Abstract
AbstractGlobal Positioning System (GPS) and Synthetic Aperture Radar Interferometry (InSAR) detected substantial ground deformation due to the 2007 Chuetsu-oki earthquake (Mw= 6.8); GPS observation detected a horizontal deformation of up to about 170 mm and subsidence of up to 30 mm, and InSAR detected up to 290 mm of line-of-sight changes. A fault model is proposed to fit the ground deformation field as well as the aftershock distribution. Our model shows that a northwest-dipping fault to the north and a southeast-dipping fault to the south, consistent with the aftershock distribution, fits well with the observed data. However, our model also suggests that the modeled faults are likely to extend to shallower depths, where aftershocks are terminated. Combining our model with the subsurface structure suggests that the earthquake rupture initiated at depth and propagated into shallower depths that are not capable of nucleating an earthquake because of the presence of unconsolidated sediments.
Highlights
Geodetic data have been widely used to detect and explore details of ground deformation associated with large earthquakes and their afterslips
The aftershock distribution derived from a dense seismic observation reveals a complicated signature, with a northwest-dipping plane to the north and a southeastdipping plane to the south (Kato et al, 2008). It indicates that the aftershocks are limited at depths deeper than approximately 8 km (Kato et al, 2008). With this point of view, we attempted to model the deformation field with five models; these are (1) a northwest-dipping fault with a top depth of 8 km to be consistent with the aftershock distribution, (2) same as (1) except that the fault is southeastdipping, (3) a northwest and southeast-dipping faults, both with their top depths of 8 km, (4) same as (3), except that the northwest-dipping fault has a subfault extending to shallow depths with the same location at the bottom and allowing the dip change, and (5) same as (4) except that the southeast-dipping fault has a subfault
Because the top depths of the deeper faults are set to be 8 km, the shallower limit of the aftershock distribution (Kato et al, 2008), our results demonstrate that the coseismic rupture has reached depths where no aftershocks occurred
Summary
Geodetic data have been widely used to detect and explore details of ground deformation associated with large earthquakes and their afterslips. We propose a fault model for the coseismic deformation field associated with the 2007 Chuetsu-oki earthquake (Mw = 6.8), using continuous GPS and L-band InSAR data. Width, depth at the top, dip angle, strike, horizontal position (two parameters), and amount of slip (strike and dip components) for each fault to best fit the observed deformation. Given these parameters, the deformation field is calculated by Green’s function of Okada (1985). With this point of view, we attempted to model the deformation field with five models; these are (1) a northwest-dipping fault with a top depth of 8 km to be consistent with the aftershock distribution, (2) same as (1) except that the fault is southeastdipping, (3) a northwest and southeast-dipping faults, both with their top depths of 8 km, (4) same as (3), except that the northwest-dipping fault has a subfault extending to shallow depths with the same location at the bottom and allowing the dip change, and (5) same as (4) except that the southeast-dipping fault has a subfault
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