Abstract: Strike-Slip Faulting in the California Borderland Region
SACRAMENTOGRILO, I.; S. M. HOWELL; J. WASHBURN; C. NOLAND; and H. WARREN, San Diego State University, San Diego, CA
The southern California borderland may contain more strike-slip faulting
than was previously thought. Interpretations of new geophysical data, such
as seismic reflection
profiles, in conjunction with geological data, indicate
that numerous closely spaced strikeslip faults are present off the coast.
These strike-slip faults probably account for as much as 4-6 mm per year
of offset between the Pacific and North American plates. Many of the faults
are active as seen by the numerous
small
earthquakes of M<4 monitored
in the borderland region. In addition, these faults cut the most recent
sediments seen on the
reflection
profiles.
In a reflection
profile about 30 km off the coast of Oceanside, the
Newport-lnglewood fault zone is clearly defined by an acoustic impedance
contrast. Within the same
reflection
profile, at least one flower structure
is present suggesting another strike-slip fault farther off to the west.
A topographic high, in conjunction with epicenter locations, suggests yet
another fault farther to the west, all within one km or so apart. Offset
rock units further support these implications. Many vertically offset units
imply that normal faults are coinciding with the strike-slip regime.
These strike-slip faults are believed to be an extension of the San Andreas fault system in the offshore region. They may have accumulated as much as hundreds of metres to a few kilometres of offset in a right-lateral sense.
AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California