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Late Pleistocene and Holocene Paleoseismology and Deformation Rates of the Pleasant Valley Fault (Nevada, USA)

Description: 

The Pleasant Valley Fault (PVF) generated a magnitude 7.3 earthquake on October 2nd, 1915. Scarps occurred along a set of 4 en-echelon arranged extending ~60 km long the west flank of the Tobin Range in Nevada. The earthquake was the first of a sequence of earthquakes that defines the Central Nevada Seismic Belt (CNSB), most prominent among them the ~M7 1932 Cedar Mountain, the 1954 Dixie Valley, and Fairview Peak earthquakes. Average displacements along the Pleasant Valley fault averaged ~2m (maximum 5.8 m) in 1915, commonly along preexisting scarps from yet earlier earthquakes.

We excavated 5 new paleoseismic trenches across the 1915 rupture, at 4 locations in the central two segments, exposing a colluvial stratigraphy showing multi-events at each site. The colluvial units are generally gravel to sandy sediments and at one site a tephra layer is present. The alluvial fan displaced and the colluvial units present different degrees of soil development, occasionally carbonate enriched. To constrain the paleoseismology timings, ~30 luminescence and one tephrochronology samples were collected. Preliminary results suggest 3 or 4 events pre-1915 during the last ~30 ka, suggesting a recurrence period of ~7 ka with the penultimate event to have occurred ~9 ka ago.

To estimate the ages of the alluvial fans displaced along the mountain front and calculate the long-term slip rates associated with the fault system, we sampled boulders (when available) and sediment for depth profiles for 36Cl terrestrial cosmogenic nuclide dating at 6 sites at relative different positions of the fans and fault system. Altogether, these results are the first to provide information about the timing, frequency, and spatial distribution of surface ruptures along the PVF during the Holocene and late Pleistocene and the average rate at which the PVF slips on the short and long term, thus filling a gap in the seismicity knowledge in the CNSB.

Session: From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia

Type: Oral

Date: 4/20/2023

Presentation Time: 04:45 PM (local time)

Presenting Author: Paula M. Figueiredo

Student Presenter: No

Invited Presentation: 

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