That Puente Hills fault that caused the quake out in Brea yesterday is the one that terrifies geologists. They used to think the Elysian Park fault was the killer--our house sits right atop that one--but turns out that one seems not to be very violent. But in the last 10K years The Puente Hills fault has snapped in a huge way four times, from what they can tell, and each of those quakes was a 7 plus. That would be ten times at least as powerful as Northridge. Furthermore, the Northridge fault directed its energy away from downtown (with explains how places as far away as Fillmore were levelled) but the Puente Hills fault would direct its energy towards downtown. I suppose that is how people in downtown felt the shaking of a quake centered in Brea so strongly (and why we scarcely noticed while we were out in Tujunga). The Puente Hills fault stretches from roughly Brea to Beverly Hills,and it has three active areas--Brea, Whittier (remember the Whittier Narrows quake in 1987?) and here. And I mean right here...downtown is square in the middle of it, and the zones width goes from just below USC to about where I am in Silverlake. In fact, I think our place is just outside the zone, not that we would shake like hell anyway. Not as bad as people on the nearby flatlands probably, built as they are on layers of sediments, but well be shook up somethimg awful. I dread the thought of it. It wont be boring, anyway. Puente Hills is a thrust fault. Everyone knows how the San Andreas fault (which cuts through the Antelope Valley down into the Coachella Valley fairly distant from us) is between two plates that slide past one another. Every once in a while the faults get stuck and then snap apart. The movement is horizontal. West of the fault goes north, east goes south. But a thrust fault is vertical movement, that is the fault zone is thrust upward. So what will happen is that the Puente Hills fault zone, in a really big quake, will sudden lurch up a meter or two, meaning that the part of town from USC up through downtown will be instantly elevated above the area south of it. I think that means that all the north south streets--Figueroa, etc--might suddenly be unuable. That is at some point past Expositiom Blvd there would be a three or even six foot drop. That is what huge quakes on thrust faults do. Gnarly, as the dudes say. No one knows when this will happen. It will happen. There is no way it will not happen. But it could be before I finish this post, or it could be in a couple thousand years. Every city on the West Coast from Anchorage (trashed in1964) to San Diego (my first earthquake memory) faces the prospect of a disastrous earthquake. That is the geologic reality of living on the Pacific Rim. Its scary as hell if you think about it much, so I dont think about it much. We try to be a little prepared, though. Just in case. Ya never know. I wasnt gonna post this. Like maybe its too creepy. But maybe people should know. A lot of you do, I know. But its amazing how many residents of this area have no idea what might happen if we roll seismic snake eyes. Now I need a drink. https://youtube/watch?v=8kfbhVHBq1A
Posted on: Sun, 30 Mar 2014 03:51:46 +0000
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