This quake has been confirmed by seismologist, and is a 3.7. If it does not move, it is near the Lion's Head fault. We mapped part of this fault (Sorlien et al. Geology, 1999). I just happen to have a seismic reflection profile across this fault-lots of little gems in my 7' by 14' home office here in suburbia. The Lion's Head fault a couple km SW of PT Sal has about 3 km of N-side up structural relief on about a 5 million year horizon....Work by, Douglas Clark (1990 field trip guide) associated with the PG&E work shows the offset of a marine terrace by this fault at a rate of 0.012-0.018 mm/yr-exceptionally slow. But, if most of the deep slip is absorbed in the fold, it need not make it to the surface. Clark says the block between the S-dipping Orcutt Frontal fault and the N-dipping Lion's head fault is uplifting with respect to sea level at 0.14 to 0.17 mm/yr....a bit faster, but not exactly screaming....the question is whether the structural relief is growing faster than that...

I don't feel like pulling out my work maps to see where I am exactly-but I think I see the Lion's head fault on this profile-it has a moderate apparent north dip, is blind (except maybe a backthrust-), and has a fault-plane reflection. I can see this fault down to about 2 km depth. The fault is probably long enough to have a quake as big as the one the other day.....but at that slow slip rate/uplift rate, could not have a large quake very often.......someone else can look this fault up on line in the SCEC data base to see what is official.....I'm supposed to provide a digital fault map of a trace of the Hosgri fault, but probably ought to grab some data and make a structure contour map on the fault instead....but it is hard to do this without additional funding, and this is not quite a NEHRP-fundable project.

The co-authors of the paper mentioned above were involved in our interpretations of the late 1990s....Chris