Seismic Emission in Geothermal Areas: Connection with Regional Seismicity

Abstract

Geothermal fields as active geophysical medium have a property of microseismic activity (seismic emission, SE). On Kamchatka (Russia) observation of small seismic signals is carried out in two locations – “Nachiki” (Nachikinsky hydrothermal field) and “Karymshina” (Paratunsky hydrothermal field). The investigations of seismic emission have been conducted on Kamchatka (Russia) since the end of the 1980s in the framework of the study of the fundamental problem of seismology connected with the possibility of monitoring overstressed medium conditions and preparation of strong earthquakes on the basis of geophysical field parameters.
The SE structure study gave an opportunity to distinguish components connected with Earth tides. It was found: (1) the response on tide impact is not stable in time; (2) the synchronization of the SE and tides is observed during some time (usually one-two months) before large (with magnitude М ≥ 6.0) earthquakes; it is manifested as stabilization of phase shift between tidal component of the SE envelope and tides on a certain level. This specific feature of the SE response on tides is used for investigation of SE connection with large earthquakes. During the SE observations period (1992-2008) 22 earthquakes with М ≥ 6.0 occurred on Kamchatka. The experimental data obtained in hydrothermal fields confirm the hypothesis about the correlation between values of stabilization level of the SE tide parameter (∆φ) with source characteristics of a preparing earthquake and its geographic position.