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Characterization of intrabasin faulting and deformation for earthquake hazards in southern Utah Valley, Utah, from high-resolution seismic imaging

Bulletin of the Seismological Society of America

By:
, , , , and
DOI: 10.1785/0120110053

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Abstract

We conducted active and passive seismic imaging investigations along a 5.6-km-long, east–west transect ending at the mapped trace of the Wasatch fault in southern Utah Valley. Using two-dimensional (2D) P-wave seismic reflection data, we imaged basin deformation and faulting to a depth of 1.4 km and developed a detailed interval velocity model for prestack depth migration and 2D ground-motion simulations. Passive-source microtremor data acquired at two sites along the seismic reflection transect resolve S-wave velocities of approximately 200 m/s at the surface to about 900 m/s at 160 m depth and confirm a substantial thickening of low-velocity material westward into the valley. From the P-wave reflection profile, we interpret shallow (100–600 m) bedrock deformation extending from the surface trace of the Wasatch fault to roughly 1.5 km west into the valley. The bedrock deformation is caused by multiple interpreted fault splays displacing fault blocks downward to the west of the range front. Further west in the valley, the P-wave data reveal subhorizontal horizons from approximately 90 to 900 m depth that vary in thickness and whose dip increases with depth eastward toward the Wasatch fault. Another inferred fault about 4 km west of the mapped Wasatch fault displaces horizons within the valley to as shallow as 100 m depth. The overall deformational pattern imaged in our data is consistent with the Wasatch fault migrating eastward through time and with the abandonment of earlier synextensional faults, as part of the evolution of an inferred 20-km-wide half-graben structure within Utah Valley. Finite-difference 2D modeling suggests the imaged subsurface basin geometry can cause fourfold variation in peak ground velocity over distances of 300 m.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Characterization of intrabasin faulting and deformation for earthquake hazards in southern Utah Valley, Utah, from high-resolution seismic imaging
Series title:
Bulletin of the Seismological Society of America
DOI:
10.1785/0120110053
Volume
102
Issue:
2
Year Published:
2012
Language:
English
Publisher:
Seismological Society of America
Publisher location:
El Cerrito, CA
Contributing office(s):
Geologic Hazards Science Center
Description:
17 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Bulletin of the Seismological Society of America
First page:
524
Last page:
540
Country:
United States
State:
Utah
Other Geospatial:
Utah Valley