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Evidence for coseismic subsidence events in a southern California coastal saltmarsh

March 1, 2017

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-km2 area 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.

Publication Year 2017
Title Evidence for coseismic subsidence events in a southern California coastal saltmarsh
DOI 10.1038/srep44615
Authors Robert Leeper, Brady P. Rhodes, Matthew E. Kirby, Katherine M. Scharer, Joseph A. Carlin, Eileen Hemphill-Haley, Simona Avnaim-Katav, Glen M. MacDonald, Scott W. Starratt, Angela Aranda
Publication Type Article
Publication Subtype Journal Article
Series Title Scientific Reports
Index ID 70193982
Record Source USGS Publications Warehouse
USGS Organization Office of the AD Hazards