T239 Geophysical Investigations of Geological Hazards (Posters)

Tuesday, 29 October 2013
9:00 AM - 6:30 PM
Hall D

USING SLAM TO SEARCH FOR SEISMOGENIC FAULTS, NORTH TAHOE-TRUCKEE AREA, CALIFORNIA

Paper number: T239-4
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Our goal is to spatially correlate earthquakes with the ground-surface trace of the faults that generated them. This tentative correlation is made using the Seismo-Lineament Analysis Method (SLAM; Cronin et al., 2008, Env & Eng Geol14(3), 199-219). SLAM now incorporates uncertainties in nodal-plane orientation to define each seismo-lineament: the ground-surface swath in which the fault trace would be located if the hypocenter location and fault-plane solution are accurate and if the fault is both emergent and approximately planar. We studied 26 earthquakes with magnitudes between 3 and 6 reported from September 1966 through 2011, with epicenters between 39.2°-39.5°N latitude and 120.3°-119.9°W longitude in the north Tahoe-Truckee area of California. Hypocenter locations are from Waldhauser's catalog of northern California events relocated using the double-difference method (ddrt.ldeo.columbia.edu). All hypocenter depths are <12 km subsea. The improved epicenter locations are 0.3-3.8 km from the initially reported single-event locations, and have reported spatial uncertainties that average <0.7 km. Focal mechanisms for most earthquakes we used are from the Northern California Earthquake Data Center catalog, recently updated by Oppenheimer and others (quake.geo.berkeley.edu/ncedc/catalog-search.html).

Tentative spatial correlations were made between earthquakes and the Dog Valley fault zone (L-lateral; strike ~40°), Polaris fault (R-lateral; strike ~147°), and two trends that exhibit geomorphic evidence of faulting but along which no faults have previously been mapped: the Martis Creek trend (inferred L-lateral; strike ~57°) and the Prosser Creek trend (inferred R-lateral; strike ~122°). These faults/trends appear to be in an orthogonal-to-conjugate relationship with each other, and pass near or through several reservoirs and dam structures whose failure might impact downstream communities including Reno. The east-west trend of the local horizontal extension axis (S1h) derived from T-axes is similar to that derived from GPS velocities of 6 nearby PBO stations (pbo.unavco.org). The GPS data indicate slow clockwise rotation and translation to the northwest relative to the Stable North American Reference Frame, consistent with right-lateral shear in the northern Walker Lane.