Coseismic deformation of the Mid Niigata Prefecture Earthquake in 2004 detected by RADARSAT/InSAR

Crustal deformation associated with the Mid Niigata prefecture Earthquake in 2004 (M-JMA (= 6.8) was detected using RADARSAT SAR interferometry. A displacement of -40 cm in the line-of-sight to the satellite was observed to the west of the main shock epicenter, and a displacement of 20 cm was observed to the east of the epicenter. Fault parameters estimated from the obtained deformation were in good agreement with those of the Centroid Moment Tensor solution for the main shock provided by the Japan Meteorological Agency. In the postseismic period, a steep gradient of deformation was found around the Obiro and the Western Muikamachi Basin faults, indicating that a fault-slip occurred in the shallow part of the fault. Since the seismicity in the shallow part of the Western Muikamachi Basin fault was very low, we believe that it must have been an aseismic slip. Crustal deformation associated with an aftershock that occurred on October 27 (M)(JMA) = 6.1) was detected, and it was ascertained that this aftershock had ruptured the conjugate plane with respect to the Obiro fault. Since locations and/or mechanisms of these faults differed significantly, it was determined that at least three faults were involved in this series of earthquakes.