Utilizing Distributed Acoustic Sensing and Ocean Bottom Fiber Optic Cables for Fault Zone Characterization

Session: Photonic Seismology
Type: Oral
Date: 4/30/2020
Time: 08:30 AM
Room: 215 + 220
Description: 

Marine fault zones, particularly fault structures immediately beneath the ocean floor, are often poorly characterized or unmapped due to a lack of both visible exposure and coverage by high-resolution seismic datasets. One sensing resource that may provide observational access to these systems are the existing networks of ocean bottom fiber optic cables; through the use of distributed acoustic sensing (DAS), these networks can be transformed into dense sensing arrays capable of broadband recording of both seismic events and the ambient noise wavefield. Recent studies (Lindsey et al. 2019, Williams et al. 2019, Sladen et al. 2019) have provided a first glimpse of the capacity of this approach in several off-shore contexts using a range of photonic interrogators and cable geometries.

We present further analysis of a marine DAS dataset, discussed in Lindsey et al. (2019), for fault zone characterization. This dataset utilized an existing scientific cable, connecting a shore station to the Monterey Accelerated Research System (MARS) cabled observatory, for DAS recording over a four-day period in 2018. Prior analysis of this dataset revealed zones where local seismic events generated converted surface waves; these events were co-located with several existing and unmapped fault zones and were presumed to be indicators of faulting. We utilize ambient noise techniques to further probe the characteristics of these fault zones, targeting internal shear velocities and scattering properties. In particular, we migrate scattered Scholte waves, observed in recovered empirical Green’s functions, to better localize the scattering features. These observations, coupled with shear wave inversions, spectral analysis and interpretive forward modeling of scattering response, provide improved constraints on these marine fault zones and highlight one of many possible geophysical uses of the marine cable network.

Presenting Author: Jonathan B. Ajo-Franklin

Authors