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Double-Difference Tomography: The Method and Its Application to the Hayward Fault, California

Department of Geology and Geophysics
University of Wisconsin–Madison
1215 W. Dayton Street
Madison, Wisconsin 53706

View larger version (70K): [in a new window]   Figure 1. A horizontal slice through the true synthetic velocity model (Kissling et al., 1994). The true velocity model in 3D is similar to a "vertical sandwich," with the velocity constant with the depth.

View larger version (34K): [in a new window]   Figure 2. Event locations (filled circles) and stations (open triangles) used for the synthetic dataset. The inversion grid used in the standard tomography and DD tomography solutions is shown as the crosses. The inversion grid points are at X = –35, –15, 0, 2, 4, 6, 20, 35 km, at Y = –60, –40 –20, 0, 20, 40 km, and at Z = 0, 3, 7, 11, 16 km.

View larger version (154K): [in a new window]   Figure 3. Horizontal slices through (a) the velocity model from standard tomography, (b) the velocity model from DD tomography. (c) the velocity difference between DD tomography solution and true model, and (d) the velocity difference between standard tomography solution and true model. Black dots indicate the earthquake hypocenters within half the grid size of the slice.

View larger version (47K): [in a new window]   Figure 4. Stations (open triangles) and Hayward fault seismicity (filled circles) between 1984 and 1998 located by the NCSN. The inversion grid used for the standard tomography and DD tomography solutions is shown as the crosses. The inversion grid points are at X = –35, –20, –10, –5, –4, –3, 0, 5, 10, 20, 35 km, at Y = –30, –20, –10, 0, 10, 20, 30 km, and at Z = 0, 4, 8, 12, 20 km.

View larger version (28K): [in a new window]   Figure 5. Hayward fault event locations. (a) NCSN catalog locations. (b) Relocations by the standard tomography method (i.e., with only absolute catalog data). (c) Relocations by the DD location method (Waldhauser and Ellsworth, 2002). (d) Relocations by the DD tomography method.

View larger version (22K): [in a new window]   Figure 6. Catalog locations in the region of latitude 37.83° to 37.91° and longitude –122.26° to –122.18°. (a) Map view of event locations in the latitude and longitude system. (b) Map view of event locations in the coordinate system rotated anticolockwise 35° with the center located at latitude 37.72° and longitude –122.06°, positive X axis directing to the northeast, positive Y axis to the northwest, and positive Z axis downward. (c) AA' cross section. (d) BB' cross section.

View larger version (20K): [in a new window]   Figure 7. Same as Figure 6, but for the event locations from the standard tomography method (only absolute catalog data).

View larger version (19K): [in a new window]   Figure 8. Same as Figure 6, but for the event locations from the DD location method (Waldhauser and Ellsworth, 2002).

View larger version (18K): [in a new window]   Figure 9. Same as Figure 6, but for the event locations from the DD tomography method.

View larger version (74K): [in a new window]   Figure 10. Across-strike vertical slices through (a) the 3D model from DD tomography, (b) the 3D model from standard tomography, (c) the velocity difference between (a) and (b). The final hypocenters within 5 km of each slice are included as black dots.

View larger version (48K): [in a new window]   Figure 11. Across-strike vertical slices through (a) the 3D resolution structure for the standard tomography and (b) the model uncertainties.