[Skywise]

http://www.livescience.com/51034-offshor...ornia.html

Massive undersea earthquakes off the coast of California could send a tsunami crashing into Los Angeles or San Diego, new research suggests.

Chris is quoted in the article, commenting on the study.

Brian

[Island Chris]

I never talked to the writer of that article. I talked to Larry Ohanlon, who works for AGU as "specialist, Social Media". I provided background to the Legg paper. Legg and other mostly focused on the strike-slip faults, which I was not referring to. The offshore strike-slip fault systems continue far south into Mexican waters, so if 300 km length ruptured in one quake, could approach M8. But, as a guess, I'd say they generally would rupture in smaller quakes: the crust is different than inland: is less thick.

What I was discussing with OHanlon was different: it was about the faults that could be responsible for the 200 km by 40 km thrust anticlines (anticlinoria=more complicated). I meant to suggest that this is completely not understood; the faults would be flatter. I provided copies of two Masters theses (I and others worked with these students) to OHanlon. By the scale of the anticlinoria, if the causative fault system is brittle/seismogenic back towards the mainland, then this produce be a M8. But, I don't have direct evidence of this.

On the other hand, a different group published a paper in 2014 that the thrust fault system between Ventura and Santa Barbara-UCSB, and west and east of there, was capable of a M7.7 to 8.1 earthquake. I am working on this fault system and it is well-imaged. However, the very large uplift events documented near Ventura are very much NOT representative of the system farther west.

I'm guessing it was Legg who was talking about big tsunamis crashing into the coast: I don't think I said that.

I have almost no experience with the media, but I have seen and heard problems like this. I suppose if it gives some attention to the offshore faults, that is a good thing. But the article Brian linked to is too alarmist. That's is probably where the worried Chinese UCSB student got my name.

Chris

[Island Chris]

The actual press release is at:

http://news.agu.org/press-release/little...alifornia/

due to my basic incoherence (?), there are a couple of problems in that. The shallow shelf around the mainland is extremely narrow compared to passive margins like the offshore east USA coast. But, the area of basins and ridges is exceptionally wide (200 km) offshore southern California and northern Baja.

The M8 quake possibility I mentioned was just logic, and it was not supposed to be a suggestion that there could be M8 quakes on the faults Legg studied. Instead, logically there could be very large quakes on the underlying flatter faults.

here is part of the story. Note that the parts that are not in quotes I did not say, but instead the author summarized whatever it is that I did say:

****************************

“Such large faults could even have the potential of a magnitude 8 quake,” said geologist Christopher Sorlien of the University of California at Santa Barbara, who is not a co-author on the new paper.

“This continental shelf off California is not like other continental shelves – like in the Eastern U.S.,” said Sorlien. Whereas most continental shelves are about twice as wide and inactive, like that off the U.S. Atlantic coast, the California continental shelf is very narrow and is dominated by active faults and tectonics. In fact, it’s unlike most continental shelves in the world, he said. It’s also one of the least well mapped and understood. “It’s essentially terra incognita.”

“This is one of the only parts of the continental shelf of the 48 contiguous states that didn’t have complete … high-resolution bathymetry years ago,” Sorlien said. And that’s why getting a better handle on the hazards posed by the Borderland’s undersea faults has been long in coming and slow to catch on, even among earth scientists, he said.


Chris