Coseismic Water Level Changes Research Articles

Long‐ and Short‐Term Effects of Seismic Waves and Coseismic Pressure Changes on Fractured Aquifers

AbstractTwo adjacent groundwater wells on the North China Platform are used to study how earthquakes impacted aquifers. We use the response of water level to solid Earth tides to document changes after earthquakes and how aquifer and fracture properties recovered to pre‐earthquake properties. We consider two models for the phase and amplitude of water level response to the lunar diurnal (O1) and semidiurnal (M2) tides: a leaky aquifer model, and a model in which fracture orientation determines the response. In the leaky aquifer model, changes arise from changes in permeability and storage; in the fracture model, changes are due to changes in apparent orientation of transmissive fractures. Responses in one well are best explained by the leaky aquifer model, and can explain the large amplitude coseismic water level and permeability changes and the non‐recoverable changes after the largest earthquake. Responses in the other well are consistent with the fracture model and show little coseismic change in water level but changes in apparent fracture orientation. Larger ground motions lead to larger coseismic water level changes and longer recovery times. We propose that the well in the more permeable and shallow aquifer has less variable pore‐pressures around the well. Larger coseismic strains from water level changes may enable longer‐lasting changes in aquifer properties. We conclude that relatively high permeability aquifers are less susceptible to impacts from seismic waves, and thus have small changes in water levels and hydrogeological properties.

Multiple mechanisms of coseismic water level changes at the Rongchang well in a seismically active area in China

We examined water level data at the Rongchang (RC) well in the Rongchang natural gas field in China's Sichuan Basin from November 2007 through 2019, where injection-induced seismicity with a magnitude of up to 5.2 has been reported. Coseismic water level changes caused by earthquakes from 3 km to 3500 km away, as well as changes in water temperature, provide a good opportunity to systematically study the mechanisms underlying the response of water level to earthquakes. Among 41 ML ≥ 3.0 local earthquakes, 20 events exceeded the magnitude-distance threshold for the water level to change. Eleven events caused water levels to rise, and only one earthquake led to a decrease in water level. For the 22 distant earthquakes with a seismic energy density greater than the threshold of 0.0017 J/m3, ten events caused rises in the water level and only the MW 7.9 Wenchuan Earthquake caused a temporary, but large, decrease in water level. In total, eight local events and 11 distant events, which were expected to cause coseismic water level changes, actually resulted in no changes. The findings imply that an earlier sizable earthquake may decrease the sensitivity of the well for a certain period of time (approximately two months). The dominant mechanisms of coseismic water level changes in response to near-, mid-, and far-field earthquakes are different. For near-field earthquakes, the drop in coseismic water level is governed by the combined effects of static strain changes and the release of trapped gas bubbles due to the strong vibration of seismic waves in the aquifer; however, only static strain changes are dominant after mid-field earthquakes. For far-field earthquakes, the dominant mechanism is aquifer softening due to growth of gas bubbles in the groundwater that is associated with weak and low frequency seismic shaking of passing surface waves.

Describing coseismic groundwater level rise using tank model in volcanic aquifers, Kumamoto, southern Japan

The change of groundwater levels after the 2016 Mw 7.0 Kumamoto crustal earthquake was evaluated using a simple conceptual hydrological model in an attempt to show the presence, intensity, and probable mechanism of water level rise observed in Kumamoto where a comprehensive observation-well network exists. A tank model was applied to verify 16 wells in the study field. In the model groundwater levels were first calibrated for the periods in ca. 2 years before the main shock using several hydrological parameters including precipitation, evapotranspiration, water recharge and discharge, and artificial recharge by irrigation. Water levels were then simulated by extrapolating this law of water fluctuating patterns for ca. 2.5 years after the main shock of the earthquake, without considering hydrogeological changes due to the earthquake. A difference in groundwater levels between observation and simulation results yields a degree of coseismic water level rises for each well. The coseismic abnormal water level increase was calculated to be ~11 m in 4–5 month after the main shock and was most significantly on the western slope of the Aso caldera rim mountains. The spatial distribution of the coseismic water increases clarified that the most dominate increasing anomalies prevail at mountain feet surrounding the plains, suggesting the occurrence of coseismic mountain water release resulting in the rise of water levels in downslope aquifers. Identified coseismic water level increases still continue up to 2.5 years after the earthquake, probably because changes in hydrogeological properties in mountain aquifers, i.e., permeability, are still sustained. Our forecasting water recovering trends require ca. 3.5–5 year after the earthquake for complete recovery to the original conditions. We demonstrated that our approaches are capable of describing coseismic water level changes and could potentially be applied to other fields.

Coseismic water level changes induced by two distant earthquakes in multiple wells of the Chinese mainland

Coseismic water level oscillations, or step-like rises and step-like drops were recorded in 159 wells throughout the Chinese mainland due to the 2015 Nepal Mw 7.8 earthquake, and 184 wells for the 2011 Japan Mw 9.0 earthquake. The earthquake magnitude, and the associated dynamic stresses, has positive roles in both the sensitivity of water level to earthquake induced change, and the amplitude and duration of resulting coseismic water level changes. Wells whose water levels are sensitive to Earth tides have high potential to response to earthquakes. Polarities of step-like changes (rises or drops) are locally controlled and spatially variable, with artesian wells generally recording water-level rises. Permeability enhancement was assessed as a mechanism responsible for step-like changes by analyzing the tidal phase responses. Permeability variations are inferred for 17 out of 95 wells with step-like changes during the Nepal earthquake and for 32 out of 105 wells following the Japan earthquake; however, only 6 wells have permeability variations after both earthquakes.

Different hydraulic responses to the 2008 Wenchuan and 2011 Tohoku earthquakes in two adjacent far-field wells: the effect of shales on aquifer lithology

Zuojiazhuang and Baodi are two adjacent wells (~50 km apart) in northern China. The large 2008 M w 7.9 Wenchuan and 2011 M w 9.1 Tohoku earthquakes induced different co-seismic water-level responses in these far-field (>1000 km) wells. The co-seismic water-level changes in the Zuojiazhuang well exhibited large amplitudes (~2 m), whereas those in the Baodi well were small and unclear (~0.05 m). The mechanism of the different co-seismic hydraulic responses in the two wells needs to be revealed. In this study, we used the barometric responses in different frequency domains and the phase shifts and amplitude ratios of the tidal responses (M2 wave), together with the well logs, to explain this inconformity. Our calculations show that the co-seismic phase shifts of the M2 wave decreased or remained unchanged in the Baodi well, which was quite different from the Zuojiazhuang well and from the commonly accepted phenomena. According to the well logs, the lithology of the Baodi well is characterized by the presence of a significant amount of shale. The low porosity/permeability of shale in the Baodi well could be the cause for the unchanged and decreased phase shifts and tiny co-seismic water-level responses. In addition, shale is one of the causes of positive phase shifts and indicates a vertical water-level flow, which may be due to a semi-confined aquifer or the complex and anisotropic fracturing of shale.

Co-seismic water level changes in response to multiple large earthquakes at the LGH well in Sichuan, China

We examined the water level data at the LGH well in Sichuan, China, from December 2007 to July 2015 and their responses to multiple large earthquakes with seismic energy densities greater than 10−4J/m3. Co-seismic water level declines were observed in response to eleven earthquakes out of twelve in the farfield, and co-seismic water level increase was observed in one nearfield case. The water level declines in the farfield showed a linear relation with the common logarithm of the seismic energy densities, whereas the water level increase in the nearfield fell away from this relation, indicating that the farfield responses and the nearfield response were produced by distinct mechanisms. We used the phase shift of tidal responses as a proxy for permeability and found that permeability enhancements were observed both in the farfield and nearfield. The co-seismic water level declines in response to the distant earthquakes could be explained by permeability enhancements caused by the passage of seismic waves through the mobilization of colloidal particles; the co-seismic water level increase in response to the nearfield case could be caused both by the compression of the static stress and by the seismic waves.

Mechanism of co-seismic water level change following four great earthquakes – insights from co-seismic responses throughout the Chinese mainland

We analyze the co-seismic groundwater level responses to four great earthquakes recorded by China's network of groundwater monitoring wells. The large number of operational wells (164 wells for the 2007 Mw 8.5 Sumatra earthquake, 245 wells for the Mw 7.9 Wenchuan earthquake, 228 wells for the Mw 9.0 Tohoku earthquake and 223 wells for 2012 Mw 8.6 Sumatra earthquake) and co-seismic responses provide an opportunity to test hypotheses on mechanisms for co-seismic water level changes. Overall, the co-seismic water level responses are complex over large spatial scales, and there is great variability both in the sign and amplitude of water level responses in the data set. As shown in previous studies, permeability change, rather than static strain, is a more plausible mechanism to explain most of the co-seismic responses. However, we find through tidal analysis of water level responses to solid Earth tide that only one third of these wells that showed a sustained post-seismic response can be explained by earthquake-induced permeability change in aquifers, and these wells had sustained (>30 days) water level changes. Wells that did not show sustained changes are more likely affected by permeability changes only immediately adjacent to the wellbore.

Coseismic water-level changes in a well induced by teleseismic waves from three large earthquakes

Three large earthquakes (the 2007 Mw 8.4 Sumatra, the 2008 Mw 7.9 Wenchuan, and the 2011 Mw 9.0 Tohoku) induce coseismic water-level increment at far fields (epicentral distances>1000km) in the Fuxin well located in the Fuxin City, northeastern China (the well with the observation of both water levels and volume strains). A comprehensive analysis for the mechanism of far-field coseismic water-level changes is performed by analyzing the in-situ permeability, Skempton's coefficient B, and with the broadband seismograms from a nearby station. We observe an undrained compaction with a decreasing permeability induced by the shaking of teleseismic waves in the far field. Shaking by teleseismic waves can induce compaction or dilatation in the aquifer of Fuxin well; is able to enhance permeability and thus build a new pore-pressure equilibrium system between the Fuxin well and the nearby Sihe reservoir (150m away from the Fuxin well). The resulting interstitial fluid flow across the region increases coseismic water levels in the aquifer of Fuxin well.

Permeability enhancement in the aquifer of Fuxin well in geothermal area of northeastern China induced by low-frequency teleseismic waves of the 2011 Mw 9.0 Tohoku earthquake

The Mw 9.0 Tohoku large earthquake induces far field (epicentral distance >1800 km) prominent coseismic water-level increase in the Fuxin well at northeastern China, which also influences volumetric strains. Different mechanisms of far-field coseismic water-level changes are analyzed by integrating these water-level/volume-strain data with broadband seismograms from a nearby station. Dilatation induced by propagating teleseismic wave (central frequency 0.02 Hz) may be the dominant mechanism of the observed water-level increases in the aquifer of Fuxin well. The dynamic energy density of ~5×10 −2 J/m 3 from the earthquake (computed from broadband seismograms), could be large enough to incur the far-field dilatation stress of ~0.35 MPa (with the strain variation of −6 ) in the aquifer. The resulting enhancement in permeability by the dilatation stress can build a new pore-pressure equilibrium between the Fuxin well and the nearby Sihe reservoir (~150 m away from the Fuxin well). The induced interstitial fluid flow in the region accounts for the sustained large-amplitude coseismic water-level increase. The Fuxin well lies in the geothermal area, and this study may also has some implications for the geothermal resource exploration. ARTICLE INFO

Analysis of the Water Level Fluctuation in Koyna-Warna Region, India

ABSTRACT Koyna region in India is known to be the largest case of the Reservoir Triggered Seismicity (RTS) in the world with Magnitude 6.3 (M 6.3) earthquake in 1967. The region is seismically active even after forty five years with occurrences of earthquakes up to M 5.0. The porous crustal rocks of Koyna – Warna region respond to changes in the prevailing stress / strain regime. These changes induce variations in the water level in bore wells before; during and after an earthquake and their study can help in understanding the earthquake genesis in the region. In this work the observed water levels in the bore wells have been analyzed and found the co-seismic water level changes in some wells. The earthquake on 14 th March 2005 with M 5.1 in Koyna – Warna region has been studied by using wavelet transformations and the results reveals the significant co-seismic changes in some of the bore wells. The Ukalu well has showed the maximum change in the water level since the epicenter is close to the well. The focal mechanism and the distance of the epicenter play important role in the variation of the water level fluctuations.

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.

Mechanism of Different Coseismic Water-Level Changes in Wells with Similar Epicentral Distances of Intermediate Field

Water-level changes at different monitoring stations are observed during the Wenchuan earthquake ( M S 8.0) in the Chinese mainland. In the intermediate field, we observed coseismic water-level changes of different amplitude in wells with similar epicentral distances. In order to study the mechanism of those coseismic water-level changes, we calculated the static strain change with the Okada dislocation model (Okada, 1992; Lin and Stein, 2004; Toda et al. , 2005). By comparing the calculated coseismic water-level change based on the poroelastic theory with the observed water-level change, we can judge whether the poroelastic theory can be applied to the aquifer of the well. From our research, we find the poroelastic theory can be applied to the area with epicentral distance≲1.5 fault rupture length. Bearing this in mind, we find that when the water-level change of those wells can be explained by the poroelastic theory and that the difference of the water-level change in wells with similar epicentral distances is mostly related to the difference of Skempton’s coefficient B . Otherwise, the water-level change may be induced by the transition of the seismic waves because it is usually larger than the one induced by the undrained dilatation and consolidation, and changes more gradually.

Co-seismic responses of water wells in Jiangsu province to 2008 Wenchuan and 2011 Japan earthquakes

Co-seismic water-level and temperature changes of the 2008 magnitude – 8.0 Wenchuan and the 2011 magnitude − 9.0 Japan earthquakes recorded at 10 observation wells in Jiangsu province are presented and analyzed. The data show that water level responded more regularly with earthquake magnitude and distance than water temperature. The response was different for wells located in different tectonic units, being weaker in central and northern plain, which has a relatively thick surface layer of loess, than southern Jiangsu, which is hilly.

Analysis of Coseismic Water-Level Changes in the Wells in the Koyna-Warna Region, Western India

Abstract We test the hypothesis that coseismic water-level changes in wells are proportional to coseismic volumetric strain by analyzing available data from the Koyna–Warna region of western India. A total of 18 cases of water-level changes have been reported at ten wells corresponding to six earthquakes of M ≥4.3 that occurred in the region from 1997 to 2005. Out of these, clear unambiguous steplike coseismic water-level changes have been observed in ten cases at five confined wells. We used basic poroelastic theory to simulate volumetric strain and corresponding water-level changes and find that all cases show consistency in sign between reported coseismic water-level changes and simulated volumetric strain. All confined wells with high strain sensitivity that are located near earthquake epicenters show good agreement in magnitude between simulated and reported volumetric strain, thereby supporting this hypothesis.

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 MS8.0 earthquake and its 15 larger aftershocks (MS≥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. MS magnitude has the strongest correlation with the coseismic water level changes comparing to MW and ML 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.

Implications of coseismic groundwater level changes observed at multiple-well monitoring stations

SUMMARY Earthquake-related groundwater level changes have been recorded by a dense network of monitoring well stations in Taiwan. At most multiple-well stations, the direction and magnitude of coseismic water level changes vary in wells of different depths. Comprehensive water level data recorded in 209 wells in the vicinity of the seismogenic fault during the 1999 M L7.3 earthquake demonstrate a preliminary 3-D distribution of coseismic changes. The largest coseismic rise at a station observed typically in a confined gravel aquifer indicates the association of the magnitude of coseismic change with characteristics, rather than depth, of the aquifer. The variation of coseismic changes in the vertical direction implies possible inconsistency between the observed water level changes and the volumetric strains calculated from simple dislocation models. At a given hypocentral distance, the coseismic change in the footwall of the ruptured segment of the fault was much greater than that of the unruptured segment. This phenomenon suggests that fault displacement plays an important role in the generation of coseismic changes. While hypocentral distance correlates well with coseismic rise or fall in the vicinity of the ruptured seismogenic fault, poor correlation is found for coseismic change further from the earthquake epicentre.

Rock dilation, nonlinear deformation, and pore pressure change under shear

The dilation of rock under shear gives rise to detectable effects both in laboratory experiments and in field observations. Such effects include hardening due to reduction in pore pressure and asymmetrical distribution of deformation following strike-slip earthquakes. In this paper, we examine the nonlinear poroelastic behavior of isotropic rocks by a new model that integrates Biot's classic poroelastic formulation together with nonlinear elasticity, and apply it to Coulomb failure criterion and pore pressure response to a fault slip. We investigate the poroelastic response of two alternative forms of a non-Hookean second-order term incorporated in the poroelastic energy. This term couples the volumetric deformation with shear strain. Like linear poroelasticity, our model shows an increase of pore pressure with mean stress (according to Skempton coefficient B) under undrained conditions. In addition, in our model pore pressure varies also with deviatoric stresses, where rising deviatoric stresses (at constant mean stress) decreases pore pressure (according to Skempton coefficient A), due to dilatancy. The first version of our model is consistent with a constant A smaller than 1/3, which is in agreement with the classic work of Skempton, but does not fit well the measured undrained response of sandstones. The second model allows A and B to vary with shear stress, and displays the experimentally observed connection between pore pressure and deviatoric stresses under undrained conditions in Berea and Navajo sandstone samples. Numerical results present in this paper predict dilatancy hardening and suggest that it should be taken into consideration in Coulomb failure stress calculations. We apply our model to the distribution of pore pressure changes in response to a fault slip. Results of numerical simulations of coseismic deformation demonstrate that due to dilatancy regions of decreasing pore pressure are larger relative to regions of increasing pore pressure. The model predictions have significant implications for coseismic water level changes and post-seismic pore pressure diffusion and crustal deformation.

Changes of Groundwater Level due to the 1999 Chi-Chi Earthquake in the Choshui River Alluvial Fan in Taiwan

Changes of groundwater levels induced by the M L 7.3 Chi-Chi earthquake on 21 September 1999 were recorded at 157 out of 179 monitoring wells in the Choshui River alluvial fan. Of those, 67 observed large groundwater-level changes, ranging from 1.0 to 11.1 m. These 157 wells are clustered at 64 stations located approximately 2 to 50 km west of the north-south-trending Chelungpu fault. Both oscillatory and steplike changes of water level were observed on the analog records at the time of earthquake, while only steplike changes were observed on the hourly digital records. Coseismic changes of groundwater level were recorded not only in the confined aquifers but also in the partially confined aquifers and the unconfined aquifers. The recovery of water-level changes took minutes to months, depending primarily on hydrogeologic conditions of the confining layers. The sign and magnitude of coseismic water-level change at a well varied with its distance from the fault. The distribution of coseismic water-level changes induced by the Chi-Chi earthquake indicates that water-level rise predominated in most of the footwall area, whereas water-level fall prevailed in a narrow zone adjacent to the fault trace. Manuscript received 31 October 2000.

Hydrological response to earthquakes in the Haibara well, central Japan - I. Groundwater level changes revealed using state space decomposition of atmospheric pressure, rainfall and tidal responses

SUMMARY For the groundwater level observed at the Haibara well, Shizuoka Prefecture, central Japan, time series analysis using state-space modelling is applied to extract hydrological anomalies related to earthquakes. This method can decompose observed groundwater level time series into five components: atmospheric pressure, tidal, and precipitation responses, observation noise, and residual water level. The decomposed responses to atmospheric pressure and precipitation are independently determined and are consistent with the expected response to surface loading. In the groundwater level at the Haibara well, 28 coseismic changes can be discerned during the period from 1981 April to 1997 December. There is a threshold in the relationship between earthquake magnitude and the well–hypocentre distance, above which earthquakes cause coseismic changes in the residual water level. All of the coseismic water level changes at the Haibara well are decreases, although 33 per cent of the estimated coseismic volumetric strain steps are contraction, which would be expected to cause water level increases. The coseismic changes in groundwater level are more closely proportional to the estimated ground motion than to coseismic volumetric strain steps, suggesting that ground motion due to earthquakes is the major cause of the coseismic water level drops and that the contribution from static strain is rather small. Possible pre- or inter–earthquake water level changes have occurred at the Haibara well and may have been caused by local aseismic crustal deformation.

Hydrological response to earthquakes in the Haibara well, central Japan - II. Possible mechanism inferred from time-varying hydraulic properties

SUMMARY 28 coseismic groundwater level decreases have been observed at the Haibara well, Shizuoka prefecture, central Japan, from 1981 to 1997. These groundwater level changes cannot be explained as the poroelastic response to coseismic static strain. We use the atmospheric pressure and tidal responses of the well, rock properties measured on core samples from the same formation and pumping test results to characterize the hydraulic and mechanical properties of the aquifer. The responses of the Haibara well to the M2 Earth tide constituent and to atmospheric pressure have varied over time. In particular, increasing amplitude and decreasing phase lags were observed after the 1993 pumping test, as well as after earthquakes that caused coseismic water level changes. The tidal response, together with the surface load efficiency derived from the atmospheric pressure response, is used to estimate the mechanical properties of the aquifer. The largest amplitude of the M2 constituent, 2.2 mm, is small enough to imply that pore fluid in this system is approximately twice as compressible as water, possibly due to the presence of a small amount of exsolved gas. Diffusion of a coseismic pressure drop near the well could account for the observed time histories of the water level changes. The time histories of the water level drops are well matched by the decay of a coseismic pressure drop at least 80 m away from the well. Removal of a small amount of gas from the formation in that location might in turn explain the coseismic pressure drops.