Spatial and Temporal Changes of Groundwater Level Induced by Thrust Faulting

Changes of groundwater level, ranging from a fall of 11.10 m to a rise of 7.42 m, induced by thrust faulting during the 1999 M_w 7.6, Chi-Chi earthquake have been recorded in 276 monitoring wells in Taiwan. Most coseismic falls appeared near the seismogenic fault as well as other active faults, while coseismic rises prevailed away from the fault. Coseismic groundwater level rises and falls correlated fairly well with hypocentral distance in the vicinity of the thrust fault. We found a major difference of coseismic changes in wells of different depths at most multiple-well stations. The recovery process of coseismic groundwater level changes is associated with the confining condition of the aquifer. Cross-formational flow is likely to play an important role in groundwater level changes after the earthquake. In the hanging wall of the thrust fault, an abnormal decline of groundwater level was observed immediately before the earthquake. The underlying mechanism of the unique preseismic change warrants further investigation.     

基于汶川地震同震地下水位变化反演含水层体应变

许多地下流体监测井在地震发生时都能记录到同震水位变化,而利用地下水位的同震响应特征以及水位固体潮效应可以反演地震对含水层产生的体应变量．本文尝试从大尺度上对大地震引起的体应变变化进行研究,为此收集了位于我国大陆不同构造活动区5口地下流体监测井两年半的水位数据资料进行分析,去除干扰项,提取出水位固体潮成分,进行调和分析求取潮汐因子,并反演出汶川MS8.0地震对这5口井所在含水层产生的体应变量．结果显示,汶川大地震对这5口井 含水层造成的体应变量基本在10-7量级. 地震引起的体应变随距离的衰减规律比较复杂,其不仅与震中距有关,而且与活动断裂带的展布和地壳岩体结构等密切相关．      

重庆井网水位水温同震响应特征分析

本文以2008年以来全球范围内发生的5次大地震为例,对重庆井网水位和水温同震响应特征进行了分析,结合井孔水文地质条件和自身观测条件,探讨了不同同震响应现象的可能成因并对其机理进行了探讨。结果表明,水位的记震能力优于水温,水位同震响应形态主要包括上升、下降和振荡三种类型,且同一口井水位对不同地震的响应形态不同;水温的同震响应形态主要包括上升和下降两种类型,其中只有荣昌华江和北碚柳荫井水温对5次地震均有同震响应,且同一口井水温对不同地震的响应形态相同。进一步分析表明,北碚柳荫井水位的同震响应能力优于荣昌华江井水位,北碚柳荫井水位的同震振幅与地震能密度成正比,并给出了其同震变化幅度与地震能量密度的对应关系。最后分别对水位和水温同震响应机理进行了探讨。     

中国大陆井水位与水温动态对汶川MS 8.0地震的同震响应特征分析

分析了汶川MS8.0地震在中国大陆引起的水位、水温同震变化特征,对比研究了2007年9月12日印尼苏门答腊MS8.5远震和汶川MS8.0近震在四川及其附近地区引起的水位、水温同震变化差异,结果表明:汶川地震在中国大陆引起的水位同震变化以上升为主,同时水位上升与下降的井点空间分布表现出一定的分区性;水位、水温同方向阶变的井点数比例高于两者反方向阶变井点数比例,当水位同震变化为振荡型时,水温以下降型为主;相对于远震,近震引起的水位、水温同震变化井点数量增加,无变化井点数量减少;所有井水位和大多数井水温同震阶变的方向都不因地震的远近、大小、震源机制或地震方位的变化而改变,个别发生水温同震升降方向变化的井点是由于水的自流状态和水位同震阶变由振荡转为阶变的改变所引起;水位同震升降性质受控于当地的地质构造环境和水文地质条件,而水温同震变化还与地震波引起的井孔中水的运动方式、水温探头放置的位置等因素有关,其机理更为复杂     

天津两井水位同震效应分析

从不同的方位对天津地区两口地震观测专用井记录到的国外7级、国内6级以上的地震进行分析。两口井所处的地理位置、地质结构、井深及其含水层岩性不同,对同一地震的表现形式也不尽相同。通过对比分析,得到井水位对地震的响应特点及几点认识：观测井孔一般对远场大震记录比较灵敏,而对近震及地方震反映不灵敏;井孔水位仪记录的水位波幅与震级、震中距有关;井孔同震效应的能力和井孔对固体潮的反映能力不一致。     

Earthquake-related Changes in Groundwater Levels at the Dogo Hot Spring,Japan

The Dogo hot spring, situated in Matsuyama City, Ehime Prefecture, Japan, is one of the oldest and most famous hot springs in Japan. The groundwater level or discharge at the spring decreased four times during the past eight or nine Nankai earthquakes. These are large interplate earthquakes that have occurred repeatedly in the western part of the Nankai Trough at intervals of 100–200 years since A.D. 684. To clarify the mechanism of these earthquake-related changes in the water level at the spring, we analyzed groundwater-level data recorded at the spring immediately after the 1946 Nankai earthquake and over the period from 1985 to 2006. We detected the other nine postseismic increases in groundwater level and no decreases, except for a large decrease of 11.4 m related to the 1946 Nankai earthquake. The increases were probably caused by ground-shaking, while the decrease was caused by a change in coseismic volumetric strain. These results lead to the following explanation of the recorded earthquake-related changes in the groundwater level at the Dogo hot spring. Both coseismic changes in volumetric strain and ground-shaking can lead to postseismic changes in groundwater pressure. The increase in groundwater pressure arising from ground-shaking is generally greater than the change in pressure associated with changes in coseismic volumetric strain; however, at the time of the Nankai earthquakes, the spring experiences a large increase in coseismic volumetric strain, leading to a considerably larger decrease in the groundwater level than the increase associated with ground-shaking. Therefore, the groundwater level at the Dogo hot spring usually increases at times of relatively large earthquakes, although the groundwater level or discharge decreases in the case of the Nankai earthquakes.     

Characteristics of coseismic water level changes at Tangshan well for the Wenchuan MS8.0 earthquake and its larger aftershocks

Coseismic water level changes which may have been induced by the Wenchuan M_S8.0 earthquake and its 15 larger aftershocks (M_S≥?5.4) have been observed at Tangshan well. We analyze the correlation between coseismic parameters (maximum amplitude, duration, coseismic step and the time when the coseismic reach its maximum amplitude) and earthquake parameters (magnitude, well-epicenter distance and depth), and then compare the time when the coseismic oscillation reaches its maximum amplitude with the seismogram from Douhe seismic station which is about 16.3 km away from Tangshan well. The analysis indicates that magnitude is the main factor influencing the induced coseismic water level changes, and that the well-epicenter distance and depth have less influence. M_S magnitude has the strongest correlation with the coseismic water level changes comparing to M_W and M_L magnitudes. There exists strong correlation between the maximum amplitude, step size and the oscillation duration. The water level oscillation and step are both caused by dynamic strain sourcing from seismic waves. Most of the times when the oscillations reach their maximum amplitudes are between S and Rayleigh waves. The coseismic water level changes are due to the co-effect of seismic waves and hydro-geological environments.     

Groundwater responses to the 2011 Tohoku Earthquake on Jeju Island,Korea

Groundwater responses at 15 monitoring wells on Jeju Island were observed in relation to the magnitude 9.0 Tohoku Earthquake off the Pacific coast of Honshu, Japan, on 11 March 2011, at 14:46:23 h local time (05:46:24 h UTC time). In coastal areas, the groundwater level responses to the earthquake were oscillatory at 12 wells, and the range of the maximum groundwater level changes was 3–192.4 cm. The response durations were approximately 1–62 min. The relationship between the maximum groundwater level changes and the response durations displayed a high correlation coefficient (r = 0.81). Groundwater temperature changes were also observed at 7 of 12 wells 3–10 min after the seismic wave arrived, and the range was from 0.01 °C to 1.20 °C. In mid‐elevation areas, the groundwater level changes appeared in three different forms: oscillatory, spiky and persistent. The groundwater temperature changes were also observed at two wells. One indicated decreasing and recovering temperatures, and the other exhibited rising and persistent temperatures. The primary temperature changes occurred 5–6 min after the earthquake and 2–3 min after the seismic wave arrived. In addition, the electrical conductivities at the depth of the transition zone were monitored, and the responses to the earthquake appeared at all three wells. Although the electrical conductivity and temperature changes were not well understood, groundwater inflow and mixing were likely caused by the earthquake, and the responses were various and site specific. The responses to the earthquake were closely related to the hydrogeological characteristics at each monitoring well, and a more detailed hydrogeological characterization is needed to understand the mechanisms related to earthquakes in general. Copyright © 2012 John Wiley & Sons, Ltd.     

夏垫断裂带地震地下流体的同震响应研究

地震地下流体已成为一种重要的地震监测手段。 本文分析夏垫断裂带上观测井的同震响应特征, 探讨观测井水位、 水温同震变化对夏垫断裂带的影响机理, 收集和整理布设在夏垫断裂带上的赵各庄井和西集井两口观测井水位和水温同震响应资料, 从响应的地震次数及发震位置、 异常幅度、 时间和形态类型等方面对其响应特征进行分析, 从震中距、 震级和井-含水层岩性等方面探讨了地下流体地震前兆异常的成因。 结果显示, 赵各庄井和西集井水位地震响应能力强于水温, 响应形态以振荡型为主, 对于M_S7.0以上地震具有显著的映震能力。 在水温资料中, 仅有赵各庄井对2008年汶川M_S8.0地震有响应, 响应幅度为0.0129℃。 综合分析认为, 井-含水层岩性影响了两井同震响应形态特征, 远场大地震产生的动态应变导致了较大的水位变幅。     

Some isotopic and hydrological changes associated with the 1999 Chi-Chi earthquake, Taiwan

Abstract   The changes in the isotopic composition of, and the groundwater level in, the Choshui River alluvial fan near the ruptured Chelungpu Fault during and following the 1999 ( M _w = 7.5) Chi-Chi earthquake in Taiwan are reported. Three aspects of the hydrological changes are noticed. First, following the Chi-Chi earthquake, the lower aquifers beneath the Choshui River fan showed a significant shift in isotopic composition towards that of the surface water in the Choshui River, suggesting enhanced exchanges of water between the river and the groundwater. Second, in some wells, water levels and isotopic compositions in different aquifers converged to the same respective values during the Chi-Chi earthquake, suggesting coseismic exchanges of water between the different aquifers, which implies enhanced permeability due perhaps to the fracturing and breaching of aquitards between the aquifers. Third, the pattern of the coseismic water-level response is distinctly different from that of the shift in the isotopic composition, suggesting that they were produced by different mechanisms.     

2011年日本Mw9.0地震引起的环渤海地区井水温度变化分析

2011年3月11日的日本M_w9.0地震在中国引起了大范围的井水温度同震变化,而水温震后持续变化的井孔多数分布在井网密度较大、距震中较近的环渤海地区。本文分析了环渤海地区水温震后变化的特征和机理。结果表明,水温震后变化形态为上升,变幅0. 005~0.976°C,空间分布在同震位移较大、张性应变较明显和地震能量密度较大的区域;依据同井水位资料,一些井孔的水温和水位震后变化特征较一致,其水温震后升高可能是地震波增大含水层渗透性的结果;另一些井孔的水位震后变化不显著,其水温震后升高可能与地震波增大井区大地热流有关。     

Case 21 water level and strain changes preceding and following the August 4, 1985 Kettleman Hills, California, earthquake

Two of the four wells monitored near Parkfield, California, during 1985 showed water level rises beginning three days before theM _w 6.1 Kettleman Hills earthquake. In one of these wells, the 3.0 cm rise was nearly unique in five years of water level data. However, in the other well, which showed a 3.8 cm rise, many other changes of comparable size have been observed. Both wells that did not display pre-earthquake rises tap partially confined aquifers that cannot sustain pressure changes due to tectonic strain having periods longer than several days. We evaluate the effect of partial aquifer confinement on the ability of these four wells to display water level changes in response to aquifer strain. Although the vertical hydraulic diffusivities cannot be determined uniquely, we can find a value of diffusivity for each site that is consistent with the site's tidal and barometric responses as well as with the rate of partial recovery of the coseismic water level drops. Furthermore, the diffusivity for one well is high enough to explain why the preseismic rise could not have been detected there. For the fourth well, the diffusivity is high enough to have reduced the size of the preseismic signal as much as 50%, although it should still have been detectable. Imperfect confinement cannot explain the persistent water level changes in the two partially confined aquifers, but it does show that they were not due to volume strain. The pre-earthquake water level rises may have been precursors to the Kettleman Hills earthquake. If so, they probably were not caused by accelerating slip over the part of the fault plane that ruptured in that earthquake because they are of opposite sign to the observed coseismic water level drops.     

2019年长宁M6.0和2018年兴文M5.7地震引起的井水位同震响应对比分析

2019年长宁M6.0地震和2018年兴文M5.7地震引起了华蓥山断裂及其附近区域8口观测井水位不同程度的响应变化。 本文对比分析各观测井水位的同震响应特征, 从地震波能量密度、 同震破裂体应变、 含水层渗透性参数变化以及断裂带控制作用几个方面探讨了其同震响应机理。 结果显示, 井水位同震响应的幅度与地震波能量密度有一定关系; 2019年长宁M6.0地震引起的井水位同震响应形态符合同震破裂体应变四象限空间分布特征, 但2018年兴文M5.7地震则不符合; 两次地震引起的含水层渗透性参数变化存在空间上的不一致性和单点各向异性, 并且断裂带自身的水文条件对井水位同震响应形态和幅度有一定的控制作用。 综合分析认为, 目前已有的几种机理无法完全解释两次地震引起的井水位同震响应现象。     

海南琼海加积井水温同震效应特征和机理初探

基于海南加积井数字化水温2007年1月-2010年4月震中距小于8 000 km、Ms≥7.8大震的同震响应资料,系统分析水温年月日正常动态特征,发现远震引起的水温同震效应特征为上升脉冲,与以往的非自流井水温同震效应以下降为主的认识不一致;水温变化幅度与震中距、震级有一定关系,加积井水温同震效应成因,可用“层内混合”作...     

金沙江水网对日本9.0级地震的同震响应及其特征与机理

本文系统介绍了金沙江水网6口观测井水位与水温动态对日本9.0级地震的同震响应, 分析了同震响应的特征与同震响应的机理。 结果表明, 4口井水位有同震响应, 同震响应形态全是振荡, 对地震波响应的时间、 振荡的幅度、 振荡的持续时间等的差异主要取决于井-含水层系统的导水系数。 结果还表明, 3口井水温有同震响应, 响应形态是不对称的V字或U字形; 水温的先期下降是井筒内上(冷)下(热)水混合作用引起的, 后期上升是井水与围岩之间的热传导引起吸热作用的结果, 各井水温升降的幅度、 持续时间等不同, 主要是井水温度梯度与水岩热传导系数不同引起的; 后期升幅总是大于先期降幅, 这可能与地震波作用使井区大地热流增强有关。     

山东省井水位对几次大地震同震响应的比较分析

采用多井对多震的方式,选取山东省地下流体观测井网中同震响应较好的6口观测井作为研究对象,分别从水位变化形态和幅度对比分析2011年日本M_W9.0地震、2012年苏门答腊M_W8.6地震和2015年尼泊尔M_W7.8地震引起的井水位变化特征,探讨引起该变化的可能机理。研究结果显示:水位同震变化形态以振荡为主;通过定量分析认为聊古一井井水位的阶升是由含水层渗透系数增大所致;位于同一断裂带上的聊古一井和鲁27井井水位在同一地震中所表现的变化形态不同,可能与两个观测井所处的地质构造条件和地震活动背景不同有关;区域应力场的变化会影响栖霞鲁07井的水位同震变化形态;水位同震变化幅度与震级、井震距存在一定关系,同时也取决于含水层水文地质条件的变化量。      

Co-Seismic Groundwater Level Changes Induced by the May 12, 2008 Wenchuan Earthquake in the Near Field

The large scales of co-seismic water level changes in mainland China were observed in response to the tragic 2008 Ms 8.0 Wenchuan earthquake. To better understand the mechanism of these hydrogeological phenomena, groundwater-level data at 17 confined wells, with an epicentral distance of <500 km, were collected. We compare the static strain predicted by dislocation theory with the volumetric strain calculated by the tide effect of the groundwater based on poroelastic theory. The results show that the sign of the co-seismic groundwater level change is consistent with the sign predicted by dislocation theory. Additionally, the magnitude of the strain calculated by the two methods is also concordant in half of the wells. In the rest of the wells, the strains inversed from the groundwater level are one or two orders of magnitude larger than the fault dislocation model. These wells mostly have an epicenter distance larger than 300 km; therefore, the dynamic stress induced by the seismic wave may be responsible for the co-seismic water level changes in these wells. According to these results, we roughly estimate that the effect range of the static stress is approximately 300 km for the Wenchuan earthquake, and the dynamic stresses dominate beyond this epicenter distance. In addition, geological and hydrogeological conditions and other mechanisms may be responsible for these changes.     

Preliminary study on coseismic step-like changes of water-level in the Dazhai well, Simao city, Yunnan Province

The study on coseismic step-like changes of water-level is of theoretical and practical significance to the mitigation of secondary hazards, identification of earthquake precursors, tracking of the subsequent shocks, and the research of crustal activity (Nur and Booker, 1972; WANG et al, 1988). A lot of researches have been done by previous geoscientists. Among them, ZHANG et al (1994) inverted stress variation in the aquifers through the analysis of coseismic step-like changes of well water level. LI (1995), WANG (2000), and FU et al (2002) studied the relationship between coseismic step-like changes of water level and future seismic activity. HUANG et al (2000) investigated the water-level changes in many wells after the occurrence of one great earthquake. However,the analysis of the quantitative relation between the coseismic step-like changes of water level and earthquakes in China has not been reported so far. This paper describes the coseismic step-like changes of water level in the Dazhai well, Simao city, Yunnan Province, and tries to discuss the possible mechanism of these changes.     

Time series decomposition of groundwater level changes in wells due to the Chi‐Chi earthquake in Taiwan: a possible hydrological precursor to earthquakes

The largest and most disastrous earthquake in Taiwan (Mw: 7·3) in the 20th century, the Chi‐Chi earthquake, hit central Taiwan at 01:47 local time on September 21, 1999. The groundwater level changes were rapid at that time. Studies have found that the rapid change in groundwater levels was a co‐seismic phenomenon. This work analyzes the possibility that the abnormal change in groundwater levels may have occurred before the earthquake. Three well stations with a total of five wells are considered. They are all near the Che‐Lung‐Pu fault, which caused the Chi‐Chi earthquake. The time series decomposition method was applied to decompose the seasonal groundwater level, the trend in groundwater levels, and the period of the change in the groundwater level. Residual groundwater levels were found by subtracting the determined seasonal, trend and period data from corresponding data for the original groundwater level. The computed residual water levels in July, August and September of 1999, were transformed into a frequency spectrum by a Fourier method. Additionally, the effects of barometric pressures on the groundwater level changes were also evaluated. Analytical results show that the spectral density functions of the irregular groundwater level in the confined aquifer at the Chu‐Shan well in September behaved differently from those in July and August. We posit that a pre‐seismic hydrogeological anomaly may have existed before the Chi‐Chi earthquake, and can be considered in future studies of anomalies associated with earthquakes. Copyright © 2007 John Wiley & Sons, Ltd.     

三峡井网地下流体动态与映震能力的初步分析

系统分析了三峡井网 8口井水位、4口井水温和 4个井台土氡 2 0 0 1年的观测数据 ,建立了各个测项的正常动态 ,并检验了其各自的映震能力。结果表明 ,8口井水位均有固体潮显示 ,其对地壳体应变的响应灵敏度为 10 - 9～ 10 - 10 体应变 /mm。井水位大多有气压效应 ,并受一定程度的降雨干扰。 4口井的水温动态相对平稳 ,日变幅一般为千分之几度。 4个井台的土氡动态起伏较大 ,变化范围在几到几十Bq/L之间。在 2 0 0 1年 10月 16日秭归县梅家河ML3 6地震前 ,有 6口井水位、1口井水温和 1个井台的土氡有异常显示 ,表明三峡井网具有较强的映震能力