HR: 1340h
AN: S53A-0177    [Abstracts]
TI: Earthquake Rupture Processes Along the Philippine Trench
AU: * Sevilla, W I
EM: wsevilla@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, University Park, State College, PA 16802 United States
AU: Ammon, C J
EM: cammon@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, University Park, State College, PA 16802 United States
AB: Earthquakes along subduction zones exhibit spatial and temporal variations in rupture processes. Recent studies have demonstrated a systematic decrease in the moment-normalized rupture duration of earthquakes with depth along the plate interface. Several shallow earthquakes were observed to exhibit anomalously long rupture duration, comparable with the durations of tsunami earthquakes. These observations were suggested to be manifestations of subduction faults with frictional properties capable of generating tsunami earthquakes. The cause of the duration variation was hypothesized to be related to physical changes in properties of subducted sediment. The Philippine trench is a setting where we can study the variations of earthquake source rupture processes along the plate interface. The trench is young ($< $ 5 Ma) with a poorly developed accretionary prism. Bathymetry, seismic reflection studies, and offshore drilling show little or no evidence of accretion of the materials from the subducting Philippine Sea plate. Eighty nine possible interplate earthquakes were selected from the Harvard CMT catalogue for the year 1989 to 2001. From these, about 30 events had adequate signal-to-noise ratios and well-constrained mechanisms to warrant further investigation. We used teleseismic broadband records of vertical component waveforms and applied multi-station deconvolution technique to extract the source time function and depth of each event. Our results showed no systematic trend of decreasing source duration with depth at the Philippine trench. The observed moment-normalized durations of all the shallow earthquakes are shorter than tsunami earthquakes. We observed a significant scatter in the relationship between source time and depth, which may reflect heterogeneity of the materials at the trench interface. The thickness of low-rigidity materials in the trench shallow region appears insufficient to affect the rupture durations and produce anomalously slow ruptures. These null results for the sediment-starved Philippine Trench support the earlier hypothesis that the variations of earthquake duration with depth in other subduction zones is related to sediment properties.
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting