Article,
Joint inversion of fault zone head waves and direct P arrivals for crustal structure near major faults
Journal of Geophysical Research, 97 (B2): 1943--1951 (February 1992)
DOI: 10.1029/91JB02748
Abstract
A newly recognized class of seismic phases, namely fault zone head
waves arising from refraction at a transfault velocity contrast,
provides additional constraints to direct P waves in inversions of
near-fault arrival time data for earthquake location and velocity
structure. Incorporation of fault zone head waves in the inversion
process increases the available data and broadens the spatial coverage
of ray paths between sources and receivers. Equally important, the
explicit recognition of fault zone head waves eliminates a source
of error resulting from misidentifying head wave first arrivals as
direct P waves. A simple algorithm for the joint inversion of fault
zone head waves and direct P phases is illustrated with observed
and synthetic data. Application to a small data set recorded by the
borehole seismic network at Parkfield, California, provides separate
seismic velocity depth profiles for the crustal blocks on the two
sides of the San Andreas fault. For depths less than 3 km the obtained
velocity contrast is 10-20\%. For greater depths it decreases to
3-7\%. Numerical tests with synthetic data show that for sources
with known locations and for well located local earthquakes (randomized
mislocation errors of up to 600 m) proper use of fault zone head
waves can significantly improve the accuracy of the fitted velocity
structure. The results of this work motivate the inclusion of fault
zone head waves in state-of-the-art joint structure-hypocenter inversions
using high quality near-fault data.
