Fault Trace Mapping and Surface-Fault-Rupture Special Study Zone Delineation of the Wasatch Fault Zone, Utah and Idaho

2020 ◽  
Author(s):  
Greg N. McDonald ◽  
Emily J. Kleber ◽  
Adam I. Hiscock ◽  
Scott E.K. Bennett ◽  
Steve D. Bowman
Keyword(s):  
Fault Zone ◽  
Special Study ◽  
Fault Rupture ◽  
Study Zone ◽  
Trace Mapping ◽  
Fault Trace ◽  
Wasatch Fault

scholarly journals The Traverse Ridge Paleoseismic Site and Ruptures Crossing the Boundary Between the Provo and Salt Lake City Segments of the Wasatch Fault Zone, Utah, United States

2021 ◽  
Vol 9 ◽  
Author(s):  
Nathan A. Toké ◽  
Joseph Phillips ◽  
Christopher Langevin ◽  
Emily Kleber ◽  
Christopher B. DuRoss ◽  
...  
Keyword(s):  
Fault Zone ◽  
Urban Areas ◽  
Salt Lake ◽  
Salt Lake City ◽  
The Holocene ◽  
Fault Segment ◽  
Segment Boundary ◽  
Lake City ◽  
Fault Trace ◽  
Wasatch Fault

How structural segment boundaries modulate earthquake behavior is an important scientific and societal question, especially for the Wasatch fault zone (WFZ) where urban areas lie along multiple fault segments. The extent to which segment boundaries arrest ruptures, host moderate magnitude earthquakes, or transmit ruptures to adjacent fault segments is critical for understanding seismic hazard. To help address this outstanding issue, we conducted a paleoseismic investigation at the Traverse Ridge paleoseismic site (TR site) along the ∼7-km-long Fort Canyon segment boundary, which links the Provo (59 km) and Salt Lake City (40 km) segments of the WFZ. At the TR site, we logged two trenches which were cut across sub-parallel traces of the fault, separated by ∼175 m. Evidence from these exposures leads us to infer that at least 3 to 4 earthquakes have ruptured across the segment boundary in the Holocene. Radiocarbon dating of soil material developed below and above fault scarp colluvial packages and within a filled fissure constrains the age of the events. The most recent event ruptured the southern fault trace between 0.2 and 0.4 ka, the penultimate event ruptured the northern fault trace between 0.6 and 3.4 ka, and two prior events occurred between 1.4 and 6.2 ka (on the southern fault trace) and 7.2 and 8.1 ka (northern fault trace). Colluvial wedge heights of these events ranged from 0.7 to 1.2 m, indicating the segment boundary experiences surface ruptures with more than 1 m of vertical displacement. Given these estimates, we infer that these events were greater than Mw 6.7, with rupture extending across the entire segment boundary and portions of one or both adjacent fault segments. The Holocene recurrence of events at the TR site is lower than the closest paleoseismic sites at the adjacent fault segment endpoints. The contrasts in recurrence rates observed within 15 km of the Fort Canyon fault segment boundary may be explained conceptually by a leaky segment boundary model which permits spillover events, ruptures centered on the segment boundary, and segmented ruptures. The TR site demonstrates the utility of paleoseismology within segment boundaries which, through corroboration of displacement data, can demonstrate rupture connectivity between fault segments and test the validity of rupture models.

Late Pleistocene Record of Off‐Fault Deformation and Vertical Slip Rates from the Wasatch Fault Zone, Utah: Implications for Fault Segmentation from Lake Bonneville Shorelines

2019 ◽  
Vol 109 (6) ◽  
pp. 2198-2215
Author(s):  
Julia Howe ◽  
Paul Jewell ◽  
Ronald Bruhn
Keyword(s):  
Fault Zone ◽  
Late Pleistocene ◽  
Salt Lake ◽  
Salt Lake City ◽  
Fault Rupture ◽  
Slip Rates ◽  
Lake Bonneville ◽  
Segment Boundary ◽  
Lake City ◽  
Wasatch Fault

Abstract In an effort to better understand the Pleistocene history of the Wasatch fault zone, we evaluate the deformation and displacement of the Bonneville and Provo high‐stand shorelines of Lake Bonneville along the Wasatch Front. We apply an automated shoreline elevation measurement application developed as part of this study to measure Lake Bonneville shoreline elevations along the Weber and Brigham City segments of the fault, adding to a previously published dataset of shoreline elevations on the Salt Lake City segment. Tectonically deformed shorelines on the footwall of the fault demonstrate elevation patterns that are inconsistent with the idea that the Pleasant View salient, a bedrock salient marking the segment boundary between the Weber and Brigham City segments of the fault, is a persistent barrier to fault rupture since the late Pleistocene. Shoreline features are elevated ∼20  m across the segment boundary as compared to shoreline features on the northern part of the Brigham City segment. We suggest the possibility that fault rupture through the Pleasant View salient has been common since the late Pleistocene and speculate that a similar relationship could exist between the Provo and Salt Lake City segments, based on similarities between the shoreline elevation patterns on the Brigham City and Salt Lake City segments of the fault. Vertical slip rates measured from displaced shorelines at the Pleasant View salient (Brigham City–Weber segment boundary) are generally higher compared to those at the Honeyville spur (Collinston–Brigham City segment boundary). Statistically significant vertical slip rates calculated from the Provo shoreline at the Pleasant View salient (0.8±0.5 to 0.9±0.6  mm/yr and 0.7±0.5 to 0.9±0.6  mm/yr) suggest that late Pleistocene vertical slip rates are slightly lower than Holocene rates; however, large uncertainties in the shoreline elevation measurements exist.

The Effectiveness of Fault Zone Regulations in California

1992 ◽  
Vol 8 (1) ◽  
pp. 57-77 ◽  
Author(s):  
Robert Reitherman
Keyword(s):  
Real Estate ◽  
Fault Zone ◽  
Active Faults ◽  
Fault Zones ◽  
Special Study ◽  
Single Family ◽  
Fault Rupture ◽  
Building Projects ◽  
Geologic Hazards ◽  
Special Studies

In 1990 a study was completed for the California Division of Mines and Geology on the effectiveness of California's fault zone regulations (the Alquist-Priolo Special Studies Zones Act and associated policies and activities). The Act, passed in 1972, instituted the following elements of a statewide mandatory approach to dealing with the hazard of surface fault rupture: state mapping of fault zones (Special Study Zones) where active faults are suspected; local government imposition of the requirement of a geologic study on new building projects within these Zones (with some single family dwellings and low-occupancy structures exempt); review procedures for the studies submitted by an applicant's geologist; prohibition of the siting of projects on active faults; notification of real estate purchasers that a property is located within a Zone. This paper presents the results of that evaluation and comments more broadly on applying the Alquist-Priolo model to other regions and to other geologic hazards.

Displacement and stress field along part of the Cobequid Fault, Nova Scotia

1969 ◽  
Vol 6 (5) ◽  
pp. 1095-1104 ◽  
Author(s):  
Gerhard H. Eisbacher
Keyword(s):  
Stress Field ◽  
Fault Zone ◽  
Maximum Compressive Stress ◽  
Clastic Rocks ◽  
The North ◽  
Total Displacement ◽  
Displacement Vectors ◽  
Lateral Displacements ◽  
Fault Trace ◽  
Southern Flank

The east-trending Cobequid Fault separates pre-Carboniferous rocks of the Cobequid Mountains to the north from Carboniferous clastic rocks along the southern flank of the mountains. A detailed study of the fault zone revealed tie predominance of right-lateral displacements. The orientation of the stress field that existed during deformation along the fault trace was determined by the study of systematic fractures in pebbles within Carboniferous conglomerate. Maximum compressive stress was aligned in a NW–SE direction, being compatible with the orientation of the displacement vectors in the fault zone. Transcurrent movement along the Cobequid Fault occurred in late Pennsylvanian time and involved both Carboniferous and pre-Carboniferous rocks; total displacement is unknown.

Sign in / Sign up

Export Citation Format

Share Document