Shallow Structure and Geomorphology of the Hosgri Strike-Slip Fault
, Offshore Central California
Johnson, Samuel Y.; Watt, Janet T.; and Hartwell, Stephen R.
[email protected]
We mapped a ~94-km-long portion of the right-lateral Hosgri Fault
from Point Sal to Piedras Blancas in offshore central California using high-resolution seismic reflection profiles, marine magnetic data, and multibeam bathymetry. The database includes 121 seismic profiles across the
fault
zone and is perhaps the most comprehensive reported survey of the shallow structure of an active strike-slip
fault
. These data document the location, length, and near-surface continuity of multiple
fault
strands, highlight
fault
-zone heterogeneity, and demonstrate the importance of
fault
trend,
fault
bends, and
fault
convergences in the development of shallow structure and tectonic geomorphology.
The Hosgri Fault
is continuous through the study area passing through a broad arc in which
fault
trend changes from ~ 338° to 328°. The southern ~40 km of the
fault
zone in this area is more extensional, resulting in accommodation space that is filled by deltaic sediments of the Santa Maria River. The central ~24 km of the
fault
zone is characterized by oblique convergence of the Hosgri
Fault
with the more northwest-trending Los Osos and Shoreline faults. Convergence between these faults has resulted in the formation of local restraining and releasing
fault
bends, transpressive uplifts, and transtensional basins of varying size and morphology. We present a hypothesis that links development of a paired
fault
bend to indenting of the Hosgri
Fault
by a strong crustal block translated to the northwest along the Shoreline
Fault
.
Two diverging Hosgri Fault
strands bounding a central uplifted block characterize the northern ~30 km of the Hosgri
Fault
in this area. The eastern Hosgri strand passes through releasing and restraining bends; the releasing bend is the primary control on development of an elongate, asymmetric, "Lazy Z" sedimentary basin. The western strand of the Hosgri
Fault
passes through a significant restraining bend and dies out northward where we propose that its slip transfers to active structures in the Piedras Blancas fold belt.
AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013