Imaging fault scarps and fault zone evolution near an oceanic transform fault using high-resolution bathymetry

Curtis W. Baden, George E. Hilley, Samuel Johnstone, Robert M. Sare, Felipe Aron, Holly Young, Christopher M. Castillo, Lauren Shumaker, Johanna M. Nevitt, Tim McHargue, & Charles Paull

Submitted August 15, 2016, SCEC Contribution #7026, 2016 SCEC Annual Meeting Poster #111

Oceanic transform faults play a fundamental role in plate tectonics by linking spreading ridge segments to each other. While ubiquitous, they produce far fewer large earthquakes than faults along other tectonic boundaries. We use high-resolution (1 m) deep-water bathymetry to examine the structure of, and offset along, transform faults in the Gulf of California. Collected by an autonomous underwater vehicle (AUV) by the Monterey Bay Aquarium Research Institute in March 2012, bathymetry and shallow seismic data provide detailed observations of fault-zone geomorphology of an active transform fault hosted in an area transitioning from continental to oceanic crust.

We found that these transform faults consist of an array of fault strands that span the observational extent of the AUV deployment, and whose activity varies in space and time to produce a complex fault zone not unlike onshore, seismogenic strike-slip faults. Fault scarps and scarp-like features were mapped and categorized by degree of lateral continuity and consistency in trend. Laterally continuous features trending parallel to the overall transform fault zone exhibit higher amplitudes and younger morphologic ages, as measured by diffusion modeling of the profile curvature of mapped features.

We observed a series of small submarine fans that were offset along the main, apparently active transform fault strand by 10-25 m. The large and consistent offsets of these synchronously formed features may be explained by seismically induced mass wasting prior to offset by either smaller-magnitude earthquakes or creep. Up to two sets of nested fan deposits of similar volume appear in CHIRP profiles collected by a subbottom profiler attached to the AUV, suggesting that fans formed periodically in response to destabilization. If correct, these inferences imply that oceanic transform faults may display both creep and stick-slip behavior at various times, which is consistent with their globally observed low seismic moment release rate.

Key Words
high-resolution bathymetry, fault zone geomorphology, oceanic transform fault, Gulf of California

Citation
Baden, C. W., Hilley, G. E., Johnstone, S., Sare, R. M., Aron, F., Young, H., Castillo, C. M., Shumaker, L., Nevitt, J. M., McHargue, T., & Paull, C. (2016, 08). Imaging fault scarps and fault zone evolution near an oceanic transform fault using high-resolution bathymetry. Poster Presentation at 2016 SCEC Annual Meeting.


Related Projects & Working Groups
Earthquake Geology