Tuesday, July 29, 2008

M 5.4 Los Angeles quakes - maps from google earth

Andrew and Jim Repka have already talked about today's LA basin earthquake. (And they got through to the moment tensor solution: a combination of right-lateral strike-slip and thrust, a snapshot of the tectonics of the LA region all in one moderate earthquake rupture.)

Here are maps from Google Earth and the USGS. Faults are color-coded based on how recently they are known to have had earthquakes. Red is historic, orange is younger than around 10,000 years old, and green and blue are somewhat older, but still young enough to worry a nervous geologist.

Here's the same information, but zoomed in:

It's not on a mapped fault, but that isn't surprising: the thrust earthquakes in LA (such as the 1994 Northridge EQ) tend to be on "blind" thrusts - faults that don't cut the surface. (They do, however, tend to raise the ground surface and create hills and mountains. Notice the topography around the aftershocks.)

It's also between two segments of mapped faults, and near the end of one of them. The geometry of the earthquake rupture makes sense there - the rocks near the tip of the right-hand fault (orange on map) should be getting compressed. If the orange fault is active. Which I'm willing to bet it is. (On a geologic time scale, at least. I can't work out possible stress changes in my head, so I'm not making an earthquake prediction.)

1 comment:

Criminal Lawyers Los Angeles said...

Just the other day we had an earthquake down here in Los Angeles and it happened early in the morning. But no, listen to this... I was watching 'shark week' on Discovery channel the night before, so when the house shook I was still sleeping and it felt like I was in a shark cage moving from side to side, and then I woke up.. :)