Abstract
Abstract The 2007 Noto Hanto Earthquake occurred on March 25, 2007, in the Noto Peninsula, central Japan. A half day after the main shock, we started installing temporary seismic stations in order to determine the precise locations of its aftershocks. Ten universities and two research institutes deployed 88 temporary seismic stations in and around the source area. The observation lasted for about 2 months. We relocated 1318 aftershocks with arrival time corrections at each station. The relocated hypocenters show relatively small errors—less than 0.2 km in the horizontal direction and less than 0.4 km depth. Most of the relocated hypocenters are about 2.0 km shallower than those determined by JMA. The distribution of the aftershocks forms a southeast-dipping plane. The main shock is located at the bottom part of their distribution. The precise aftershock distribution extends into a shallower area than the original, and it coincides with sea floor-ward extension of the active faults previously known from a sonic reflection survey. Heterogeneous distribution of the aftershocks on the fault plane shows low seismicity just above the main shock hypocenter, and middle-size aftershocks are distributed on the periphery of the main shock. A precursory event (M 4.4) that occurred 0.6 s before the main rupture is located close to the M 2.2 foreshock that occurred 12 min before it.
Highlights
An earthquake with a local body wave magnitude (Mjma 6.9, Mw 7.1 by USGS) occurred in the Noto Peninsula, central Japan, at 0:41, March 25, 2007 (UT) (Fig. 1)
The 2007 Noto Hanto Earthquake occurred on March 25, 2007, in the Noto Peninsula, central Japan
A half day after the main shock, we started installing temporary seismic stations in order to determine the precise distribution of the aftershocks
Summary
An earthquake with a local body wave magnitude (Mjma 6.9, Mw 7.1 by USGS) occurred in the Noto Peninsula, central Japan, at 0:41, March 25, 2007 (UT) (Fig. 1). This earthquake was named the 2007 Noto Hanto Earthquake by the Japan Meteorological Agency (JMA). Some offshore active faults were reported off the Noto Peninsula (Katagawa et al, 2005), and they may be related to the present event. One of the main aims of this study is to clarify the relation between the offshore faults, the geological faults on lands, and the aftershock distribution. SAKAI et al.: AFTERSHOCKS OF THE 2007 NOTO HANTO EARTHQUAKE BY A DENSE OBSERVATION
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