EARTHQUAKE 28.02.2013 with MwGCMT=6.8, I0=5–6 (Southeastern coast of Kamchatka)

Abstract

The February 28, 2013 earthquake (MwGCMT=6.8), which occurred on the southeast coast of Kamchatka, is discussed. The instrumental hypocenter location reported by the KB GS RAS is φ=50.67N, λ=157.77E, h=61 km. Three magnitudes were obtained: local magnitude ML=6.9, code-wave magnitude Mc=6.6, mo-ment magnitude Mw=6.7. The focal mechanisms of the February 28, 2013 earthquake and its aftershocks with ML≥6 correspond to the tectonic conditions of subhorizontal compression in the NW–SE direction. For most of these mechanisms, the shallow plane falls under Kamchatka, which corresponds to the geometry of the subduction zone. The small-focus aftershocks cloud of the February 28, 2013 earthquake has the 5828 km size and is extended in the north-east – south-west direction. The aftershock process has the three-phase character and can be considered as a stream of seismic events decreasing in time with three successive stages with different attenuation modes. The change in attenuation modes is associated with strong after-shocks. The duration of the decaying aftershock process is ~ 100 days. The February 28, 2013 earthquake was felt with intensity ranged from 2 to 5–6 on the MSK-64 scale in 33 localities (Δ=81–493 km). The mac-roseismic impact area was about 56∙103 km2. The mainshock and its four strong aftershocks have a similar picture of macroseismic manifestations: the macroseismic effect is larger on the east coast of Kamchatka; the strongest shakes has been observed in Severo-Kurilsk (Paramushir Island). The elongation of the isoseist along the Kamchatka eastern coast has been observed, which is typical for Kamchatka earthquakes. The strong ground motions from the February 28, 2008 earthquake has been recorded using the Kamchatka net-work of digital accelerographs. The level of peak amplitudes for this earthquake is consistent with average trends in the Kamchatka region. Attenuation parameters are typical for Kamchatka. The shallow layer of the seismic focal zone of the Kuriles and South Kamchatka, in which the February 28, 2013 earthquake was recorded, is one of the most active seismic areas in the North-West Pacific. Earthquakes with M>8 were re-peatedly occurred here, causing a tsunami and intensity of shakes up to 9 on the MSK-64 scale in the south of Kamchatka.