Ridgecrest, California earthquake sequence (Searles Valley) - July 2019

Dan Robinson

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Jan 14, 2011
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An interesting seismic event event of significance is ongoing in southern California this week. The Searles Valley, CA earthquake sequence is occuring in the Eastern California Shear Zone, an active region of tectonic deformation and stress. This activity is happening separate from the San Andreas system. Tonight's M7.1 is the third in a series of northward-migrating M7+ events starting with the M7.2 Landers earthquake in 1992 and preceded most recently by the 1999 M7.1 Hector Mine earthquake.

The faulting in these regions is complex. The Landers rupture involved multiple faults and was preceded by a ~M6 foreshock, similar to the Ridgecrest events so far. Landers also is thought to have triggered the nearby M6.5 Big Bear quake 3 hours later on an unrelated but nearby fault. It remains to be seen if the Ridgecrest sequence will continue in a similar fashion.

This event is the largest to occur in southern California since Hector Mine in 1999.

M7.2 Landers 1992:
Southern California Earthquake Data Center at Caltech

M7.1 Hector Mine 1999:
Southern California Earthquake Data Center at Caltech
 
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Fortunately, this region is very isolated and none of the rupturing faults connect to the critical ones near the coast. Having said that, the most dangerous faults in California have been inactive for an uncomfortable period. I'm of the personal opinion that any prolonged shaking or displacement in a region where energy has been building for years raises some risk.


la-1554252698-klbwi6rtti-snap-image.png
 
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Always packed and ready to go for the big one. I was fortunate enough to make it to both Loma Prieta 89" and Northridge in 94." Now days, I would not suggest anyone "chase" a catastrophic earthquake in CA unless you have some serious newspaper experience and know how to survive urban crime. Both Loma Prieta and Northridge had some tense moments although I took the chance and was armed with a Glock. Just like when I came across the slot machine looters as surge waters receded in Biloxi after Katrina, you have to play the game of ignoring criminals and never take their pictures. I would never travel alone to such an event again.EQ-07-st.jpg
 
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Dan Robinson

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I'm on the road west toward SoCal today for my first earthquake chase, part of this event. I would have left right after the mainshock, but had an important family event last week followed by a car repair. My target is the south end of the M7.1 rupture zone between Ridgecrest and Barstow for hopefully a M5 or greater aftershock. I'm picking this area for a strong aftershock, as it is in a seismic gap between the Searles Valley rupture and the Landers/Hector Mine ruptures. There was an M5 event in Barstow a few months after Hector Mine, so I feel the same could occur with this sequence. The chances are good for at least an M4 since the aftershock sequence is still ongoing. I plan to stay there for a little over a week to see what happens, planning on touring some of the M7.1 surface rupture in the meantime.
 
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I'm on the road west toward SoCal today for my first earthquake chase, part of this event. I would have left right after the mainshock, but had an important family event last week followed by a car repair. My target is the south end of the M7.1 rupture zone between Ridgecrest and Barstow for hopefully a M5 or greater aftershock. I'm picking this area for a strong aftershock, as it is in a seismic gap between the Searles Valley rupture and the Landers/Hector Mine ruptures. There was an M5 event in Barstow a few months after Hector Mine, so I feel the same could occur with this sequence. The chances are good for at least an M4 since the aftershock sequence is still ongoing. I plan to stay there for a little over a week to see what happens, planning on touring some of the M7.1 surface rupture in the meantime.
Just don't become addicted to crack..... šŸ˜‚
 

Dan Robinson

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Everything along the fault trace was offset, bu the fenceline is the most dramatic example I've seen so far since it has posts very close to either side of the fault. The main highway offset has been repaired already, but some of the dirt roads have offsets. Still out taking pictures and will post a few more soon. Very interesting stuff!
 

Dan Robinson

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A few more shots:

Fresh scarp along fault surface rupture near Ridgecrest with about 18 inches of vertical displacement, about 2 feet or so horizontal:

july1617g.jpg

Another dirt road offset by the fault surface rupture near Trona Pinnacles:

july1617f.jpg

Drone shot of the surface rupture trace going through the fence (posted earlier):

july1617k.jpg

So far, the M4.5 is the only earthquake I've felt. I've been in a dozen or so M3s (some very close) and many more 2s but have not felt any of them.
 
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James K

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Nice pic's & descriptions Dan Robinson!

Those offsets & cracks in the ground would be fascinating to see up close in person...but I wouldn't to be near that place. The thought of the ground moving below me is downright scary (not to mention things falling/buildings collapsing/etc)

Now being in a chopper above the open desert at just the right time/place, when that thing let loose, watching cracks form & the shift happen...that would be awesome!
 

Dan Robinson

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It would be safe to be standing outside right on top of the fault when it goes. You could stand straddling the fault, providing you could even remain standing during the shaking (probably better to sit down on it!). The only risk there would be falling over during the shaking and maybe breathing in the dust kicked up from the ground. The main dangers during quakes are indoors where things can collapse and objects can fall on you. Out in the open like here, it would be an amusement park ride. The holy grail would be to capture the surface rupture as it happened, so far that has only occurred once during a quake in Hualien, Taiwan:


The Hualien quake was a thrust event where movement was more vertical. In SoCal, most of the major faults are transform (strike-slip) where the bulk of movement is horizontal.

BTW, here is the USGS map of surface ruptures from the M6.4 and M7.1 events. I have not yet made it to the M6.4 trace since there has been plenty to see with the much more impressive M7.1 trace.

RidgecrestSurface Ruptures.jpg
 

Dan Robinson

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Had a M4.6 this evening that happened while I was driving back to the hotel (grrrr!) so I didn't feel it. My hotel room cameras caught it, but the shaking was much lighter than yesterday's M4.5.

Joe, that looks like a landslide fissure, where one side is pulling away. Big landslides can happen during earthquakes, but along the faults that produce them, the rocks don't pull apart, they are simply sliding past each other (staying in contact before and after).

Here is a USGS faq on that:
Can the ground open up during an earthquake?
 
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I wonder if the movement and the shaking felt on each side would be similar. My guess would be that relative to the earth one side would move more than the other, but that may not be the case. Very interesting stuff.
 

James K

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Mar 26, 2019
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@Dan Robinson:
Makes sense that you'd be (relatively) safe outside...especially in a place like that where there isn't even trees to fall on you.
I don't think I'd want to stand or sit right on the fault though! .lol. Still seems like there's a pretty good chance of injury - depending on how it moves

That capture from Taiwan was interesting to watch! Sat there and let it go through multiple times

And I agree, the holy grail would absolutely be to capture the surface rupture as it happened...in particular from the sky above! Probably little chance in the open desert (that'd be extreme luck!). In an urban area(truly scary), with all the security cameras recording its only a matter of time

Interesting.. looking at that map, its atleast 2 separate faults that went?

So in general that's the threshold for being able to feel an earthquake? M4+ ??

---------
@Joshua Nall:
Good question. And yep interesting stuff.
 

Dan Robinson

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This is what an earthquake chase looks like. At least there is time to read Stormtrack and post!

july1819a.jpg

A lot of the M3s have DYFI (did you feel it) reports on the USGS site, but I have yet to feel one. My first night here, I had cameras rolling when a M3.4 hit close by. I didn't feel it and the objects I had pointed the cameras at (water bottles and coat hangers) didn't show any movement. With the 3s I'd assume you'd need it to be very shallow and very close to feel it, though the felt reports for some of the 3s are a good distance away.

Here is the realtime quake site where you can see the reports:
 
Jan 6, 2019
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This is what an earthquake chase looks like. At least there is time to read Stormtrack and post!
Where/how far was any (even minor) fault line from that current position you had there ?
Like the fence/road images..

did have other info in here, but just seemed not to fit as partially off track, not really more about detection and pre-warn.
 
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Dan Robinson

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The surface rupture from the M 7.1 event is visible on the road just ahead there. I targeted here since a lot of the aftershocks have been pretty close to this spot, at least the ones I have access to. The rest of them are inside the military base to the north.