SCEC Award Number 20152 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Using 3D seismic data to study damage zones
Name Organization
Emily Brodsky University of California, Santa Cruz
Other Participants Alongi, Travis (Graduate Student, UC Santa Cruz)
Kluesner, Jared (USGS, PCMSC)
Brothers, Danny (USGS, PCMSC)
SCEC Priorities 2d, 3a, 3e SCEC Groups FARM, Geology, SAFS
Report Due Date 03/15/2021 Date Report Submitted 05/06/2021
Project Abstract
Damage zones can observationally link earthquake physics to mechanics beyond elasticity. The extent of distributed damage affects earthquake rupture propagation, its associated strong motion, and perhaps even the distribution of seismicity around the fault. There are very few 3D observations of damage. Here we constrain the Palos Verdes Fault damage zone offshore California using existing 3D seismic reflection datasets. We use a novel algorithm to identify faults and fractures in a large seismic volume consisting of 4.8 x 108 points and examine the spatial distribution of damage. Our results from the Palo Verdes Fault Zone show that damage is focused around mapped faults and that damage decays with distance from the fault, reaching the undisturbed and mostly unfractured background at a distance of 2.2 km from the fault. The identified damaged zone appears to obey power law behavior at the outer edges of a 3 strand fault network, with a power law exponent of 0.68, this trend extrapolates to a probability of 1 at the mapped fault location. The power law like scaling of apparent fractures with distance from fault is striking similar to outcrop studies, but extends to distances seldom accessible. We find that fracturing in the damage zone increases with depth to around 500 m and at greater depths may be more strongly controlled by lithological grain size, induration, and unit thickness.
Intellectual Merit This project uses active source imaging to measure fault zone damage in three dimensions and parameterize it in a way that is accessible to numerical models and geological observations. It provides a missing link in connecting the non-elastic part of the earthquake process to quantifiable observations.
Broader Impacts This funding has supported graduate student Travis Alongi, who is an non-conventional reentry student. Alongi is making excellent progress and passed his qualifying exams this year.

In addition, the grant has launched a partnership between the USGS Coastal Science office and SCEC. This Coastal office was not previously engaged in SCEC despite their mandate to study all offshore faults of California. USGS Coastal scientists have now begun attending SCEC meetings and are engaged in the collaboration.

Exemplary Figure Figure 3. Perspective view of Thinned Fault Likelihood attribute results in high confidence ranges (0.75–1) along the Palos Verdes fault zone. The rainbow colormap ranges from red to violet, where violet is the greatest probability of a fault. The attribute is projected on a strike-perpendicular line and an interpreted and Monterey horizon. Note the variable width of the damage zone along strike, and how the results for thinned fault likelihood are concentrated around the fault.