[SSS16-P03] Convergence boundary and velocity between Amur and Okhotsk plates in northern Hokkaido inferred by GNSS velocity data
Keywords:GNSS measurements, crustal deformation, collision zone, northern Hokkaido
Several block models are constructed, and the boundary is estimated by using geodetic data in this region (e.g., Loveless and Meade, 2010), but comprehensive discussion considering geological structure, the Bouguer gravity anomaly and earthquake distribution is lacked. To verify the insistence that the boundary between Amur and Okhotsk plates exists onshore in northern Hokkaido, we estimate the location of the boundary, convergence velocity and elastic thickness applying a dislocation model for collision zone by Shimazaki and Zhao (2000) to represent velocity field observed by Global Navigation Satellite System (GNSS). Most of previous studies for northern Hokkaido fixed location of the boundary arbitrary. Therefore, we treated the boundary location as unknown parameters and estimate it in this study.
Estimated location of the collision boundary is in ENE-WSW direction and roughly consistent with boundary of seismicity, geological structure, and Bouguer gravity anomaly. Geological structures would behave as a kinematic boundary. Estimated thickness of elastic zone is 21.6-28.8 km. Indicator of seismic activity in vertical direction; D90’s and Moho depth are 20-30 km and 30 km, respectively. In this model, determination accuracy of thickness is lower than the other parameters, however consistent with the discontinuous depth indicates that estimation of other parameters would show plausible value. Estimated velocity is 13.7-18.9 mm/yr, and these values are consistent with results by other studies that estimated velocity between some plates. The boundaries that estimated by discrete data, geology, seismology, and our result, roughly consistent with each other. Therefore, possibility that the boundary between Amur and Okhotsk plates is located onshore of northern Hokkaido became increasingly high.