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

[Dan Robinson]

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

 

[James K]

When google'ing this earthquake, I came across an interesting site:
earthquaketrack.com/p/united-states/recent

 

[Warren Faidley]

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.

 

[Dan Robinson]

The San Andreas is at or very near its failure point in SoCal. One of the subjects that fascinates me the most. In 2017 I went out to tour and photograph it from Parkfield to the Salton sea so I could go back after the earthquake occurs and have some before-after fault movement/surface rupture sequences:

San Andreas Fault Tour: Parkfield to the Salton Sea, California

 

[Warren Faidley]

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.

 

[Dan Robinson]

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.

 

[Warren Faidley]

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.....

 

[Dan Robinson]

Haha, I originally planned to stay in Barstow, but a quick Google search revealed that would be a very bad idea.

 

[Dan Robinson]

Here is the surface rupture east of Ridgecrest and 2 to 3 foot offset in the fence along Highway 178. Pretty incredible.

 

[Joe Cameron]

Here is the surface rupture east of Ridgecrest and 2 to 3 foot offset in the fence along Highway 178. Pretty incredible.

What about the power lines to the left, was one side offset from the other at the same time,
did that shift occur for that distance also ?

 

[Dan Robinson]

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]

Chase a success!!! Just had a M4.5 centered a few miles away! Car was rocking!

 

[Dan Robinson]

A couple more shots. 3-foot horizontal offset on a dirt road with about a foot of vertical displacement:



Drone shot of the surface rupture through the desert:



Vertical offset of nearly 2 feet with double scarp. The dirt road on the left was originally level!

 

[Joe Cameron]

Do those faults have a name assigned to them ?

Is that the same fault in all those images "Ridgecrest" ?

 

[Dan Robinson]

Video from today's M4.5:

Both the M6.4 and M7.1 producing faults were unmapped prior to this event. This is within the Eastern California Shear Zone, a region that has seen many events of this size.