Abstract
AbstractWe present crustal deformations in southern Kii peninsula, southwest Japan, before and after the SE off the Kii peninsula earthquake sequence of September 5, 2004, which were obtained from repeated surveys of dense GPS network. Disaster Prevention Research Institute (hereafter DPRI), Kyoto University made a reoccupation of their dense GPS network network that was occupied in February-March, 2004, right after the event to obtain crustal deformations associated with this event. Since we do not have the data just before the event, we apply an inversion of displacements of GEONET sites during the period from February-March to August, and interpolate displacements at DPRI’s sites using the inverted fault model. Southward movements of about 2 cm are obtained in the middle of Kii peninsula, while displacements are rotated to southwest on the west side. These characteristics of horizontal displacement field cannot be explained only by a pure thrust faulting, but additional sources such as right-lateral faulting on a NW-SE trending fault are required.
Highlights
On September 5, 2004, two earthquakes of M7.1 and 7.4 hit the central and southwest Japan
Right after the occurrence of the SE off the Kii peninsula earthquakes, we reoccupied these sites in order to detect coseismic and postseismic movements
Small steps between August and September, which can be seen in only GEONET stations, are coseismic deformations associated with the SE-off the Kii peninsula earthquake sequence
Summary
On September 5, 2004, two earthquakes of M7.1 and 7.4 hit the central and southwest Japan. The Geographical Survey Institute (hereafter GSI) observed displacements associated with this sequence of earthquakes and showed southward to southwestward movements up to cm in this region (GSI, 2004) This coseismic movement c The Society of Geomagnetism and Earth, Planetary and Space SciCopy right ences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. We decided to reoccupy our network in order to obtain coseismic and postseismic movements for the precise estimate of average velocity field. A site (SENK) with a 1.5 m tall stainless pillar was established in 2002 Right after the occurrence of the SE off the Kii peninsula earthquakes, we reoccupied these sites in order to detect coseismic and postseismic movements. Euler poles of Eurasia plate relative to no-net-rotation frame in NUVEL-1A (DeMets et al, 1994) and Amurian-Eurasia plate by Heki et al (1999)
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