SCEC Award Number 19105 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title The Mid-Channel thrust and its role in large, multi-segment earthquakes on the Ventura-Pitas Point fault system
Name Organization
John Shaw Harvard University
Other Participants Andreas Plesch
Jessica Don
SCEC Priorities 1a, 3a, 2e SCEC Groups Geology, CXM
Report Due Date 03/15/2020 Date Report Submitted 03/26/2020
Project Abstract
This past year’s work focused on analysis of 2- and 3-D industry seismic reflection data and extensive well control, including dipmeter logs and horizon tops, to constrain the geometry and kinematics of the offshore Ventura - Pitas Point fault system (Redin et al., 1998; Don et al., 2019). Based on these data constraints, we generated a series of balanced cross sections using both inverse and forward modeling based on fault-related folding theories (Figure 3). These sections demonstrate that the offshore fold geometries are consistent with a ramp-flat-ramp geometry for the Pitas Point fault, with the mid-crustal flat located in the Miocene Monterey/Rincon shales. This geometry is nearly identical to that of the onshore Ventura fault (Hubbard et al., 2014), and thus supports the proposed linkage of the Ventura and Pitas Point faults (Sorlien and Nicholson, 2015; Levy et al, 2019).
Intellectual Merit This research directly addresses the prospects for large, thrust fault earthquakes on the Ventura-Pitas Point fault system in the Western Transverse Ranges. The work directly contributes to our knowledge of active fault systems and associated hazards, and also furthers the methodologies for characterizing active blind thrust faults. This work is an outgrowth of the Ventura Special Fault Study area.
Broader Impacts This research directly contributes to the improvement of SCEC Community Models (CFM) and will inform future earthquake rupture forecasts (ERF's) used for UCERF and similar regional hazard assessments. The project has involved a female graduate student at Harvard, contributed to educational courses at Harvard University serving our undergraduate majors.
Exemplary Figure Figure 3: Cross sections showing offshore geometry of the Pitas Point fault system and its linkage with the Mid-Channel fault system (location Figure 1). A) Uninterpreted seismic reflection profile showing data projected from nearby wells. B) Interpreted seismic reflection profile showing linkage of Pitas Point and Mid-Channel fault systems. Dip changes, cutoffs, and discontinuous reflectors constrain the location of the Mid-Channel and Pitas Point thrusts. C) Geologic cross section of Dos Cuadras anticline / Pitas Point fault, Pitas Point anticline / Mid-Channel fault, and Mid- Channel anticline / Mid-Channel fault. Red lines are faults, with arrows indicating slip sense. Dark blue-green dashed lines are axial surfaces. Horizons colored based on stratigraphy, with internal stratigraphy shown in yellow. Dashed red lines are inactive faults or bedding parallel thrusts.