Abstract
Abstract We applied an inverse method developed by Zhao et al. (J. Geophys. Res., 97, 19909–19928, 1992) to 42,834 P and 18,263 S wave arrival time data observed at 152 seismographic stations for 1143 local earthquakes at depths between 0 and 200 km in order to estimate three-dimensional P and S wave velocity structures beneath the Hokkaido corner, Japan-Kurile arc-arc junction. High- and low-velocity zones were clearly imaged in the Hidaka Mountain Range at depths shallower than 35 km. The low-velocity anomalies of P and S waves were found to be distributed in the mantle wedge at depths between 35 and 100 km beneath the volcanic front, as also observed in the Tohoku region. Another low-velocity zone was found to exist in the fore-arc region at depths of 50–70 km above the plate boundary; this zone was not detected in Tohoku, suggesting that the dehydration process in the fore-arc region is different from that in the Tohoku region.
Highlights
The velocity structure of seismic waves is one of the most important physical parameters used to investigate heterogeneities in the crust and the mantle of the earth
The Kurile Islands arc is moving toward the southwest at a speed of 6–11 mm/year relative to the North American plate (DeMets, 1992) and has been colliding against the northeastern Japan arc since middle Miocene, forming the arc-arc type Hidaka collision zone (HCZ) in and around the Hokkaido corner
High- and low-velocity zones of P waves were clearly imaged in the Hidaka Mountain Range (HMR) at depths of 5, 20 and 35 km, results consistent with those obtained by Takanami (1982) and Miyamachi and Moriya (1984)
Summary
The velocity structure of seismic waves is one of the most important physical parameters used to investigate heterogeneities in the crust and the mantle of the earth. According to the NUVEL-1A model the Pacific plate around the Hokkaido corner moves in a N63◦W direction at a speed of 83 mm/year relative to the North American plate (DeMets et al, 1994). There is yet another plate-like motion in the Hokkaido corner. The Kurile Islands arc is moving toward the southwest at a speed of 6–11 mm/year relative to the North American plate (DeMets, 1992) and has been colliding against the northeastern Japan arc since middle Miocene, forming the arc-arc type Hidaka collision zone (HCZ) in and around the Hokkaido corner (see Kimura, 1996). The Hidaka Mountain Range (HMR) located at the HCZ is uplifting as a result of these processes
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