Earthquake Probabilities for the Wasatch Front region in Utah, Idaho, and Wyoming

Wong, I., W. Lund, C. DuRoss, P. Thomas, W. Arabasz, A. Crone, M. Hylland, N. Luco, S. Olig, J. Pechmann, S. Personius, M. Petersen, D. Schwartz, R. Smith, and S. Bowman (2016). Earthquake Probabilities for the Wasatch Front region in Utah, Idaho, and Wyoming, Utah Geological Survey Miscellaneous Publication 16-3,  418 pp.

Paleoseismology of the Promontory Segment, East Great Salt Lake Fault

Dinter, D. A., and J. C. Pechmann (2014). Paleoseismology of the Promontory Segment, East Great Salt Lake Fault, U.S. Geol. Surv. Final Technical Rept., Award No. 02HQGR0105, 23 pp, http://earthquake.usgs.gov/research/external/reports/02HQGR0105.pdf
ABSTRACT
With funding from this project, we collected 367 km of high resolution seismic reflection data in the Great Salt Lake in 2003 and 2006: 205 km in the north arm and 162 km in the south arm, where the north and south arms are defined as the parts of the lake north and south of the railroad causeway, respectively.  Because the quality of the north arm data that we obtained was insufficient to meet the goals of the project, we collected an additional 380 km of data with new, state-of-the-art instrumentation in 2009 and 2010: 160 km in the north arm and 220 km in the south arm. The 2009 fieldwork was part of a collaborative industry-funded study. The 2010 field work was carried out using boat and equipment time that became available after the successful completion of a seismic reflection study in Utah Lake for another USGS/NEHRP-funded study.
We used the seismic reflection data to map the Great Salt Lake fault (GSLF) and associated subsidiary faults in the north arm of the Great Salt Lake and to revise an analogous map for the south arm of the lake that we constructed for a previous USGS/NEHRP-funded project. We also mapped the trace of the Carrington fault, another major normal fault in the Great Salt Lake, using our seismic reflection data and high-resolution bathymetry data for the lake.  Based on the geometry of our mapped surface trace for the GSLF, variations in the amount of lakebed offset along this fault, and other evidence for recency of faulting, we hypothesize that the GSLF consists of the following four segments from north to south (with end-to-end length measurements): the Rozel segment (≥ 18 km), the Promontory segment (≥27 km), the Fremont Island segment (24 km), and the Antelope Island segment (35 km).
Seismic reflection profiles across the GSLF in the north arm show clear evidence for individual paleoearthquakes in the form of stratigraphically limited subsidiary faults and monoclines and coseismic bedding rotations adjacent to the fault. Based on these types of features, we have identified seismic event horizons for two or three paleoearthquakes on the Rozel segment and two or three paleoearthquakes on the Promontory segment , all within ~8 m of the lake bottom.  A possible fourth Promontory segment earthquake is suggested by the higher fault scarps along this segment. The earthquake event horizons that we have identified in this study can be cored and dated to establish a paleoearthquake history for the Rozel and Promontory segments of the GSLF. In the meantime, based on comparisons with the depths of dated event horizons on the Antelope Island and Fremont Island segments, it seems reasonable to assume that the average recurrence interval of 4200 ±1400 years that we have determined for these two segments is also applicable to the Rozel and Promontory segments