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.

This paper is concerned with the main stages in the setting-up and technical development of a system specializing in physical and chemical parameters of groundwater at a network of wells and springs in the Petropavlovsk Geodynamic Test Area, Kamchatka. The focus is on a description of hydrogeochemical and hydrogeodynamic precursors to Kamchatka earthquakes (М w = 6.6-7.8) that occur a few weeks to a few months before a seismic event, manifesting themselves in anomalous changes in chemical composition and groundwater level. The precursors are discussed in application to their use at specialized councils on earthquake prediction. It is shown that the system of automated observation of groundwater parameters at wells as developed at the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences (KB GS RAS) is capable of identifying hydrogeodynamic precursors of water level in near real time and of providing, in some particular cases, quantitative estimates of pre-seismic and coseismic of deformation in water-saturated rocks. This can be useful in geophysical monitoring and intermediate-term prediction of strong earthquakes for the Kamchatka region.

Abstract⎯The hardware complex that was produced by OOO Polynom, Khabarovsk, for registration of the level, temperature, and electrical conductivity of ground water in wells and meteorological parameters (atmospheric pressure, air temperature) at a measurement frequency from 5 min to 1 h is described. The equipment is installed in the wells of Kamchatka and has been used for several years to register variations caused by earthquakes in the parameters of ground waters. Different variations in measured parameters of ground waters due to strong earthquakes of February 28, 2013, M W = 6.8 and May 24, 2013, M W = 8.3 are registered with this equipment in wells YuZ-5 and E-1. The registered variations and their systematization are described taking into account the mechanisms of a seismic impact on the state of the well-water-saturated rock system. Keywords: well, water level, electrical conductivity, hardware complex, earthquake, Kamchatka DOI: 10.3103/S0747923917040065 INTRODUCTION Strong earthquakes can be accompanied by different variations in the levels, temperature, and chemical composition of ground water in wells. In Kolylova (2006Kolylova ( , 2010, we termed them hydrogeoseismic variations and showed that the features of their manifestation are determined by different seismic impacts on the state of the "well-water-saturated rock" system.The changes in the static stress field during the formation of ruptures in the earthquake foci and corresponding variations in the stress-strain state of the water-saturated rocks manifest themselves in coseismic jumps of the increase or decrease in the water level during the first few minutes after the arrival of seismic waves. Dynamic strain of water-saturated rocks and shaking of a well bore can also be accompanied by various co-and postseismic effects in the changes of levels and chemical composition of ground waters under the passage of seismic waves from strong earthquakes. Such effects are described in numerous works, e.g., Kopylova, 2001Kopylova, , 2006Kopylova et al., 1994;Wang and Manga, 2010. When studying them, the researchers focus their attention primarily on the explanation of hydrogeodynamic and hydrogeochemical processes of their formation and general estimation of an impact of strong earthquakes on the state of the fluid-saturated geological medium.

⎯This paper considers the chemical composition and classification of ground water at seven flowing wells and four springs using materials from the 2014 hydrogeochemical sampling and from continuous observations conducted by the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences (KB GS RAS) in 1989-1999. We estimated the saturation of ground water discharges at individual vents with alumosilicate, carbonate, and sulfate secondary minerals, following the behavior of saturation over time. We have found that the ground water undergoes an increase in the saturation with secondary minerals during large earthquakes that produced shaking of intensity I = 5-6 on the MSK-64 scale. Such changes in the saturation of ground water with secondary minerals are less pronounced during the precursory periods before earthquake occurrence. We discuss desirable future developments of the observational system at wells and springs in order to look for new types of hydrogeochemical precursors to earthquakes.