Three-dimensional investigation of a 5 m deflected swale along the san andreas fault in the carrizo plain

Sinan O. Akçiz, Lisa Grant Ludwig, Olaf Zielke, Ramon Arrowsmith

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Topographic maps produced from Light Detection and Ranging (LiDAR) data are useful for paleoseismic and neotectonic research because they provide submeter representation of faulting-related surface features. Offset measurements of geomorphic features, made in the field or on a remotely sensed imagery, commonly assume a straight or smooth (i.e., undeflected) pre-earthquake geometry. Here, we present results from investigation of an ∼20 cm deep and >5 m wide swale with a sharp bend along the San Andreas fault (SAF) at the Bidart fan site in the Carrizo Plain, California. From analysis of LiDAR topography images and field measurements, the swale was initially interpreted as a channel tectonically offset ∼4:7 m. Our observations from exposures in four backhoe excavations and 25 hand-dug trenchettes show that even though a sharp bend in the swale coincides with the trace of the A.D. 1857 fault rupture, the swale formed after the 1857 earthquake and was not tectonically offset. Subtle fractures observed within a surficial gravel unit overlying the 1857 rupture trace are similar to fractures previously documented at the Phelan fan and LY4 paleoseismic sites 3 and 35 km northwest of Bidart fan, respectively. Collectively, the fractures suggest that a post-1857 moderate-magnitude earthquake caused ground cracking in the Carrizo and Cholame stretches of the SAF. Our observations emphasize the importance of excavation at key locations to validate remote and ground-based measurements, and we advocate more geomorphic characterization for each site if excavation is not possible.

Original languageEnglish (US)
Pages (from-to)2799-2808
Number of pages10
JournalBulletin of the Seismological Society of America
Volume104
Issue number6
DOIs
StatePublished - Dec 1 2014

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San Andreas Fault
excavation
plains
fans
Excavation
Fans
Earthquakes
earthquakes
rupture
neotectonics
earthquake
gravels
Faulting
ground-based measurement
earthquake magnitude
Gravel
imagery
Topography
gravel
topography

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Three-dimensional investigation of a 5 m deflected swale along the san andreas fault in the carrizo plain. / Akçiz, Sinan O.; Ludwig, Lisa Grant; Zielke, Olaf; Arrowsmith, Ramon.

In: Bulletin of the Seismological Society of America, Vol. 104, No. 6, 01.12.2014, p. 2799-2808.

Research output: Contribution to journalArticle

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