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Characterization of fault behavior along the central San Andreas Fault, California

Posted on:2005-08-15Degree:Ph.DType:Dissertation
University:Arizona State UniversityCandidate:Young, Jeri JoanneFull Text:PDF
GTID:1450390008481216Subject:Geology
Abstract/Summary:
Rupture characterization of the central San Andreas fault system (SAF) provides the basis for seismic hazard evaluations and the interpretation of fault segmentation. Although the central SAF is capable of producing large earthquakes, such as the Fort Tejon 1857 earthquake; its paleoseismic history is largely incomplete. We tested fault behavior models with paleoseismic data collected from the Cholame segment of the SAF, and with synthetically paleoseismic data. We simulated paleoseismic site conditions to determine the resolution of various paleoseismic data. We conducted paleoseismic investigations at the Las Yeguas 4 site to determine earthquake frequency and amount of offset from the last ground-rupturing event. We interpreted 3 ground-rupturing events, and one ground-shaking event. Two ground-rupturing earthquakes occurred between 1030 to 1300 and 1390 to 1460 cal A.D. The most recent event (MRE) occurred between cal. A.D. 1390 to 1460 age and 1865. Based on historic records and detailed analysis of pollen concentrated from sediments in my excavations, the MRE is interpreted as the 1857 Fort Tejon earthquake. Three-dimensional excavation of an alluvial fan edge indicates that 3.0 +/- 0.70 meters of near-fault slip occurred during the 1857 event. The Cholame segment did not have a, higher frequency of earthquakes as expected when compared to neighboring segments. Synthetic radiocarbon and earthquake ages were generated by random selection from normal distributions that define the frequency of deposition within a trench and the time between earthquakes, respectively. For earthquake recurrence intervals less than 200 years, R.I.s calculated based on hounding radiocarbon ages and associated earthquake events have uncertainties of approximately 40% (1sigma). Recurrence intervals need to he two times greater than the frequency of carbon deposition to adequately record earthquake occurrence. Uncertainties in recurrence intervals indicate that resolution of temporal irregularity of earthquakes is higher for sites with medium or better carbon deposition frequencies. Therefore, discerning irregularity in palooearthquake recurrence becomes more well-resolved in fault systems with high carbon deposition and/or long recurrence intervals. Poor resolution with paleoseismic data sets modeled in this study suggest that most paleoseismic sites do not have the necessary site conditions to adequately record earthquakes; making the determination of appropriate fault behavior models problematic.
Keywords/Search Tags:Fault, Central, Earthquake, SAF, Recurrence intervals, Paleoseismic data
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