二船式による2007年能登半島地震震源域の反射法地震探査

概要

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In 2007, the northwestern part of the Noto peninsula, central Japan, was struck by damaging earthquakes of MJMA 6.9. To correlate seismogenic source faults with geologic structure we con-ducted seismic reflection profiling of the focal areas. We used two vessels: a gun-ship with a 1,500cu. inch air-gun and a cable-ship with a 1.2-km-long, streamer cable and a 480cu. inch air-gun. Com-mon mid-point seismic reflection data was acquired by total 150km-long seismic lines. The obtained seismic sections portray faults, that displaced the shallowest part of the reflectors. A deeper ex-tension of the active fault was traced down to 4km in depth on the seismic section. The deeper extension of the imaged fault accords well with the linear distribution of the hypocenters of aftershocks, providing direct evidence of fault reactivation at depth. Seismic sections suggest the three tectonic phases; the early Miocene rifting, late Miocene, and Late Pliocene to Quaternary shortening deformation. The 2007 Noto Hanto earthquake was generated by reverse and strike-slip faulting of Miocene normal fault under a compressional stress regime with a WNW-ESE trending P-axis. The ruptured fault segment is strongly controlled by transfer faults, which was formed during the rifting.
東京大学の論文
2008-03-26