Description

Over the last ~150 years contrasting modes of slip have distinguished the locked southern San Andreas Fault (SAF) from the creeping central section (Figure 1; e.g., Tok and Arrowsmith, 2006). However, reports following the 1857 Fort Tejn Earthquake the last great SAF earthquake to impact southern California suggest that the 1857 rupture extended at least 80 km to the northwest of Cholame, CA, far into the creeping section (Sieh, 1978 from Wood, 1955, Johnson, 1905, and Barton, 1876). In Siehs dissertation (1977), he references a figure drawn by Johnson (1905) which indicates the rupture displaced a corral by several meters 20 km northwest of Parkfield: Johnson (1905, p. 76) remarks that Mr. Tracey in 61 [1861] traced [the] crack into San Benito Cy. [County], at least 80 km northwest along the fault from Cholame. In my judgement, the crack almost certainly refers to fresh fissuring and not to the general pre-existing rift topography. Thus the 1857 rupture extended into San Benito County. Johnsons crude sketch of a corral, here assumed to be somewhere near the head of Cholame Creek about 40km northwest of Cholame, suggests that he observed it to be offset about 10 to 30 feet (3 to 9 m) in 1905. This may indicate several meters of slip in 1857 at points well northwest of Cholame.
StatusFinished
Effective start/end date2/1/121/31/15

Funding

  • DOI: US Geological Survey (USGS): $17,644.00

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rupture
San Andreas Fault
crack
earthquake
topography
creek