Determining Slip Rates and Deformation History of Offshore Faults Using AUV and ROV
Conrad, J. E.; Paull, C. K.; McGann, M.; Edwards, B. D.; Ryan, H. F.; Caress, D. W.; and Lundsten, E.
The seismic hazard posed by faults offshore southern California is not well understood because the slip rate and rupture frequency of offshore faults are difficult to determine. Numerous active and potentially hazardous faults are offshore southern California but not included in probabilistic seismic hazard assessments because this information is unavailable. An important focus of ongoing research, therefore, is to develop and apply methods to determine slip rates associated with offshore faults.
High-resolution bathymetric surveys were collected with an autonomous underwater vehicle (AUV) developed at the Monterey Bay Aquarium Research Institute to generate 1-m bathymetric grids of the seafloor that have a vertical resolution of 11 cm and to simultaneously collect CHIRP reflection profiles with similar resolution within selected areas off southern California. These data were then used to guide a remotely operated vehicle (ROV) equipped with a vibracoring system capable of collecting precisely located sediment cores that are up to 1.5 m length as well as horizontal cores from the faces of outcropping beds.
These methods were used to date offsets in submarine channel walls and a slump scar cut by the San Diego Trough and Palos Verdes faults, yielding slip rates of 1-2 mm/yr and 4-5 mm/yr, respectively. A transect of 9 vibracores collected ~25 m apart across the Palos Verdes fault provide data similar to trenching on land and demonstrate the occurrence of Holocene faulting. The combination of high-resolution bathymetry, seismic reflection data, and 14C dating of precisely located samples shows promise as a technique to determine slip rates and deformational history of submarine faults.
AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013