earthquake fault

Exams And Earthquakes

So in November last year in New Zealand there was a really bad earthquake overnight (it was a 7.8) and the next day the whole fucking country had exams and in the city I live in my school was one of the only schools that actually had an exam the day of/after the earthquake (it was on a Monday morning at exactly 12.01am) . the fucking city i live in was shut down because the earthquake was on our fault line and it was unsafe but my school is in a “safe zone suburb” so it had to have exams. My school wasn’t actually open unless you were a student sitting an exam and the only exam that day was a year 11 exam. I sat that exam and five minutes into it there was a 5.3 aftershock. we weren’t allowed to leave for another 40 minutes so it was just a room full of sleep deprived year 11 students silently crying because we couldn’t even get under the desks during even more aftersocks or we’d automatically fail. Later when we could leave all the year 11s got out of that exam so quickly it turns out that all over the school year 11s were crying because we all thought we were going to die in a fucking maths exam. We had a full week of exams during aftershocks and I can honestly say I have never bonded with my year group more than in that week when we thought we would all die.

vimeo

Well I can’t not share this there’s a seismogram on the very front of it. I’ll let the caption give details:

The earthquake of M5.8, the largest on the Korean Peninsula, occurred in Korea, which was called the “Earthquake Safety Zone,” in 2016. Gyeongju City suffered a great deal of damage due to the ineffectiveness of the Korean government and the insecurity of safety. By the year 2017, there have been about 500 earthquakes, and Koreans are living in fear of an earthquake that will happen anytime soon.

Magnitude Rituals is an image of praying that no earthquake will happen in Korea. The former Korean peninsula country, which was a farming country, had a ritual to pray for rain in the sky every drought season. In this regard, this work expresses a sacrifice to wish an earthquake not to happen. The image consists of two frames. The image on the left represents the progress of the ritual, and the image on the right represents the situation where the value of the graph representing the earthquake converges to zero and the process of the earthquake is reversed.

What I wanted to pursue in my work was the communication of messages in contrast to Korean tradition and shamanic images and sophisticated mathematical graphics. On the surface, it is an image that seems to have nothing to do with each other, but as the ritual process progresses, it expresses that the figure indicating the earthquake in the graph is stopping, so that the audience can appreciate the image and slowly understand it.

We Asked a Seismologist How Fucked California Would Be in a 'San Andreas'–Style Earthquake

Maybe you’ve heard that some of this summer’s allotment of CGI skyscraper-snapping is going to come from a disaster movie called San Andreas, starring Dwayne Johnson. This might have left you with questions like “Where can I find a stupidly large screen to watch this stupidly large movie on?” and “Can Dwayne Johnson’s year possibly get any better?”

But this fictional movie is about a real geological feature of the West Coast: the San Andreas Fault. Major earthquakes can happen along this underground ridge where two tectonic plates rub together, and they really do threaten California’s population centers. That means in addition to the questions above, about the career of the giant, Canadian-America actor formerly named after a geological formation, San Andreas also raises questions about how much Los Angeles and San Francisco need to worry about geology-based catastrophes like the ones in the film.

Continue

3

After the Titanic struck an iceberg and sunk in 1912, Canadian inventor Reginald Fessenden resolves to try and prevent such a tragedy from happening again. He creates the “Fessenden Oscillator” that can use sound to see objects in the water, exactly as dolphins do. While he hoped it would save countless lives by detecting submarines in the war, neither the British or Americans would use this technology at the time.

It was finally taken seriously a decade later, and the result rippled throughout our history with safer ship navigation, echo-location to spot fish for catching, help for seismologists to chart earthquake fault lines, and more. 

Hear the rest of this story in our history of sound with HOW WE GOT TO NOW.

ATTENTION: An earthquake warning has been issued for Southern California areas over the next few days.

The areas include:

• Orange
• LA
• Ventura
• San Diego
• San Bernadino
• Riverside
• Kern
• Imperial counties

This has come to light after over 140 seismic activities have been recorded near Bombay Beach along the Salton Sea. While it’s not easy to predict an earthquake, it has been advised that the risk is significantly greater through October 4th.

Please spread the word so that people who live in these areas can be prepared. Make sure you pack an emergency kit complete with a flashlight, batteries, sufficient water/food supplies, shoes and warm clothing.

(image: UCGS)

Gearhart Elementary School is sandwiched between the ocean and a wetland, through which no roads exist and none can be built, because the ground there will liquefy in an earthquake
—  Kathryn Schulz, “The Really Small Ones.”

A follow-up to her Pulitzer Prize-winning piece, Kathryn Schulz writes about a measure to move schools in Seaside, Oregon, to safer ground.

2

In 1906, the seismologist Henry Reid developed the “elastic rebound theory” to explain earthquakes. When rocks begin to press against each other, they initially bend, like a spring, to accommodate the opposing forces. Eventually, when the rocks reach a point where they cannot bend further, they break. The bent rocks snap back, or rebound, to their original shape. The break is the fault itself, and the shock waves emanating from the rebound are the earthquake. The shock waves vibrate through the Earth, making it “ring” like a bell.

A fault is a rock fracture along which movement occurs. Normal faults develop where the crust stretches apart, as in the East African Rift Valley. In thrust faults, which are found at subduction zones, the rocks on one side of the fault are pushed up and over those on the other side. A third type of fault is the strike-slip fault, where the rocks on either side of the fault slip by each other horizontally. The San Andreas Fault is a strike-slip fault.

Learn more about earthquakes in the Gottesman Hall of Planet Earth

youtube

A series of drone-based video shots around Kathmandu, touring the devastation after the earthquake.

youtube

Discovery Channel video gives you a chance to fly along the San Andreas Fault

So, about that earthquake advisory...

At this point, it seems that the whole internet has heard the story about how a swarm of earthquake activity near the Salton Sea in Imperial County, California, has raised the chances of a large earthquake on the San Andreas Fault, and an earthquake advisory was issued detailing all of this. If many headlines and reactions to them are to believed, the Big One is imminent, and large swathes of southern California are about to bite the big one.

So, how much of this is true? Do we need to worry?

Well, the raised probability aspect is, in fact, true - or it is according to our best understanding of how faults interact with each other. But we’re talking a raise to a maximum of a 1% chance in the next seven days. One percent! Or less! I don’t think I’ve ever seen a 1% chance of something bad happening get magnified into It Is Imminent And About To Happen, but that’s how this story is increasingly being spun. It’s misleading at best, and harmful at worst, when one major initial purpose of the earthquake advisory was simply to acknowledge that scientists are paying attention to what’s going on down there instead of just ignoring it.

Wait, but it did go up? How, then?

Faults are actually a lot like people. They undergo a lot of stress from day to day. For people, stress can come from a lot of things, but for faults, it mainly comes from the long-term motion of tectonic plates. People have a whole lot of different coping mechanisms to not break under the stress, but all faults share the same coping mechanism: friction. Just like you may have a breakdown when you can’t handle the stress in your life, faults break when the amount of stress they’ve accumulated is too much for friction to resist. That breaking process is an earthquake.

Most of the stress on a fault comes from plate motion, but other earthquakes on nearby faults can also add stress to the picture. The bigger the earthquake, the more stress it inflicts on everything around it. But, unlike stress accumulation from plate motions, the stress change from another earthquake is pretty instantaneous. It’s possible - and has happened - for an earthquake to set off another one within seconds, hours, or even a couple of days, but the longer you go since that earthquake, the more apparent it becomes that the stress change wasn’t enough to send any other faults into breakdown mode.

So - that increase in earthquake likelihood on the San Andreas, up to maybe as high as one percent last week, came from the stress changes from this earthquake swarm on top of the regular tectonic stresses. The odds are lowering again now that the swarm itself is slowing down.

But the bigger issue is - is that increase actually something to worry about?

I’d say not particularly, no, and I’m not alone among seismologists here.

Firstly - there are lots of swarms like this near the Salton Sea. They happen a couple of times per decade, and they tend to last for a few days. Swarms in this area in 2008 and 2012 had earthquakes with magnitudes in the low 5s; the largest one this time around has been a 4.3. These earthquakes all occur on faults that are not the San Andreas, and so far, there is zero historic precedent for one of these swarms directly preceding earthquake on the San Andreas, or any other fault. All of these swarms also raised stresses on the San Andreas, raised the odds of a larger quake to something like what they were last weak, just without a formal earthquake advisory issued - and nothing happened. This is enough precedent that, basically, if there IS a Big One soon, it was very close to happening anyway regardless of the current swarm. It’s entirely possible that a swarm event could eventually be the proverbial straw that broke the camel’s back, but there just isn’t enough energy involved in one of these swarms to bring the fault from Not Particularly Close to Big One. It won’t be the cause in and of itself.

Secondly - earthquakes that aren’t parts of swarms also affect stresses on nearby faults. The larger the earthquake, the more substantial the stress change, and the longer the period of increased hazard. Things like the 1992 M7.3 Landers or the 2010 M7.2 El Mayor Cucapah earthquakes kicked the San Andreas a lot harder than this week’s swarm of 4s did, but that didn’t set it off, either. If a similar earthquake advisories has been published after those, the percentages would’ve looked scarier than 1%. Earthquake scientists were actually pretty worried after Landers and its M6.4 aftershock near the San Andreas in Big Bear, and that’s not the case right now. We’re observing, but nobody’s particularly worried. Basically, faults affect each other all the time, it’s just that those effects are usually not the immediate triggering of another large earthquake.

Thirdly - the southern San Andreas is considered the highest hazard fault in the state already, but we’ve been living with it that way for a long time. The last earthquake on the part of the San Andreas was sometime in the late 1600s, and the average time between earthquakes on that section of the fault is more like 200 to 250 years. This is a section scientists have been saying is due for a while, which is what brings on the extra attention when there’s a swarm, and the extra nervousness. The most recent USGS statistical earthquake forecast - based on everything we know about every fault in the state - puts the odds of a M6.7 or greater on the southern San Andreas Fault at 19% within the next 30 years and the odds of a M7.5 or greater at 17.3%. That’s the baseline we’re living with, and this swarm hasn’t changed it by very much or for very long. And for another southern California point of comparison, your odds of getting into an accident on a Los Angeles freeway in any given year are higher than the yearly odds of a San Andreas earthquake, let alone your odds of being hurt in that earthquake.

So then…why issue a statement at all?

This kind of thing shows that scientists acknowledge the swarm, acknowledge it’s in an area that has already had media attention for being high hazard, and acknowledge that people are nervous. (Which, hooboy, the advisory did fail as an effective acknowledgment of nerves, looking at the reaction it’s caused.) It’s also some insurance against anyone who can claim later that “nobody said anything about the risk” if this becomes the unprecedented case where the swarm does lead to a damaging earthquake. That was the case with a swarm in central Italy in 2009 which eventually lead to a M6.4. The L’Aquila earthquake killed a bunch of people, and the scientists involved ended up on trial for manslaughter for ostensibly not acknowledging the change in risk. The whole L’Aquila situation was a huge mess of bad communication and bad policy, and that part of Italy didn’t have the precedent of lots of swarms without a bigger quake like the Imperial Valley does, but hey. It happened. We want to avoid that here in California.

Another important goal of advisories like that is to remind people, yes we’re on an active plate boundary and we have earthquakes. Yes, preparedness kits are a good idea. A lot of folks seem to misread “check your emergency kit” as “you’re gonna need it really soon” though, which is…a problem that may be hard to work around. But if you can’t use small earthquakes as a motivator to prepare for big ones, that’s a problem, too. If people are only motivated to prepare in hindsight after getting wrecked by a large earthquake, that’s not an effective mitigation strategy. I absolutely always tell people to use small ones as a reminder to prepare for big ones, but media storms like this are just a sign that scientists need to watch our phrasing, too…