey of Ministry of Land and Resources on 2011 February 28

and

March

30,

(http://www.cgs.gov.cn/xwl/ddyw/201603/t20160309_277664.html, http://www.cgs.gov.cn/xwl/ddyw/201603/t20160309_277724.html).

3 Analysis methods 7

respectively

3.1 Identification of water level changes induced by earthquakes

In general, water level changes induced by earthquakes are related to seismic energy density. A threshold value of 10-3 J/m3 of seismic energy density is required to initiate sustained water level changes (Wang and Manga, 2010b; Yan et al., 2014). To identify potentially earthquake-induced water level changes, the energy densities (J/m3) of worldwide earthquakes were calculated according to log 𝑟 = 0.48𝑀 - 0.33log 𝑒 0.4, where M is the magnitude of the event, r is the epicenter distance in km (Wang and Manga,

2010a).

The

NEIC

(National

Earthquake

Information

Center,

http://earthquake.usgs.gov/earthquakes/search/) earthquake catalog was used. In order to not miss any earthquake, we lower the threshold value to 10-4 J/m3. Then we examine whether these events induced any water level changes in the four wells. Totally, two types of earthquake-induced water level changes were identified: transient dynamic oscillations and sustained changes. Here we mainly focus on sustained water level changes which were induced by 5 events with epicentral distance from 1035 to 4824 km. Seismic energy density of the 5 events ranged from 9.94×10-4 to 6.72×10-2 J/m3. The maximum energy density was caused by the 2011 Tohoku MW 9.0 earthquake which occurred at a distance of 2613 km from the monitoring site TY. Table 2 lists the 5 events used in this study, their geographic locations, magnitude, epicentral distance and energy density at the studied wells. The distribution of the earthquake epicenters are showed in Figure 1.

3.2 Tidal analysis of groundwater level 8

Temporal variations of the tidal parameters reflect changes in an aquifer’s hydraulic properties. Specifically, phase shifts are sensitive to permeability changes and the amplitude changes can be caused by small storage changes (Hsieh et al., 1987; Doan et al., 2006). So tidal parameter can be used to constrain parameters of the formation and to draw inferences about which of those properties changed after earthquakes (Elkhoury et al., 2006; Xue et al., 2013).

In this work, tidal signal were decomposed from the observed water level data and the tidal parameters were calculated with the program Baytap-G (Ishiguro and Tamura, 1985; Tamura et al., 1991). The program Baytap-G can identify four components from water level and barometric pressures, irregular noise, long period trend, barometric response and observed tides. Before doing the tidal analysis, possible steps and spikes caused by instrument malfunctions or maintenance works were removed manually. The water level data were resampled as hourly data from minute sample. A sliding window (window length: 31 days, step: 4 days) was used for analyzing the time-dependent Earth tide parameters. The theoretical volumetric strain tides were selected to calibrate the water level tides. The tidal factors, phases, and amplitudes of the tidal constituents M2, S2, O1, S1/K1 were selected from the Baytap-G output, where tidal factor is defined as the amplitude ratio of observed water pressure to theoretical volumetric strain tide. Negative phases correspond to time lags. The calculating error was given as Root Mean Square Error (RMSE). It should be noted that S1/K1 and S2 are not pure gravitational tides, but also contain an unknown contribution of radiational – sometimes called thermal – tides (Agnew, 2007). The M2 wave is more 9

stable with larger amplitude and less RMSE than O1. Thus, for the discussion with respect to Earth tides, the focus of this work is on the purely gravitational tidal bands M2 and O1.

4 Results 4.1 Water level changes induced by earthquakes

In term of water level changes induced by the 5 events, detail information was listed in Table 3. Both co-seismic offset changes (rise and fall) and oscillations (without persistent changes) were induced during the passage of seismic waves. Offset (rise or fall) co-seismic water level changes were induced by all of the 5 earthquakes in TY, QX and XY wells, and were induced by one earthquake in JX well. The offset amplitudes range from 0.01 to 0.99 m with recovery periods of several hours to tens of days. Oscillations were recorded in JX well after the occurrence of 4 earthquakes. The oscillations maintained several minutes with small amplitudes (0.1-2 cm). For the same earthquake, epicentral distances and seismic energy density did not show any obvious difference between the offset and oscillation changes.

4.2 Tidal behavior changes induced by earthquakes

Figure 4 shows that the M2 tidal parameters varies from May 2007 to May 2019 in the 4 wells. Tidal behavior changes induced by earthquakes only occurred in TY and QX wells. Table 4 listed detailed information of tidal behavior changes induced by earthquakes in TY and QX wells. In TY well, the M2 tidal factor and phase shift showed 10

opposite changes character, i.e., tidal factor of water level decreased after 4 earthquakes with amplitudes ranged from 0.29 to 2.55 GPa. At the same time, phase shift increased with amplitudes ranged from 2.89° to 42.88°. The maximum tidal change was induced by the 2011 Tohoku MW 9.0 earthquake. In QX well, tidal factor and phase shift showed significant changes in the same sign after 5 earthquakes. Synchronous increase of tidal factor and phase shift were recorded after two earthquakes, i.e., the 2007 Sumatra MW 8.5 and the 2012 Sumatra MW 8.6 earthquake. Synchronous decrease of tidal factor and phase shift were recorded after three earthquakes, i.e., the 2008 Wenchuan MW 7.9, the 2011 Tohoku MW 9.0 and the 2015 Nepal MW 7.8 earthquake. The increase tidal factor ranged from 0.88 to 6.27 GPa, and the phases shift ranged from 16° to 75°. The decrease tidal factor ranged from 1.67 to 5.88 GPa, and the phase shifts ranged from 23.35° to 79.78°. After each earthquake, the tidal parameters stayed at high or low level and did not recover to pre-earthquake level except following the 2015 Nepal MW 7.8 earthquake. An additional change of unidentified reason in tidal behavior occurred in 2009 showed the same pattern of changes induced by earthquakes. In XY and JX wells, the temporal variation of the tidal signal was relatively stable. No any significant change was recorded after each earthquake.

5 Discussion In this work, we have presented water level changes caused by five large earthquakes in four wells in a rift basin. Both oscillations and offset (rise and fall) changes in water level were recorded after multiple large earthquakes. The tides were 11

decomposed from well water level, and the tidal factors and phase shift were calculated with Baytap-G program. While, tidal behavior and water level changes did not always occurred simultaneously.

In terms of the five earthquakes, since the static strain caused by the slipping of faults cannot induce such large changes in water level. Even for the nearest 2008 Wenchuan MW7.9 earthquake and for the largest 2011 Tohoku MW 9.0 earthquake, the static strain caused by the Wenchuan and the Tohoku earthquake is about -7.9×10-10 and 3.1×10-9 respectively, which could cause several millimeters of water level changes, far smaller than the observed water level changes. The dynamic strain is a possible candidate.

In terms of the same earthquake, epicentral distance and seismic energy density did not show significant difference. While, different wells recorded water level changes of different polarities. For instance, after the 2011 Tohoku MW 9.0 earthquake, rise and recovery changes in water level were recorded in QX wells, fall of water level were recorded in TY and XY wells, and oscillations were recorded in JX well. According to earthquake-induced permeability changes model, the polarities may be related to local hydraulic gradient (Wang and Manga, 2010b). Co-seismic rise of water level will occur if the permeability enhanced in the up-gradient of the well and co-seismic drop of water level if permeability enhanced in the down-gradient of the well (Shi et al., 2015). To examine the relationship between local hydraulic gradient and earthquake-induced water level changes, we collected the groundwater flow field data before (28 February 12

2011) and after (30 March 2011) the 2011 Tohoku MW 9.0 earthquake. Figure 1 shows the contour map of groundwater level height relative to sea level. Figure 5 shows the corresponding cross-section through QX, XY and JX well. The results show that QX well is located in the center of the basin with flat landform and less local hydraulic gradient. XY and JX wells are located in the margin of the basin with steep terrain and large local hydraulic gradients. It is noted that the aquifer material in JX is mainly sandstone and gravel which is different from other wells with solid rocks. The depth of penetration in JX is higher than other wells relative to mean sea level. The shock waves from earthquakes will travel faster in solid rock than sandy gravels and clayey soils hence more new fractures can occur along paths of solid rock. This can lead to falling or rising of water levels depending on whether the new fractures are dry or wet. From Table 3, all the water level variations in all the wells except JX undergo falling and rising changes. So different aquifer material and local hydraulic gradients could be the reason why different water level responses were recorded in the four wells. In addition, JX well is located in a groundwater depression cone, up-gradient area, hence the water level is always rising slightly. Obvious rising of water level was recorded at center of the depression cone after the 2011 Tohoku MW 9.0 earthquake (Figure 5 CC’ profile).

Tidal factor and phase shift between the water level and the Earth tides were used as a proxy for storativity and permeability changes in the well-aquifer system (Doan et al., 2006; Elkhoury et al., 2006; Xue et al., 2013). The results of water level tidal response showed that the JX well has the smallest mean tidal factor of 1.4 GPa and mean phase shift of -11.9°. The smaller tidal factor and negative phase shift means 13

higher storativity and higher horizontal permeability (Cooper et al., 1965; Acworth et al., 2017; Shih, 2017). In such situation, the well hydraulically coupled to the formation. The higher the permeability of the aquifer is, the easier oscillations occurred during the passage of seismic waves. The better the storativity of a reservoir is, the smaller the response amplitude of tidal and seismic waves would be. This may result in higher shaking energy required for offset water level changes than oscillation. Thus, earthquake tends to induced water level oscillational changes in JX well. The ranges of tidal factor and phase shift are 4.5-7.5 GPa and −8.5-40.1° in TY well, 1.0-8.8 GPa and −79.9-23.7° in QX well, 4.3-6.7 GPa and −8.2-16.8° in XY well, respectively.

Earthquake-induced water level and tidal behavior changes did not occurred simultaneously. For instance, offset water level changes occurred without tidal behavior changes after five earthquakes in XY well. The amplitudes of offset water level changes ranged from 0.01 to 0.75 m in XY well. While offset water level and tidal behavior changes were recorded after multiple earthquakes in TY well with offset water level changes of 0.01-0.06 m and in QX well with offset water level changes of 0.02-0.99 m, which means that these two wells are sensitive to seismically dynamic strain. In terms of tides, the tidal factor and phase shift in the TY, QX and XY well had no obvious difference during the period of no earthquakes, which means that other local hydrogeological structure may affect water and tidal behavior. It is noteworthy that TY well penetrates the damage zone of Jiaochen faults which is a listric faults on the northwestern edges of the Taiyuan Basin playing a controlling role in the rift basin. The QX well is located in the Taigu–Qixian developed earth fissure area of Taiyuan rift 14

Basin. The fissures are connected to deep hidden faults and their average annual active rate is 1-3 cm (Peng et al., 2018; Tang et al., 2018). Recent studies indicated that hydraulic properties inferred from tidal behavior within fault damage zone are more sensitive and vulnerable than that away from the fault damage zone (Xue et al., 2016; Yan et al., 2016). In this study, the two wells of TY and QX well located in the fault or earth fissure area showed significant changes in tidal factors and phase shifts after multiple earthquakes, indicating that permeability and storativity changed after the passage of seismic waves, while the XY wells away from active fault did not show any significant change. The different response patterns to seismically dynamic strain indicate that fault and earth fissure may be the reason of sensitive water level and tidal behavior changes.

In terms of earthquake-induced tidal change, there are three types of plausible physical mechanisms (Barbour et al., 2019).(1) radial flow model suggests that M2 tides should have negative phase shift and positive correlation between tidal factor and phase shift (Hsieh et al., 1987), (2) vertical flow (leakage) model suggests that M2 tides should have positive phase shift and negative correlation between tidal factor and phase shift (Roeloffs et al., 1996; Wang et al., 2018), (3) fracture-dominated flow model suggests that M2 and O1 tides have phases of opposite sign (Bower, 1983). For the four wells in this work, M2 and O1 tides do not have phases of opposite sign (Figure 4 and 6). The single fracture-dominated flow model was firstly excluded. For the TY well, the M2 tides induced by earthquakes have positive phase shift and negative correlation between tidal factor and phase shift, which suggests that earthquakes induced vertical flow 15

changes. For the QX well, the M2 tides induced by earthquakes have negative or positive phase shift and positive correlation between tidal factor and phase shift, which suggests that earthquakes induced mixture flow (both vertical and radial flow) changes (Figure 7).

Another interesting issue is that both increase and decrease of tidal factor and phase shift were recorded in the QX well following some earthquakes. Clogging or unclogging of fractures due to earthquakes could not explain such large changes in Earth tides. The QX well is located in the developed earth fissure area and the screened interval is very long hence there could be non-equilibrium between some intervals of the wellbore. Partial clogging of the screened interval or communication between the screened interval and the overlying gravel aquifer or even the surface could be the explanation for such large changes in tidal parameters. The fact that a non-earthquake tidal changes in 2009 also led to similar tidal behavior related to earthquakes, which could be evidence that earthquakes affected the near-wellbore environment.

The earthquake-induced well water level and tidal behavior changes may be correlated with the hydrogeological condition, fault systems, geometry of well-aquifer system and local stress state, but at this stage no clear models was proposed. Further research or predictive models are required to predict situations in areas without monitoring data.

6 Conclusions

16

In this work we analyzed water level and tidal behavior changes caused by five large earthquakes in four wells in the Taiyuan rift Basin from 2007 to 2019. Different water level and tidal behaviors were recorded in the wells after multiple large earthquakes. The JX well with higher storativity and higher permeability mainly recorded oscillation changes, which suggests that higher seismic energy density might be required to cause sustained water level changes in such wells. The other three wells, TY, QX and XY, recorded sustained water level changes after multiple large earthquakes. In which tidal behavior changed in the TY and QX wells after some large earthquakes. The TY well penetrates the damage zone of the listric Jiaochen faults playing a controlling role in the Taiyuan rift Basin. The QX well is located in the Taigu– Qixian developed earth fissure area. Both wells located in fault damage zone or developed earth fissure area showed synchronized water level and tidal behavior changes after multiple earthquakes, which suggested that fissures play an important controlling effect to earthquake-induced water level and tidal behavior changes.

Different tidal behavior were recorded in the TY and QX well after earthquakes. In the TY well, M2 tides induced by earthquakes have positive phase shift and negative correlation between tidal factor and phase shift, which suggests that earthquakes induced vertical flow changes. In the QX well, M2 tides induced by earthquakes have negative or positive phase shift and positive correlation between tidal factor and phase shift, which suggests that earthquakes induced mixture of both vertical and radial flow.

Acknowledgements 17

This work was supported by a grant of National Key R&D Program of China (2018YFC150330505) and National Natural Science Foundation of China (U1602233 and 41503114).

References

Acworth, R.I., Rau, G.C., Halloran, L.J.S., Timms, W.A., 2017. Vertical groundwater storage properties and changes in confinement determined using hydraulic head response to atmospheric tides. Water Resources Research, 53(4): 2983-2997. Agnew, D.C., 2007. Earth Tides. In: Gerald, S. (Ed.), Treatise on Geophysics. Elsevier, Amsterdam, pp. 163-195. Barbour, A.J., Xue, L., Roeloffs, E., Rubinstein, J.L., 2019. Leakage and Increasing Fluid Pressure Detected in Oklahoma's Wastewater Disposal Reservoir. 124(3): 2896-2919. Beresnev, I., Gaul, W., Vigil, R.D., 2011. Direct pore-level observation of permeability increase in twophase flow by shaking. Geophys. Res. Lett., 38(20): L20302. Bower, D.R., 1983. Bedrock fracture parameters from the interpretation of well tides. Journal of Geophysical Research: Solid Earth, 88(B6): 5025-5035. Bower, D.R., Heaton, K.C., 1978. Response of an aquifer near Ottawa to tidal forcing and the Alaskan earthquake of 1964. Canadian Journal of Earth Sciences, 15(3): 331-340. Brodsky, E.E., Roeloffs, E., Woodcock, D., Gall, I., Manga, M., 2003. A mechanism for sustained groundwater pressure changes induced by distant earthquakes. J. Geophys. Res., 108(B8): 2390. Cooper, H.H., Bredehoeft, J.D., Papadopulos, I.S., Bennett, R.R., 1965. The response of well-aquifer 18

systems to seismic waves. J. Geophys. Res., 70(16): 3915-3926. Crews, J.B., Cooper, C.A., 2014. Experimental evidence for seismically initiated gas bubble nucleation and growth in groundwater as a mechanism for coseismic borehole water level rise and remotely triggered seismicity. Journal of Geophysical Research: Solid Earth, 119(9): 7079-7091. Doan, M.L., Brodsky, E.E., Prioul, R., Signer, C., 2006. Tidal analysis of borehole pressure: A tutorial, Schlumberger-Doll Research Report, University of California, Santa Cruz. Elkhoury, J.E., Brodsky, E.E., Agnew, D.C., 2006. Seismic waves increase permeability. Nature, 441(7097): 1135-1138. Faoro, I., Elsworth, D., Marone, C., 2012. Permeability evolution during dynamic stressing of dual permeability media. J. Geophys. Res., 117(B1): B01310. Geballe, Z.M., Wang, C.Y., Manga, M., 2011. A permeability-change model for water-level changes triggered by teleseismic waves. Geofluids, 11(3): 302-308. Guo, C., Shi, J., Zhang, Z., Zhang, F., 2019. Using tritium and radiocarbon to determine groundwater age and delineate the flow regime in the Taiyuan Basin, China. Arabian Journal of Geosciences, 12(6): 185. Guo, Q., Wang, Y., Ma, T., Ma, R., 2007. Geochemical processes controlling the elevated fluoride concentrations in groundwaters of the Taiyuan Basin, Northern China. Journal of Geochemical Exploration, 93(1): 1-12. Han, Y., Yan, S., Ma, H., 2008. Investigation and assessment of groundwater resources and their environmental problems in six basins of Shanxi province. Geological Publishing House, Beijing. Hsieh, P.A., Bredehoeft, J.D., Farr, J.M., 1987. Determination of aquifer transmissivity from Earth tide analysis. Water Resources Research, 23(10): 1824-1832. 19

Ishiguro, M., Tamura, Y., 1985. BAYTAP-G in TIMSAC-84. Computer Science Monographs, 22: 56117. Jonsson, S., Segall, P., Pedersen, R., Bjornsson, G., 2003. Post-earthquake ground movements correlated to pore-pressure transients. Nature, 424(6945): 179-183. King, C.Y. et al., 1999. Earthquake-related water-level changes at 16 closely clustered wells in Tono, central Japan. J. Geophys. Res., 104(B6): 13073-13082. Kinoshita, C., Kano, Y., Ito, H., 2015. Shallow crustal permeability enhancement in central Japan due to the 2011 Tohoku earthquake. Geophysical Research Letters, 42(3): 773-780. Kocharyan, G. et al., 2011. Hydrologic response of underground reservoirs to seismic vibrations. Izvestiya Physics of the Solid Earth, 47(12): 1071-1082. Leggette, R.M., Taylor, G.H., 1935. Earthquakes instrumentally recorded in artesian wells. Bulletin of the Seismological Society of America, 25(2): 169-175. Linde, A.T., Sacks, I.S., Johnston, M.J.S., Hillt, D.P., Bilham, R.G., 1994. Increased pressure from rising bubbles as a mechanism for remotely triggered seismicity. Nature, 371(6496): 408-410. Manga, M. et al., 2012. Changes in permeability caused by transient stresses: Field observations, experiments, and mechanisms. Rev. Geophys., 50(2): RG2004, doi:10.1029/2011RG000382. Matsumoto, N., Roeloffs, E.A., 2003. Hydrological response to earthquakes in the Haibara Well, central Japan; II, Possible mechanism inferred from time-varying hydraulic properties. Geophysical Journal International, 155(3): 899-913. Peng, J., Meng, L., Lu, Q., Deng, Y., Meng, Z., 2018. Development characteristics and mechanisms of the Taigu–Qixian earth fissure group in the Taiyuan basin, China. Environmental Earth Sciences, 77(11): 407. 20

Quilty, E.G., Roeloffs, E.A., 1997. Water-level changes in response to the 20 December 1994 earthquake near Parkfield, California. Bull. Seismol. Soc. Am., 87(2): 310-317. Roeloffs, E., Renata, D., Barry, S., 1996. Poroelastic Techniques in the Study of Earthquake-Related Hydrologic Phenomena, Advances in Geophysics. Elsevier, pp. 135-195. Roeloffs, E.A., 1998. Persistent water level changes in a well near Parkfield, California, due to local and distant earthquakes. Journal of Geophysical Research, 103(B1): 869-889. Rojstaczer, S., Wolf, S., Michel, R., 1995. Permeability enhancement in the shallow crust as a cause of earthquake-induced hydrological changes. Nature, 373(6511): 237-239. Rojstaczer, S.A., Wolf, S.C., 1992. Permeability changes associated with large earthquakes; an example from Loma Prieta, California. Geology, 20(3): 211-214. Shi, Y., Liao, X., Zhang, D., Liu, C.-p., 2019. Seismic Waves Could Decrease the Permeability of the Shallow Crust. Geophysical Research Letters, 10.1029/2019gl081974. Shi, Z., Wang, G., 2014. Hydrological response to multiple large distant earthquakes in the Mile well, China. Journal of Geophysical Research: Earth Surface, 119(11): 2448-2459. Shi, Z., Wang, G., 2015. Sustained groundwater level changes and permeability variation in a fault zone following the 12 May 2008, Mw 7.9 Wenchuan earthquake. Hydrological Processes, 29(12): 2659-2667. Shi, Z., Wang, G., Manga, M., Wang, C.-Y., 2015. Mechanism of co-seismic water level change following four great earthquakes – insights from co-seismic responses throughout the Chinese mainland. Earth and Planetary Science Letters, 430: 66-74. Shi, Z., Zhang, S., Yan, R., Wang, G., 2018. Fault Zone Permeability Decrease Following Large Earthquakes in a Hydrothermal System. Geophysical Research Letters, 45(3): 1387-1394. 21

Shih, D.C.-F., 2017. Groundwater storage inferred from earthquake activities around East Asia and West Pacific Ocean. Journal of Hydrology, 544: 363-372. Steinberg, G.S., Steinberg, A.S., Merzhanov, A.G., 1989. Fluid mechanism of pressure growth in volcanic (magmatic) systems. Modern Geology, 13(3-4): 257-265. Tamura, Y., Sato, T., Ooe, M., Ishiguro, M., 1991. A procedure for tidal analysis with a Bayesian information criterion. Geophysical Journal International, 104(3): 507-516. Tang, Q. et al., 2013. Geochemistry of iodine-rich groundwater in the Taiyuan Basin of central Shanxi Province, North China. Journal of Geochemical Exploration, 135: 117-123. Tang, W., Yuan, P., Liao, M., Balz, T., 2018. Investigation of Ground Deformation in Taiyuan Basin, China from 2003 to 2010, with Atmosphere-Corrected Time Series InSAR. Remote Sensing, 10(9): 1499. Wakita, H., 1975. Water wells as possible indicators of tectonic strain. Science, 189(4202): 553-555. Wang, C.-Y., Doan, M.-L., Xue, L., Barbour, A.J., 2018. Tidal Response of Groundwater in a Leaky Aquifer—Application to Oklahoma. 54(10): 8019-8033. Wang, C.-Y., Manga, M., 2010a. Hydrological response to earthquakes and a general metric. Geofluids, 10: 206-216. Wang, C.Y., Chia, Y., Wang, P.-l., Dreger, D., 2009. Role of S waves and Love waves in coseismic permeability enhancement. Geophys. Res. Lett., 36(L09404). Wang, C.Y., Manga, M., 2010b. Earthquakes and water. Lecture notes in earth sciences, 114. Springer, Berlin-Heidelberg, 225 pp. Wang, R., Woith, H., Milkereit, C., Zschau, J., 2004. Modelling of hydrogeochemical anomalies induced by distant earthquakes. Geophysical Journal International, 157(2): 717-726. 22

Weaver, K.C., Doan, M.-L., Cox, S.C., Townend, J., Holden, C., 2019. Tidal Behavior and Water-Level Changes in Gravel Aquifers in Response to Multiple Earthquakes: A Case Study From New Zealand. Water Resources Research, 55(2): 1263-1278. Xie, X., Jiang, W., Sun, C., Yan, G., Feng, X., 2008. Comparison study on Holocene paleoseismic activities among multi-trenches along the Jiaocheng fault zone, Shanxi. Seismology and Geology, 30(2): 412-430. Xue, L., Brodsky, E.E., Erskine, J., Fulton, P.M., Carter, R., 2016. A permeability and compliance contrast measured hydrogeologically on the San Andreas Fault. Geochemistry, Geophysics, Geosystems, 17(3): 858-871. Xue, L. et al., 2013. Continuous Permeability Measurements Record Healing Inside the Wenchuan Earthquake Fault Zone. Science, 340(6140): 1555-1559. Yan, R., Wang, G., Shi, Z., 2016. Sensitivity of hydraulic properties to dynamic strain within a fault damage zone. Journal of Hydrology, 543(2016): 721-728. Yan, R., Woith, H., Wang, R., 2014. Groundwater level changes induced by the 2011 Tohoku earthquake in China mainland. Geophysical Journal International, 199(1): 533-548. Yan, R., Woith, H., Wang, R., Wang, G., 2017. Decadal radon cycles in a hot spring. Scientific Reports, 7(1): 12120.

23

Table 1. Basic information of the four wells.

Well Lat(°)

Lon(°)

QX

37.71

37.37

112.43

112.23

Screen interval

W.D

(m)

(m)

(mm)

765.78

480-765.78

150

Alt(m)

name TY

Dep

823.52

753.19

Drilling Aquifer lithology

442.19

291.65-410

date Limestone & dolomite

1981 Jan.

Metamorphic

1973

volcaniclastic rock

Aug

110

Fine sandstone XY

37.15

111.77

766.00

502.93

403-502

127

1982 Apr intercalated with shale

JX

37.18

111.90

738.00

77.58-86.67，

Loess and sandy clay

101.86-110.99，

sand gravel

143.48-146.59，

fine sand with subclay

1981

166.19-170.00，

fine sand with subclay

May

201.99-220.18，

sand gravel

283.90-301.64

Sandstone and mudstone

315

146

Note: Lat, Lon, Alt means Latitude, Longitude and Altitude of the well site respectively. Dep means Well depth; W. D means Well diameter.

24

Table 2. Earthquake events that induced obvious water level changes in the four wells.

EQ ID

Date

Energy density (J/m3)

Epicentral distance (km)

Lat(°)

Lon(°) Mag

TY

QX

XY

JX

TY

QX

XY

JX

1 2007/9/12

-4.44

101.37

8.5

4824 4783 4749 4755

1.96E-03 2.01E-03 2.06E-03 2.05E-03

2 2008/5/12

31.00

103.32

7.9

1120 1082 1035 1046

2.20E-02 2.44E-02 2.79E-02 2.70E-02

3 2011/3/11

38.30

142.37

9.0

2613 2637 2682 2670

6.72E-02 6.53E-02 6.20E-02 6.29E-02

4 2012/4/11

2.29

93.08

8.6

4406 4364 4322 4331

3.61E-03 3.72E-03 3.83E-03 3.80E-03

5 2015/4/25

28.14

84.70

7.8

2785 2759 2713 2725

9.94E-04 1.02E-03 1.08E-03 1.06E-03

Note: ID, earthquake index; Lat, Lon, latitude and longitude of earthquake epicenter; Mag, magnitude of earthquake. Seismic energy density was calculated according to the formula developed by Wang and Manga (2010a).

25

Table 3.Water level changes induced by the 5 earthquakes in the 4 wells

EQ

ID 1

TY well

Res

fall

QX well

XY well

JX well

WL (m) △WL (m) Res WL (m) △WL (m) Res WL (m) △WL (m) Res WL (m) △WL (m)

50.54

-0.05

2 no data

fall

32.47

-0.02

rise

12.76

0.03

osc

13.6

0.001

rise

27.82

0.99

rise

13.43

0.75

rise

14.14

0.848

3

fall

46.83

-0.06

rise

26.32

0.81

fall

16.91

-0.27

osc

13.55

0.02

4

fall

39.13

-0.03

fall

24.66

-0.05

fall

22.23

-0.01

osc

12.51

0.002

5

fall

31.38

-0.01

fall

21.45

0.17

fall

31.98

-0.12

osc

13.47

0.001

Note: EQ_ID is same as Table 2. Res represents response polarity. WL denotes water level before earthquakes; △WL denotes relative difference of water level before and after each earthquake.

26

Table 4.Tidal behavior changes induced by earthquakes in TY and QX wells.

TY well

QX well

EQ_ID T.F.(GPa) △T.F. (GPa) Phase (°) △Phase (°)

T.F.(GPa) △T.F. (GPa) Phase (°) △Phase (°)

1

7.06

-0.49

10.7

4.53

6.96

0.88

-8.95

16.00

2

7.06

-1.37

2.205

28.52

7.55

-5.78

3.18

-79.78

3

7.06

-2.55

-3.66

42.88

7.64

-5.88

5.17

-74.00

4

5

No change

37.69

No change

2.06

6.27

-68.32

75.65

5

5.1

-0.29

37.84

2.89

7.74

-1.67

5.67

-23.35

Note: EQ_ID is same as Table 2. T.F. and Phase denoting tidal factor and phase shift before earthquake; △T.F. and △Phase denoting relative difference of tidal factor and phase shift before and after each earthquake.

27

Figure 1. Location of the study area and water wells. The insert shows locally topographical features and major active faults in the Taiyuan Basin. Contour indicates groundwater level height relative to sea level. AA’, BB’, and CC’, indicate profiles across the QX, XY and JX well respectively. Distribution of the main active faults in the Taiyuan Basin: F1, Jiaocheng fault; F2, Longjiaying fault; F3, Qixianfault; F4, Pingyao–Taigu fault; F5, Hongshan–Fancun fault; F6, Yuci–Beitian fault; F7, Sanquan fault; F8, Tianzhuang fault.

28

Figure 2. Aquifer geochronology and lithology in the four wells.

29

Figure 3. Time series of groundwater level changes (black curves) recorded from May 2007 to May 2019. Grey stems show daily rainfall at the water level site. The vertical dashed line in the left panels indicates the origin time of the 11 March 2011 Tohohu MW 9.0 earthquake (ID is 3 in Table 2). The right panels show zoom in time series from 3 to 23 March 2011.

30

Figure 4. Phase shift and tidal factor of M2 Earth tide from 2007 to 2019. The dashed vertical lines correspond to origin time of the earthquakes with the same ID listed in Table 2. The red triangles indicate phase shifts corresponding to the left vertical axis and the blue cycles indicate tidal factors corresponding to the right vertical axis. The grey error bars indicate Root Mean Square Error (RMSE) of the tidal analysis.

31

Figure 5.Cross-section of water column height through QX, XY and JX well. See location in Figure 1. The right panels show zoom in the left panels.

32

Figure 6. Phase shift and tidal factor of O1 Earth tide from 2007 to 2019. The dashed vertical lines correspond to origin time of the earthquakes with the same ID listed in Table 2. The red triangles indicate phase shifts corresponding to the left vertical axis and the blue cycles indicate tidal factors corresponding to the right vertical axis. The grey error bars indicate Root Mean Square Error (RMSE) of the tidal analysis.

33

Figure7. Relationship between the tidal factors and phase shift changes induced by earthquakes.

Abstract: Seismically induced water level and tidal behavior changes were analyzed in four wells (TY, QX, XY and JX) in the Taiyuan rift Basin. One of the wells (JX) with higher storativity and higher permeability mainly recorded oscillation changes, which suggests that higher seismic energy density might be required to cause sustained water level changes in such wells. The other three wells recorded sustained water level changes following multiple large earthquakes, in which two of the wells located within fault damage zone or developed fracture area showed synchronized water level and tidal behavior changes after earthquakes. Moreover, the two wells recorded different tidal behaviors (positive or negative correlation between tidal factor and phase shift), which suggested that far field earthquake caused the mixture of vertical flow and radial flow. We suggest that local hydro-geological setting and fissures connected to the aquifer play an important controlling role in earthquake-induced water level and tidal behavior 34

changes.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Highlights: 1. Water level and tidal behavior changes were analyzed in a rift basin in response to multiple large earthquakes. 2. Earthquake induced water level and tidal behavior changes showed different response pattern.

35

3. Hydro-geological setting and fissures play an important role to earthquakeinduced water level and tidal behavior changes.

36