SCEC Award Number 21182 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 Travis Alongi, Graduate Student
Danny Brothers and Jared Kluesner, Collaborators
SCEC Priorities 2d, 3a, 3e SCEC Groups Geology, FARM, Seismology
Report Due Date 03/15/2022 Date Report Submitted 04/13/2022
Project Abstract
Damage zones can observationally link earthquake physics to mechanics beyond
elasticity. The extent of distributed damage affects an earthquake’s propagation,
its associated strong motion and perhaps even the distribution of seismicity
around the fault. However, 3D observations of damage remain limited. Here we
constrain damage zones offshore California using existing 3D seismic reflection
datasets. Our current results from the Palo Verdes Fault zone show that damage
is most concentrated around mapped faults and decays exponentially to a
distance of 2.2 km, where fracturing with distance from the mapped fault and
reaches a clearly defined and relatively undamaged background values for all
examined depths and lithologies (450 m to 2.2 km). We also find that the damage
decay and background level damage in the background differs for each unit
indicating that lithology is a major control on damage variability, but not depth.
Qualitatively less brittle units, such as siltstone, appear to have damage that
decays slowly, but also have low background damage levels and the opposite is
true for sandstone and conglomerate. Surprisingly, these differences in damage
decay and background level balance each other out to result in a consistent
damage zone width regardless of lithology or depth. We will follow up on these
observations by exploring potential damage asymmetry and the relationship to
folding. This work is being performed by UC Santa Cruz graduate student Travis
Alongi in collaboration with Danny Brothers and Jared Kluesner of the USGS.
Intellectual Merit This work has introduced a fundamentally new method to study damage zones, which are thought to play a major role in earthquake rupture dynamics. We can know provide true 3-D images in-situ of the damage zone of a major fault.
Broader Impacts This work has supported graduate student Travis Alongi, who is a mature re-entry student embarking on a PhD in geophysics. It has also supported a new collaboration between the USGS Coastal Hazards Office and SCEC that has extended the applicability of SCEC science to the offshore environment.
Exemplary Figure Figure 2. The left figure shows an example of dip-steered diffusion filtered seismic data in black
and white color scale(location shown in Figure 1). Overlain, the vertical teal line is the manually
mapped central strand, the dark purple is the western strand, and the navy blue is the eastern
strand. The transparent to red is the Thinned Fault Likelihood fault detections. The multi-color
horizontal lines are mapped 3D horizon-surfaces projected onto the inline and mark lithological
contacts or unconformities that have been tied to well logs. These horizons are used as upper
and lower bounds to constrain the fracture probability as a function of distance for each lithology
within the Chevron volume, which are shown in the semi-log plots on the right of the figure. Note
the different exponential fit slopes in different geologic units and variable background (horizontal