Abstract-A method for point estimation of coseismic volume deformation from amplitudes of earthquake generated changes in the water level and from the tidal sensitivity of the water level is presented. Application of this method is illustrated by six Kamchatka earthquakes of 1997-2004 with m w = 6.2-7.8 that occurred 128-316 km from the YuZ 5 well. Estimates of coseismic deformation provided by the level gage observations and by the model agree in amplitude and sign. The model reproduces an extended dislocation source in a homogeneous elastic isotropic half space. Source rupture parameters correspond to focal mechanisms from the CMT international catalog. Consistence in experimental and theoretical estimates of the volume coseis mic deformation indicates the high strain resistance properties of YuZ 5 borehole and the possibility of quantitative estimation of seismotectonic deformation from high precision water level measurements with time resolution not lower than 10 minutes.

-Forced and free oscillations of water level were recorded in the YuZ-5 well, Kamchatka due to the passage of seismic waves from the Sumatra-Andaman earthquake of December 26, 2004, M w = 9.3, hypocentral distance 8250 km. The greatest amplitude of water level oscillations, at least 5 cm, was observed during the onset of seismic surface waves with a typical period of 20-50 s. The total duration of the forced and free water level oscillations was about ten hours. The available theoretical models that describe oscillations of water level in a well due to seismic waves and rapid injection of water were used to estimate the transmissivity of the aquifer. The values obtained exceed by at least two orders of magnitude the transmissivity derived from pumping test measurements. A hypothesis was proposed to explain the temporary increase in aquifer transmissivity during the passage of seismic waves by invoking disturbances in the structure of the crack-pore space and a sharp increase in aquifer rock permeability.

The relevance of hydrogeological precursors (HGPs) study is justified by the need to obtain reliable information about the spatio-temporal manifestations and the relationships of HGPs with the parameters of subsequent earthquakes for seismic forecasting. In the review the data on repeated manifestations of HGPs before strong earthquakes obtained from long-term observations in five deep wells on the Kamchatka Peninsula (Far East of Russia) are presented. The analysis of the correlation of HGPs occurring in several wells is carried out in comparison with earthquake parameters characterizing both earthquake sources (magnitude, linear size of the source) and the impact of earthquakes in the area of wells (specific energy density in wave, intensity of shaking). It is shown that the manifestation of HGPs in several wells is observed before earthquakes with Mw = 6.6–7.8 at epicentral distances up to the first hundreds of km to observation wells in the near and intermediate zones of the sources with the ratio of the epicentral distances and the source sizes no more than 1–5. A feature of our study was the use of certain types of HGPs in water-level changes for predictive assessments of the strong earthquakes in the Kamchatka Peninsula. The review presents precursors in water-level changes detected in real time and the corresponding earthquake forecasts, which were recognized as successful according to the conclusions of the expert council on earthquake prediction.

The high-precision water level measurements with a sampling interval of 5-10 min were carried out in 1996-2017 in the YuZ-5 well, Kamchatka. In the obtained time series, water level variations caused by the passage of seismic waves (hydrogeoseismic variations-HGSV) during 19 earthquakes with М w = 6.8-9.1 which occurred at epicentral distances of 80-14.6 thousand km are revealed. Based on the HGSV morphological features, four main types of these variations are distinguished: oscillations (I); short (up to tens of hours) water level rises (II) superimposed on oscillations; short rises (III); and long (1.5-3 months) drawdowns (IV). The dependence of the occurrence of the revealed GHSV types on earthquake parameters (magnitude and distance), specific energy density and maximum seismic wave velocity, and the amplitude-frequency content of ground motion is analyzed based on the records at a nearest seismic station. Based on several case studies, hydrogeodynamic processes of HGSV formation are investigated using numerical modeling. It is shown that the forced and free amplitude fluctuations in the water level (types I and II) can arise due to the enhancement of groundwater pressure variations in the well-water-bearing rock system during the passage of surface seismic waves with periods corresponding to the resonant frequency of the well (τ = 44.6 s). The rise in the water level in well lasting for tens minutes to hours (types II and III of HGSV variation) is caused by the short increase in pressure under violation of the steady water flow in the direct vicinity of the well; strong local earthquakes accompanied by ground shaking with intensity I msk-64 ≥ 5 cause sustained drawdowns (type IV) due to pressure drop with the amplitudes up to 0.1 bar within a radius of up to a few hundred meters from the well.

This paper describes the water level variations in wells YuZ-5 and E-1 in Kamchatka during the Zhupanovsky earthquake that occurred on January 30, 2016 (Mw=7.2, Н=180 km). The distances from the Zhupanovsky earthquake epicenter to wells E-1 and YuZ-5 were 70 and 80 km, respectively. In well YuZ-5, the water level raised by 9.4 cm during 45 minutes after the seismic wave arrival. This effect was caused by a combination of a co-seismic rise in the water level due to the volumetric compression of the water-bearing rocks during fracturing in the earthquake source and an impulse increase in the fluid pressure near the wellbore during the seismic shocks. We estimated the amplitude of the coseismic water level increase (h=7.3 cm) and the strain value resulting from the volumetric compression of the water-bearing rocks, which is consistent with the estimated value of the coseismic volumetric deformation in the area of the well at the depth of 500m: D1 =-4.510-8. This estimation was based on the model of the dislocation source in the homogeneous isotropic elastic half-space with the parameters of the Zhupanovsky earthquake focal mechanism. After the earthquake, the water level dropped for three months at an amplitude of about ~40 cm. In order to estimate the radius of the well sensitivity to the pressure drop source, we used the model of water level lowering that followed the pressure drop in the aquifer at a distance to the well as a result of the improved filtration properties of the water-bearing rocks after the seismic shocks. The estimated radius of the well sensitivity, R is 450 m. For 3.5 months before the Zhupanovsky earthquake, ~20 cm increase in the water level was observed, which is anomalous in comparison with the average seasonal variations of the water level, as shown by the long-term observations. In our opinion, such a rise in the water level occurred in the process of the earthquake preparation, and can thus be viewed as its precursor. In well E-1, a sequence of water level changes manifested a hydrogeodynamic precursor: the water level dropped at an increased rate for 21 days before the earthquake, and raised at an amplitude of 3.7 cm during one month after the earthquake. The hydrogeodynamic precursor detected in real time gave grounds for forecasting a highly probable strong earthquake at a distance of up to 350 km from wells E-1 within a month. This forecast was reported to the Kamchatka Branch of the Russian Expert Council (KB REC) on January 21, 2016. The Zhupanovsky earthquake occurred on January 30, 2016, and its magnitude, time and location correlated with the prediction. The case of this earthquake shows that the Kamchatka Branch of the Federal Research Center 'Geophysical Survey of RAS' has the system of water level observations and data processing, which is capable of diagnosing (close to real time and retrospectively) different types of hydrogeoseismic variations in the water level in wells in case of strong seismic events, and detecting the hydrogeodynamic precursors of strong earthquakes.