Abstract
AbstractThe 2007 Chuetsu-oki Earthquake (Mj= 6.8) occurred in the eastern margin of the Japan Sea where high strain rates have been observed and many large earthquakes have occurred. The main shock was located near the Western Nagaoka Basin active fault system dipping in the westward direction. We estimated the well-resolved hypocenter location around the main shock rupture zone from the differential arrival times obtained by both manual picking and waveform cross-correlation analysis. From the relocated aftershock distributions, we successfully resolved the detailed fault structures activated by the main shock. The estimated fault model resolves four individual fault segments. The fault model suggests that the main shock predominantly ruptured the southeastward dipping fault planes. On the other hand, the aftershocks around the hypocenter of the main shock occurred on both the northwestward and southeastward dipping fault planes. Both fault planes around the hypocenter of the main shock may have been nearly coincidentally ruptured during the main shock.
Highlights
The 2007 Chuetsu-oki Earthquake occurred at 10:13 AM (JST = UT + 9 h) on July 16, 2007 with a Japan Meteorological Agency (JMA) magnitude (Mj) of 6.8 (Fig. 1)
The source region of the main shock was located in the eastern margin of the Japan Sea, which is a region of many active faults and folds comprising a series of anticline structures and reverse faults (Okamura et al, 1998)
The ordinary seismic activity before the main shock, illustrated by the light red color in Fig. 3, mainly distributes in the 15- to 20-km depth range around the lower limit of the aftershock depth distributions
Summary
The 2007 Chuetsu-oki Earthquake occurred at 10:13 AM (JST = UT + 9 h) on July 16, 2007 with a Japan Meteorological Agency (JMA) magnitude (Mj) of 6.8 (Fig. 1). The aftershock activity was lower than that recorded for previous intraplate earthquakes such as the 1995 Hyogo-ken Nanbu Earthquake (Mj = 7.3), 2000 Western Tottori Earthquake (Mj = 7.3), and 2004 Mid Niigata Earthquake (Mj = 6.8) (JMA, 2007). The 2007 Chuetsu-oki Earthquake occurred in the Niigata-Kobe Tectonic Zone where high strain rates have been observed from GPS data analyses (Sagiya et al, 2000). Many large earthquakes have occurred along this active fault zone, such as the 1828 Echigo-Sanjo Earthquake (M = 6.9), 1964 Niigata Earthquake (Mj = 7.5), and 2004 Mid Niigata Earthquake. The Western Nagaoka Basin active fault system has westward dipping faults
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