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Seismic Monitoring of Fragile Geologic Features Near Avila Beach, Ca.

Description: 

Fragile Geologic Features (FGF’s) are increasingly being investigated to provide independent constraints on seismic hazard analysis results, and in particular estimates of the elapsed time period (fragility age) since the occurrence of ground shaking strong enough to knock down the feature. In places where the hazard curves for ground motion exceedance are inconsistent with the length of time a feature has been exposed to those ground motions, seismic monitoring experiments can provide insights into the local site response in the vicinity and adjacent to these features, which can reduce uncertainty in the hazard analysis and improve information gained from the FGF survival. In this experiment, multiple FGF’s are located on a chert formation that protrudes out of the surrounding marine terrace sediments. Seismic instruments have been deployed at three sites on the marine terrace around the chert formation and on two distinct chert outcrops adjacent to the FGF’s. The terrace sites includes both 3-component surface accelerometers and 3-component broadband seismometers. The outcrop sites are 3-component accelerometers, anchored to the chert. The array consists of 24 channels total sampled continuously at 200 sps, and transmitted real-time to UCSB via IP radio and cellular telemetry. The terrace stations form an approximate isosceles triangle, 130 meters on each side, with one station within 10 meters of the western most FGF, and the other FGF outcrop along the center of the southern side of the triangle. Extensive site characterization has been conducted using non-invasive multi-method surface techniques to determine the subsurface structure around these sites. While seismic activity is relatively quiet in this part of the California central coast, there have been a number of regional events, and a few small local events that have been recorded since the array was deployed in late 2018. We provide an overview of the array and present site response analysis of the events recorded to date. The event data are available at the UCSB data portal, https://neesbolt.eri.ucsb.edu/data-portal.

Session: From Sensors and Networks to Site Characterization and Site Response: Coming Full Circle

Type: Oral

Date: 4/18/2023

Presentation Time: 02:45 PM (local time)

Presenting Author: Jamison Steidl

Student Presenter: No

Invited Presentation: 

Authors