Paleoseismologic evidence for large-magnitude (M-w 7.5-8.0) earthquakes on the Ventura blind thrust fault: Implications for multifault ruptures in the Transverse Ranges of southern California

Detailed analysis of high-resolution seismic reflection data, continuously cored boreholes and cone penetrometer tests (CPTs), and luminescence and 14 C dates from Holocene strata folded above the tip of the Ventura blind thrust fault constrain the ages and displacements in the two most recent earthquakes. These two earthquakes are recorded by a prominent surface fold scarp and a stratigraphic sequence that thickens across an older buried fold scarp, and occurred soon after about 700-900 years ago (most recent event) and between 3-5 ka (penultimate event). Minimum uplift in these two scarp-forming events was ~6 m for the most recent earthquake and ~4.5 meters for the penultimate event. Individual uplifts of this amount require large magnitude earthquakes, probably in excess of Mw7.5 and likely involving rupture of the Ventura fault together with other Transverse Ranges faults to the east and west. The proximity of this large reverse-fault system to major population centers, including the greater Los Angeles region, and the potential for tsunami generation during ruptures extending offshore along the western parts of the system, highlight the importance of understanding the complex behavior of these faults for probabilistic seismic hazard assessment.