scholarly journals Coevolving early afterslip and aftershock signatures of a San Andreas fault rupture

2021 ◽  
Vol 7 (15) ◽  
pp. eabc1606
Author(s):  
Junle Jiang ◽  
Yehuda Bock ◽  
Emilie Klein
Keyword(s):  
San Andreas Fault ◽  
Three Dimensional ◽  
Time Span ◽  
Structural Factors ◽  
Fine Scale ◽  
Fault Rupture ◽  
Zone Structure ◽  
San Andreas ◽  
Stress Changes ◽  
Large Earthquakes

Large earthquakes often lead to transient deformation and enhanced seismic activity, with their fastest evolution occurring at the early, ephemeral post-rupture period. Here, we investigate this elusive phase using geophysical observations from the 2004 moment magnitude 6.0 Parkfield, California, earthquake. We image continuously evolving afterslip, along with aftershocks, on the San Andreas fault over a minutes-to-days postseismic time span. Our results reveal a multistage scenario, including immediate onset of afterslip following tens-of-seconds-long coseismic shaking, short-lived slip reversals within minutes, expanding afterslip within hours, and slip migration between subparallel fault strands within days. The early afterslip and associated stress changes appear synchronized with local aftershock rates, with increasing afterslip often preceding larger aftershocks, suggesting the control of afterslip on fine-scale aftershock behavior. We interpret complex shallow processes as dynamic signatures of a three-dimensional fault-zone structure. These findings highlight important roles of aseismic source processes and structural factors in seismicity evolution, offering potential prospects for improving aftershock forecasts.

scholarly journals A revised position for the primary strand of the Pleistocene-Holocene San Andreas fault in southern California

2021 ◽  
Vol 7 (13) ◽  
pp. eaaz5691
Author(s):  
Kimberly Blisniuk ◽  
Katherine Scharer ◽  
Warren D. Sharp ◽  
Roland Burgmann ◽  
Colin Amos ◽  
...  
Keyword(s):  
Los Angeles ◽  
Southern California ◽  
San Andreas Fault ◽  
Slip Rate ◽  
Large Magnitude ◽  
Slip Rates ◽  
San Andreas ◽  
The Pacific ◽  
Large Earthquakes ◽  
Dependent Probability

The San Andreas fault has the highest calculated time-dependent probability for large-magnitude earthquakes in southern California. However, where the fault is multistranded east of the Los Angeles metropolitan area, it has been uncertain which strand has the fastest slip rate and, therefore, which has the highest probability of a destructive earthquake. Reconstruction of offset Pleistocene-Holocene landforms dated using the uranium-thorium soil carbonate and beryllium-10 surface exposure techniques indicates slip rates of 24.1 ± 3 millimeter per year for the San Andreas fault, with 21.6 ± 2 and 2.5 ± 1 millimeters per year for the Mission Creek and Banning strands, respectively. These data establish the Mission Creek strand as the primary fault bounding the Pacific and North American plates at this latitude and imply that 6 to 9 meters of elastic strain has accumulated along the fault since the most recent surface-rupturing earthquake, highlighting the potential for large earthquakes along this strand.

Interpretation of seismic reflection profiling data for the structure of the San Andreas fault zone

1983 ◽  
Vol 73 (6A) ◽  
pp. 1701-1720
Author(s):  
R. Feng ◽  
T. V. McEvilly
Keyword(s):  
Fault Zone ◽  
Seismic Reflection ◽  
San Andreas Fault ◽  
Velocity Model ◽  
Seismic Reflection Profile ◽  
Lateral Velocity ◽  
Zone Structure ◽  
Ray Method ◽  
Velocity Change ◽  
San Andreas

Abstract A seismic reflection profile crossing the San Andreas fault zone in central California was conducted in 1978. Results are complicated by the extreme lateral heterogeneity and low velocities in the fault zone. Other evidence for severe lateral velocity change across the fault zone lies in hypocenter bias and nodal plane distortion for earthquakes on the fault. Conventional interpretation and processing methods for reflection data are hard-pressed in this situation. Using the inverse ray method of May and Covey (1981), with an initial model derived from a variety of data and the impedance contrasts inferred from the preserved amplitude stacked section, an iterative inversion process yields a velocity model which, while clearly nonunique, is consistent with the various lines of evidence on the fault zone structure.

On: “Three‐dimensional imaging of steeply dipping structure near the San Andreas fault, Parkfield, California” by John N. Louie, Robert W. Clayton, and Ronan J. LeBras, (GEOPHYSICS, 53, 176–185, February 1988).

Geophysics ◽  
1988 ◽  
Vol 53 (10) ◽  
pp. 1364-1365 ◽  
Author(s):  
J. H. McBride
Keyword(s):  
Survey Data ◽  
Fault Zone ◽  
Complex Terrain ◽  
San Andreas Fault ◽  
Three Dimensional ◽  
Migration Process ◽  
Prestack Migration ◽  
San Andreas ◽  
Survey Line ◽  
Lateral Heterogeneities

Louie et al. (1988) apply to COCORP survey data a prestack migration process, which they describe, to image better reflections associated with structure in the upper 5 km of the San Andreas fault zone near Parkfield, California. They demonstrate the usefulness of this approach in an area along the survey where, as they point out, the CMP-stacking process may be particularly troublesome. While the authors were sensitive to the extreme lateral heterogeneities in and about the fault zone, the crooked survey line, and the complex terrain in which the survey was mounted (McBride and Brown, 1986), I suspect they were nevertheless a little too zealous in discounting, in this case, the value of conventional stacking applied and interpreted judiciously. Moreover, Louie et al. imply that their approach yields previously unobtained results; however, this is not the case.

scholarly journals Three‐dimensional imaging of steeply dipping structure near the San Andreas fault, Parkfield, California

Geophysics ◽  
1988 ◽  
Vol 53 (2) ◽  
pp. 176-185 ◽  
Author(s):  
John N. Louie ◽  
Robert W. Clayton ◽  
Ronan J. LeBras
Keyword(s):  
Seismic Reflection ◽  
San Andreas Fault ◽  
Three Dimensional ◽  
Summation Method ◽  
Ultramafic Rocks ◽  
Back Projection ◽  
Lateral Velocity ◽  
Full Wave ◽  
San Andreas ◽  
Vertical Fault

Shot gathers from the Parkfield, California, deep crustal seismic reflection line, recorded in 1977 by COCORP, reveal coherent events having horizontal to reverse moveouts. These events were migrated using a multioffset three‐dimensional Kirchhoff summation method. This method is a ray‐equation back projection inversion of the acoustic wave field, which is valid under the Born, WKBJ, and far‐field assumptions. Migration of full‐wave acoustic synthetics, having the same limitations in geometric coverage as the COCORP survey, demonstrates the utility of the imaging process. The images obtained from back projection of the survey data suggest that the Gold Hill fault carries ultramafic rocks from the surface to 3 km depth at a dip greater than 45 degrees, where it joins the San Andreas fault, which may cut through more homogeneous materials at shallow depths. To the southwest, a 2 km Tertiary sedimentary section appears to terminate against a near‐vertical fault. The zone between this fault and the San Andreas may be floored at 3 km by flat‐lying ultramafics. Lateral velocity inhomogeneities are not accounted for in the migration but, in this case, do not seriously hinder the reconstruction of reflectors.

Reconciling Precariously Balanced Rocks (PBRs) with Large Earthquakes on the San Andreas Fault System

2015 ◽  
Vol 86 (5) ◽  
pp. 1345-1353 ◽  
Author(s):  
Lisa Grant Ludwig ◽  
James N. Brune ◽  
Abdolrasool Anooshehpoor ◽  
Matthew D. Purvance ◽  
Richard J. Brune ◽  
...  
Keyword(s):  
San Andreas Fault ◽  
Fault System ◽  
San Andreas ◽  
San Andreas Fault System ◽  
Large Earthquakes
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