All, the abstract below is of interest. I have been working on and off on this fault system for about 15 years, and found out a couple of weeks ago that I should be funded for 2014 to work on it more. It extends to west of Point Conception, so indeed it is a very long oblique thrust system. The largest historical quakes were M6.7 or so on this system, except 1812, which was >M7. The problem with the 1812 quake is there is not agreement on where it was. The San Cayetano fault was trenched and there is a 5 m slip event in that trench that is 17 century or later. The authors propose 1812. I suspect 1812 was out near Santa Rosa Island, for other reasons.

T23C
CONTROL ID: 1818920
TITLE: Evidence for large-magnitude paleo-earthquakes on the Ventura fault: Implications for earthquake recurrence, fault slip rate, and seismic hazard assessment in southern California

AUTHORS (FIRST NAME, LAST NAME): Lee J Mcauliffe1, James Francis Dolan1, Judith Hubbard2, John H Shaw2, Thomas L Pratt3, Edward J Rhodes4
INSTITUTIONS (ALL): 1. Department of Earth Sciences, University of Southern California, Los Angeles, CA, United States.
2. Department of Earth & Planetary Sciences, Harvard University, Cambridge, MA, United States.
3. US Geological Survey, Seattle, WA, United States.
4. Department of Earth and Space Sciences, University of California, Los Angeles, Los Angeles, CA, United States.
ABSTRACT BODY: New borehole, high-resolution seismic reflection, and geochronologic data reveal the ages and displacements of the two most recent large-magnitude earthquakes on the Ventura fault, the central segment of a large, multi-fault reverse fault system that extends for >200 km along the southern edge of the central and western Transverse Ranges fault system. Based on geomorphology and analysis of high-resolution seismic data acquired in 2010, we drilled 17 hollow stem auger boreholes and cone penetrometer tests along two transects across the locus of most recent folding above the Ventura fault. At Day Road in downtown Ventura, our 23-m-deep boreholes revealed a well-bedded alluvial section with many units that are traceable continuously along the entire 375 m length of the transect. Stratigraphic relationships indicate that the prominent topographic scarp at this site records ~6 m of uplift during fold growth in the most-recent earthquake on the underlying Ventura blind thrust ramp. Similarly, sedimentary growth observed in the borehole cross section indicates ~4.5 m of growth during the penultimate event, with an event horizon located at the base of a growth interval between 4 and 8.5 m depth south of the scarp. Six 14C and 14 OSL ages collected from the four hollow-stem auger boreholes at this site constrain the timing of the two most recent events on the Ventura blind thrust fault to post-2900 B.P. and 4700 ± 350 to 5460 ± 330 years before present; dating of additional shallow luminescence samples should help narrow the age range of the MRE. The large amounts of uplift in the two folding events indicate that they formed in response to large-displacement, and therefore large-magnitude earthquakes, likely involving rupture of the Ventura fault together with thrust ramps to both the west (e.g., Pitas Point fault) and east (Southern San Cayetano and eastern San Cayetano faults). These thrust faults form the middle section of a >200-km-long, east-west belt of large, interconnected reverse faults that extends along the southern edge of the Transverse Ranges. Although each of these faults represents a major seismic source in its own right, we are exploring the possibility of even larger-magnitude, multi-segment ruptures that may link these faults to other major faults to the east and west. The proximity of this large reverse-fault system to several major population centers, including the metropolitan Los Angeles region, and the potential for tsunami generation during offshore ruptures of the western parts of the system, emphasize the importance of understanding the behavior of these faults for seismic hazard assessment.