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2012.12.18 update
[DONET observed the earthquake off Sanriku]


A moderate-to-large earthquake occurred off Sanriku, Japan at 17:18 JST on 7 December 2012. It is considered to be one of the aftershock of the 2011 Tohoku earthquake of which focal mechanism is a normal fault caused by an outer-rise earthquake.

JAMSTEC has installed DONET (Dense Oceanfloor Network System for Earthquakes and Tsunamis) with 20 observatories at Kumanonada and the seismic waves of the earthquake off Sanriku have been observed clearly by the DONET observatories. Figures 1 and 2 show observed seismic waves which were detected by the broadband seismometers. The first arrivals of P-wave were observed at about 17:20 JST and large amplitude waves were observed 5-10 seconds later from the first arrivals.

Figure 1: Up-down components of broadband seismograms. The first arrivals of P-wave were observed at about 17:20 JST.

Figure 2: Enlarged figure of the aqua-shaded part in Figure 1. Large amplitude waves were detected 5-10 seconds later from the first P-wave arrivals.