Abstract
AbstractAn intermediate-strength earthquake of magnitudeMj6.8 occurred on July 16, 2007, centered beneath the Japan Sea a few kilometers offshore of Niigata Prefecture in central Japan. We constructed a dense GPS network to investigate postseismic deformation after this event, choosing our GPS sites carefully so as to complement the nationwide GPS GEONET array. Coseismic displacements caused by the mainshock detected at some GEONET sites were used to estimate coseismic fault parameters. The results indicate that the geodetic data can be explained by a combination of two rectangular faults dipping northwest and southeast. Minor but definite postseismic deformation was detected largely in the southern part of the dense network. The time series of site coordinates can be characterized by a logarithmic decay function, and the estimated time constant seems to be almost similar in range to that of the 2004 Mid-Niigata Prefecture Earthquake. We also found a possible site instability at 960566 (Izumo-zaki, GEONET) caused by a small, local landslide associated with the mainshock and therefore concluded that the data obtained at this site should not be used for coseismic or postseismic analysis.
Highlights
The 2007 Chuetsu-oki Earthquake (Mj 6.8) occurred beneath the Japan Sea a few kilometers offshore of Niigata Prefecture, in central Japan, on 16 July 2007 (Fig. 1)
Coseismic displacements caused by the mainshock detected at some GEONET sites were used to estimate coseismic fault parameters
A detailed aftershock distribution was obtained by Kato et al (2008) using the doubledifference technique (Zhang and Thurber, 2003) to reveal southeast-dipping alignments of seismicity in the southern part of the focal area
Summary
The 2007 Chuetsu-oki Earthquake (Mj 6.8) occurred beneath the Japan Sea a few kilometers offshore of Niigata Prefecture, in central Japan, on 16 July 2007 (Fig. 1). Coseismic displacements caused by the mainshock detected at some GEONET sites were used to estimate coseismic fault parameters. The time series of site coordinates can be characterized by a logarithmic decay function, and the estimated time constant seems to be almost similar in range to that of the 2004 Mid-Niigata Prefecture Earthquake.
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