Papers Published

1. Lees, J.M. and Malin, P.E., Tomographic images of P wave velocity variation at Parkfield, California, J. Geophys. Res. (USA), vol. 95 no. B13 (1990), pp. 21793 - 804 .
   (last updated on 2007/04/09)

   Abstract:
   Tomographic inversion is applied to delay times from local earthquakes to image three dimensional velocity variations near Parkfield, California. The 25×20 square km region is represented by nearly cubic blocks of 0.5 km per side. Arrival times of P waves from 551 local earthquakes, with depths of 0 to 15 km, were used as sources producing 3135 rays covering the target region. The results of the inversion show correlation with some of the local geological and geophysical features. Station corrections removed the long-wavelength anomaly associated with the contrast of the Salinian block southwest of the San Andreas fault versus the Franciscan to the northeast. A velocity low located a few kilometers northwest of Parkfield (depth 2.5-3.5 km), appears to lie along the gradient of the large Bouguer gravity anomaly associated with the Parkfield syncline. The authors speculate on the geological meaning of these features and interpret them either as part of the local strike slip tectonics or a shallow crustal detachment

   Keywords:
   Earth crust;faulting;seismology;tectonics;