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Combining Dark Fiber and Seismic Interferometry to Measure Physical Properties of Faults in the Imperial Valley

Description: 

Using interferometry, aftershocks of large events can be treated as a network of virtual seismometers to allow detailed measurements along the fault trace. The Virtual Seismometer Method (VSM) is a technique that provides precise estimates of the Green Function (GF) between earthquakes (Curtis et al., 2009; Hong and Menke, 2006). This isolates the portion of the data that is sensitive to the source region and dramatically increases our ability to see into tectonically active features, such as at depth in active fault zones.

By comparison, fiber optic sensors enable dense (meter-scale) sampling of the seismic wavefield over large distances (10's of km). When an earthquake is recorded by such an array, we see detailed ground motion, including highly scattered arrivals that are a record of heterogeneities along the entire path between the source and each channel along the length of the fiber. When used in combination, these two technologies allow us to obtain high quality measurements of physical properties around active faults, even with small magnitude events.

Here, we present results from the Imperial Valley Dark Fiber Experiment, which recorded thousands of local earthquakes during its deployment, including a large swarm near the southern end of the Salton Sea and a sequence of events along the Imperial Fault, south of the array. We illustrate the methodology and the sensitivity of the technique with respect to earthquake magnitude, distance and relative geometries, and contrast the application of dense DAS fiber with more traditional seismic arrays. We inverted the resulting GFs to measure the seismic velocity and attenuation of the active region, allowing us to identify large structural heterogeneities and estimate the local faulting and fracture patterns.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

Session: Above the Seismogenic Zone: Fault Damage and Healing in the Shallow Crust [Poster]

Type: Poster

Date: 4/19/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Eric Matzel

Student Presenter: No

Invited Presentation: 

Authors