Borehole geoacoustic measurements in the system of complex geophysical monitoring and earthquakes forecast in Kamchatka

New methods of monitoring of stress-strain states of geological environment have been used for many years in the Petropavlovsk-Kamchatsky testing area. In this paper we estimate the results of using these methods. The data of borehole geoacoustic measurements and electromagnetic measurements with underground electric antennas form the basis of these methods. We analyze the results of the monitoring and compare them with the data of hydrogeochemical and hydrogeodynamic observations to make conclusions about the seismic hazard for Kamchatka region every two weeks. The complex borehole data example shows changes of stress-strain states of geological environment in the zone of the Petropavlovsk-Kamchatsky testing area in time vicinity of the Tohoku megaearthquake (M=9.0, Japan, March 2011) and the strongest Zhupanovsky earthquake (M = 7.2, Kamchatka January 2016).