The age and origin of small offsets at van matre ranch along the san andreas fault in the Carrizo Plain, California

J. Barrett Salisbury, Ramon Arrowsmith, Nathan Brown, Thomas Rockwell, Sinan Akciz, Lisa Grant Ludwig

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)639-653
Number of pages15
JournalBulletin of the Seismological Society of America
Volume108
Issue number2
DOIs
StatePublished - Apr 1 2018

Fingerprint

San Andreas Fault
trucks
plains
Earthquakes
Catchments
earthquakes
Fans
Sediments
drainage
fans
earthquake
sediments
slip
Fault slips
alluvial fan
drainage basin
Geomorphology
Landforms
trench
fill

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

The age and origin of small offsets at van matre ranch along the san andreas fault in the Carrizo Plain, California. / Salisbury, J. Barrett; Arrowsmith, Ramon; Brown, Nathan; Rockwell, Thomas; Akciz, Sinan; Ludwig, Lisa Grant.

In: Bulletin of the Seismological Society of America, Vol. 108, No. 2, 01.04.2018, p. 639-653.

Research output: Contribution to journalArticle

Salisbury, J. Barrett ; Arrowsmith, Ramon ; Brown, Nathan ; Rockwell, Thomas ; Akciz, Sinan ; Ludwig, Lisa Grant. / The age and origin of small offsets at van matre ranch along the san andreas fault in the Carrizo Plain, California. In: Bulletin of the Seismological Society of America. 2018 ; Vol. 108, No. 2. pp. 639-653.
@article{2bdc07ebe06545fba53a27f1bf0baa85,
title = "The age and origin of small offsets at van matre ranch along the san andreas fault in the Carrizo Plain, California",
abstract = "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.",
author = "Salisbury, {J. Barrett} and Ramon Arrowsmith and Nathan Brown and Thomas Rockwell and Sinan Akciz and Ludwig, {Lisa Grant}",
year = "2018",
month = "4",
day = "1",
doi = "10.1785/0120170162",
language = "English (US)",
volume = "108",
pages = "639--653",
journal = "Bulletin of the Seismological Society of America",
issn = "0037-1106",
publisher = "Seismological Society of America",
number = "2",

}

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

PY - 2018/4/1

Y1 - 2018/4/1

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.

UR - http://www.scopus.com/inward/record.url?scp=85045035549&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85045035549&partnerID=8YFLogxK

U2 - 10.1785/0120170162

DO - 10.1785/0120170162

M3 - Article

AN - SCOPUS:85045035549

VL - 108

SP - 639

EP - 653

JO - Bulletin of the Seismological Society of America

JF - Bulletin of the Seismological Society of America

SN - 0037-1106

IS - 2

ER -