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Abstract The San Gabriel, Chino, and San Bernardino sedimentary basins in Southern California amplify earthquake ground motions and prolong the duration of shaking due to the basins' shape and low seismic velocities. In the event of a major earthquake rupture along the southern segment of the San Andreas fault, their connection and physical proximity to Los Angeles (LA) can produce a waveguide effect and amplify strong ground motions. Improved estimates of the shape and depth of the sediment‐basement interface are needed for more accurate ground‐shaking models. We obtain a three‐dimensional basement map of the basins by integrating gravity and seismic measurements. The travel time of the sediment‐basementP‐to‐Sconversion, and the Bouguer gravity along 10 seismic lines, are combined to produce a linear relationship that is used to extend the 2D profiles to a 3D basin map. Basement depth is calculated using the predicted travel time constrained by gravity with anS‐wave velocity model of the area. The model is further constrained by the basement depths from 17 boreholes. The basement map shows the south‐central part of the San Gabriel basin is the deepest part and a significant gravity signature is associated with our interpretation of the Raymond fault. The Chino basin deepens toward the south and shallows northeastward. The San Bernardino basin deepens eastward along the edge of the San Jacinto Fault Zone. In addition, we demonstrate the benefit of using gravity data to aid in the interpretation of the sediment‐basement interface in receiver functions.
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Evidence for coseismic subsidence events in a southern California coastal saltmarsh
Abstract Paleoenvironmental records from a southern California coastal saltmarsh reveal evidence for repeated late Holocene coseismic subsidence events. Field analysis of sediment gouge cores established discrete lithostratigraphic units extend across the wetland. Detailed sediment analyses reveal abrupt changes in lithology, percent total organic matter, grain size, and magnetic susceptibility. Microfossil analyses indicate that predominantly freshwater deposits bury relic intertidal deposits at three distinct depths. Radiocarbon dating indicates that the three burial events occurred in the last 2000 calendar years. Two of the three events are contemporaneous with large-magnitude paleoearthquakes along the Newport-Inglewood/Rose Canyon fault system. From these data, we infer that during large magnitude earthquakes a step-over along the fault zone results in the vertical displacement of an approximately 5-km2area that is consistent with the footprint of an estuary identified in pre-development maps. These findings provide insight on the evolution of the saltmarsh, coseismic deformation and earthquake recurrence in a wide area of southern California, and sensitive habitat already threatened by eustatic sea level rise.
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- Award ID(s):
- 1140116
- PAR ID:
- 10469672
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 7
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/srep44615
