← Back to Sessions

The Rocks That Did Not Fall: A Multidisciplinary Analysis of Near-Source Ground Motions From an Active Normal Fault

Description: 

On July 08, 2021 a M6.0 normal faulting event rocked Little Antelope Valley near the California-Nevada border, the latest major earthquake to occur in the central Walker Lane. Earthquake hazard along the eastern Sierra south of Reno is dominated by range-bounding normal faults like the ones playing host to this earthquake sequence, motivating our effort to better characterize it. In the 1990s, a series of field surveys in this region identified numerous fragile geologic features that were deemed unlikely to remain standing in the event of strong shaking. This included several sites in Meadowcliff Canyon, on the hanging wall of the 2021 event and only 6 km from the rupture surface. Despite this proximity, the fragile geologic features in the canyon remain intact today. In this work, we endeavor to unravel this mystery by combining advanced source characterization techniques with detailed analyses of strong ground motion. High-precision hypocentral locations reveal a clear mainshock fault plane striking north-north-west and dipping down to the east. The mainshock nucleated near the base of this structure, which did not break the surface but triggered aftershocks updip and to the north and south. Application of Bayesian source spectral analyses indicate that the mainshock event had a relatively high-stress drop (~ 20 MPa), and that within the aftershock sequence, there is a clear trend of increasing stress drop with hypocentral depth along the fault plane. Peak ground acceleration and velocity recordings at regional stations agree well with the NGA-West2 suite of active crustal ground motion models, and would predict PGA of ~0.3g at the Meadowcliff site, an amplitude likely sufficient to topple fragile geologic features. However, our preliminary analyses indicate that while the level of ground motion may be high, the pulse duration for this high stress-drop event at the Meadowcliff site may be too short to supply the impulse necessary to damage these features. This study provides a unique vantage point from which to interpret rarely observed strong motion recording from close to an active normal fault.

Session: Normal Faults: From Source to Surface [Poster]

Type: Poster

Date: 4/18/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Daniel T. Trugman

Student Presenter: No

Invited Presentation: 

Authors