HR: 14:40h
AN: S53C-05    [Abstracts]
TI: A New Approach for Combining GPS and Seismic Data in Kinematic Inversions
AU: * Custodio, S
EM: susana@crustal.ucsb.edu
AF: Institute for Crustal Studies, Institute for Crustal Studies, Girvetz Hall, University of California Santa Barbara, Santa Barbara, CA 93106-1100, United States
AU: Page, M T
EM: pagem@physics.ucsb.edu
AF: United States Geological Survey, 525 South Wilson Ave., Pasadena, CA 91106-3212, United States
AU: Archuleta, R J
EM: ralph@crustal.ucsb.edu
AF: Institute for Crustal Studies, Institute for Crustal Studies, Girvetz Hall, University of California Santa Barbara, Santa Barbara, CA 93106-1100, United States
AB: Both GPS and seismic data are routinely used in kinematic inversions of earthquakes. These two types of data are very different: GPS traditionally records the static field, while seismographs record the dynamically radiated wavefield. The two datasets complement each other as they record different components of the seismic field. Therefore, they should be used together in earthquake source inversions. Most joint inversions of GPS and seismic data simply invert all the data (static and dynamic) at the same time. In this procedure, the different datasets must be weighted, and these weights are generally determined empirically. Commonly, GPS data are given a weight that is orders of magnitude larger than that given to seismic data. Is this approach correct? We have developed a new method to combine GPS and seismic data that avoids empirical weighting, and more importantly, takes into account the resolving power of both datasets. This new approach consists of a two-step process: in the first step we invert the static field, thus obtaining the cumulative slip on the fault. This inversion is performed on an irregular grid specifically designed to take into account the spatially heterogeneous resolution of the static data. In particular, the irregular grid accommodates the strong attenuation of the static field with distance (and consequently with depth). The second step consists of an inversion of the seismic data to find the full space-time evolution of slip on the fault. Here, the spatial distribution of slip is constrained by that inferred from the static inversion. It is highly desirable to constrain the seismic inversion given the intrinsic strong trade- offs between temporal and spatial source parameters. Because this two-step approach takes into account the resolution of each dataset, it naturally eliminates artifacts from the resulting slip models. We applied this two-step inversion to the 2004 M6 Parkfield, California, earthquake. We use 43 3-component accelerograms and 13 3- component GPS displacement measurements. All the data were recorded very close to the fault, constituting an excellent dataset to test our method. We discuss the results of our two-step approach, emphasizing the effect of the irregular grid used to determine the static slip solution. We also discuss the possibility that the earthquake started as a super-shear rupture. We compare our final model with models obtained by inversion of individual datasets and with other joint inversions. Finally, we examine robust features and identify artifacts still present in the final slip model.
DE: 0545 Modeling (4255)
DE: 1200 GEODESY AND GRAVITY
DE: 3260 Inverse theory
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: 2007 Fall Meeting