Papers Published

1. Malin, P.E. and Lou, M. and Rial, J.A., F_R waves: A second fault-guided mode with implications for fault property studies, Geophysical Research Letters, vol. 23 no. 24 (1996), pp. 3547 - 3550 [96GL03424] .
   (last updated on 2007/04/09)

   Abstract:
   Previous work has shown that earthquake S-waves can become fault zone guided-waves. We present observational evidence for a second type of earthquake-generated, fault-guided seismic wave, apparently involving coupled P- and S-waves. Our data are from a fault located in igneous rocks in Owens Valley, California. In analogy to standard Love and Rayleigh waves, we suggest that purely S-type modes be indicated on seismograms by double prime F_L double prime and the new coupled P- and S-type by double prime F_R double prime . Since F_R waves are sensitive to both the local P- and S-wave velocities, their presence implies unique conditions in and near the fault. Modeling of our seismograms suggests a differential reduction in these velocities, with a larger change in bulk modulus than in shear modulus. We propose that this reduction is due to unsaturated fractures within the core of the fault. We view F_R waves as a new tool for detecting and characterizing highly fractured fault zones, providing important information on the relation of earthquakes and subsurface fluid conduits.

   Keywords:
   Earthquakes;Rock mechanics;Geographical regions;Velocity;Geometry;