Anomalies in the Dynamics of Subsoil Gases at the Petropavlovsk-Kamchatskii Test Site within the Vicinity of the Time of the Magnitude 7.2 January 30, 2016 Deep-Focus Earthquake

Abstract

A negative bay-shaped anomaly in radon volume activity (VA Rn) with an advance time of 10 days was recorded at a network of subsoil gas observing stations in the Petropavlovsk-Kamchatskii Test Site area before the Zhupanov earthquake (ZhE) of January 30, 2016 whose magnitude was 7.2 and the depth of focus was equal to 177 km. The anomaly was simultaneous with a positive anomaly in the concentration of molecular hydrogen. After a lapse of 98 hours after the ZhE, a sharp increase in VA Rn was recorded by gas-discharge counters at the INS site installed in a well. The increase lasted approximately 2 days and is treated as a postseismic effect in the subsoil radon field. This disturbance was followed by two periods (February 5 through 19 and February 23 to March 15) of “high-frequency” oscillations at frequencies of 0.3–6 day–1. These are thought to have been due to self-excited processes in the annular space. The oscillations are separated by a disturbance that is interpreted as a precursory anomaly before the magnitude 6.4 March 20, 2016 earthquake that occurred at a distance of ~300 km from Petropavlovsk-Kamchatskii. The precursory anomaly before the March 20 earthquake is believed to have been due to a high strain sensitivity of the hydrogeological system due to a change in the state of stress and strain in the earth after the ZhE whose epicenter was 100 km from the recording site.