> This quake was larger than the destructive 1994 Northridge quake, which measured 6.6 magnitude.
This isn't entirely accurate. While it's "score" was higher, the magnitude doesn't account for things like the type of fault, the type of movement, the depth, the soil, the duration of movement, etc.
Northridge was far more severe than this one, with an "apparent magnitude" greater than 9.
Don't get me wrong, this one sucks for all the people affected, no doubt, but as someone who lived through Northridge very close to the epicenter, it's sort of personal to me.
There are earthquakes, and then there is the ground shaking that results from earthquakes.
The magnitude scale that is most used is an expression of the total energy release in the earthquake is called the 'moment magnitude' or 'work magnitude' because it's measured in those units (Newton meters or dyne-cm). It is calibrated to be similar to the original Richter scale, which was an empirical, I believe unitless, scale based directly on seismometer readings. If someone credible says that an earthquake is a 3 or a 7 or something, they are almost certainly referring to the moment magnitude. The 1989 Loma Prieta event was a M 6.9 event, Northridge was M 6.6 or 6.7.
There is another measure called the 'intensity' that you may be referring to with the 'apparent magnitude' reference. This is a non-quantitative, basically ranked categorical description of the amount of ground shaking and subsequent damage that occurred. The most common intensity scale is the Modified Mercalli intensity scale; it is usually (and correctly) denoted in Roman numerals. The Wikipedia page for the Mercalli scale [1] is good, however I prefer [2]. The intensity has a sort of tree-falling-in-the-woods element to it: the categories are based on how people and the built environment respond to the earthquake, so did earthquakes in the 4.6 billion years before humanity have intensities? They had magnitudes.
Quantitatively, ground shaking is measured as 'peak ground acceleration', a force, usually compared to gravity 'g' (i.e., 9.81 m/s^2), as 'peak ground velocity' which is a velocity (m/s), or as 'peak ground displacement' which is a distance.
The intensity of an earthquake will be related to the peak ground acceleration and velocity, as well as the duration of the shaking. These are functions of both the earthquake properties (magnitude, faulting style, depth) as well as the properties of the ground in the region of the earthquake, and the distance from the earthquake (as the amplitude of the waves decreases with distance). Solid rock does not shake nearly as much as loose or wet sediment, for example, and some geologic basins that are deep pockets of sediment surrounded by bedrock can amplify earthquake waves and make the shaking locally much worse than it was elsewhere, even closer to the earthquake. This was a big deal in Loma Prieta, for example--the damage in Oakland, built on water-saturated sediment, was worse than in some of San Jose, or in my (current) house in the Santa Cruz mountains just a few km away (I was safely dodging tornadoes in Tulsa at the time).
Northridge was violent beyond belief. I lived less than a mile from the epicenter at the time. I remember it distinctly because I stayed up coding all night. It hit at 4:31 AM (the image of the digital clock on the shelf is seared into my mind). It felt as what I can only describe as a train going through the house.
It's also larger than the 1989 Loma Prieta earthquake that destroyed a lot of San Francisco, which was 6.9.
A lot of this also has to do with how close to populated areas the earthquake is, and if the same quake happened today, the damage would be much less due to better construction.
Was giving my daughter a bath when it started. At first I thought I was fainting, because it was a really slow rolling motion like I was on a boat. Then noticed the shower door moving.
My daughter kept saying she wanted to go see the earthquake. I think she thought it was outside.
Same about the fainting. I was standing in line at Target on the 4th, and I could have sworn I was gonna pass out there and then until the lady behind me asked if anyone else had felt that. Then I noticed the aisle signs swinging!
When you go to that area and stand on one of the mountains -- say, on the west ridge of Death Valley -- you can clearly see how the region is a bunch of vertical columns of continental crust that have toppled over, like dominoes. If I call correctly, as the North American plate is pushed up, it gets pulled apart (because the Earth is spherical?) and the cracked pieces fall onto each other. The valleys in between fill with sediment over time, but get deeper also as the mountains roll over further.
Point is, I wonder if this was the sound of Badwater Basin (lowest point in North America) getting a little bit lower...
Today's earthquake was a strike-slip earthquake, where two parts of the crust slide laterally by each other on a fault plane inclined close to vertically in the crust. The fault is probably oriented NW-SE [1], parallel to the San Andreas fault, although from the pattern of energy release from the earthquake (known as the focal mechanism[2] or moment tensor[3]) it also could be on a NE-SW oriented fault, with the direction of shear being the opposite. Because this was a strike-slip earthquake on a vertically-inclined fault, there won't be more than a few cm of uplift or subsidence of any parts of the earth's surface.
The domino-style faulting that occurs in the Basin and Range of the US, basically from Owens Valley to Salt Lake City, is an expression of 'normal faulting' (rather than strike-slip faulting). Normal faults are inclined from the horizontal, and the block of crust above the fault slides down the fault, like down a ramp. After a lot earthquakes (hundreds to thousands of M6+ earthquakes) the blocks have rotated on a horizontal axis quite a bit, so that they are no longer upright [4]. Furthermore, and quite importantly, as a result of this faulting, the crust (or at least the upper crust where the faulting happened) is both thinner from top to bottom than it was previously, and wider than it was previously--we say that the crust got 'extended' because it is horizontally lengthened/widened. You are absolutely right that Death Valley is forming in this kind of environment.
There are two main reasons for crustal thinning and extension. One reason is that the boundary of that part of the crust moved away, so the crust stretched or extended to fill the gap. The other is that the crust was too thick and high, so it spread out. The continents are kind of like rafts of granite floating on more dense, hot, ductile rock below (the mantle). The density contrast between the lighter crust and the mantle is sort of like icebergs floating in sea water, so most of the continents are below the surface of the ocean basins. When a big mountain range is built that gets high, it also has to have a thick root to support its surface elevation, like the undewater part of an iceberg. However, the crust isn't always strong enough to support a big mountain range for a long time, and so it will break apart under the force of gravity and spread out laterally, reducing the gravitational potential energy contrast between the (formerly) high mountains and the surrounding lower elevation crust.
It is thought that in the western US, both processes (the moving boundary condition, and the gravitational collapse and spreading of the crust) have been the cause of the crustal extension that produced the domino-style block faulting. The big collapse was probably during the Miocene, say about 15 million years ago, which produced a lot of the faults and smaller mountain ranges that we see today. Many geologists think that California was one or two hundred kilometers closer to Colorado, and the area that is now Nevada and western Utah was narrower and much higher--say a mean elevation of over 10,000 feet. This has been nicknamed the 'Nevadaplano' in reference to the Altiplano of Bolivia and Peru, which is an analogous geologic feature. I think that there is also a slight component of extension between the North American and Pacific plates at this latitude, i.e. the Pacific plate is mostly sliding by North America on the San Andreas and parallel faults, but it might also be moving away from North America (i.e. Kansas) at a few mm per year.
You can see something similar in the Valley of Fire in Overton, Nevada. If you go on a Fire Canyon Road and look south, you can see the green hills in the back with red rocks in the middle and white in the foreground. It’s pretty surreal.
Recent LA transplant here. Fight or flight did not kick in. Instead, I was mostly confused and kinda paced about the flat while the earth shook. I always imagine myself acting quick on my feet like a movie hero. Two learnings; I know what an earthquake feels like and I need to increase my disaster preparedness.
Here to plug the American Red Cross emergency apps. They have high quality, offline-available info on preparation and survival of various natural disasters. I believe they also push out real time info on them about relief efforts, shelters, etc. Here is the Earthquake app: https://apps.apple.com/us/app/earthquake-american-red-cross/...
Maybe the timing was coincidental, but it looked like reddit was down for a few minutes after the earthquake (I checked some other sites to make sure it wasn't just my router being silly after power
came back). Reminded me a bit of how almost every news website (barring Slashdot) went down on 9/11. I wonder how many sites could handle the load if a serious disaster happened. Makes me reconsider where I'll be able to get info when something bad happens
I grew up in Ridgecrest during the time it became known for earthquakes (e.g. https://www.youtube.com/watch?v=8k8f2gJjXkQ&feature=share ). That commercial isn't far off in that it got to the point that we no longer ran for cover. I remember watching TV and feeling the ground roll underneath me and not being phased.
Random notes:
- The epicenters tends to be relatively close (<20 miles) and relatively shallow (<10 miles).
- I think the 7.1 brings this into the territory of stronger than we had growing up.
- I've seen people mention that it didn't impact a densely populated area. Normally I feel the same relief about that except this time I know the people which brings a different perspective
- My biggest concern is for those who were evacuated from the hospital in the 100 degree weather. A childhood friend's dad is bedridden, trying to recover, and is now out in the heat.
- I've seen reports of roads to towns like Trona being closed off. Unsure if that is all routes and how long until they re-open but that is probably my next biggest concern.
I was in the 8.8 earthquake in chile (2010), near the epicenter. for the following days, a lot of replicas over 7.0 occurred. if your construction follows the regulations, it will be fine (some minor repairs), but any structural damage can and will be the death sentence for that structure. In those times, we were worried about the lack of water,food and electricity.a big freezer stuffed with food can last a week without electricity, because of the insulation and the amount of water inside
We were rocking pretty good in Orange County. Can't imagine being at the epicenter. It lasted long enough to where we start questioning if we needed to do anything.
The sound is the worst part for me. Nothing else even comes close to replicating it. All the little things rattling, and the deep rumbles of your whole house moving around.
I had my first earthquake a few years a go and it is for sure a weird feeling. I’ve never felt an entire building move until that, it’s a unique feeling
I'm flying to LA next week for the first time, and am a little worried after the quakes. I appreciate much of the comments on preparedness and observing what's happening around you, but am looking for some more details, like:
- how to spot "unreinforced masonry" in order to avoid it?
- why is a strong table to be looked for inside, to get underneath it?
- I would imagine basements are bad to be in, is that so?
- I would imagine upstairs is a bad place to be too, right?
- does the ground really split underneath your feet?
If my time in Japan has taught me anything, it’s to get under something. The big danger is stuff nearby toppling onto you and immobilizing you. Bookshelves, wardrobes, floating cabinets, drop ceilings, and such can hurt you unless you pop under a table or desk quickly.
In Japan, they have earthquake simulators that drive this point home. The old version is a truck whose bed is fitted with a simulated apartment on hydraulic shakers. The newer version is VR.
Your second concern is fire. In Japan, gas is always run through a sensor that cuts the line if shaking is too intense. I’m not sure if California has the same. If there’s a gas leak nearby, that’s the next serious danger after falling objects.
As someone living on the second floor of a rather old (built in 1940s) apartment building in Northern California, I’d love to hear any suggestions for ensuring it’s safe in the event of an earthquake like this.
> The quake caused further damage to a U.S. weapons testing facility outside Ridgecrest, the Naval Air Weapons Station China Lake, although details were sparse early Saturday. “NAWS China Lake is not mission capable until further notice; however, security protocols remain in effect,” the naval base said on its Facebook page after the latest temblor. The installation is the Navy’s largest single landholding, sprawling over 1.1 million acres, an area larger than Rhode Island.
[+] [-] jedberg|6 years ago|reply
This isn't entirely accurate. While it's "score" was higher, the magnitude doesn't account for things like the type of fault, the type of movement, the depth, the soil, the duration of movement, etc.
Northridge was far more severe than this one, with an "apparent magnitude" greater than 9.
Don't get me wrong, this one sucks for all the people affected, no doubt, but as someone who lived through Northridge very close to the epicenter, it's sort of personal to me.
[+] [-] cossatot|6 years ago|reply
The magnitude scale that is most used is an expression of the total energy release in the earthquake is called the 'moment magnitude' or 'work magnitude' because it's measured in those units (Newton meters or dyne-cm). It is calibrated to be similar to the original Richter scale, which was an empirical, I believe unitless, scale based directly on seismometer readings. If someone credible says that an earthquake is a 3 or a 7 or something, they are almost certainly referring to the moment magnitude. The 1989 Loma Prieta event was a M 6.9 event, Northridge was M 6.6 or 6.7.
There is another measure called the 'intensity' that you may be referring to with the 'apparent magnitude' reference. This is a non-quantitative, basically ranked categorical description of the amount of ground shaking and subsequent damage that occurred. The most common intensity scale is the Modified Mercalli intensity scale; it is usually (and correctly) denoted in Roman numerals. The Wikipedia page for the Mercalli scale [1] is good, however I prefer [2]. The intensity has a sort of tree-falling-in-the-woods element to it: the categories are based on how people and the built environment respond to the earthquake, so did earthquakes in the 4.6 billion years before humanity have intensities? They had magnitudes.
Quantitatively, ground shaking is measured as 'peak ground acceleration', a force, usually compared to gravity 'g' (i.e., 9.81 m/s^2), as 'peak ground velocity' which is a velocity (m/s), or as 'peak ground displacement' which is a distance.
The intensity of an earthquake will be related to the peak ground acceleration and velocity, as well as the duration of the shaking. These are functions of both the earthquake properties (magnitude, faulting style, depth) as well as the properties of the ground in the region of the earthquake, and the distance from the earthquake (as the amplitude of the waves decreases with distance). Solid rock does not shake nearly as much as loose or wet sediment, for example, and some geologic basins that are deep pockets of sediment surrounded by bedrock can amplify earthquake waves and make the shaking locally much worse than it was elsewhere, even closer to the earthquake. This was a big deal in Loma Prieta, for example--the damage in Oakland, built on water-saturated sediment, was worse than in some of San Jose, or in my (current) house in the Santa Cruz mountains just a few km away (I was safely dodging tornadoes in Tulsa at the time).
[1]: https://en.wikipedia.org/wiki/Modified_Mercalli_intensity_sc... [2]: https://www.mcsweeneys.net/articles/levels-of-the-mercalli-s...
[+] [-] robomartin|6 years ago|reply
[+] [-] seaish|6 years ago|reply
A lot of this also has to do with how close to populated areas the earthquake is, and if the same quake happened today, the damage would be much less due to better construction.
[+] [-] org3432|6 years ago|reply
[+] [-] thebeefytaco|6 years ago|reply
I didn't even feel the one yesterday either.
[+] [-] Justin_K|6 years ago|reply
[deleted]
[+] [-] cortesoft|6 years ago|reply
My daughter kept saying she wanted to go see the earthquake. I think she thought it was outside.
[+] [-] pizza|6 years ago|reply
[+] [-] Deimorz|6 years ago|reply
More info in this article (linked to from the one above): http://temblor.net/earthquake-insights/southern-california-m...
[+] [-] ajkjk|6 years ago|reply
Point is, I wonder if this was the sound of Badwater Basin (lowest point in North America) getting a little bit lower...
[+] [-] cossatot|6 years ago|reply
Today's earthquake was a strike-slip earthquake, where two parts of the crust slide laterally by each other on a fault plane inclined close to vertically in the crust. The fault is probably oriented NW-SE [1], parallel to the San Andreas fault, although from the pattern of energy release from the earthquake (known as the focal mechanism[2] or moment tensor[3]) it also could be on a NE-SW oriented fault, with the direction of shear being the opposite. Because this was a strike-slip earthquake on a vertically-inclined fault, there won't be more than a few cm of uplift or subsidence of any parts of the earth's surface.
The domino-style faulting that occurs in the Basin and Range of the US, basically from Owens Valley to Salt Lake City, is an expression of 'normal faulting' (rather than strike-slip faulting). Normal faults are inclined from the horizontal, and the block of crust above the fault slides down the fault, like down a ramp. After a lot earthquakes (hundreds to thousands of M6+ earthquakes) the blocks have rotated on a horizontal axis quite a bit, so that they are no longer upright [4]. Furthermore, and quite importantly, as a result of this faulting, the crust (or at least the upper crust where the faulting happened) is both thinner from top to bottom than it was previously, and wider than it was previously--we say that the crust got 'extended' because it is horizontally lengthened/widened. You are absolutely right that Death Valley is forming in this kind of environment.
There are two main reasons for crustal thinning and extension. One reason is that the boundary of that part of the crust moved away, so the crust stretched or extended to fill the gap. The other is that the crust was too thick and high, so it spread out. The continents are kind of like rafts of granite floating on more dense, hot, ductile rock below (the mantle). The density contrast between the lighter crust and the mantle is sort of like icebergs floating in sea water, so most of the continents are below the surface of the ocean basins. When a big mountain range is built that gets high, it also has to have a thick root to support its surface elevation, like the undewater part of an iceberg. However, the crust isn't always strong enough to support a big mountain range for a long time, and so it will break apart under the force of gravity and spread out laterally, reducing the gravitational potential energy contrast between the (formerly) high mountains and the surrounding lower elevation crust.
It is thought that in the western US, both processes (the moving boundary condition, and the gravitational collapse and spreading of the crust) have been the cause of the crustal extension that produced the domino-style block faulting. The big collapse was probably during the Miocene, say about 15 million years ago, which produced a lot of the faults and smaller mountain ranges that we see today. Many geologists think that California was one or two hundred kilometers closer to Colorado, and the area that is now Nevada and western Utah was narrower and much higher--say a mean elevation of over 10,000 feet. This has been nicknamed the 'Nevadaplano' in reference to the Altiplano of Bolivia and Peru, which is an analogous geologic feature. I think that there is also a slight component of extension between the North American and Pacific plates at this latitude, i.e. the Pacific plate is mostly sliding by North America on the San Andreas and parallel faults, but it might also be moving away from North America (i.e. Kansas) at a few mm per year.
[1]: https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511...
[2]: https://en.wikipedia.org/wiki/Focal_mechanism
[3]: http://seismo.berkeley.edu/~rallen/eps122/lectures/L12.pdf
[4]: https://en.wikipedia.org/wiki/Tilted_block_faulting
[+] [-] iscrewyou|6 years ago|reply
[+] [-] Stratoscope|6 years ago|reply
In the meantime, I wonder if there are any good photos of them? I wouldn't know what to search for.
[+] [-] fumar|6 years ago|reply
[+] [-] reilly3000|6 years ago|reply
[+] [-] Rebelgecko|6 years ago|reply
[+] [-] epage|6 years ago|reply
Random notes:
- The epicenters tends to be relatively close (<20 miles) and relatively shallow (<10 miles).
- I think the 7.1 brings this into the territory of stronger than we had growing up.
- I've seen people mention that it didn't impact a densely populated area. Normally I feel the same relief about that except this time I know the people which brings a different perspective
- My biggest concern is for those who were evacuated from the hospital in the 100 degree weather. A childhood friend's dad is bedridden, trying to recover, and is now out in the heat.
- I've seen reports of roads to towns like Trona being closed off. Unsure if that is all routes and how long until they re-open but that is probably my next biggest concern.
[+] [-] nwallin|6 years ago|reply
[+] [-] longemen3000|6 years ago|reply
[+] [-] alex_young|6 years ago|reply
"Scientists said it the fault causing the quakes appears to be growing."
[+] [-] ramenmeal|6 years ago|reply
[+] [-] technological|6 years ago|reply
First time felt earthquake .. Surreal experience
[+] [-] kart23|6 years ago|reply
[+] [-] nerdbaggy|6 years ago|reply
[+] [-] fiblye|6 years ago|reply
[+] [-] vegiraghav|6 years ago|reply
[+] [-] chenster|6 years ago|reply
[deleted]
[+] [-] oska|6 years ago|reply
[+] [-] saagarjha|6 years ago|reply
[+] [-] brianzelip|6 years ago|reply
- how to spot "unreinforced masonry" in order to avoid it?
- why is a strong table to be looked for inside, to get underneath it?
- I would imagine basements are bad to be in, is that so?
- I would imagine upstairs is a bad place to be too, right?
- does the ground really split underneath your feet?
[+] [-] beders|6 years ago|reply
[+] [-] Arnie0426|6 years ago|reply
[+] [-] pizza|6 years ago|reply
[+] [-] nihonde|6 years ago|reply
In Japan, they have earthquake simulators that drive this point home. The old version is a truck whose bed is fitted with a simulated apartment on hydraulic shakers. The newer version is VR.
Your second concern is fire. In Japan, gas is always run through a sensor that cuts the line if shaking is too intense. I’m not sure if California has the same. If there’s a gas leak nearby, that’s the next serious danger after falling objects.
[+] [-] jedberg|6 years ago|reply
Do NOT get in a doorway, unless it is one without a door. The door is more dangerous than any other damage.
Do NOT run outside, unless it's faster than getting under a table. And if you do go outside, get away from power lines.
[+] [-] carlivar|6 years ago|reply
[+] [-] ekianjo|6 years ago|reply
[+] [-] dewiz|6 years ago|reply
[+] [-] maddyboo|6 years ago|reply
[+] [-] 4gotmypw|6 years ago|reply
[+] [-] nuclear_eclipse|6 years ago|reply
> The quake caused further damage to a U.S. weapons testing facility outside Ridgecrest, the Naval Air Weapons Station China Lake, although details were sparse early Saturday. “NAWS China Lake is not mission capable until further notice; however, security protocols remain in effect,” the naval base said on its Facebook page after the latest temblor. The installation is the Navy’s largest single landholding, sprawling over 1.1 million acres, an area larger than Rhode Island.