This could be a real bad idea to post this without OK of co-authors..and without the papers being accepted (or even complete) .but I wrote it in a couple hours today, and we had recently had some discussion of writing on this page, and it might be useful to get some feedback. I reserve the right to not use comments/editing...nut I will read them.

The purpose of this abstract is for an invited talk that I will be giving in a couple of weeks at Cal State Northridge. I assume my audience will be mostly earth science students and some faculty.

There will be a SCEC workshop late this month on some related issues that I will go to and may or may not present something on.....and I will probably send this abstract to one of the conveners to see what he thinks...maybe have him distribute it to the attendees if he sees fit...

So...is this readable to people with some earth science background (Penny, Canie, Don, Roger, for example). Is it interesting? What is not clear? Amateur scientists?

So, how come I can write this in perhaps 2 hours but can't seem to write papers quickly?
Chris

Fault bends in 3D, vertical and horizontal motions, the Palos Verdes and Santa Monica Mountains anticlinoria and the faults upon which they fold
Christopher Sorlien (UCSB), Kris Broderick (now at Exxon-Mobil), Leonardo Seeber (LDEO), Marc Kamerling (Venoco).

With contributions by Ray Sliter (USGS), Mike Fisher (USGS), Bill Normark (USGS), and Bruce Luyendyk (UCSB).

The most damaging earthquakes to Los Angeles over the last couple decades have been on blind or partially blind thrust faults. Complex anticlines with lengths of tens of km (“anticlinoria”) absorb the thrust component of slip on the underlying faults. “Restraining trends” between double bends in non-vertical strike-slip faults contribute vertical motions but cannot explain the anticlinoria. Since we know the 3D geometry of the Santa Monica-Dume fault, we use trigonometry to calculate the expected increase of structural relief for a full range of slip directions and slips magnitudes, and compare this to the measured structural relief of a ~4 Ma horizon. The moderately-dipping offshore Santa Monica fault is thus a left-lateral fault with oblique left-reverse slip in its Dume restraining trend, and clockwise rotation of its northern hanging-wall. The Santa Monica Mountains anticlinorium extends far to the east of that restraining trend and therefore cannot be explained by the shallow slip on the Santa Monica-Dume fault. There must be a blind thrust component deeper on that fault, or there must be blind thrust slip on an underlying reactivated Miocene detachment fault. The Malibu Coast fault also contributes to onshore vertical motions, being vertical and left-lateral offshore and dipping north and being left-reverse oblique onshore.

The Palos Verdes fault has an onshore restraining trend that contributes to uplift of the Palos Verdes Hills. However, the offshore southwest limb of the Palos Verdes anticlinorium is linear and continuous for 50 km before stepping to the south. The 3D orientation of the Palos Verdes fault cannot explain the full Palos Verdes anticlinorium. Instead, we interpret a NE-dipping partially blind thrust-separation fault whose tip is near the base of the 800 m-high seafloor San Pedro Escarpment. In our regional work, we find that offshore areas are wet because they are subsiding, and onshore coastal areas are dry because they are uplifting, with only very rapid sedimentation able to keep subsiding areas dry. Santa Monica basin likely subsided at almost 1 mm/yr since the Miocene. If San Pedro Basin is subsiding at a similar rate, then significant blind thrust slip on this San Pedro Escarpment fault is required beneath onshore and offshore Palos Verdes anticlinorium to keep its crest from sinking. Our representation of the San Pedro Escarpment fault aligns in 3D with the Compton thrust ramp of Shaw and Suppe (1996) as represented in the SCEC Community Fault Model (CFM), and thus may be the same fault. Modeling of 4.5 mm/yr GPS-based shortening in northern Los Angeles by Argus et al. (2005) suggests 9 mm/yr of slip on a blind thrust fault. This is far more than has been proposed for the Puente Hills thrust (Shaw and Shearer, 1999), so there is plenty of leftover slip available beneath the Palos Verdes anticlinorium, part of which may be on deep faults that extend far offshore. If the Compton thrust ramp is extended offshore to the base of San Pedro Escarpment, its area doubles. If deep faults are creeping only north of downtown Los Angeles (Argus et al., 2005), then the Compton thrust could be seismogenic beneath much of Los Angeles basin.