The Deformation Field Across the Pacific-North America Plate Boundary
in Northern California from EDM, GPS, and VLBI Observations
M H Murray(1,2),
P Segall(1),
W H Prescott(3),
N E King(3),
M Lisowski(4),
R Burgmann(5),
J T Freymueller(6),
S D P Williams(7),
B Romanowicz(2)
(1)Geophysics Dept., Stanford Univ., Stanford, CA 94305-2215;
(2)Seismographic Station, UC Berkeley, CA;
(3)USGS, Menlo Park, CA; (4)USGS, Hawaiian Volcano Obs., HI; (5)Geology Dept., UC Davis, CA;
(6)Geophysical Instit., UA Fairbanks, AK; (7)IGPP, SIO, La Jolla, CA
Abstract
We have initiated an effort to combine geodetic observations
collected over the last 25 years to determine the crustal
deformation field of the Pacific-North America plate
boundary in northern California.
We use three principal data sets:
1) Geodolite trilateration (EDM) measurements collected by
the USGS from 1973 to 1989;
2) very-long-baseline interferometry (VLBI) measurements
collected by NASA from 1983 to 1992; and
3) Global Positioning System (GPS) measurements collected
by the USGS and several university research groups since
1985, including from the Bay Area Regional Deformation
(BARD) permanent GPS network since 1991.
Solutions with weak coordinate constraints derived from
these observations are combined using Kalman filter
techniques to minimize biases due to inhomogeneous
reference networks.
We estimate average rates of interseismic
deformation and co- and post-seismic displacements
due to the 1989 Loma Prieta, 1992 Cape Mendocino, and
other major earthquakes.
The resulting deformation field allows us to address
several outstanding issues, such as the stability of the
Sierra Nevada/Great Valley block, the rate of convergence
across the Coast Ranges, and the distribution of
deformation across the San Andreas fault system from
Parkfield to Cape Mendocino.
We estimate three-dimensional models of surface creep and
deep slip along the major faults, and investigate their
uncertainty and resolution to better characterize rates of
strain accumulation and provide a more realistic
assessment of earthquake hazards.
We also investigate time-dependent variations in crustal
deformation to constrain properties of the crust and mantle
beneath major fault zones.
Velocities of sites relative to stable North America
with 95% confidence regions.
To be presented at the American Geophysical Union meeting, December, 1996.
Crustal Deformation and Fault Mechanics
Last modified: 22 Nov 96