HR: 0800h
AN: S51B-0166    [Abstracts]
TI: Investigation of Subducting Slab beneath Northeastern Taiwan from Sp Converted Phases
AU: * Wu, W
EM: wennan@eqkc.earth.ncu.edu.tw
AF: Wen-Nan, No.300, Jhongda Rd, Jhongli, 320 Taiwan
AB: The converted waves from upper plate boundary of the subducting slab denoted as Sp phase recorded by the Central Weather Bureau Seismographic Network (CWBSN) for events in northern Taiwan provide us an advantageous opportunity to construct the geometry of upper boundary of descending Philippine Sea Plate (PSP). The events were chosen for the region with latitude of 24.4 degree N - 25.2 degree N, longitude of 121.5 degree E - 122.2 degree E, depth from 50 -300 km, and time period of January 1991 to Mary 2003 for magnitude greater than 4.0. We apply the polarization filter analysis, particle motion diagram and theoretical travel time to the digital 3-compoent short period seismograms to identify the conceivable Sp converted phases. The initial velocity model with subducting slab was used for theoretical travel time calculation based on the recent tomographic results. The model is constructed firstly by considering a fixed velocity contrasts among the discontinuities. The dip angle and latitude location of slab are allowed to change to obtain the best travel time to the data. Several tests had been made for the inversion. Considering variance reduction of the all observed data to the constructed models by grid searching technique, variance reduction is not in satisfactory. Further studies by grouping the events in north-south and northwestern-southeastern trend were examined. Although the geometry of subducting slab might be difficult to model due to disadvantage in tectonic setting of northeastern Taiwan, which is located to northern subducting slab, the most possible image of the slab from the clear identified converted phases is sketched.
DE: 7220 Oceanic crust
DE: 7230 Seismicity and seismotectonics
DE: 7205 Continental crust (1242)
DE: 1734 Seismology
DE: 1744 Tectonophysics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting