A Geophysical Investigation of Shallow Deformation Along an Anomalous Section of the Wasatch Fault Zone, Utah, USA

McBride, John H.; Stephenson, William J.; Thompson, Tom; Harper, M.P.; Eipert, A.A.; Hoopes, John C.; Tingey, David G.; Keach, R. William; Okojie-Ayoro, A. O.; Gunderson, Kellen L.; Meirovitz, Casey; Hicks, Taryn; Spencer, Christopher J.; Yaede, Johnathan R.; Worley, David M.

doi:10.2113/gseegeosci.14.3.183

Cited by 5 publications

(1 citation statement)

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“…The same seismic data set may be used to create velocity tomograms and seismic reflection images; that is, the two methods complement one another without additional field work. For example, McBride et al (2008) create a first-arrival tomogram from their survey data on the Wasatch fault, Utah, to constrain source and receiver static corrections when creating a seismic reflection image of a site with complex topography and large lateral velocity gradients. They then support their reflection interpretation of a fault-bounded graben by inspection of the seismic tomogram.…”

Section: Discussionmentioning

confidence: 99%

Outcrops and well logs as a practicum for calibrating the accuracy of traveltime tomograms

et al. 2015

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We have developed two case studies demonstrating the use of high-resolution seismic tomography and reflection imaging in the field of paleoseismology. The first study, of the Washington fault in southern Utah, USA, evaluated the subsurface deposits in the hanging wall of the normal fault. The second study, of the Mercur fault in the eastern Great Basin of Utah, USA, helped to establish borehole locations for sampling subsurface colluvial deposits buried deeper than those previously trenched along the fault zone. We evaluated the seismic data interpretations by comparison with data obtained by trenching and logging deposits across the Washington fault, and by drill-core sampling and video logging of boreholes penetrating imaged deposits along the Mercur fault. The seismic tomograms provided critical information on colluvial wedges and faults but lacked sufficient detail to resolve individual paleoearthquakes. IntroductionTime-space patterns of earthquake recurrence and magnitude reflect the pulse of the earthquake engine and are the primary parameters required for seismic hazard analysis of faulting (McCalpin, 2009). The pulse period indicates the recurrence interval of large earthquakes, and the pulse strength is the earthquake's magnitude. Knowing these two parameters is important for establishing earthquake risk in an inhabited region.Geologic mapping and regional geophysical surveys provide information on the locations and lengths of faults, but establishing the earthquake history requires excavating and logging unconsolidated deposits that are several hundred thousand years or fewer in age. High-resolution seismic surveys are useful in site characterization, especially prior to excavation. However, the results are commonly limited by resolution and complex stratigraphy adjacent to the faults, where vertically stacked colluvial wedges contain crucial information concerning the number and magnitudes of earthquake events represented in the subsurface deposits (e.g., Stephenson et al., 1993;Morey and Schuster, 1999;McCalpin, 2009).We present two case studies of normal faulting, in which seismic methods image faulted deposits prior to excavation. In both cases, the subsurface deposits were subsequently logged, and the results compared with the seismic interpretations. This "postmortem" cri-

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Section: Discussionmentioning

confidence: 99%