Abstract
We analyze Global Navigation Satellite System (GNSS) within the San-in Shear Zone (SSZ), Southwest Japan, in order to clarify the width of the inelastic deformation zone in the lower crust beneath it. We assumed multiple discrete fault dislocations distributed below the seismogenic depth in a channel to represent inelastic deformation in the lower crust. Kinematic models at 68% confidence level at three profiles indicate that deformation can be explained by a deep inelastic deformation zone with a width of 0.5–56.0 km, 0.5–79.5 km, and 0.0–58.5 km, for the Eastern, Central and Western profiles, respectively; and a relative moving rate between the two blocks sandwiching the zone of 6.2–8.0 mm/year. In Eastern Tottori, the center of the estimated inelastic zone coincides with the source region of the 1943 Tottori earthquake. In Central and Western Tottori, the channel is in agreement with the source regions of the 2000 Western and the 2016 Central Tottori earthquake. Current GNSS network provides a limited contribution to constraining the width of the deformation in the lower crust.
Highlights
The existence of a strain concentration zone along the San-in district in Southwest Japan, the San-in Shear Zone (SSZ) (Fig. 1), has been identified from the nationwide Global Navigation Satellite System (GNSS) Earth Observation Network System (GEONET) data (Nishimura and Takada 2017)
We show that inelastic deformation in the lower crust is distributed in a channel beneath the SSZ, with a relative motion between the two blocks constraining the inelastic zone of 6.2–8.0 mm/ year
Optimum models based on the horizontal displacement for the analyzed time period along three profiles suggest the relative speeds of 6.4–7.9 mm/year for the blocks sandwiching the deformation zones in Eastern, Central and Western Tottori (Fig. 2)
Summary
The existence of a strain concentration zone along the San-in district in Southwest Japan, the San-in Shear Zone (SSZ) (Fig. 1), has been identified from the nationwide Global Navigation Satellite System (GNSS) Earth Observation Network System (GEONET) data (Nishimura and Takada 2017). This concentration zone is a ~ 50 km width right-lateral shear zone, where high seismicity has been reported (e.g., Kawanishi et al 2009), hosting 17 crustal earthquakes with magnitude larger than 6 for the last 100 years. Their model explains a systematic shift in the azimuth of the Meneses‐Gutierrez and Nishimura Earth, Planets and Space (2020) 72:10
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