Source Parameter Studies of Historical and Recent Earthquakes of the Cascadia Subduction Zone and Mendocino Triple Junction Region

We are comparing the seismograms of recent (post-1989) earthquakes to those of historic earthquakes (pre-1966) recorded at the same (or similar) station locations to determine how comparable the historic earthquakes are to recent events with well determined hypocenters and rupture parameters. The seismograms of recent events will be used as empirical Greens functions in a deconvolution process to more accurately determine the directivity and rupture process of the older events. Our initial work in the Cascadia Subduction zone has focused on earthquakes within the subducting Pacific plate occurring in 1939, 1946, 1949 and 1965, in locations similar to the 1999 Satsop and 2001 Nisqually earthquakes. Preliminary analysis of waveform information suggests that the 1949 Olympia earthquake has a different rupture history to the east and south of the epicenter, as compared to the Nisqually earthquake. In the Mendocino Triple Junction region, we have focused on modeling smaller magnitude earthquakes using an earth simplification transform. We will calibrate the technique using several intermediate magnitude events that have occurred on the Mendocino fault and within the Gorda plate.