Hydrogeological Responses to Distant Earthquakes in Aseismic Region

Abstract

For the first time precise measurements of the groundwater level variations in the territory of the Mikhnevo geophysical observatory in an aseismic region (Moscow region, Russia) have been carried out since February 2008 at a sampling rate of 1 Hz. The groundwater level variations under quasi-stationary filtration are considered indicators of the dynamic deformation of a fluid-saturated reservoir represented by carbonate-terrigenous sediments. Both permanent (long-term) factors—atmospheric pressure, lunar-solar tides, and periodic (short-term) ones—seismic impacts from distant earthquakes, are used as probing signals for analyzing the filtration parameters of aquifers of different ages. Hydrogeological responses to the passage of seismic waves from earthquakes with magnitudes of 6.1–9.1 with epicentral distances of 1456–16,553 km was recorded in 2010–2023. Dependences of dynamic variations of the pore pressure in the upper weakly confined and lower confined aquifers on the ground velocity are approximated by different regression functions. Spectral analysis of hydrogeological responses made it possible to identify coseismic and postseismic effects from distant earthquakes. The postseismic effects in the form of an episodic increase in the pore pressure may be caused by a skin effect—clogging of microcracks nearby the wellbore by colloidal particles under intensive seismic impact.