SELF-CONSISTENT RETRIEVAL OF SOURCE PARAMETERS USING MANTLE WAVES

The large number of high-quality stations from global networks (e.g., WS, GEOSCOPE) allows for rapid and robust recovery of source parameter s of large earthquakes. We present a self-consistent analysis of surfa ce waves in terms of directivity parameters. The boxcar is often used to recover source parameters but is rarely a faithful representation o f an event's time function. We demonstrate that more reliable estimate s of directivity parameters can be obtained when we take into account the source time function (STF) of the event. A low-frequency STF is ob tained from first (R1) and second (R2) orbit Rayleigh waves in the ran ge 2 to 15 mHz, with a spectral synthesis and inversion method. We mea sure the differential amplitudes between data and 3D synthetics. We us e the R1/R2 ratio of differential amplitudes to invert, in a single na rrow-frequency band, for the event's apparent rupture azimuth and velo city. For the M-w 8.1 Chile 1995 event, data are consistent with unila teral southward propagation, with a velocity of about 2.4 km/sec. For the M-w 7.9 Mexico 1995 earthquake, the rupture propagated toward the NW at about 2.0 km/sec. Our low-frequency estimates agree with broadba nd studies of both events and can be retrieved rapidly on a routine ba sis after a large earthquake.