HR: 0800h
AN: G21C-0674    [Abstracts]
TI: Biannually repeating slow slip events in an uncoupled segment of the Ryukyu Arc, SW Japan
AU: * Kataoka, T
EM: kata-oka360@mail.sci.hokudai.ac.jp
AF: Dept. Natural History Sci., Hokkaido Univ., N10 W8 Kita-ku Sapporo, Hokkaido, 060-0810, Japan
AU: Heki, K
EM: heki@mail.sci.hokudai.ac.jp
AF: Dept. Natural History Sci., Hokkaido Univ., N10 W8 Kita-ku Sapporo, Hokkaido, 060-0810, Japan
AB: At the Ryukyu Trench, SW Japan, the Philippine Sea Plate (ph) subduct toward NW. The overriding Ryukyu Arc is composed of three nearly rigid blocks with little interseismic elastic deformation. The South Ryukyu Block (sr), the westernmost part of Japan, is known for extremely fast plate convergence (~12 cm/yr) by the the ph subduction and the oceanward movement of the arc due to active opening of the Okinawa Trough. There ph and sr are gdecoupled,h i.e. large interplate thrust events do not occur. Yarai et al. (2004) found repeating slow slip events (SSE) there by analyzing the movement of Hateruma, the southernmost island of the arc, by GPS observations. Here we studied these SSE from the movements of six GPS points in five islands on sr during 1997-2007, and report their time constants, recurrence intervals, consistency between slips and plate convergence, predictability of events. The events occur mostly in spring and fall, but this apparent seasonality is caused by their rather regular biannual recurrences. The time constants ranged between 0.1 and 0.15 years, twice as long as those in Cascadia although their recurrence intervals (~6 months) were only ~1/2 of those in Cascadia (~13 months). SSE signals were clearly seen both in horizontal and vertical coordinates of GPS points in the islands Ishigaki and Iriomote, as well as Hateruma, and we estimated the fault parameters of the SSE as the ph-sr interplate events. Their slip directions were consistent with the plate convergence direction, and the typical amount of slip (~ 6 cm, Mw ~6.6) coincided with the convergence in 1/2 year. The depths of the faults were 20-40 km, which corresponds to the transient depth between seismogenic and freely sliding zones. This situation is similar to Shikoku and Cascadia except that there are no large thrust events at gseismogenic zonesh in Ryukyu. The amounts of slips had significant correlation with the time lengths until the next events, suggesting the time-predictable characteristics of the events. These SSE are unique in two points, i.e. (1) the first repeating SSE found in an uncoupled subduction zone, (2) best recorded SSE sequence with nearly 20 events and 3-D crustal movement data associated with the events.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Geodesy [G]
MN: 2007 Fall Meeting