Abstract
AbstractIn 2004, we started monitoring crustal deformation at Kumano-nada in the Nankai trough using the GPS/Acoustic technique. We observed a large southward seafloor displacement of ∼30 cm associated with the off Kii Peninsula earthquake, which occurred in September 2004, between our two survey campaigns in August and November 2004. The observed seafloor displacement is larger than that predicted from a slip model derived solely from GPS measurements on land. This may indicate the earthquake fault is slightly shallower and extends move to the NW than previously estimated.
Highlights
Recent development of the GPS geodetic technique and wide spreading GPS network array, like the GEONET, have revealed semi-realtime crustal deformations throughout the Japan Island (Sagiya, 2004)
The GPS/Acoustic technique for measuring seafloor displacement was first developed by a group at SIO (Scripps Institution of Oceanography), combining acoustic ranging between a transducer at the sea-surface and PXP(s) on the seafloor
In Japan, a several research groups have applied this technique to the subduction zones along the Japan trench and the Nankai trough, where complex distribution of asperities is expected
Summary
Recent development of the GPS geodetic technique and wide spreading GPS network array, like the GEONET, have revealed semi-realtime crustal deformations throughout the Japan Island (Sagiya, 2004). Exact array position relative to above determined array is estimated by a fixed-point survey near the array center, which simultaneously makes acoustic measurements to all the PXPs under the assumption that the pre-determined array geometry is unchanged. Considering typical frequency (∼0.5 Hz) and amplitude (∼1 m) of buoy motion, errors in the interpolation amount to 10–20 cm This large error behaves randomly and effect on the final estimate of the array position is reduced with a long time span of data. We towed the buoy in a rough circle around each PXP to obtain well-distributed data. This ensures that position estimate of each PXP is not biased by differences in survey tracks. The difference between array positions estimated from the moving and from the fixed-point surveys
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