JpGU-AGU Joint Meeting 2017

Presentation information

[EJ] Oral

S (Solid Earth Sciences) » S-SS Seismology

[S-SS10] [EJ] Crustal Deformation

Mon. May 22, 2017 9:00 AM - 10:30 AM Convention Hall B (International Conference Hall 2F)

convener:Ryosuke Doke(Hot Springs Research Institute of Kanagawa Prefecture), Tadafumi Ochi(Institute of Earthquake and Volcano Geology, Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology), Chairperson:Takuya Nishimura(Disaster Prevention Research Institute, Kyoto University), Chairperson:Shigeru Nakao(Department of Earth and Environmental Sciences, Graduate School of Science and Engineering, Kagoshima University)

9:15 AM - 9:30 AM

[SSS10-02] Postseismic Deformation following the 1995 Kobe, Japan, Earthquake Detected by Space Geodesy

*Manabu Hashimoto1, Taku Ozawa2, Takuya NISHIMURA1, Hiroshi Munekane3, Mikio Tobita4 (1.Disaster Prevention Research Institute, Kyoto University, 2.National Research Center for Earth Sciences and Disaster Resilience, 3.Geospatial Information Authority, 4.Japan Aerospace Exploration Agency)

Keywords:1995 Kobe earthquake, Postseismic deformation, GPS, SAR interferometry, Rokko fault zone

A Mw 6.8 earthquake hit the city of Kobe, southwest Japan, and its surrounding area on January 17, 1995, and claimed more than 6,400 fatalities. The source faults, trending in the NE-SW direction, are estimated beneath the foothill of the Rokko Mountains, which are located north of the city and the highest peak is 931 m high, but it has a dominant right lateral strike slip components. The Rokko Mountains may have been built by the motion of active faults, but the uplift during the 1995 earthquake may not be enough. Therefore there is a possibility that postseismic deformation contributes to the building of the Rokko Mountains.

In order to study the postseismic deformation following the Kobe earthquake, we collected all available space geodetic data during about 20 years, including ERS-1/2, Envisat, JERS-1, ALOS/PALSAR and ALOS-2/PALSAR-2 images and continuous GPS data, and reanalyzed them. Especially, temporal continuous GPS observation made by the Geographical Survey Institute (present the Geospatial Information Authority), Japan in and around the Kobe area is important. We recalculated coordinates of these continuous GPS stations with recent PPP procedure using reanalyzed orbits and clocks of satellites. We made DInSAR and PSInSAR analyses of SAR images using ASTER-GDEM ver.2 or GSI DEM.

Time series analysis of JERS-1 images revealed line-of-sight (LOS) decrease of the Rokko Mountains. PSInSAR results of ALOS/PALSAR also revealed slight uplift north of the Rokko Mountains that uplifted by 20 cm coseismically. These observations suggest that the Rokko Mountains might have uplifted during the postseismic period.

LOS increase in a wedge shaped region between two active faults east of the Rokko Mountains in the vicinity of the NE terminus of the source fault of the Kobe earthquake. The LOS increase is also confirmed by ERS-1/2, Envisat and ALOS/PALSAR images. These facts indicate that the subsidence between these two faults continued up to 2010. Continuous GPS observation during the first two years of the postseismic period shows north-south extension with right lateral motion between these two faults.

These observations suggest that the Rokko Mountains may have uplift till 2010. On the other hand, active faults near the NE terminus continued to slip with the formation of graben-like structure, due to coseismically loaded stress.