Features of Fluid-Dynamic Processes in a Seismically Active Region (Case Study of Kamchatka Peninsula, Russia)

Abstract

The effects of 19 earthquakes (M_w = 6.8−9.0, epicentral distances 80–14600 km) are considered on data of long-term precision water level observations in the YuZ-5 well, Kamchatka Peninsula. Four types of water level variations were identified: I—oscillations, II—oscillations with short-term rise, III—short-term rises, IV—long-term decreases. Manifestations of the selected types of water level variations are determined by the intensity of seismic impact corresponding to the ratio of magnitude and earthquake’s epicentral distance, the calculated values of specific density of energy in seismic wave, maximum velocity and amplitude-frequency composition of maximum phases in the earthquake record, obtained from broadband seismic waveforms at the nearest station. Dynamic deformation of water-bearing rocks during the passage of seismic waves is accompanied by different hydrogeodynamic processes in the “well—water-bearing rock” system including amplification of water pressure variations in the wellbore, short-term impulses of pressure near the wellbore, water pressure decrease at distances up to hundreds of meters from the well due to increased permeability of water-bearing rocks during intense shocks. Based on water level variations modelling, we show evaluation criteria for possibility of their occurrences. These criteria include the presence of certain frequencies in composition of seismic wave (oscillations), values of amplitudes and relaxation times of water pressure impulses (short-term level rises), presence of geological objects with variable permeability in the vicinity of the well.