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 M_w = 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 superimposed on oscillations (II); 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.

Anomalies in the ionic and gas composition of groundwater before earthquakes (hydrogeochemical precursors, hereinafter HGCP) are considered according to data of systematic observations in ten self-flowing wells and springs in seismically active regions of Russia (Kamchatka Peninsula), Uzbekistan, Japan, and Iceland. Using an extended set of earthquake parameters, it was shown that HGCP were manifested for 1–9 months in the near and intermediate zones of the future earthquake sources with M_w = 5.3–7.8. Such properties of hydrogeochemical precursors allow their use for predicting the magnitude and time of expected seismic events, as well as their impact in the observation area. A model is presented for a registered precursor in the form of the ionic composition of groundwater in self-flowing well based on observational data on concentrations of anions and cations and on a mathematical model for the mixing of two waters of contrastingly different composition in a zone of increased conductivity. Calculations for one of the wells are presented as an illustrative example of the chemical composition of two mixing waters in the aquifer and in the wellbore. This model and observational data are used to estimate parameters of the disturbed state of the well–aquifer system during the preparation of an earthquake: the relaxation time of the water pressure pulses (t₀) and the movement time of mixed water (τ₀). The morphology and duration of HGCP are controlled by relations between t₀ and τ₀. The further development of HGCP studies and their application in predicting earthquakes require a technical modernization of the system of hydrogeochemical observations and the development of HGCP models for individual wells.

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 (atmos

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...

Repeated manifestations of hydrogeochemical anomalies in groundwater ion content variations before local strong earthquakes were recorded in three flowing wells of the Petropavlovsk-Kamchatsky test site. A model of changes in chemical composition of groundwater is considered using observational data and modeling of two waters mixing with contrasting composition in a zone of increased permeability in aquifer. Hydrodynamic parameters of the model—relaxation time of water pressure impulses and the time of mixed water movement in aquifer and wellbore—can vary from days to hundreds of days in individual wells. These parameters determine the duration and morphological features of anomaly in mixed water from a well. Using observational data from self-flowing well M-1, an assessment was made of chemical composition and mineralization of two mixing waters and their ratio in mixed water under background conditions and during the preparation of earthquake on 2 March 1992, M_w = 6.9.