Papers Published

1. Leary, P.C. and Malin, P.E. and Phinney, R.A. and Brocher, T. and VonColln, R., Systematic monitoring of millisecond travel time variations near Palmdale, California, J. Geophys. Res. (USA), vol. 84 no. B2 (1979), pp. 659 - 66 .
   (last updated on 2007/04/09)

   Abstract:
   Repeated measurements of P wave travel time changes have been completed near the San Andreas fault, 25 km west of Palmdale, California. Spanning a 2-year period from June 1974, these observations were made on 0.1- to 8.5-km base lines and have a worst case accuracy of ±4 ms. The observation area was centered around Bouquet Reservoir where the P wave source, a marine air gun, was secured. Systematic and continuous arrival time fluctuations are observed that lasted from hours to days and ranged from 1 to 10 ms (Δt/t≃10^-3-10^-2). The results are interpreted in terms of P wave velocity variations in a water-filled cracked medium in which velocity changes are due to the opening of microcracks during incremental strain. The time scale of anomalous velocity behavior is constrained to be less than the diffusion time of water into newly opened cracks. In this regime little prospect exists of detecting long-term earthquake precursors

   Keywords:
   Earth crust;fluctuations;groundwater;monitoring;seismic waves;