Intraplate earthquakes induced by reactivation of buried ancient rift system along the eastern margin of the Japan Sea - Intraplate Earthquakes - page 233

a

1 42˚ 1 42˚ 1 42˚ 1 42˚

140˚ 140˚ 140˚ 140˚

138˚ 138˚ 138˚ 138˚

1793 1 793

Pacific
Sea

1983
M7.7

1

1848

1704

17 04

94 1694 1

830

1896

896 89

1914 1 11

Japan
Sea

1804

2008

1 1804

200

850 850 8550

1833 1833

1900

11

1894

1 4

2007
Chuetsu-Oki

1964
M7.5

1

1762 176 17

2007
Noto

1751

1 175 75 751 751

1683

1847 847

2004
Chuetsu

PAC

PS

145˚ 145˚ 145˚ 145˚

140˚ 140˚ 140˚ 140˚

Figure 9.1 Seismotectonic setting in northern Honshu, Japan (modified after Kato et al ., 2009 ) .
(a) The Niigata-Kobe Tectonic Zone (NKTZ) is outlined by the broken line and contractional zones
based on geological studies are drawn as gray-shade zones (Okamura et al .( 2007 ) ). Fault locations of
recent major earthquakes and epicenters of historical large earthquakes with a magnitude greater than
7.0 are plotted as rectangles and circles, respectively (Usami, 2003 ) . Three stars denote the epicenters
of the 2004 Niigata-ken Chuetsu earthquake, the 2007 Chuetsu-Oki earthquake and the 2007 Noto-
Hanto earthquake. The inset shows the location of the studied area (black framed rectangle). PAC,
Pacific plate; PSP, Philippine Sea plate.

9.2 Data and method

Permanent seismic networks have been operated on the Japanese islands by the National
Research Institute for Earth Science and Disaster Prevention (NIED), the Japan Meteoro-
logical Agency (JMA), and various universities. Nevertheless, the average spacing of these
stations (from 20 to 30 km) is insufficient for resolving the detailed velocity structures in the