HR: 11:05h
AN: S12A-04    [Abstracts]
TI: Examining Structural Control on Earthquake Rupture Directivity in Subduction Zones
AU: * Llenos, A L
EM: allenos@mit.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, MS 24, Woods Hole, MA 02543
AU: McGuire, J J
EM: jmcguire@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, MS 24, Woods Hole, MA 02543
AB: Structural features associated with fore-arc basins may strongly influence the rupture processes in large subduction zone earthquakes. Previous studies (Wells et al., 2003; Song and Simons, 2003) demonstrated that a significant percentage of the seismic moment release is concentrated beneath the gravity lows resulting from fore-arc basins. To better determine the nature of this correlation and to examine its effect on rupture directivity, we calculate the second order moments of the slip distributions of a set of earthquakes that occurred in circum-Pacific subduction zones and ranged from Mw 7.0-8.4. We compare synthetic and observed seismograms by measuring frequency-dependent amplitude and arrival time differences of the first orbit Rayleigh waves. The point-source synthetic seismograms are constructed based on the centroid locations reported in the Harvard CMT catalog. At low frequencies, the amplitude and arrival time anomalies in the observations primarily result from the spatial and temporal extent of the actual earthquake rupture compared to the point-source model. We generate synthetics using both 1-D (PREM) and 3-D earth models. The 3-D synthetics are calculated using the spectral element method code of Komatitsch and Tromp (1999), which incorporates the ``crust2.0`` 3-D crustal model (Laske et al.) that significantly improves the modeling of the first orbit Rayleigh wave arrivals. We find that for a given earthquake, 3-D Green's functions result in a longer earthquake duration estimate than 1-D Green's functions. 3-D Green's functions also reduce the scatter in the amplitude anomalies better than when the measurements are made with 1-D Green's functions. We then use the amplitude and arrival time measurements in a non-linear inversion to estimate the second moments which describe the rupture length, width, duration and propagation velocity for each earthquake. These results will be compared to trench-parallel gravity anomalies reported by Song and Simons (2003) to find a correlation between fore-arc structure illuminated by the gravity anomalies and earthquake rupture characteristics.
DE: 7200 SEISMOLOGY
DE: 7209 Earthquake dynamics (1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Seismology [S]
MN: Fall Meeting 2005