The Trembling Earth

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First-hand documentaries from the Tohoku quake and tsunami

Several eye-witnesses of the March 11 M9.0 in Japan have posted chilling first-hand footage of their experiences. The following two videos document the entire disaster, from the shaking until deep into the tsunami.

First, here’s the harrowing video taken by a professional storm chaser who happened to be in Otsuchi, Japan doing volunteer work for Save Japan Dolphins when the earthquake roared along the coast. He struggles to keep his balance at the tail end of the earthquake, then they hop in their car and spend eight precious minutes fleeing to high ground with the rest of the alarmed population. These guys are clearly professionals; they have incredible composure. As they navigate their way through town you hear radio correspondence with a second car behind them full of other dolphin activists, the Sea Shepherds. While the tsunami roils its way into the bay from the open ocean, the water level creeps up and floods the seaside industrial buildings. As usual with footage of the tsunami, it keeps on coming, getting higher and higher against all belief.

This next video is unprecedented: a high-def dashboard camera in a bus records the entire event, most of it from in/on the tsunami! It was recently recovered, and we get to witness its journey. It would be marvelous if someone who knows Japanese could do a little translation of this report. Watch this; the following text is a spoiler.

It’s incredible to watch as the bus helplessly bobs with mounds of urban flotsam, but the literally immersive perspective reveals fascinating gradients in the velocity and height of the tsunami’s flow as it rages through city streets. The bus seems for a while fortunately stuck in an eddy behind a huge concrete building… until it gets entrained in a rapid flow and slammed up against something, at which point debris pierces the windshield, water rushes in, and the camera dies.

There’s at least one more street-level recording of the tsunami pouring into town. Once again what begins high and dry ends up so far below water it defies imagination.

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Swaying high-rises and resonance frequencies

In a post a few weeks ago I linked to a humbling video of high-rise buildings in Tokyo swaying after the 9.0 quake. Well, those buildings were full of tens of thousands of people, plenty of whom had cameras. That video was only the beginning; below are many more that capture the dramatic oscillation of the towering steel edifices.

The swaying is especially clear in the following video, likely filmed during the 7.9 aftershock that happened shortly after the 9.0. The tsunami is already on the news, and smoke is billowing from the distance. It must have been alarming to start shaking again while watching the startling consequences of the first quake unfold.

The triplet of skyscrapers below is linked together by walkways high in the air. Clearly the walkways were engineered with earthquakes in mind, as they collapse and bend while the buildings swing differently.

From inside one of the swaying towers you can hear the surrounding building creak:

While high-rises do rattle and shake from earthquakes, the “gentle” swaying is a result of their resonant response to the low frequency waves unleashed by large earthquakes. Imagine an especially tall building being pushed to the side, from the bottom. The huge building has a lot of inertia, and it takes time for the force at the bottom to be transmitted up through the beams to the top. When the forces reach the top (a matter of less than a second, probably) the whole building will be in motion, moving to the side. If you suddenly stop the bottom, the top maintains its momentum and overshoots this position until the structure’s stiffness halts it and the elastic property that allowed it to flex forces it to recover that deformation and swing back the other way. This single impulse (pushing the building to the side a finite distance) results in an oscillation of the un-anchored end of the building (the top) as the force imparted at its base is gradually dampened or absorbed by flexing, heating, and creaking of the beams.

Now, if instead of stopping the bottom of the building you reverse it and push it back the other way, this would amplify the distance the top has to travel once it swings back, adding momentum to the return oscillation and enhancing the swaying. The same thing goes on when you push someone on a swing: you give them pushes just as they swing “forth” so that the energy you input into the system is added to the energy they already have being pulled forth by gravity. If you pushed them as they were coming at you, all of your energy would be expended resisting the force of their swing “back,” and the system (you and the swinger) would lose all of its energy. To make a tall building really sway, the seismic waves must drag its base back and forth at a frequency that matches that of the building’s natural oscillation–its resonant frequency. That is to say, if you “plucked” a building and let it wobble it would do so at a frequency that is determined by its material properties, geometry, and weight, among other things. If you then continue to shake it at that same frequency, you’ll accentuate the motion, just like the swing set, causing “resonance.”

Taller buildings have lower natural resonant frequencies than short buildings, meaning that if a broad spectrum of seismic wave frequencies is released, buildings with different resonant frequencies will sway differently. Small 2-story houses have extremely high resonant frequencies, and are thus more susceptible to the very sharp seismic waves experienced most strongly near the epicenter of a quake. Sky-scrapers may start swaying at huge distances from a quake, where high-frequency waves have died off and all that are left are the low-frequency seismic waves people can barely feel (we have even higher resonant frequencies than houses, if you want to think of it that way: it’s sort of why a bus braking hard makes us fall over whereas a train stopping for hundreds of yards leaves us upright).

In fact, there’s an impressive video from the May 2008 M8.3 Wenchuan earthquake in central China… filmed over 1,000 miles away in Taipei! At the top of Taipei101, currently the second tallest building in the world, is a “tuned mass damper”, essentially a giant dense metal pendulum designed to counteract the swaying of the building due to wind or earthquakes. On the afternoon of the Wenchuan quake, tourists looking at the orb witnessed it in action as it counterbalanced the passing seismic waves from the distant quake.

The video illustrates just how slow this swaying is. Without the pendulum for reference it is unlikely anyone would have noticed.

On the other hand, the magnitude of each oscillation in the Tokyo high-rises is almost certainly enough to have made plenty of their occupants nauseous. Fortunately the slow swaying keeps their contents from being thrown around too violently, making them among the safer places to be in a quake.

Earthquake early warning in action

No country would have been better prepared for such a massive earthquake than Japan. Straddling the boundaries between four converging tectonic plates, Japan is one of the most earthquake prone nations in the world, and is probably the most earthquake savvy. They have world-class networks of monitoring instruments including seismometers, tide gauges, and GPS locating stations; they routinely practice for massive quakes, which they are often visited by; and they have something Californians at this point still only dream of: an earthquake early warning system.

Screenshot of Japan's earthquake early warning system in action during the Tohoku quake. The upper panel shows a projected shaking intensity level at the computer's location, the middle panel shows a countdown until shaking begins, and the lower panel shows the current calculation of the earthquake's size.

The idea behind it is simple: the electromagnetic waves needed to transmit a warning travel effectively instantaneously, while seismic waves travel at “only” a few kilometers per second, delaying their arrival to distant locations. It’s exactly like lightning and thunder–the flash is nearly instantaneous for everyone, but the immediate cracking thunder up close differs from the delayed rolling rumble heard from far away, which is why we count the time between the flash and the bang to judge how far away a strike was (~five seconds per mile, in case anyone needed a reminder). The analogy isn’t entirely complete. Earthquakes aren’t the product of some abrupt electromagnetic signal like thunder is produced by lightning. In effect what early warning systems do is take the loud, close thunderclap and warn people tens of miles away that they’ll hear a rumble soon.

For people close to the epicenter of an earthquake, the time between detection of the quake and the onset of shaking where they are is minimal, so early warning is of little use. People farther away, however, have potentially tens of seconds’ warning that the seismic waves are on their way. Unfortunately for the utility of the system, the intensity of shaking dies off with distance, so it’s the people closest to the epicenter who need the most warning. Too bad… for most quakes. The system is at its most ideal for a massive quake like the 9.0 last month, which took nearly three minutes to produce and ended up rupturing hundreds of kilometers along the coast, effectively stretching the epicenter–or at least the source of seismic waves–so that cities that weren’t near the epicenter still ended up being close to a part of the fault that ruptured. In that case, the 30 second warning for the onset of shaking helpfully prepared people for the intensifying shaking after 3 minutes of rupture propagation.

In an earlier post I highlighted an amateur video showing the warning system in action. Thanks to the similarly excited Dr. Matthew d’Alessio at Cal State Northridge, I can guide you to an excerpt from one of Japan’s TV networks as the alert for the 9.0 quake preempts coverage of parliamentary proceedings:

The video gives an eerie perspective of the event unfolding: the quake is detected and reported long before shaking reaches Parliament, and the staff at the news studio have only just begun to realize the gravity of the event as the shaking intensifies. Only once the shaking has died down does attention shift to the dire tsunami warning.

The mere seconds of warning afforded by earthquake detection apparently pale in comparison to the minutes we have for tornadoes, days we have for hurricanes, and weeks we have for flood events, but they do allow you to drop crucial tasks and focus on the calamity at hand before it gets the best of you, a function automated systems are even better at!

The technology behind this is impressive, and by no means beyond the grasp of the U.S., but the development of a useful system requires a major budget, and the U.S. is busy… prioritizing. But that’s a subject for many a different blog.

In Japan, the software that runs these systems is developed by scientists and private companies, and has a variety of manifestations.

I’ll leave you to marvel at the system in action in a few different cases. As more information is processed from the ever-increasing number of seismometers detecting the earthquake, the epicenter and magnitude are revised, altering the estimates of arrival time and shaking level at the site, in a format unfortunately reminiscent of a painful scene in a certain NBC mini-series…

Here’s a little wall-mounted device that tells you all you need to know–don’t mind that this guy fakes the quake (maybe a test?):

Here’s a family taking appropriate action in an earlier, much milder quake:

The revision of magnitude calculations is common–in most cases it happens well after the earthquake, as data comes in from seismic stations around the world that help constrain just how much energy was released. It’s especially common after the so-called great earthquakes, which produce such large waves for so long that they drown out their own signals on seismograms, making them especially difficult to analyze. In any earthquake, however, realtime assessment of the magnitude is a dicey game. That’s not to say it produces inaccurate results from the data–there just isn’t enough data when only a few seismometers have been shaken yet! As more sensors detect the earthquake, a more robust magnitude and location can be determined. It’s more or less the same reason you have to watch replays from multiple angles to truly disagree with sports referees.

Japanese videos of the Tohoku earthquake and tsunami

So many videos of the March 11 M9.0 Tohoku earthquake and ensuing tsunami exist that collecting and disseminating them is a daunting task. In my three earlier posts on the subject I referred you to a variety of perspectives of both events (the quake and the tsunami). Since then plenty more clips have emerged, and continue to. I’ll make an attempt to guide you to a few of the more spectacular or interesting ones; the rest can be found through potentially endless browsing among the chain of “related videos” on YouTube.

The earthquake

The following surveillance video is one of the few that I’ve found recorded from a well-mounted stationary camera, removing the shakiness of handheld cameras that makes it difficult to discern real ground motion. As the camera remains strongly braced against the ceiling/wall, we can much more clearly see the motion of the contents of this building as it sways in the quake. The footage is from a 5th floor office in Koto Ward, Tokyo. Note the duration of shaking–over two minutes!–and pay attention to changes in the direction of shaking. The two most remarkable aspects of this footage are the variability in direction and intensity of shaking. The shaking we observe doesn’t reflect true ground motion, but rather the building’s response to that force from below. The building twists and wobbles as it’s shaken from beneath, perhaps adding to the fluctuating intensity of the shaking. The large source area of the earthquake (a huge patch of the subduction interface that ruptured) also contributes to the fluctuations in shaking as waves from early in the earthquake bounce around beneath the city and interfere with incoming waves from the later parts of the rupture. Shaking intensifies as it proceeds, likely representing both the interference of old and new waves and the gradual approach of the earthquake wave source southward as the rupture propagated down the coast, closer to this building.

The next clip was filmed outside and only coincidentally captured the quake, unlike most of the others in which people had enough time to run and grab their cameras.

Here a couple of young American tourists witnesses the quake in a Tokyo park. The rustling trees and alarmed birds provide a glimpse of quakes sans humans, while the warning siren adds an eerie gravity to the situation.

The tsunami

All of the videos of the tsunami I have seen are powerful, terrifying, and staggering to watch. Here are a few Japanese videos of it pouring into coastal harbors on the northeast coast, filmed from shore-front office buildings.

The most astounding part of these videos is how quickly the surge in sea level overtakes the seawalls and surges inland. It happens so quickly and easily it seems almost calm, belying the utter violence of torrents of water pouring into the city streets.

The tsunami easily overtakes the seawall in Shiogama, and the warning siren adds a chillingly stoic urgency to the unfolding disaster. “This is really happening” is the message I get.

Another video from just down the pier in Shiogama, where passenger ferries wait at a floating boarding platform. This video is filled with markers to indicate how high the water rises–watch especially the loading ramps and the bottom of the 2nd or 3rd floor balcony the videographer is standing on.

[Updated 4/18/11 10:35am]: Here’s a 3rd video of the tsunami overtopping a seawall, this time in Kesennuma port. The utter devastation wrought by the tsunami surge is plain to see here: it destroys absolutely everything in its path–everything you think it might wipe out from the beginning of the video… it does. This is how you end up with those scenes of utterly razed coastal towns. I can’t imagine this cameraman wasn’t utterly fearing for his life.

Below is yet another unbelievable video of the tsunami swelling into Kesennuma. This one is chock full of massive ships being swept through town, and like the other ones it shows the sea continue to flood inland to an astonishing depth.

This next video is a long one (~10 minutes), but well worth watching to see the full beginning of the tsunami unfold. There are fascinating eddies, currents, and surges to watch interact; you see how easily boats can get tossed around; and believe me, it doesn’t get truly intense until the end, even after you thought the worst was past. It’s like the first quake video above: don’t be fooled by the duration or waning intensity of the disaster at hand. In both cases it just gets worse and worse.

Finally two much shorter clips of the wave crashing ashore. The first I haven’t been able to find the raw clip of, but the news excerpt will suffice. The perspective is from the ground in what appears to be a similar area to–if not the very same–the region filmed so famously from the helicopter as the flaming black goo surged ashore. The clip of interest is short, and it’s merely of the wave cresting and crashing, but it is a formidable sight to see with its towering height:

Here watch the incredible volume of water surging forth as it’s launched over a breakwater and then speeds rapidly ashore:

The last video I want to share today serves as an incredible illustration of the age-old wisdom that a deep drawback of the sea forebodes a devastating surge back inward. Don’t go collect fish when you see the ocean get sucked out! Throughout this video there are various items for scale that give a staggering perspective on just how low the sea has dropped in advance of the inward surge of the tsunami:

I have hardly referred you to a fraction of the videos out there, so if you’re in awe of these there are plenty more to be found by clicking through the related videos on YouTube. As you watch these videos that bring you closer to the scene and evoke some vicarious experience of the terror, do consider the plight of those millions displaced; there are links to major aid organizations in the right-hand panel.

Footage of the March 11 tsunami around the Pacific

Plenty of news organizations have been collecting the extensive footage of last week’s tsunami generated by the M8.9 earthquake in Japan, so following along with them is a great way to keep up with the utterly humbling images from the interface between humanity and this planet’s powerful nature.

In particular the BBC has compilations of video from Japan, CNN has a scary view, and the L.A. Times has some footage from the California coast.

A good place to start is with the BBC’s superb explanatory video describing how tsunamis form. Despite the ocean-wide impact of Friday’s tsunami ($50 million in damage along even the CA coast alone), the risk that the U.S. faces from a locally-generated tsunami varies depending on where you live. In particular, although the entire west coast is a tectonic plate boundary, only the northern portion of it is a subduction zone, capable of producing the huge displacements of the seafloor that spawn tsunamis. An L.A. Times article begins to explain that SoCal’s earthquakes don’t pose a tsunami threat.

Here are a couple of humbling tsunami videos from Japan that I haven’t seen widely circulated on the major English news networks. In each of these the incessant and ever-increasing influx of water is almost unbearable to watch and gives a clear sense of the power behind this natural phenomenon.

You can find the other videos here and in this overwhelming film posted on facebook.

Our plight here on the west coast of the U.S. pales in comparison to the utter destruction Japan is facing, but footage of the surge coming ashore in California and Oregon serves as an eye-opening reminder of the tsunami’s power. In this beautiful video we see the surge in sea level coursing through San Francisco Bay toward the coast of Berkeley.

In that video the incoming water has slowed and risen into an elegant series of waves, which crash ashore onto an exposed beach. The waves immediately inundate the shoreline, revealing the elevated sea level driving them. You’ll also notice sharp waves reflected from the shore, crossing the incoming waves almost perpendicularly. Great illustration of constructive and destructive interference.

The tsunami surges into San Francisco Bay on the morning of March 11. The bay bridge and hilly SF skyline are visible in the background. Photographed by Steven Winter. Thanks to http://www.geomika.com/blog/ for highlighting it.

There are many more videos of the wave entering San Francisco Bay, as well as some great time lapse views of other coastal areas, and an impressive shot of one surge barreling through Santa Cruz Harbor that clearly illustrates how so much damage was done by a relatively small wave.

Tidal gauge stations and buoys are another great way to view the effects of the wave all around the Pacific. In Japan, tide gauges are still recording rapidly oscillating water levels along the shore. These hardly compare to the water levels associated with the initial onset of the tsunami, but the Pacific ocean is still clearly in much more tumult than it was in the relaxed days before the quake.

Tidal gauging station from the central coast of Japan on March 11, recording the onset of the tsunami. The green line below is the "risidual," which is effectively the difference between the water level and the expected tide.

Check out other tidal records from Japan yourself:

http://www1.kaiho.mlit.go.jp/KANKYO/TIDE/real_time_tide/sel/index_e.htm

Thanks to friends, relatives, and colleagues alike for directing my attention to some of these amazing perspectives.

More unique perspectives of the 8.9 quake

As expected, videos continue to surface from people all over Japan documenting the shaking, rattling, and swaying of everything. Below I have collected some of the more interesting sights.

I recommend visiting Highly Allocthonous where Chris Rowan has summarized the which, what, where, and how of this massive quake. He’s also put together some nice little diagrams illustrating the more technical concepts.

The whole country of Japan shook for a very long time on Friday afternoon (their time). Beaches, farms, rural villages, forests, mountains, trains, and high-rise office or apartment buildings rattled for around two minutes while the plate boundary deep beneath them unzipped.

In Tokyo, the towering steel high-rises swayed with the low frequency waves passing through–a humbling sight from any perspective:

People’s responses to the shaking varied. This man has an understandably difficult time comprehending the emotional response of his neighbors. He’s alarmed at how much worse than the 7.2 foreshock two days prior this earthquake turns out to be. He runs outside into a cacophony of rattling structures:

This awesome video demonstrates Japan’s earthquake early warning system in effect. When the first seismometers in the country pick up the high-amplitude waves from this quake and determine its epicenter, an electronic signal is broadcast instantaneously, far in advance of the much slower seismic waves. This person has at least 30 seconds warning before the brunt of the shaking arrives. The shaking also gets worse and worse as it goes on–something many people would not be prepared for and anyone would find quite alarming.

In addition to informing people through the software shown in the previous video, the early warning system stops trains around the country to prevent derailment at high speeds. These folks are on one of the stopped trains when the waves start passing:

Here are some other videos I’ve stumbled across:

Other than the cameraman, these folks very aptly demonstrate the appropriate earthquake protection procedure while their apartment shakes heavily. On the other hand these fellows don’t seem to realize the import of the situation, although they appear to be only “gently” rocking in the upper stories of a building, like these office workers whose video doesn’t capture much apparent motion, but whose dialogue reveals the eerie sensation they’re witnessing.
In this video the quake rocks a 6th-floor bookstore.
Here we see the quake rocking a snowy temple, one that no doubt has experienced hundreds of these before. Watch the trees shake!
A shocked man sits helplessly in his car as the city trembles and the power goes out.
A transit station shakes noisily for a long time while commuters crouch to avoid being knocked off their feet.

In these videos it is indeed clear that despite extensive training drills, people are often overcome by the surprise and novelty of such a huge quake. In most cases, running outside is not a good strategy–imagine windows and cornices crashing down from the building you were in, or tiles sliding off the roof. Doorways are only safe to the extent that you can get yourself within a shear wall–your real security depends on the strength of the wall. Heavy, compact furniture is most often your best bet. Don’t let curiosity and surprise get the best of you!

Japan quake felt over >2500km radius

One of the many remarkable features about this planet’s largest quakes (like the one that just happened in Japan) is their truly global effect. Be it the tsunami or seismic waves perceptible and imperceptible, most parts of the planet have been touched significantly by the 8.9.

Let’s start with perceptible seismic waves, i.e., ones people don’t need sensitive instruments to detect. The elastic energy released by this earthquake was enough to set the ground rippling at frequencies and amplitudes people can percieve at distances of greater than 2,500 kilometers (over 1,500 miles).

Shaking intensity as reported online by citizens of east Asia. Data points are colored by intensity and sized by city population. The USGS Did-You-Feel-It page (click image for link) contains the original data and plots of response time and attenuation with distance.

Note the felt reports in Taiwan and Beijing. This affected radius is quite comparable to the huge swaths of the globe that felt both the M8.8 Maule, Chile event last year (most of South America) and the 2004 9.1 Sumatra, Indonesia quake (most of southeast Asia and India):

Felt reports from the other M~9 earthquakes that have occurred since the advent of the USGS's Did You Feel It surveys.

Not only did the perceptible shaking stretch far around the globe in all of these cases, but sizeable elastic waves detected only by sensitive seismometers rippled through the solid crust (and bounced around deep in the mantle), observably circling the globe several times.

Seismic events larger than M~6.5 tend to be recorded globally on broadband seismometers–those that can detect a broad range of frequencies, from sharp local jolts to the long, slow undulations of large, distant quakes. I’ll have another post on seismic waves and attenuation later, for now suffice it to demonstrate the following: Below is a seismic record from northern California showing waves from the 7.2 “foreshock” in Japan on March 9.

Northern California seismic recording of a 7.2 in Japan on March 8 (9th in Japan). Read this like a book; each line represents 15 minutes of recording, so where the oscillations last >15 minutes the records overlap, making it a bit messy. Basically, the ground oscillated detectably in California from the distant quake. The amplitude of ground motion is small, and the frequency of the largest waves is 1 per ~30 seconds, meaning it takes the ground 30 seconds to oscillate one way then back the other, slower than your bedroom fan... no wonder we can't sense it without seismometers.

Compare that to the Mar 11 M8.9 in virtually the same location recorded on the same instrument:

Magnitude 8.9 earthquake in Japan recorded in northern California. The amplitude of ground motion is literally off the charts, but since the frequency is relatively low, we couldn't feel the waves passing though they certainly were.

Now, check out yesterday’s:

March 11 seismic record section from northern California

At the top of the record section is the messy, high-amplitude disruption from the initial passage of the 8.9’s surface waves. Just before 12:00 UTC you can see the dense green squiggle that represents the arrival of seismic waves from a 7.1 aftershock in Japan, with the early high-frequency waves superimposed on the low frequency oscillations continuing from the 8.9.

Several large Japanese aftershocks are apparent throughout the next few hours (in the low- to mid- M6 range, represented by occasional dense, high-frequency squiggles). The record in the background continues to undulate irregularly as elastic waves reverberate through the Earth, bouncing off of the dense metal core, refracting and reflecting off of every boundary or irregularity they come to. Imagine someone jumping into an undisturbed swimming pool–or try it yourself!–and watch as the initial coherent rings of waves bounce off the walls and turn the pool surface into a sloshy, ripply mess. That’s what has happened to the planet.

At around 02:00 UTC another extended period of oscillation begins. This likely represents the (much-diminished) seismic waves from the original earthquake re-circling the globe. Hopefully someone with more seismology expertise than myself will soon put together a nifty stacked plot like this one from 2004 illustrating this repetition.

Of course, the tsunami still has the Pacific ocean sloshing about, roiling in turbulent currents where it reaches the shallow topography of coastlines.

You can see just how turbulent and dangerous this ocean-wide surge of water can be in this video from the coast of northern California, taken as the tsunami arrived. Pay attention to the speed with which the water rises and falls.

Many thanks to Aron Meltzner for doing some superb video sleuthing and pointing me to many of the tsunami clips. I may post a compilation of more footage from all around the Pacific in the near future.

Japan’s 8.9 quake and the Pacific tsunami

Everyone–scientists and public alike–has been inundated with information and media about yesterday’s gargantuan earthquake in the subduction zone off the coast of Japan. Its occurrence at midday in one of the most technologically advanced countries in the world has offered some unprecedented views of the phenomena accompanying Great earthquakes.

The tsunami generated by the Magnitude 8.9 earthquake pours ashore along the Iwanuma coast in Japan on March 11. Image courtesy http://www.nola.com

There is an innumerable multitude of videos of the quake happening, which YouTube has already begun compiling on its CitizenTube channel. No doubt this collection will grow and grow in the coming hours and days. Here are some highlights:

A grocery store rocks relentlessly as workers scramble to hold up jostling goods:

Two high-rise buildings sway threateningly toward each other while officeworkers across the street look on

There’s also a noisy video of the city shaking filmed from outside on the street:

In this immediately post-quake video you hear the eerie wail of civil defense sirens warning of the imminent tsunami:

A video I find particularly fascinating is this footage from inside a laboratory of some fancy seismic safety equipment doing what it’s supposed to: buffering the countertop equipment from the shaking of the room around it

Everyone has no doubt seen the truly horrific footage of the tsunami surging inland on the hard-hit northern coast of Japan, compiled here by the BBC.

This was the 5th largest earthquake humans have ever recorded with instruments, surpassed by a 1957 9.0 on the Kamchatka peninsula, the 2004 9.1 in Sumatra, the 1964 9.2 in Alaksa, and Chile’s 9.5 in 1960. The energy released by this earthquake was tremendous, and is still ringing the globe. People may be surprised to hear the relatively low casualty count of such a sizable temblor (tsunami aside), but this tends to be the M.O. of subduction zone megathrust quakes. Although they represent the unzipping of a vast swath of Earth’s crust, the ruptures are buried deep and emerge far offshore, meaning that despite ground shaking that lasts for hundreds of seconds, only modest accelerations are experienced on land, nothing strong enough to bring down buildings.

As is common, the New York Times has some excellent graphics illustrating what went on.

Unfortunately, I must get on with the day’s actual research, so I’ll update this post a bit later. Feel free to add links to info, images, etc. that you find. Callen Bentley at Mountain Beltway blog has a good summary post and links to blogs a-plenty covering this event. I’ll be back once today’s to-do list is all checked off!

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