ILPYRSKOE EARTHQUAKE March 13, 2013 with Mwreg=5.8, ML=6.2, КS=13.9, I0p=8 (Kamchatsky Isthmus)

The strong (Mwreg=5.8, ML=6.2) near-surface seismic event (Ilpyrskoye earthquake) occurred at 03h12m on 13 March, in the Kamchatka Isthmus. It was the strongest earthquake between 1962 and 2013 for this area. The greatest macroseismic effect was observed at a distance of ~30 km, I=6–7 on the scale MSK-64. We used two independent methods for determining its regional focal mechanism: 1) regional moment tensor in-version using broadband waveforms; 2) solution based on polarities of the P waves. The results are similar: the focal mechanism of Ilpyrskoye earthquake is thrust faulting with strike-slip component; the compression axis is subhorizontal and is oriented in the north-east – south-west direction. The mechanisms for the two strongest aftershocks were also identified, as a result, a change in focal movements during the aftershock process was revealed.The analysis of the aftershock process which consists of two stages with different de-cay character was performed. The process lasted ~ 75 days. About 200 aftershocks ML=3.0–5.7 (КS=7.5–12.9) were recorded, hypocenter depth estimations vary from 0 to 10 km for about 80 % of them. The strongest aftershock was on May 6, 2013 with ML=5.7, Mwreg=4.8, at which the change in focal movements occurred. According to the results of near real time processing, aftershock cloud of Ilpyrskoye earthquake had a pronounced linearity and a great length, which was an artifact. The main cause of the artifact is the minimum number of stations involved in determining the hypocenters of most aftershocks and their quasi-linear disposition. The confidence areas within which solutions are equivalent are shown. We concluded that Ilpyrskoye earthquake is a serious argument that the area of compression between the Okhotsk and North American plates is extended further to the east and the border passes through the Kamchatka Isthmus