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Holocene behavior of the Brigham City segment: implications for forecasting the next large-magnitude earthquake on the Wasatch fault zone, Utah

Bulletin of the Seismological Society of America

By:
, , and
DOI: 10.1785/0120110214

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Abstract

The Brigham City segment (BCS), the northernmost Holocene‐active segment of the Wasatch fault zone (WFZ), is considered a likely location for the next big earthquake in northern Utah. We refine the timing of the last four surface‐rupturing (~Mw 7) earthquakes at several sites near Brigham City (BE1, 2430±250; BE2, 3490±180; BE3, 4510±530; and BE4, 5610±650 cal yr B.P.) and calculate mean recurrence intervals (1060–1500  yr) that are greatly exceeded by the elapsed time (~2500  yr) since the most recent surface‐rupturing earthquake (MRE). An additional rupture observed at the Pearsons Canyon site (PC1, 1240±50 cal yr B.P.) near the southern segment boundary is probably spillover rupture from a large earthquake on the adjacent Weber segment. Our seismic moment calculations show that the PC1 rupture reduced accumulated moment on the BCS about 22%, a value that may have been enough to postpone the next large earthquake. However, our calculations suggest that the segment currently has accumulated more than twice the moment accumulated in the three previous earthquake cycles, so we suspect that additional interactions with the adjacent Weber segment contributed to the long elapse time since the MRE on the BCS. Our moment calculations indicate that the next earthquake is not only overdue, but could be larger than the previous four earthquakes. Displacement data show higher rates of latest Quaternary slip (~1.3  mm/yr) along the southern two‐thirds of the segment. The northern third likely has experienced fewer or smaller ruptures, which suggests to us that most earthquakes initiate at the southern segment boundary.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Holocene behavior of the Brigham City segment: implications for forecasting the next large-magnitude earthquake on the Wasatch fault zone, Utah
Series title:
Bulletin of the Seismological Society of America
DOI:
10.1785/0120110214
Volume
102
Issue:
6
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:
2265
Last page:
2281
Country:
United States
State:
Utah