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November 21, 2012Posted by on
A new video from Japan [embedded below] shows liquefaction occurring at a scale and scope that I haven’t seen before in video footage. The video is from Urayasu town, Chiba Prefecture–an industrial suburb of Tokyo that appears to be sited on made land adjacent to Tokyo Bay. No wonder it sloshes so heavily: made land (fill) is particularly susceptible to liquefaction. We just can’t pack things down the way nature can over millennia.
The video starts in the aftermath of the March 11, 2011 M9.0 Tohoku earthquake, where sediment-filled ground water is bubbling up through gaps in the pavement, or any other fractures that represent escape routes. Within minutes, the M7.9 aftershock hits, and you can see light poles, trees, and buildings shaking violently. All the while, the engineered infrastructure sloshes and bobs, essentially floating on a thick package of fluid-saturated mush. The differential swaying you observe is effectively the dramatic reduction of seismic wave velocity in the loose, fluid-supported substrate. The sound you hear is largely the metal guard rails creaking as they’re stretched and bent. The oscillations last for a very long time.
Liquefaction commonly accompanies large earthquakes in areas where a shallow groundwater table supports suspension of soft soils when it’s shaken. I’ve posted videos of the phenomenon before. It occurs during any earthquake that strikes an area with the right mix of water-saturated sediments. It was widespread throughout Christchurch in each of their big jolts in 2011, and occurred pervasively in the shoreline areas of Japan during their monstrous 2011 quake. Fractures opened during shaking provide conduits for this newly mobile soil slurry to escape surface-ward under the weight of dry material above, producing sand volcanoes, like the one pictured in the righthand image of this blog’s banner.
After watching these videos, it’s clear why this phenomenon results in such destruction, particularly to pipelines and underground utilities. Water main failures may add to the fluid pressure mobilizing all the soil.
When you hear about the danger of living on “fill” and the destruction of liquefaction, these illustrative clips should come to mind.
November 5, 2012Posted by on
Saturday [November 3, 2012] marked the ten-year anniversary of the largest quake to hit the U.S. since 1964, and the 1906 SF quake before that. The M7.9 Denali earthquake tore a ~250 mile gash through Alaskan glaciers and pine forests along the Denali Fault, which runs beside the eponymous mountain also known as Mt. McKinley, North America’s highest peak.
Much like the Haida Gwaii earthquake last week, the Denali quake shook mainly sparsely populated areas, so it was much more probable that anyone feeling it would be on the outer fringes of the shaking from the massive temblor. Indeed footage from a home in Anchorage, 160 miles from the epicenter, shows slow rocking–that telltale sign that some place moderately far from you is really getting hammered. Despite the low frequency of the shaking in this video, its strength is clear, and it lasts a very long time–another sign that you’re on the fringes of a huge earthquake.
One of the many legacies of this earthquake was that it put the trans-Alaska oil pipeline to the test. The pipeline crosses the Denali fault nearly perpendicularly, and was constructed with the knowledge and anticipation of offset along the fault. For ~1,000 feet on either side of the fault, the pipeline’s supports rest in tracks that allow it to shift laterally and bend as the ground beneath it carries the tracks in opposite directions. The structure was designed anticipating an earthquake of magnitude 8.0 with 20 feet of coseismic lateral displacement. At nearly the anticipated size, the Denali quake was a resoundingly successful test of earthquake engineering, which spared us an enormous environmental disaster.
Both its size and its geometry suggest that this rupture may be an excellent modern analogue to the earthquake that ripped along the San Andreas Fault in 1857, before southern California was heavily populated. It thus serves as an excellent source of modern data (seismic recordings, satellite imaging, GPS velocities) to help understand what a repeat of the San Andreas rupture will be like. For example, seismic records from the Denali quake are used in structural engineering tests of seismic safety design, simulating the type of shaking that may be expected around Los Angeles in the next SAF quake.
The USGS hosts a great set of photos from the spectacular Denali fault rupture, including offset glaciers, newly formed waterfalls across the scarp, huge landslides, and my personal favorite: this unfortunate tree that was growing directly atop the fault trace and got sheared in half.
November 1, 2012Posted by on
Last weekend a large quake rocked the Pacific Coast of Canada. In my post about it I mentioned that not much footage had surfaced. There’s still rather little, largely–I suspect–because of the quake’s remote epicenter. Nonetheless it was a very large quake, so the distant, low-frequency waves swung chandeliers and played with people’s balance across western Canada. The videos people have posted so far are collected in the compilation below. In all but the last, the quiet, slow rocking indicates substantial distance from the source of the shaking (that is to say, ~the epicenter). The last video appears to be much nearer the epicenter given the relatively high frequency and violence of the shaking (skip to 3:00 minutes in the video if you’re eager to just that exciting part).
Earthquakes’ high-frequency energy gets dissipated quickly as they ripple outward, relative to the long-period, low-frequency waves. You observe this effect when a car drives by you with the bass thumpin’: you hear (or feel!) the deep resonant rhythm, but unless you’re inside the car, you can’t hear the high-pitched song going on above it, which gets absorbed by vibration of the car parts.
Slow rocking is a tell-tale sign that a big earthquake is going on and that you’re very far from its epicenter.
October 29, 2012Posted by on
Amidst the dire warnings and general alarm about the legitimately fearsome Hurricane Sandy, you may or may not have heard about the massive quake that rocked Canada’s remote Pacific coast on Saturday night, and the modest tsunami is sent racing across the Pacific.
At 8:04pm Saturday (PDT) the M7.7 quake rippled out from beneath Haida Gwaii, an archipelago off the British Columbia coast formerly known as the Queen Charlotte Islands. The quake was partially right-lateral, partially thrust, on a relatively steeply dipping reverse fault plane–just a bit north of the Cascadia subduction zone. At the latitude of the quake, the North American tectonic plate is not overriding the Juan de Fuca oceanic plate, but is grinding sideways along the Pacific Plate [pdf], akin to what’s happening in California, but with a bit more convergence.
The earthquake struck a very sparsely populated reach of the North American Pacific coast, but it was large enough to be felt south to Vancouver, BC and Bellingham, Washington; north to Juneau, Alaska, and inland all the way to Edmonton, Alberta. Not much footage of the quake has surfaced, but the Vancouver Sun has plenty of eye-witness accounts, and thanks to IRIS we can watch the quake ripple across the USArray of seismometers, now largely occupying the U.S. Mississippi River Valley.
In most cities the shaking was just moderate, but because of the rupture’s immense size it went on for over a minute. Although footage is rare, the quake’s location offers a unique vision of the quaking: thousands of miles of mountainous BC forest rustling and swaying in the nighttime mist, with few but bears to watch it happen.
A tsunami was unleashed that was a foot or so high as it lapped the shores of Washington and Oregon, but grew to the better part of a meter–with some reports of up to 5 feet–as it washed ashore in Hawaii.
Three hours after the quake, sirens were sounding along the Hawaiian coastline, in a successful drill of the emergency system. Although the waves were ultimately small, I wouldn’t call this a false alarm: a tsunami was observed, models showed potentially damaging wave heights, and the civil warning system was activated. If you’ve got the technology, use it! Sorry your balmy Saturday evening was interrupted…
Most would agree that this was a great test and an excellent reminder to those living a little farther south along the Pacific Coast: one day this earthquake could be yours. Shaking the coastal forests for two minutes is fine; shaking Vancouver, Seattle, and Portland for two minutes will be a little messier.
October 23, 2012Posted by on
The big seismological news that started off this week was the guilty verdict in the trial of Italian seismologists and government officials indicted for multiple manslaughter after the M6.3 L’Aquila earthquake of April 2009.
Natural hazards scientists the world over greeted this news with shock and dismay, and science-savvy folks of all stripes have expressed outrage about the verdict, let alone the trial itself. Angry scientists commonly lament this “trial against science,” and bewildered editorialists decry the absurdity of convicting and imprisoning seismologists for failing to warn people of an impending earthquake, a feat which I’m confident people generally understand to be impossible.
The problem is… Much of this outrage grossly oversimplifies the case, and in fact is commonly based on a fallacious understanding of the trial. It behooves everyone editorializing upon it to understand the nuanced details of the situation. A news feature from the journal Nature last year illuminates these details, providing a complete narrative of the unfortunate incidents that led to this dismaying conviction.
Scientists on Trial: At Fault? – Nature News Feature
In fact the trial was not about failure to predict an earthquake. Rather, the scientists were prosecuted for not fulfilling their alleged duty to properly prepare the populace for an earthquake. This is not so subtle a distinction. This reality shows the case to have more merit than the straw-man accusation of “failure to predict an earthquake,” but it still raises some important questions about how scientists should be expected to act when communicating to the public.
A fantastic synopsis of the incident, the trial, and its implications for the future of expert-to-public communication is publicly available to listen to from the Seismological Society of America, and is an essential prerequisite for informed discussion about this trail.
In that recording, Tom Jordan, director of the Southern California Earthquake Center and chair of the international group commissioned by the Italian government to report on the status of earthquake forecasting operations (ICEF: the International Commission on Earthquake Forecasting for Civil Protection), presents the short history of this incident and discusses the sophisticated questions it raises. His commission’s report is also available to view and is a more technical document, but an important read if your profession involves natural hazard or risk assessment.
Okay Then, What Happened?
I highly encourage you to read the Nature article or listen to Tom Jordan’s SSA talk, but if you can’t muster the patience for those, this synopsis of those synopses may serve as a rough outline of the incident.
L’Aquila, a city in one of Italy’s most earthquake-prone regions, had a series of tiny earthquakes beginning in October 2008. The series escalated through March 2009, during which time a local man started issuing earthquake “predictions” based on radon measurements. These unfounded warnings had no scientific merit but began to alarm the populace as the region continued to suffer frequent small tremors. On March 30, fearing an unwarranted panic, civil protection officials cited this man for inciting public alarm and “forbade him from making any public pronouncements.” In an untimely misfortune, a 4.1 earthquake then struck the region.
Fearing further alarm, the head of the Department of Civil Protection called for an immediate meeting of the National Commission for Forecasting and Predicting Great Risks, in L’Aquila. Given the fluctuating spread and suppression of misinformation, the lack of accurate information, and thus the context of alarm and confusion, it’s not surprising that the press’s involvement at and around this hastily arranged meeting spelled doom for reasoned communication of the real risks. As Tom Jordan et al.’s report mildly explains,
“[during an earthquake sequence] earthquake probabilities may vary over orders of magnitude but still remain low in an absolute sense (<1% per day). Translating such low-probability forecasts into effective decision-making is a difficult challenge.”
Indeed the seismologists and civil protection authorities apparently grappled with how to explain that this ongoing earthquake swarm did not substantially increase the already substantial regional hazard of earthquakes. They discussed the empirical history of earthquake swarms and how they rarely (<2% of the time) resulted in large mainshocks, but were careful to state that that specific risk couldn’t be excluded. They turned their focus instead to dispelling the alarm caused by untested and poorly vetted prediction schemes. Unfortunately, they let the audience guide their discussion. When faced with the unanswerable question of whether there was an imminent large earthquake to worry about, phrased with disarming cultural charm–“so we should go have a nice glass of wine?”–the vice-director of the Department of Civil Protection was jovially lured into a fatal appeasement of the citizens’ fears. “Absolutely.”
Then the most unfortunate coincidence of all occurred. This was one of those <2% when the swarm unleashes a big one. That night (April 6) the M6.3 roared out from the hillsides and collapsed 20,000 buildings in and around L’Aquila, killing 309 people.
The prosecution was brought by several men who had lost their entire families after deciding notto sleep outside as would have been customary after the small preceding shocks. As one of them claimed,
“[the messages from the commission meeting] may have in some way deprived us of the fear of earthquakes. The science, on this occasion, was dramatically superficial, and it betrayed the culture of prudence and good sense that our parents taught us on the basis of experience and of the wisdom of the previous generations.”
Of course it is absurd to lay this loss on the shoulders of scientists, when so many individual decisions and uncontrollable instances led to these specific deaths. A more direct culprit that comes immediately to mind is earthquake-vulnerable construction. The twist here is that the populace had already accounted for that in their cultural custom of sleeping outside after quakes. In their eyes the “official word”–twisted and accidental as it had been–contradicted their understanding of safety “procedures” and misled them into harm. In essence, the scientists failed to fill an information vacuum: they dispelled the alarmism but didn’t replace it with the facts, or even appropriate guidance about the existing earthquake risk. Whether it was their civil duty to do so, and whether their failure to constituted criminal negligence or worse, was subsequently left up to the courts, and now we see how that turned out.
The ICEF report explains the problem precisely:
“Information vacuums can spawn informal predictions and misinformation, and … relying solely on informal communications between scientists and the public invites confusion. In this context, the deployment of systematic and transparent procedures for operational earthquake forecasting must be seriously considered.”
The series of unfortunate incidents and hastily orchestrated public outreach that led to this dismaying conviction invite challenging questions about the role of scientists in public policy and the complicated endeavor that is risk communication and mitigation. They also underscore the need for unified (or uniform) and culturally aware procedures, and offer some lessons that will guide the development of these. Understanding what to tell people about inherently unpredictable risks is hard enough, but when colloquial notions about the risk supplant proper information from authoritative sources, the reversal of these culturally ingrained practices becomes truly formidable.
At the end of the ICEF report, the authors lay out a roadmap for responsible operational earthquake forecasting. Their guidelines are informed by current technologies and practices, and call for continued efforts to test quake forecasting models. In the end they leave us with a sort of mantra of the seismological community:
While the responsible scientific research on earthquake predictability should be encouraged and operational forecasting capabilities should be developed, these activities cannot substitute for civil protection actions well in advance of earthquakes, for example in the design and planning of new buildings, or retrofitting of older ones identified as being at risk. Preparing properly for earthquakes means being always ready for the unexpected, which is a long-term proposition.
With a full understanding of the L’Aquila debacle, I expect that seismologists and the public can maintain a productive and orderly discussion as we develop more useful ways of understanding and communicating earthquake hazard. California’s got a big head start, since we’ve been training you for decades what it means to live in Earthquake Country.
October 20, 2012Posted by on
On Tuesday evening (Oct. 16, 2012) just after 7pm Eastern a modest quake rippled out from a few kilometers beneath Maine.
At a meager 4.0 the quake was quite harmless, but it was a surprising jolt for a rather large region not accustomed to periodic tremors. Cameras filming all manner of council meetings captured the interruption.
In most views the quake is only apparent as a light noise and mild rattling (“I’ve never been in an earthquake my whole life and that was it?” says one woman), but in at least one of them–presumably much closer to the epicenter than the others–the room suffers a sizable jolt that sends its occupants scurrying (by the way: not what to do).
Although the rattled populace (including most of New Hampshire, much of Vermont, upstate New York, and the Boston metro area) reacted with mild alarm and substantial disbelief, New England is no stranger to earthquakes. As the USGS explains, Boston and New York have been rattled by earthquakes since before America was America, including damaging earthquakes in 1638, 1737, 1755, and 1884. Central New Hampshire suffered a moderate (M5.6) quake in 1940, and let’s not forget the M5.2 that rocked a region around upstate New York in 2002. As with most quakes around this region, this one likely resulted from reactivation of an ancient seam in the crust, long dormant but tweaked just right by the complex and evolving stresses across the continent. These minor quakes pop off quite irregularly and of course unpredictably.
For a more comprehensive list of earthquakes in your New England state, have a look at the USGS’s state earthquake history pages. They’re not as rare as you think!
October 18, 2012Posted by on
The Great ShakeOut is happening now! Millions of people across the country are practicing their Drop, Cover, and Hold On, using the video below to guide their drills. Take this opportunity to think about, talk about, and practice what you would do in an earthquake. Think about it everywhere you go today: what would you do if an earthquake hit now? The Earthquake Country Alliance has some answers for you.
October 15, 2012Posted by on
On October 15, 1979, a M6.9 earthquake struck the Imperial Valley of southern California/northern Baja. In 2006 a M6.7 earthquake rocked the island state of Hawaii, damaging thousands of buildings at a cost of $73 million. On October 16, 1999, people throughout the U.S. southwest were rolled from their slumber by the massive M7.1 Hector Mine earthquake that struck the Mojave desert at 2:46am. And of course… on October 17, 1989, the Battle of the Bay baseball World Series was interrupted in San Francisco by the devastating M6.9 Loma Prieta earthquake. …And let’s not forget the 1935 M6.3 Helena, Montana earthquake of October 19, part of a series that cost the city dearly, and should serve as a reminder that the intermountain west and the Rocky Mountain front are not free from seismic danger.
This year the drill has expanded far beyond California, incorporating participating agencies in countries around the world. The U.S. is divided into official ShakeOut regions, including many individual states and some at-risk regions like the New Madrid seismic zone, each with their own specific issues when it comes to earthquake hazard. Nearly the whole country is covered, so I encourage ALL of you to sign up and Shake Out.
In most of the U.S. the drill takes place on Thursday, October 18, at 10:18am. In the Central U.S. the drill will take place on February 7, to mark the largest of the 1811-12 New Madrid quakes, and Utah will hold theirs on April 17. Participation is voluntary, unless your employer or educator has opted in for you, but already one third of California’s population is registered. Globally, 17 million people are signed up. Of course it behooves everyone to know what to do in an earthquake, and what resources you will have available, so there’s hardly any reason not to join in.
Visit http://www.earthquakecountry.info/ for information on what to do before, during, and after an earthquake, and to obtain resources for your own drill. Every family that faces the threat of earthquakes (that’s all of you) should know how to find each other and cope with the aftermath. You should also brush up on your Drop, Cover, and Hold On. No doorways. No triangle of life. No sprinting down the stairs to the street like a frantic animal. Stay in place and get under something sturdy. The Earthquake Country Alliance has put together an informative set of instructions on how to protect yourself in a wide variety of situations.
Sign up for the drill, and get the word out to your friends and coworkers. This is invaluable practice. We can’t predict earthquakes, but we do now how to deal with them. The best defense we have as individuals is our own awareness and preparation.
Share your ShakeOut plans or experiences in the comments, to help pool preparedness plans.
September 25, 2012Posted by on
This morning the American Red Cross released a brand new app designed to help guide you before, during, and after an earthquake. This app is a must-have if you live in earthquake country, which we’ve recently been reminded means pretty much all of us. It’s a great thing to have if you live out west, where we’re plagued by earthquakes that will undoubtedly recur in our lifetimes, but the simple checklists and guidelines contained in the app are invaluable to people living in less quake-savvy regions, where earthquakes are a remote, distant risk not often considered.
It’s free, and it’s chock full of both information and practical tools. It basically turns your mobile device into an all-in-one post-quake tool, info center, and instruction guide. I think you’ll want to have it.
The app includes step by step instructions–and checklists! to keep you on task–for before, during, and after an earthquake.
There’s a special page that helps you easily set up and share your emergency plan. This is key. This is a step that everyone is repeatedly told to take, but so few take it seriously. With this app–in like three clicks of the buttons–you have an emergency plan that you can share with your whole family. Brilliant. Do it.
Map functions are also included, showing you the locations and shaking intensities of earthquakes close to your location, as well as maps showing nearby Red Cross shelters that have been set up.
Of course the program wouldn’t be complete without links to a companion Red Cross First Aid app with emergency tips and instructions, as well as a quick link to donate money to their disaster recovery funds.
This app brilliantly exploits the many functions of a smartphone, taking full and clever advantage of its role in disseminating crucial information straight to our pockets.
September 24, 2012Posted by on
Photographer Shawn Clover, whose clever and chilling project “The Earthquake Blend” I’ve posted about before, has expanded the project with a second installment. Shawn describes the delay, explaining the exacting standards he strives for when recreating the photos. His perfectionism regarding vantage, lighting, and lack of new obstructions is what makes the photography so chilling. As in Part I, the juxtaposition of modern life in SF with scenes of the same locations just a few generations before presents a really eye-opening way of viewing earthquake risk, and bringing the threat to life. These photographs could easily constitute a quake awareness campaign throughout the city.
Have a look through his second set of photo blends. They’re in turn amusing and terrifying. Brilliant work, Shawn.
Hat tip to Christoph Grützner of Paleoseismicity for bringing this to my attention.