HR: 1400h
AN: T43A-03    [Abstracts]
TI: INFLUENCE OF FOREARC STRUCTURE ON THE EXTENT OF GREAT SUBDUCTION ZONE EARTHQUAKES
AU: * McGuire, J J
EM: jmcguire@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept of Geology and Geophysics, MS24, Woods Hole, MA 02540, United States
AU: Llenos, A
EM: allenos@mit.edu
AF: Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program, Dept of Geology and Geophysics, MS24, Woods Hole, MA 02540, United States
AB: Structural features associated with forearc basins appear to strongly influence the rupture processes of large subduction zone earthquakes. Recent studies demonstrated that a significant percentage of the global seismic moment release on subduction zone thrust faults is concentrated beneath the gravity lows resulting from forearc basins. To better determine the nature of this correlation and examine its effect on rupture directivity and termination, we estimated the rupture areas of a set of Mw 7.5-8.7 earthquakes that occurred in circum-Pacific subduction zones. We compare synthetic and observed seismograms by measuring frequency- dependent amplitude and arrival time differences of the first orbit Rayleigh waves. At low frequencies, the amplitude anomalies primarily result from the spatial and temporal extent of the rupture. We then invert the amplitude and arrival time measurements to estimate the second moments of the slip distribution which describe the rupture length, width, duration and propagation velocity of each earthquake. Comparing the rupture areas to the trench-parallel gravity anomaly (TPGA, Song and Simons 2003) above each rupture, we find that in 12 of the 14 events considered in this study the TPGA increases between the centroid and the limits of the rupture. Thus, local increases in TPGA appear to be related to the physical conditions along the plate interface that favor rupture termination. Owing to the inherently long time scales required for forearc basin formation, the correlation between the TPGA field and rupture termination regions indicates that long-lived material heterogeneity rather than short time-scale stress heterogeneities are responsible for arresting most great subduction zone ruptures.
DE: 7209 Earthquake dynamics (1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: 2007 Joint Assembly