Present-day and Long-term Uplift Across the Western Transverse Ranges of
Southern California
Abstract
It has been known for decades that the present-day shortening rates
across the Western Transverse Ranges (WTR) in southern California are
rapid, reaching 10-15 mm/yr near the heavily populated Los Angeles area.
However, only recently have geodetic measurements of vertical motion in
the WTR been sufficiently dense to resolve a tectonic vertical signal.
In this study, we show that much of the geodetically-derived vertical
velocity field in the WTR can be attributed to the interseismic signal
of strain accumulation on reverse faults. We invert geodetic and
geologic data for slip rate and interseismic coupling on faults using a
kinematic model consisting of faults embedded in an elastic crust over
an inviscid mantle. This method allows us to infer the permanent,
long-term component of vertical motions from recoverable, short term
motions. We infer that much of the geodetically observed 3-4 mm/yr of
differential vertical motion across the WTR, involving subsidence along
the Santa Barbara coastline and uplift of the Santa Ynez Range, can be
attributed to recoverable elastic deformation associated with
interseismic locking on faults dipping under the WTR. The sum of
dip-slip rates across the WTR decreases from 10.5-14.6 mm/yr on the east
side near Ventura, California to 5-6.2 mm/yr across the western side of
the Santa Barbara Channel. The total moment accumulation rate in both
the Santa Barbara Channel and the combined San Fernando Valley-LA Basin
regions is equivalent to about two M=7 earthquakes every 100 years.