Abstract
Abstract Based on the fact that interseismic deformation of collision zones is generally described by slip along a detachment at depth, I attempt to interpret the deformation of the Izu collision zone in terms of a detachment model. The systematic deviation of the GPS velocities of the Izu Peninsula (Nov. 1998–June 2000) from the Philippine Sea-Eurasian relative plate motions is fitted by the slip on the detachment at a depth of 15–20 km with a rate of 3 cm/yr. On June 26, 2000, seismo-magmatic activity that started near Miyakejima expanded NW by 20 km close to Kozushima in association with dike intrusion over a few months. The horizontal movements associated with this event, however, spread over wide areas in central Honshu. Simple dike intrusion models cannot explain these movements. To explain these, I hypothesize that a 20 cm of rapid slip occurred on the detachment at the time of this event. The abnormal crustal movements in the Tokai-central Honshu-Kanto region then started after the event. I propose that they represent delayed diffusive transfer of the slip on the detachment over surrounding low viscosity layers, such as nearby rupture zones of great earthquakes.
Highlights
Since the middle of 2000, two spectacular tectonic events have occurred in and south of central Honshu, Japan
Based on the island displacements detected by GPS (Kaidzu et al, 2000), it has been inferred that dike intrusion amounting to a volume of ∼1 km3 occurred in the crust between Miyakejima and Kozushima associated with this seismic swarm (Yamaoka, 2000; Nishimura et al, 2001; Ito and Yoshioka, 2002; Furuya et al, 2003)
I propose that this is the origin of the horizontal movements observed in the Tokai–central Honshu–Kanto region; that is, they represent delayed transfer of the slip on the detachment beneath the Izu Peninsula, that occurred at the time of the Miyake-Kozu event, over the nearby low viscosity layers
Summary
Since the middle of 2000, two spectacular tectonic events have occurred in and south of central Honshu, Japan. I propose that this is the origin of the horizontal movements observed in the Tokai–central Honshu–Kanto region (the Tokai slow event); that is, they represent delayed transfer of the slip on the detachment beneath the Izu Peninsula, that occurred at the time of the Miyake-Kozu event, over the nearby low viscosity layers. To model the anomalous crustal deformation after the Miyake-Kozu event, Takahashi and Seno (2005) solved these equations using the finite difference method They assumed that the plate and the viscous layer have thicknesses of 30 km and 20 m, respectively, put a ramp-shaped displacement of 20 cm on the detachment with a rise time of 85 days during the Miyake-Kozu event, and determined the diffusion coefficient matching the arrival times of horizontal displacements in the Tokai district. The overall pattern is similar to that observed (Fig. 4)
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