HR: 0830h
AN: S11D-0332    [PDF]
TI: Holocene Fault Activity Beneath the Great Salt Lake: Correlating Near-Surface Faults with Bathymetric Surface Gradients
AU: * Hennes, A M
EM: ahennes@geo.arizona.edu
AF: University of Arizona, Department of Geosciences 1040 E. 4th St., Tucson, AZ 85721 United States
AU: Johnson, R A
EM: johnson@geo.arizona.edu
AF: University of Arizona, Department of Geosciences 1040 E. 4th St., Tucson, AZ 85721 United States
AB: Fault scarps along the Wasatch Front are evidence of seismically active normal faults that have accommodated east-west extension along the eastern margin of the Basin and Range province since the Tertiary. These well-defined, large-offset normal faults juxtapose Precambrian rocks of the Wasatch Range against thick syntectonic Tertiary and younger strata in the Salt Lake Basin. A system of similar listric normal faults with large offsets are imaged in industry seismic reflection data from beneath the Great Salt Lake just to the west of the Wasatch Front. Offsets near the surface on these listric faults are evident in several seismic profiles from the Great Salt Lake and suggest that displacement has continued at least through the Tertiary. Some of these young faults may have movement recent enough to breech the surface and produce a scarp. Interpretation of high-resolution seismic data (Colman et al., 2002) reveals episodes of major faulting since 13.5 ka that offset the surface. Fathometer-recorded water depths collected during the dense industry seismic program cover approximately 70 percent of the Great Salt Lake and allow a unique opportunity to construct a detailed bathymetric map of part of the Great Salt Lake. Geostatistical analysis of the water depth reveals the expected relatively smooth overall bathymetric surface of the floor of the Great Salt Lake, but also shows that it is disrupted by several abrupt changes in the bathymetry. A plot of the gradient magnitude, or rate of change of the bathymetry, indicates several linear features with steep surfaces much like fault scarps that trend along the regional fault fabric. Areas of highest gradient magnitude may indicate areas of most recent offset and may delineate the aerial extent of more recent fault activity. These anomalous surface gradients correlate well with seismically defined normal faults that run along the western margin of Promontory Point and Antelope Island, as well as along the northern side of Carrington Island, suggesting that major intra-basin and basin-bounding normal faults do breach the surface over much of their lengths. Development of laterally continuous fault scarps in a flat, internally drained basin indicates very recent fault activity beneath the Great Salt Lake.
UR: http://www.geo.arizona.edu/~/ahennes/Research.htm
DE: 0905 Continental structures (8109, 8110)
DE: 7205 Continental crust (1242)
DE: 7223 Seismic hazard assessment and prediction
DE: 8015 Local crustal structure
DE: 8109 Continental tectonics--extensional (0905)
SC: Seismology [S]
MN: 2003 Fall Meeting