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+--- Thread: 5.4 La Habra, CA (/showthread.php?tid=81)
5.4 La Habra, CA - Skywise - 03-29-2014
Felt that one good. Not hard, just a very long rumble with rumbling noise. For me, easily 30 seconds plus. I'm, 21 miles away as the crow flies.
Brian
RE: 5.4 La Habra, CA - Island Chris - 03-29-2014
The USGS summary is interesting.
http://earthquake.usgs.gov/earthquakes/eventpage/ci15481673#summary
It says "could" be associated with Puente Hills thrust. The Puente Hills thrust is clearly imaged on industry seismic reflection data in the upper few km, as published by Shaw and Shearer (1999). This shallow part of the fault projects in 3D down to the 1987 Whittier earthquake. But, the focal mechanism shows more of a NW dip:
http://earthquake.usgs.gov/earthquakes/eventpage/ci15481673#scientific
and the aftershocks make a clear NE-SW alignment. Perhaps this is a tear fault (lateral ramp). It would be interesting to see these quakes in 3D.
I'll go into Gocad and see what the Southern California Earthquake Center Community Fault Model looks like there, and try and post this.
Chris
RE: 5.4 La Habra, CA - Island Chris - 03-29-2014
[attachment=12]Hi all. I'm adding an attachment for a 3D view of the faults from the Southern California Earthquake Center. I'll explain the post in a following post, as I have never tried graphics before.
Chris[attachment=11]
I could have brought all the quakes into Gocad, but I have not done that in 8 years and would have to find an old IMAC and run my BASIC program on it, and it would take me 2 days. I should rewrite the program to run in modern windows (Like I have time).
OK, the upper left map is epicenters from SCEC page. The upper right is the SCEC Community Fault Model view in Gocad software. I tilted it a degree or so so that faults represented as vertical will show up (Newport-Inglewood for example). Craig Nicholson of UCSB and Andreas Plesch of Harvard have been working to use seismicity to more accurately represent faults, which are not likely to be perfectly vertical.
I scaled this fault map to be same scale as the SCEC map, then made a polygon around quakes and copied it to the Gocad map.
The lower left is an oblique view, The Red arrow points to approximately 7.5 km below the main shock. It is below the Puente Hills thrust fault segments and so not on this fault, as I suggested in my first post.
I put my full name on the graphic, since this graphic may be of wider interest. I am Christopher "Chris" Sorlien, Associate Research Geologist at University of California, Santa Barbara, working from home office on some island in southern New England. I published a paper in 2013 about offshore faulting and folding in this area, that also discusses that the big faults project beneath Los Angeles.
Ran out of coffee: going for walk.
Chris
Brian was getting discouraged, and there have been few posts, and this has been going on for years. So, I said that interest will pick up with a major quake. Not major, but careful what you wish for.
I also said I would try and post graphics, so did so. Guess I have to make graphics half page across?
Chris
RE: 5.4 La Habra, CA - PennyB - 03-29-2014
(03-29-2014, 04:20 AM)Skywise Wrote: Felt that one good. Not hard, just a very long rumble with rumbling noise. For me, easily 30 seconds plus. I'm, 21 miles away as the crow flies.
Brian
Of course we had a quake...it is March 27! I was noting the reports of "felt" on the So Cal EQ Center Board...and then checked depth of the quake. Seems that it wasn't felt quite as intensely as I thought it would be.
Looks as if the long quiet spell in So Cal is over???
RE: 5.4 La Habra, CA - Skywise - 03-29-2014
(03-29-2014, 01:21 PM)Island Chris Wrote: Hi all. I'm adding an attachment for a 3D view of the faults from the Southern California Earthquake Center.
Nice graphics, Chris. Thanks for posting them.
I know Lucy Jones was saying this "may" be associated with the Puente Hills Thrust, but it's pretty clear from your graphics it's much deeper.
If, IF, I ever get my own 3d quake program running, I've planned for it to be able to import the fault model. Alas... so many distractions.
Brian
RE: 5.4 La Habra, CA - Skywise - 03-29-2014
SCSN already has this quake front page.
http://www.scsn.org/index.html
Lots of good graphics.
Anyone watch Lucy Jones during the live press conferences? Was it just me or was she squirming with the stupid silly reporter questions... trying to constrain her irritation?
Regardless, she gave some great information, notably pushing folks to visit earthquakecountry.info to get preparedness information.
Brian
4.1 aftershock - Skywise - 03-29-2014
Just had a 4.1 aftershock, strongest so far. Pretty good rumble. I already had ABC7's live seismocam running in another window so it was fun to watch it dancing in real time.
Brian
RE: 5.4 La Habra, CA - Island Chris - 03-29-2014
Hey Brian,
guess we just have to be patient until good science posts on Earthwaves are of some interest.
All: Here are some things about the 4.1 aftershock. It is NE of the rest of the aftershocks by a couple of km. So, it can be considered a triggered aftershock (in the past, on Earthwaves, we have called these "far field aftershocks" FFA). Not very far, but outside of the mainshock rupture. Kingdom Suite software ruler says that the WNW-ESE length of Palos Verdes Peninsula is 15 km, about the same distance as the aftershock length. This seems way too long for a M5.1. But, this may be because of the shallow depth: much of the rupture may have been in sedimentary rocks.
Stating the obvious, I'd be a bit concerned if I lived in Los Angeles metro. These quakes are tickling faults capable of catastrophe. As the links say, only 5% or whatever chance of a larger quake, but that might be enough to make sure you don't have a TV over the crib (or whatever).
Chris
RE: 5.4 La Habra, CA - Skywise - 03-29-2014
(03-29-2014, 10:17 PM)Island Chris Wrote: Stating the obvious, I'd be a bit concerned if I lived in Los Angeles metro. These quakes are tickling faults capable of catastrophe. As the links say, only 5% or whatever chance of a larger quake, but that might be enough to make sure you don't have a TV over the crib (or whatever).
Well, I already have (since before the quakes) a few items strapped to the wall. For example, my stack of two computer towers and UPS are tied to the wall they're next to so they don't tip over. I do have a shelf that should be tied up but if it tips, it'd be away from people considering where it is.
Brian