The velocity field along the San Andreas Fault in central and southern California

The velocity field within a 100-km-broad zone centered on the San Andreas fault between the Mexican border and San Francisco Bay has been inferred from repeated surveys of trilateration networks in the 1973–1989 interval. The velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the San Andreas fault in the Transverse Ranges of southern California. Across-strike profiles of the fault-parallel component of velocity exhibit the expected sigmoidal shape, whereas across-strike profiles of the fault-normal component of velocity are flat and featureless. No significant convergence upon the fault is observed even along the big bend sector of the fault. Simple dislocation models can explain most of the features of the observed velocity field, but those explanations are not unique. About 35 mm/yr of relative plate motion is accounted for within the span of the trilateration networks. Geologic studies indicate that the secular slip rate on the San Andreas fault is about 35 mm/yr. The agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes. The relative motion observed across the San Andreas fault (35 mm/yr) plus that observed across the Eastern California shear zone (8 mm/yr) accounts for most (43 mm/yr) of the observed North America-Pacific relative plate motion (47 mm/yr).

[1]  C. Sanders.  Earthquake depths and the relation to strain accumulation and stress near strike‐slip faults in southern California , 1990 .

[2]  K. Furlong,et al.  Geometry and evolution of the San Andreas Fault Zone in northern California , 1989 .

[3]  J. Weertman.  Continuum distribution of dislocations on faults with finite friction , 1964 .

[4]  R. Parker.  Understanding Inverse Theory , 1977 .

[5]  J. C. Savage,et al.  Strain accumulation in southern California, 1973–1984 , 1986 .

[6]  J. Rice,et al.  Stressing of locked patches along a creeping fault , 1985 .

[7]  J. B. Walsh.  Mechanics of strike‐slip faulting with friction , 1968 .

[8]  R. Weldon,et al.  A kinematic model of southern California , 1986 .

[9]  J. M. Davidson,et al.  Tectonic motion in the western United States inferred from Very Long Baseline Interferometry measurements, 1980–1986 , 1987 .

[10]  T. Rockwell,et al.  Late Quaternary rate of slip along the San Jacinto fault zone near Anza, southern California , 1990 .

[11]  H. Kanamori,et al.  A seismotectonic analysis of the Anza Seismic Gap, San Jacinto Fault Zone, southern California , 1984 .

[12]  D. Jackson,et al.  Aseismic crustal deformation in the Transverse Ranges of Southern California , 1987 .

[13]  W. Prescott,et al.  Geodetic measurement of horizontal deformation in the northern San Francisco Bay region, California , 1986 .

[14]  P. Bird,et al.  Kinematics of present crust and mantle flow in southern California , 1984 .

[15]  R. V. Sharp,et al.  Preliminary slip-rate table and map of late-Quaternary faults of California , 1984 .

[16]  T. McEvilly,et al.  Interpretation of seismic reflection profiling data for the structure of the San Andreas fault zone , 1983 .

[17]  Wayne Thatcher,et al.  Nonlinear strain buildup and the earthquake cycle on the San Andreas Fault , 1983 .

[18]  J. C. Savage,et al.  Asthenosphere readjustment and the earthquake cycle , 1978 .

[19]  J. Weertman.  Relationship between displacements on a free surface and the stress on a fault , 1965 .

[20]  T. Davis,et al.  Structural transect of the western Transverse Ranges, California: Implications for lithospheric kinematics and seismic risk evaluation , 1988 .

[21]  J. Rice,et al.  Crustal deformation in great California earthquake cycles , 1986 .

[22]  W. Prescott.  The determination of displacement fields from geodetic data along a strike slip fault , 1981 .

[23]  C. King,et al.  Comments on “Relationship between displacements on a free surface and the stress on a fault” by J. Weertman , 1973, Bulletin of the Seismological Society of America.

[24]  S. Ward.  Pacific-North America plate motions - New results from very long baseline interferometry , 1990 .

[25]  J. C. Savage,et al.  Regional deformation near Palmdale, California, 1973–1983 , 1984 .

[26]  C. R. Allen,et al.  Fault slip in southern California , 1985 .

[27]  W. Prescott,et al.  Discussion on displacement analysis: Detection of crustal deformation , 1986 .

[28]  K. Kasahara,et al.  A strike-slip fault in a laterally inhomogeneous medium , 1977 .

[29]  M. Johnston,et al.  Surface shear stress, strain, and shear displacement for screw dislocations in a vertical slab with shear modulus contrast , 1977 .

[30]  J. C. Savage,et al.  Geodolite measurements of deformation near Hollister, California, 1971–1978 , 1979 .

[31]  D. Jackson,et al.  Dislocation model for aseismic crustal deformation at Hollister, California , 1986 .

[32]  M. Zoback,et al.  Implications of an Elastic Analysis of In Situ Stress Measurements Near the San Andreas Fault , 1982 .

[33]  R. Sibson.  Fault zone models, heat flow, and the depth distribution of earthquakes in the continental crust of the United States , 1982 .

[34]  J. C. Savage,et al.  An apparent shear zone trending north-northwest across the Mojave Desert into Owens Valley, eastern , 1990 .

[35]  Thomas L. Davis,et al.  A cross section of the Los Angeles Area: Seismically active fold and thrust belt, The 1987 Whittier Narrows earthquake, and earthquake hazard , 1989 .

[36]  J. Sauber,et al.  Geodetic measurement of deformation in the Loma Prieta, California Earthquake with very long baseline interferometry , 1990 .

[37]  V. Li,et al.  Modeling surface deformations at complex strike‐slip plate boundaries , 1988 .

[38]  D. Turcotte,et al.  Comment on 'An Analysis of Strain Accumulation on a Strike Slip Fault' , 1974 .

[39]  Richard G. Gordon,et al.  Current plate motions , 1990 .

[40]  J. C. Savage,et al.  Deformation across the Salton Trough, California, 1973–1977 , 1979 .

[41]  J. C. Savage.  Equivalent strike‐slip earthquake cycles in half‐space and lithosphere‐asthenosphere earth models , 1990 .

[42]  Thomas H. Jordan,et al.  Geodetic measurement of tectonic deformation in the Santa Maria Fold and Thrust Belt, California , 1990 .

[43]  A. Nur,et al.  The accommodation of relative motion along the San Andreas fault system in California , 1980 .

[44]  J. C. Savage.  Effect of crustal layering upon dislocation modeling , 1987 .

[45]  M. Zoback,et al.  Crustal strain near the Big Bend of the San Andreas Fault: Analysis of the Los Padres‐Tehachapi Trilateration Networks, California , 1990 .

[46]  J. C. Savage,et al.  Geodetic determination of relative plate motion in central California , 1973 .