TY - JOUR
T1 - The age and origin of small offsets at van matre ranch along the san andreas fault in the Carrizo Plain, California
AU - Salisbury, J. Barrett
AU - Arrowsmith, Ramon
AU - Brown, Nathan
AU - Rockwell, Thomas
AU - Akciz, Sinan
AU - Ludwig, Lisa Grant
N1 - Funding Information:
The authors heartily thank their field assistants: Caitlyn Fischman, Matthew Marin, Eui-jo Marquez, Nik Midttun, Juliet Olsen, Michael Say, Jessica Sutton, and Alana Williams. Also, a special thanks to L. Bidart for access to the Van Matre Ranch (VMR) property. Discussions with Kate Scharer have been particularly helpful. Thanks to Kelin Whipple and Duane DeVecchio for comments on an earlier version of this article. Thanks to two anonymous reviewers and Associate Editor Richard Briggs for their constructive comments. This research was supported by the Southern California Earthquake Center (SCEC; Contribution Number 7152). SCEC is funded by National Science Foundation (NSF) Cooperative Agreement EAR-1033462 and U.S. Geological Survey (USGS) Cooperative Agreement G12AC20038. Salisbury’s work on the very high-resolution topography using structure from motion was supported in part by a strategic University Partnership between Arizona State University and NASA’s Jet Propulsion Laboratory.
Funding Information:
The authors heartily thank their field assistants: Caitlyn Fischman, Matthew Marin, Eui-jo Marquez, Nik Midttun, Juliet Olsen, Michael Say, Jessica Sutton, and Alana Williams. Also, a special thanks to L. Bidart for access to the Van Matre Ranch (VMR) property. Discussions with Kate Scharer have been particularly helpful. Thanks to Kelin Whipple and Duane DeVecchio for comments on an earlier version of this article. Thanks to two anonymous reviewers and Associate Editor Richard Briggs for their constructive comments. This research was supported by the Southern California Earthquake Center (SCEC; Contribution Number 7152). SCEC is funded by National Science Foundation (NSF) Cooperative Agreement EAR-1033462 and U.S. Geological Survey (USGS) Cooperative Agreement G12AC20038. Salisbury’s work on the very high-resolution topography using structure from motion was supported in part by a strategic University Partnership between Arizona State University and NASA’s Jet Propulsion Laboratory
Publisher Copyright:
© 2018, Seismological Society of America. All rights reserved.
PY - 2018/4
Y1 - 2018/4
N2 - To better understand the relationship between geomorphology and fault slip, we investigated the origins of topographic depressions previously interpreted as beheaded channels representing small offsets at Van Matre Ranch (VMR) along the San Andreas fault, Carrizo Plain, California. We excavated four fault-parallel trenches (T1–T4) across depressions and sampled for single-grain postinfrared infrared-stimulated luminescence (p-IR IRSL) age estimates of channel fill. Only T2 sediments are young enough (0.38±0.06 ka) to be associated with a nearby drainage (sourced ∼12 m southeast [SE]), providing a short-term slip rate of 31.6+9/−6.6 mm/yr. The age of the T2 channel fill falls within the uncertainty ranges of the penultimate through fourth event back as dated at Bidart Fan ∼12 km northwest (NW). Hand-excavated exposures at nearby T1 indicate that the T2 channel sediments have experienced at least two earthquake events and that the T1 beheaded gully is a fosse between two small offset alluvial fans (∼10 m radius). Reconstructing the alluvial fan apex shows that offset at this location in the 1857 Mw 7.8 Fort Tejon earthquake was ∼4 m. Therefore, offset in the penultimate earthquake is <∼8 m at the VMR site because we cannot discount that T2 channel sediments experienced four earthquakes. Interestingly, buried channel ages are older at other trenches (4.26–8.12 ka), indicating distant, larger drainage basin sources SE of the study area. Our results indicate that for the Carrizo Plain, (a) there may be appreciable high-frequency variation in paleoearthquake offset along strike and in successive earthquakes at a point; (b) beheaded topographic depressions on the downstream side of the fault have the potential to, but do not necessarily, capture drainage basins on the upstream side of the fault with continued slip; and (c) small catchments may not produce channel landforms or deposits as frequently as has been suggested.
AB - To better understand the relationship between geomorphology and fault slip, we investigated the origins of topographic depressions previously interpreted as beheaded channels representing small offsets at Van Matre Ranch (VMR) along the San Andreas fault, Carrizo Plain, California. We excavated four fault-parallel trenches (T1–T4) across depressions and sampled for single-grain postinfrared infrared-stimulated luminescence (p-IR IRSL) age estimates of channel fill. Only T2 sediments are young enough (0.38±0.06 ka) to be associated with a nearby drainage (sourced ∼12 m southeast [SE]), providing a short-term slip rate of 31.6+9/−6.6 mm/yr. The age of the T2 channel fill falls within the uncertainty ranges of the penultimate through fourth event back as dated at Bidart Fan ∼12 km northwest (NW). Hand-excavated exposures at nearby T1 indicate that the T2 channel sediments have experienced at least two earthquake events and that the T1 beheaded gully is a fosse between two small offset alluvial fans (∼10 m radius). Reconstructing the alluvial fan apex shows that offset at this location in the 1857 Mw 7.8 Fort Tejon earthquake was ∼4 m. Therefore, offset in the penultimate earthquake is <∼8 m at the VMR site because we cannot discount that T2 channel sediments experienced four earthquakes. Interestingly, buried channel ages are older at other trenches (4.26–8.12 ka), indicating distant, larger drainage basin sources SE of the study area. Our results indicate that for the Carrizo Plain, (a) there may be appreciable high-frequency variation in paleoearthquake offset along strike and in successive earthquakes at a point; (b) beheaded topographic depressions on the downstream side of the fault have the potential to, but do not necessarily, capture drainage basins on the upstream side of the fault with continued slip; and (c) small catchments may not produce channel landforms or deposits as frequently as has been suggested.
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U2 - 10.1785/0120170162
DO - 10.1785/0120170162
M3 - Article
AN - SCOPUS:85045035549
SN - 0037-1106
VL - 108
SP - 639
EP - 653
JO - Bulletin of the Seismological Society of America
JF - Bulletin of the Seismological Society of America
IS - 2
ER -