Abstract
In this study, Sentinel-1 and Advanced Land Observation Satellite-2 (ALOS-2) interferometric synthetic aperture radar (InSAR) and global positioning system (GPS) data were used to jointly determine the source parameters and fault slip distribution of the Mw 6.6 Hokkaido eastern Iburi, Japan, earthquake that occurred on 5 September 2018. The coseismic deformation map obtained from the ascending and descending Sentinel-1 and ALOS-2 InSAR data and GPS data is consistent with a thrust faulting event. A comparison between the InSAR-observed and GPS-projected line-of-sight (LOS) deformation suggests that descending Sentinel-1 track T046D, descending ALOS-2 track P018D, and ascending ALOS-2 track P112A and GPS data can be used to invert for the source parameters. The results of a nonlinear inversion show that the seismogenic fault is a blind NNW-trending (strike angle ~347.2°), east-dipping (dip angle ~79.6°) thrust fault. On the basis of the optimal fault geometry model, the fault slip distribution jointly inverted from the three datasets reveals that a significant slip area extends 30 km along the strike and 25 km in the downdip direction, and the peak slip magnitude can approach 0.53 m at a depth of 15.5 km. The estimated geodetic moment magnitude released by the distributed slip model is 6.16 × 10 18 N · m , equivalent to an event magnitude of Mw 6.50, which is slightly smaller than the estimates of focal mechanism solutions. According to the Coulomb stress change at the surrounding faults, more attention should be paid to potential earthquake disasters in this region in the near future. In consideration of the possibility of multi-fault rupture and complexity of regional geologic framework, the refined distributed slip and seismogenic mechanism of this deep reverse faulting should be investigated with multi-disciplinary (e.g., geodetic, seismic, and geological) data in further studies.
Highlights
On 5 September 2018 at 18:07:59 (UTC), a moderate earthquake with a magnitude of Mw 6.6 struck eastern Iburi of Hokkaido Island, northeastern Japan
The estimated geodetic moment magnitude released by the distributed slip model is 6.16 × 1018 N m, which corresponds to an event magnitude of Mw 6.50
The estimated geodetic moment magnitude released by the distributed slip model is 6.16 × 10 N m, which corresponds to an event magnitude of Mw 6.50
Summary
On 5 September 2018 at 18:07:59 (UTC), a moderate earthquake with a magnitude of Mw 6.6 struck eastern Iburi of Hokkaido Island, northeastern Japan. 2019, 11, 1667 can be supplied with a high accuracy by near-field geodetic measurements, for example, measurements from GNSS stations, which completely record coseismic displacements and interferometric synthetic aperture radar (InSAR) observations with a good spatial coverage [11,12]. Such high-precision coseismic surface observations can provide a valuable opportunity to determine the orientations of seismogenic faults and to develop a deeper understanding of the focal mechanism of this event. The Coulomb stress change was calculated based on our preferred distributed slip model, and the possibility of multi-fault rupture and complexity of seismotectonics and seismogenesis of the 2018 event were discussed
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