Papers Published

1. Malin, P.E. and Blakeslee, S.N. and Alvarez, M.G. and Martin, A.J., Microearthquake imaging of the Parkfield asperity, Science (USA), vol. 244 no. 4904 (1989), pp. 557 - 9 .
   (last updated on 2007/04/09)

   Abstract:
   Microearthquake data from a downhole seismometer network on the San Andreas fault appear to outline two aseismic asperities that may correspond to the locations of the foreshocks and main shocks of the Parkfield characteristic earthquakes. The source parameters of the microearthquakes show that a few of the earthquakes have significantly higher stress drops than most. Furthermore, the magnitude-frequency statistics suggest that at local magnitude 0.6, the cumulative number of small events begins to fall off the usual Gutenberg-Richter (b=-1) relation, in which the number of events increases exponentially with decreasing magnitude. The downhole seismometer data establish a baseline from which the evolution of the earthquake process at Parkfield can be monitored and suggest that different mechanical conditions from those that lead to the typical Gutenberg-Richter relation may be operating for the smallest Parkfield microearthquakes

   Keywords:
   Earth crust;earthquakes;faulting;seismology;