SEISMICITY of KAMCHATKA and COMMANDER ISLANDS in 2015

The seismicity review of Kamchatka and surrounding territories for 2015 is given. In the Kamchatka earthquake catalogue, the minimum local magnitude of completeness is MLmin=3.5, and for earthquakes with h≥350 km under the Okhotsk sea MLmin=3.6. The Kamchatka earthquake catalogue for 2015 with ML3.5, published in the Appendix to this issue, includes 1213 events. 92 earthquakes of the catalogue with ML=3.0–6.5 were felt in Kamchatka and surrounding areas with seismic intensity I=2–6 according to the MSK-64 scale. For all events with ML5.0 that occurred in 2015 in the KB GS RAS area of responsibility, an attempt to calculate the seismic moment tensor (SMT) was made. There are 32 such events in the regional catalogue. For 28 earthquakes the SMT and depth h of the equivalent point source were calculated successfully. The calculations were performed for the SMT double-couple model using a nonlinear algorithm. In 2015, a typical location of the earthquake epicenters was observed in the Kamchatka zone. In 2015, the seismicity level in all selected zones and in the region as a whole correspond to the background one according to the “SESL’09” scale. The number of recorded events with ML3.5 and strong earthquakes with ML5.0 is close to the average annual value. Anomalous and significant events were not recorded.

An Awakening Magmatic System beneath the Udina Volcanic Complex (Kamchatka): Evidence from Seismic Unrest of 2017–2019

—The Udina volcanic complex located in the southeastern part of the Klyuchevskoy group of volcanoes in Kamchatka remained dormant for several thousand years, but the magmatic system beneath the area may be awakening judging by seismic unrest. Seismicity in the area is characterized by data from permanent regional seismic stations and campaign local stations, as well as by data of the Kamchatka earthquake catalog. Seismic activity having nucleated at shallow depths in the vicinities of the Udina volcanoes since October 2017 may reflect a beginning cycle of volcanism. The earthquakes are mainly long-period (LP) 0.5–5 Hz events, which are commonly attributed to the movement of viscous magma and resonance phenomena in magma conduits. Such earthquakes may be a response to inputs of new magma batches to the plumbing system that feeds the volcanoes and thus may be precursors of volcanic unrest. Seismic campaigns of May–July 2018 near the Udina complex provided more rigorous constraints on earthquake coordinates and origin depths and showed that most of the earthquakes originated within 5 km beneath the Bolshaya Udina Volcano. Seismic tomographic inversion using the LOTOS code revealed a zone of high P-wave velocities, low S-wave velocities, and a high vP/vS ratio directly beneath the volcano. Such a combination of parameters typically occurs in active volcanic areas and marks intrusion of partially molten magma and/or liquid fluids. The velocity anomaly detected in 2018 is shallower than that recovered in 2014–2015. The seismic evidence, along with the available geological and geophysical data, record the movement of viscous magma related to the Udina feeding system in the middle crust, which is implicit proof for connection between the intermediate crustal and deep mantle magma sources renewed after a long lull.

KAMCHATKA AND COMMANDER ISLANDS

The seismicity review of Kamchatka and surrounding territories for 2014 is given. In Kamchatka earthquake catalogue minimum local magnitude of completeness is MLmin=3.5, and for earthquakes under the Okhotsk sea with h≥350 kmMLmin=3.6. The Kamchatka earthquake catalogue for 2014 with ML3.5, published in the Appendix to this annual, includes 1114 events. 86 earthquakes of the catalogue with ML=3.35–6.2 were felt in Kamchatka and surrounding areas with seismic intensity I ranged from 2 to 5 according the MSK-64 scale. For all events with ML5.0 occurred in the area of responsibility of the KB GS RAS in 2014, an attempt to calculate the seismic moment tensor (SMT) was made. There are 40 such events in the regional catalogue. For 36 earthquakes, the SMT and depth h of the equivalent point source were calculated successfully. The calcu-lations were performed for the SMT double-couple model using a nonlinear algorithm. In 2014, a typical location of the earthquake epicenters was observed in the Kamchatka zone. In 2014, the seismicity level in all selected zones and in the region as a whole corresponded to the background one according to the “SESL’09” scale. The number of recorded events with ML3.6 and strong earthquakes with ML5.1 is close to the average annual value. Anomalous and outstanding events were not recorded.

KAMCHATKA AND COMMANDER ISLANDS

The seismicity of Kamchatka and surrounding territories for 2013 is viewed. The minimum local magnitude of completeness is MLmin=3.25 in the Kamchatka earthquake catalogue totally, and MLmin=4 for earthquakes under the Okhotsk sea (with h≥350 km). The Kamchatka earthquake catalogue of 2013 with ML≥3.6, which includes 1750 events, is published. 146 earthquakes of published catalog with ML=3.6–7.8 were felt with seismic intensity ranged from 2 to 7 of the MSK-64 scale in Kamchatka and surrounding areas. Focal mechanisms were determined in two ways: 1) from first motion P-wave arrivals for 107 earthquakes; 2) using waveforms for 25 earthquakes. The background seismicity level (SESL’09) within the Kamchatka responsibility zone was extremely high in 2013. It exceeded the rate of seismicity in all previous years of observations. There were 6672 earthquakes, including 129 events with КS≥11.5 (ML≥5) in the region during the year. The mechanisms of 107 earthquakes were defined. 148 earthquakes were felt with intensity from 2 up to 7 on the territory of Kamchatskii Krai, North Kuril Islands, and Komandor Islands. There were several unusual events in 2013. The strong earthquake with magnitude Mw=5.8 on March 13 in the area of the Kamchatka Isthmus (Il'pyr earthquake), which is a rare phenomenon for the Northern Kamchatka. There was the strongest deep earthquake in the world (Mw=8.3) on May 24 under the Sea of Okhotsk (Okhotsk earthquake) at the depth of 630 km. The event caused an abnormal macro-seismic effect. The intensive earthquake swarm was observed in the Avacha Bay (Mwmax=6.1) in May 2013. It is the strongest earthquake swarm registered by the Kamchatka network during the period of detailed seismological observations since 1962

Groundwater chemical anomalies connected with the Kamchatka earthquake (M=7.1) on March 1992

The energy released by the earthquakes occurred in the seismogenetic area of the southern Kamchatka (Russia) from January 1977 to December 2004, reveals an increase in the peak energy in the period 1992–1999. This increase is related to the occurrence of seven earthquakes with magnitude ranging from 6.9 to 7.7; the first of these earthquakes happened on 2 March 1992 with M=7.1. For many years, hydro-geochemical data have been collected with a mean sampling rate of three days, in the form of the most common ions and gases in the water of deep wells and natural springs of a network operating in the south area of the Kamchatka, where the capital city Petropavlovsk is located. The collected data were analysed and differences in the trend and in the spectral content of some hydro-geochemical parameters at the springs were pointed out before and after the occurrence of the March 1992 earthquake, indicating clear post-seismic effects. Then an evident increase in the Carbon Dioxide and in the Hydrogen content appeared practically at each measurement site during the two-four years preceding the earthquake, so that long term precursors can be claimed. Finally, an anomalous decrease in the Carbon Dioxide content at the springs was revealed two/three months prior the earthquake, as a middle term precursor. The earthquake on March 1992 was the event nearest (90–120 km) to the measurement sites that happened in last thirty years.