Title: To see the world in a grain of sand: Sedimentary signals of young faulting along an old strand of the San Andreas Fault
Speaker: Dr. Julie Fosdick
Assistant Professor, University of Connecticut
Abstract: Continental-scale transform faults along active tectonic plate boundaries create
some of Earth’s most dynamic mountainous geography and large variations in
microclimates and biodiversity. In the Transverse Ranges of southern California, the San
Andreas Fault system accommodates tectonic motion between the Pacific and North
American plates and generates large-magnitude earthquakes, posing extreme seismic risk
to the >22 million people in the densely populated Greater Los Angeles and Inland Empire
areas. A central goal among geoscientists today is to achieve higher precision of
deformation rates across faults at both short (e.g., decadal to millennial) and long-term
(e.g., million-year) timescales to fully understand earthquake cycles, tectonic histories on
crustal-scale faults, and seismic hazards. This study presents new data from along the
Mission Creek fault strand – a major geologic structure within the San Andreas Fault
system – that is currently mapped as inactive. Our sedimentological and detrital
provenance study from the San Gorgonio Pass region of the San Andreas Fault system
suggest more recent faulting along the Mission Creek fault strand since ~100,000 years
ago, with implications for maximum fault slip rates that are comparable to the present-day
geodetic slip rate for the southern San Andreas Fault. This knowledge provides important
long-term context for understanding present rates of continental deformation, uplift history
of the Transverse Ranges, and seismic risk in southern California. In other words, the
Mission Creek fault strand might be active!
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