Papers Published

1. Ben-Zion, Y. and Malin, P., San Andreas fault zone head waves near Parkfield, California, Science (USA), vol. 251 no. 5001 (1991), pp. 1592 - 4 .
   (last updated on 2007/04/09)

   Abstract:
   Microearthquake seismograms from the borehole seismic network on the San Andreas fault near Parkfield, California, provide three lines of evidence that first P arrivals are `head' waves refracted along the cross-fault material contrast. First, the travel time difference between these arrivals and secondary phases identified as direct P waves scales linearly with the source-receiver distance. Second, these arrivals have the emergent wave character associated with refracted head waves. Third, the first motion polarities of the emergent arrivals are reversed from those of the direct P waves. The presence of fault zone head waves in local seismic network data may help account for scatter in earthquake locations and source mechanisms. The fault zone head waves indicate that the velocity contrast across the San Andreas fault near Parkfield is approximately four percent. Further studies of these waves may provide a way of assessing changes in the physical state of the fault system

   Keywords:
   Earth crust;earthquakes;faulting;seismic waves;seismology;