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Abstract Observations of shallow fault creep reveal increasingly complex time‐dependent slip histories that include quasi‐steady creep and triggered as well as spontaneous accelerated slip events. Here we report a recent slow slip event on the southern San Andreas fault triggered by the 2017Mw8.2 Chiapas (Mexico) earthquake that occurred 3,000 km away. Geodetic and geologic observations indicate that surface slip on the order of 10 mm occurred on a 40‐km‐long section of the southern San Andreas fault between the Mecca Hills and Bombay Beach, starting minutes after the Chiapas earthquake and continuing for more than a year. Both the magnitude and the depth extent of creep vary along strike. We derive a high‐resolution map of surface displacements by combining Sentinel‐1 Interferometric Synthetic Aperture Radar acquisitions from different lines of sight. Interferometric Synthetic Aperture Radar‐derived displacements are in good agreement with the creepmeter data and field mapping of surface offsets. Inversions of surface displacement data using dislocation models indicate that the highest amplitudes of surface slip are associated with shallow (<1 km) transient slip. We performed 2‐D simulations of shallow creep on a strike‐slip fault obeying rate‐and‐state friction to constrain frictional properties of the top few kilometers of the upper crust that can produce the observed behavior.
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A revised position for the primary strand of the Pleistocene-Holocene San Andreas fault in southern California
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.
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- Award ID(s):
- 1848547
- PAR ID:
- 10223622
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 7
- Issue:
- 13
- ISSN:
- 2375-2548
- Page Range / eLocation ID:
- eaaz5691
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1126/sciadv.aaz5691
