Mendenhall seminar @ USGS: Quakes on Wasatch Fault

Mendenhall Postdoctoral Research Seminar

Scott Bennett, USGS – Golden, CO

When: Wednesday, March 4, 2015 – 12 Noon

Where: Via WebEx and National Center, Room 1C400 (Visitor Center)

Details:

How Big and How Frequent Are Earthquakes on the Wasatch Fault in Utah? Using Paleoseismology and Lidar to Evaluate Earthquake Rupture Patterns

The 350-km-long Wasatch fault zone (WFZ) consists of ten west-dipping normal fault segments at the eastern boundary of the Basin and Range Province, Utah. Fresh fault scarps at the foot of the Wasatch Mountains indicate that large earthquakes have recently occurred on the WFZ, as first documented by G.K. Gilbert in the 1880s. The most recent earthquake predates written records and European settlement in the 1840s, leaving paleoseismologists to the tasks of determining the size and frequency of past earthquakes and estimating the current seismic hazard. Over three decades of paleoseismic trench research having produced abundant earthquake timing data along the central WFZ. These data have been interpreted as evidence for ruptures during large (M≥7.0) Holocene (<11 ka) earthquakes that were restricted to a single fault segment. However, uncertainties in earthquake timing permit earthquake correlations that allow for longer ruptures that spanned segment boundaries. To improve rupture length estimates and evaluate the persistence of Holocene rupture termination at central WFZ segment boundaries, a collaborative team from the USGS and the Utah Geological Survey conducted four paleoseismic trench studies near these boundaries. Data from paleoseismic trenches constrain the timing and surface displacement of Holocene earthquakes and, when integrated with results from adjacent trenches, provide new constraints on surface rupture length and earthquake magnitude. We have also analyzed new high-resolution (8 pts/m2) airborne lidar data along the central WFZ, which provide unprecedented elevation information for lake shoreline features associated with late Pleistocene Lake Bonneville. These faulted shoreline features serve as strain markers across the WFZ, permitting precise fault offset estimates near WFZ segment boundaries for the past ~10­–20 kyr. I will summarize paleoseismic and geomorphic constraints on the extent of recent surface-rupturing earthquakes and evidence for non-persistent rupture terminations at segment boundaries along the central Wasatch fault zone. These findings will permit a more accurate characterization of the earthquake hazard in the Wasatch Front region.

WebEX Info

Topic: (20) Mendenhall Seminar: Scott Bennett
Date: Wednesday, March 4, 2015
Time: 12:00 pm, Eastern Standard Time (New York, GMT-05:00)
Meeting number: 711 911 008
Meeting password: (This meeting does not require a password.)
Host Key: 819057

Click the following link to view or edit your meeting information, or to start your meeting.

https://usgs.webex.com/usgs/j.php?MTID=ma9173d91eae3b204e00fa0183c819b10

Teleconference: National Center in Reston, VA Dial In: x4848
DOI Dial In Number: 703-648-4848
Non-DOI Toll Free Dial In Number: 1-855-547-8255*
Security Code: 91930 followed by the # sign

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