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Fault Trace Mapping Along the Creeping Section of the Central San Andreas Fault

Description

This study focuses on mapping faults along the Creeping Section of the San Andreas Fault (CSAF) in California between San Juan Bautista (121.54°W 36.85°N) and Parkfield (120.41°W 35.87°N). I synthesize high-quality base data, including and lidar topography from B4, EarthScope, and USGS 3DEP, recent maps of decadal-scale along-fault shear strain, and aerial and satellite imagery. Using these data, I produced (covering 150 km at 1:10,000 scale) three geospatial map datasets with attributes: geomorphic indicators of faulting, surficial geology, and active fault traces.The CSAF's creeping movement, though likely not associated with large earthquakes, has the potential to cause damage to infrastructure. Accurate fault mapping facilitates fault displacement hazard assessment. This type of work is useful for California state regulations, particularly the Alquist-Priolo Act of 1972, providing insights for engineering site assessments and fault exclusion zones. I discern, categorize, and rank geomorphic indicators to support fault line placement. This approach contributes to the identification of surface expression of creeping faults where the surface has undergone alteration in response to displacement along the fault. I created a surficial geologic map spanning from San Juan Bautista to the southern extent of EarthScope lidar coverage (120.59°W 36.03°N). I categorized each fault as either a primary or secondary fault trace and further broke them into confidence levels based on interpretations of indicators along with structural geologic reasoning and topographic patterns. Accessible target areas containing initial low confidence mapping or interesting structures were visited in the field. Zones along the creeping section exhibit structures such as a pressure ridge found 25 km north of Parkfield, sigmoidal faults and sagponds observed near Paicines Ranch (121.29°W 36.68°N), en-echelon faults, horsetail splays and Riedel shear structures near Lewis Creek (120.87°W 36.29°N). Controls on the structural style along the CSAF are the results of geologic units through which the faults cut and fault zone width and trend.

ContributorsPowell, Joseph Hoss (Author) / Arrowsmith, Ramon (Thesis advisor) / Scott, Chelsea (Thesis advisor) / DeVecchio, Duane (Committee member) / DeLong, Stephen (Committee member) / Arizona State University (Publisher)

Created2023

Spatio-Temporal Mapping of Plate Boundary Faults in California Using Geodetic Imaging

Description

The Pacific–North American plate boundary in California is composed of a 400-km-wide network of faults and zones of distributed deformation. Earthquakes, even large ones, can occur along individual or combinations of faults within the larger plate boundary system. While research often focuses on the primary and secondary faults, holistic study of the plate boundary is required to answer several fundamental questions. How do plate boundary motions partition across California faults? How do faults within the plate boundary interact during earthquakes? What fraction of strain accumulation is relieved aseismically and does this provide limits on fault rupture propagation? Geodetic imaging, broadly defined as measurement of crustal deformation and topography of the Earth’s surface, enables assessment of topographic characteristics and the spatio-temporal behavior of the Earth’s crust.

We focus here on crustal deformation observed with continuous Global Positioning System (GPS) data and Interferometric Synthetic Aperture Radar (InSAR) from NASA’s airborne UAVSAR platform, and on high-resolution topography acquired from lidar and Structure from Motion (SfM) methods. Combined, these measurements are used to identify active structures, past ruptures, transient motions, and distribution of deformation. The observations inform estimates of the mechanical and geometric properties of faults. We discuss five areas in California as examples of different fault behavior, fault maturity and times within the earthquake cycle: the M6.0 2014 South Napa earthquake rupture, the San Jacinto fault, the creeping and locked Carrizo sections of the San Andreas fault, the Landers rupture in the Eastern California Shear Zone, and the convergence of the Eastern California Shear Zone and San Andreas fault in southern California. These examples indicate that distribution of crustal deformation can be measured using interferometric synthetic aperture radar (InSAR), Global Navigation Satellite System (GNSS), and high-resolution topography and can improve our understanding of tectonic deformation and rupture characteristics within the broad plate boundary zone.

ContributorsDonnellan, Andrea (Author) / Arrowsmith, Ramon (Author) / DeLong, Stephen (Author) / College of Liberal Arts and Sciences (Contributor)

Created2017-03-21