This week I’m attending the Seismological Society of America annual meeting in Salt Lake City, Utah. The society was founded in the wake of the 1906 San Francisco earthquake, so the annual meetings generally coincide with the quake’s April 18 anniversary.
Salt Lake City’s pioneer past is still evident overlooking the Wasatch front from the Utah State Capitol
This year’s conference is held in Salt Lake City, at the foot of the gorgeous and seismically ominous Wasatch Mountains. As such the conference is nominally focused on earthquake hazards in the U.S. intermountain west. The organizers have done a marvelous job arranging events, public lectures, and coordinating with Utah’s statewide ShakeOut drill on Wednesday in order to raise public awareness of the risks posed by the Wasatch Fault.
Below are details on the two big public events, if you’re in Utah and looking for some straight-from-the-source earthquake info. I’ll report more throughout and after the week on other goings-on at the conference, including the discussion and results from my own session on what stops earthquake ruptures, and a big field trip to see the Wasatch fault and SLC’s seismic preparedness on Saturday.
Public Events
The Great Utah ShakeOut http://www.shakeout.org/utah/
Wednesday, April 17
10:15am
Everywhere – under a table!
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.
This is a big week in U.S. (and world) earthquake history. In the U.S. we mark the anniversaries of several major, important earthquakes that have struck the country.
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.
Capitalizing on that spate of anniversaries, and on the early date in the U.S. school year, a host of quake-dedicated agencies have organized the fifth annual ShakeOut drill.
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.
200 years ago this February 7, on the western frontier of European settlement in North America, the pioneering westward expanders and the natives whose land they were colonizing were thrown from their sleep in the deep wee hours of a winter night by the culminating temblor of a harrowing, months-long sequence of major earthquakes, aftershocks of which continue to this day.
Map of shaking intensity interpolated from historic accounts of the 2:15am mainshock of the New Madrid sequence. Map courtesy Susan Hough, USGS.
The so-called New Madrid earthquakes–named for a small Missouri settlement near the modern-day borders of Kentucky, Tennessee, Illinois, Indiana, and Arkansas that lay nearest the center of this cataclysmic seismic sequence–are the largest to have struck the eastern United States since well before they became the United States. In the recorded history of western settlement of North America, no quakes outside of the mountainous west match them in size and scope, and only a few come close.
Plenty of peoplehave been and will be reporting on these earthquakes as we celebrate their bicentennial, including the organizers of the Great Central U.S. ShakeOut, which took place this morning to commemorate the massive culminating temblor of the sequence that started in December 1811. Even mapping software purveyor ESRI has put together a commemorative compilation of informative and beautiful interactive maps about the quakes (super cool compilation! If you click on one link in this post, let it be that one). It is worth reading some of these syntheses and reviews because the earthquake series itself makes a captivating narrative. It’s nearly impossible to imagine the terror with which these relentless temblors must have stricken the settlers, who were already braving the “wild” frontier of a foreign continent. Even the mid-continent’s native inhabitants had not experienced such a thing in scores of generations, and in the early 19th century no one would have had any reasonable framework in which to explain the occurrence of massive earthquakes.
Because the New Madrid quakes occurred so early in our country’s recorded and geographic history, piecing together the events with a modern understanding of earthquakes and plate tectonics has required a great deal of sleuthing, and some of the details gleaned about them remain controversial, most notably their magnitudes (were they more like M7 or more like M8?). The uncertainty regarding the exact size of these earthquakes compounds the issue of determining the seismic hazard posed by recurrence of major earthquakes in the New Madrid Seismic Zone. To understand how seismicity may continue in southeastern Missouri we can look for patterns in the prehistoric record of earthquakes, but ideally we would like some idea of what forces caused these earthquakes to happen here. This remains an open question, and one in particular for which the question of the quakes’ magnitudes may be a crucial bit of information. Researchers have tried to use modern seismicity to constrain the behavior of large earthquakes in the New Madrid Seismic Zone, and some have interpreted the ongoing small quakes there as the tail end of an unsurprising aftershock sequence, suggesting that they don’t represent heightened seismic risk, but that in fact New Madrid is as likely as any number of other places in the eastern U.S. to have more major temblors.
The ongoing scientific controversy over ambiguous interpretation of details of these quakes stems from the nature of the data. Researching “pre-instrumental” earthquakes is a pursuit that fuses seismology, history, and social science, in an effort to understand historic written accounts of the earthquakes in the context of their time and cultural setting. A somewhat recent article in Seismological Research Lettersdescribes the endeavor of anecdotal seismology, and through some colorful examples illustrates how historical reports can be translated into seismological data, clarifying the sources of interpretive ambiguity. The marriage of historical and seismological research to inform our model of seismic events in the eastern U.S. could be and has been the subject of many volumes, so I can’t hope to cover it here.
Instead I’ll draw analogy to this incredible sequence of earthquakes through videos and pictures from recent events, hopefully grounding some of the legendary accounts in footage of real and recognizable phenomena.
To the extent that people have learned about the New Madrid earthquakes of 1811-1812, they have often heard of them referred to as the largest quakes to ever strike the U.S. Ask California [1857 & 1906] and Alaska [too many to name] and you’ll find this claim is far from true. Along with this hyperbolic appraisal comes the legendary confluence of phenomena eyewitnesses allegedly reported: the Mississippi running backwards, giant fountains of water issuing from the Earth, trees being thrown to the ground, and land sinking into the river. The unimaginable chaos of these phenomena all occurring in the midst of violent shaking defies belief, but contemporary earthquakes and modern video recording technology allow us to ground them in reality, and perhaps to understand them as more modest individual events that have been amplified in intensity by their conflation and coincidence in legend. We can see examples of all four in much more modest earthquakes:
1. The Mississippi running backwards
It’s difficult to imagine what possible physical phenomenon could have led to this observation/claim… unless you understand that the New Madrid quakes–just like all other large temblors–resulted from slip along several geologic faults. At the surface, fault slip breaks and displaces the ground, moving one side in a direction opposite the other. In the case of the causative Reelfoot Fault, the surface trace cut right across the Mississippi River channel, dropping an upstream portion of the river relative to the adjacent reach downstream. This warping has been thoroughly investigated and modeled, and thanks to the September 4, 2010 Darfield earthquake–a M7.1 event that ripped across rivers on New Zealand’s flat Canterbury Plain–we have a beautiful modern analog of the occurrence.
Aerial view of the Horata River spilling off of the fault scarp formed by the September 24, 2010 Darfield earthquake in New Zealand. Image courtesy Dr. Mark Quigley, University of Canterbury, Christchurch, NZ.
Where the 2010 NZ rupture fault sliced across the Horata River, it diverted the water into surrounding farmland, effectively changing the course of the flow. This is precisely analogous to the diversion of the Mississippi that led to both the damming and formation of Reelfoot Lake, and the temporary diversion of river flow back upstream.
2. Fountains of water issuing from the Earth
There are a few processes that may combine to produce this effect. In the past year we’ve seen plenty of examples of sand volcanoes, the eruptive results of shaking-induced soil liquefaction. When subjected to seismic waves (as in this New Zealand aftershock, or the Tohoku quake below), these sand blows can be squeezed into fountains of substantial height. The force of a larger and longer earthquake would undoubtedly increase the height these reach.
Extrusion of liquefied sediment by seismic waves isn’t the only coseismic phenomenon that may throw water high into the air: seiching–harmonic oscillation–of small bodies of water may throw water against their banks and up into the air. We’ve seen this dramatically demonstrated in swimming pools during a M7.2 earthquake, but natural ponds don’t necessarily have the splashing power of sharp corners and hard edges in concrete-walled pools. Nonetheless, with these two phenomena operating in tandem, the amount of water being thrown into the air by the quake would certainly be fodder for tales–legendary or not–of high fountains from the Earth.
3. Trees being thrown to the ground
Videos from several modest (M ~6) earthquakes in the past few years have revealed just how much trees can be wrenched around during shaking. Under the accelerations of earthquakes, trees’ own weight can be a more powerful force than high winds. Here a stand of neighborhood trees sways in a mere 4.4 earthquake in Christchurch:
In a M6 we see through the windows the same effect:
Finally, video the USGS captured at practically the epicenter of the M6.0 2004 Parkfield earthquake shows fairly violent lashing of late summer oaks in the California Coast Ranges.
A tree along the San Andreas Fault in Wrightwood, CA, had its top snapped off in an 1812 earthquake, from which it grew two new crowns. The tree no longer exists, but others like it can be found along the 1906 rupture near Point Arena in NorCal. Image from "Mixed Matters"
Though the effects shown above do not amount to trees being thrown to the ground, the earthquakes that produced them were much smaller than the ones that struck Missouri. We have clear evidence along the San Andreas Fault of trees whose tops were snapped off during the 1906 earthquake. This is a common effect in the epicentral region of large quakes.
4. Land sinking into the river
This phenomenon is akin to but distinct from the Mississippi being diverted and running backwards. In fact the underlying process is more closely related to the processes that give rise to sand blows. Shaking liquefies water-saturated soils and they lose their shear strength, rendering them unable to support gravitational loads. Thus the land slumps, under its own weight or the weight of trees, houses, or riverboat moorings, downhill towards unencumbered free edges like river banks. This “lateral spreading” is commonly observed along river banks shaken by earthquakes, and results in lowering and inundation of the ground surface. Examples abound from earthquakes as geographically and tectonically various as the 1964 Good Friday event in Alaska, the 1906 San Francisco earthquake, the 2010 Haiti earthquake, and the 2010 El Mayor-Cucapah earthquake. In all of these events vast swaths of land shook loose and slumped ocean- or river-ward, and effectively “sank”.
The video examples compiled above may not match the apparent drama of those recounted from 1811-12 Missouri, but I find it easy to imagine the cumulative results of decades and decades of re-telling on the details of these accounts. In any case, large earthquakes produce remarkable effects, and although many people around the world witness or experience earthquakes, still relatively few witness the truly violent shaking that occurs near an earthquake’s source. Written and oral accounts give us the most thorough picture, even if we have to take them with a grain of salt. Video may gradually be replacing verbal accounts in objectivity (no relying second-hand information!), but it has yet to become as widely distributed and available as individual eye-witnesses.
Next time you strike up a conversation about these earthquakes, consider yourself informed about many of the features that defined them, but by all means gather more information on your own. My two favorite informative links are the following:
On Tuesday, February 7, 2012–the 200th anniversary of the biggest of the New Madrid earthquakes–nine states in the central U.S. will conduct a regional earthquake drill put on by ShakeOut, a consortium of organizations and agencies concerned with earthquake research, hazard mitigation, and emergency preparation. Participation is voluntary, but public agencies, school districts, universities, and private companies are all registered and are taking advantage of both public awareness and prepared publicity materials to develop and exercise their disaster plans. The prepared publicity materials include descriptions of reasonable scenario earthquakes, including M6.5 quakes in the New Madrid Seismic Zone, the Wabash Valley Seismic Zone, or a more generic description for an unforeseen quake that may occur outside of these notable zones of seismicity. The ShakeOut website also includes images and media to share, as well as video and audio recordings to play during the allotted time of the drill.
As with the Great California ShakeOut, I encourage everyone to participate. Officially the drill is to take place at 10:15am, but I encourage everyone who’s considering participating to conduct their own earthquake “drills” everywhere they go: once an hour, stop yourself and think “what would I do if an earthquake hit this very moment?” Consider that you would have very little warning, and you may be in a very inopportune place. You won’t always have a sturdy table to dive under in the safety of your own home.
The drill this week focuses on a collection of states centered around the New Madrid seismic zone, a collection which comprises the region of strongest shaking and most damage in the 1811-1812 earthquakes. Missouri, Arkansas, Illinois, Indiana, Kentucky, Tennessee, Mississippi, and Alabama all suffered substantial shaking during the huge quakes of those years’ winter. Oklahoma is included thanks both to its proximity to New Madrid and to its own seismic hazard, manifest in late 2011 when the Wilzetta Fault lurched to life and rattled homes across the state. This is by no means an exclusive list. Although MO, IL, and IN have had their share of moderate quakes, plenty of other U.S. states are at risk, and as we saw in August, sizable quakes are apt to occur almost anywhere.
Think about the recent quakes in Oklahoma and Virginia, and ask yourself whether you would have been prepared had they been bigger, worse, or closer to you! Take advantage of the resources these government agencies have put together to raise awareness and prepare our country for inevitable seismic disasters!
Twenty two years ago this very day the San Francisco Giants were preparing to play their cross-bay rivals, the Oakland Athletics, in the 1989 World Series–the so-called Battle of the Bay. It was just after 5pm on a beautiful October afternoon, and the nation’s eyes were glued on television coverage from Candlestick Park in southeastern San Francisco. Hordes of Bay Area residents had swarmed bars and gathered at home after early departures from their offices in order to watch a game so crucial to everyone’s pride in the rivalry.
Evening news had begun, and classes were still in session at UC Santa Cruz, 70 miles down the peninsula. At 5:04 and 15 seconds, residents of the forested mountains around Santa Cruz were thrown from their places by a giant lurch of the ground. A sizable fault plane adjacentto the San Andreas beneath the Santa Cruz Mountains had slipped, although the rupture didn’t make it to the ground surface. As the sides of the fault ground past each other, seismic waves emanated westward toward the coast, and rocked the city of Santa Cruz.
USGS animation of shaking intensity produced by the Loma Prieta earthquake
Downtown Santa Cruz was devastated, and people fled buildings on the UC campus, all before cities up the peninsula had even an inkling of an idea that this earthquake was underway. As the seismic waves raced northward through San Francisco, BART operators were ordered to halt their trains, and Candlestick Park started bouncing. With scores of miles separating them from the epicenter, the baseball fans had the roaring rumble of P-waves to herald the quake’s violent shaking, but with nowhere to go and not nearly enough time, the stadium erupted into screams as S-waves rippled through and yanked the decks back and forth. As TV transmission cut out from the stadium, the rest of the country stared shocked and agape at the World Series logo silently standing in on their screens.
Meanwhile the seismic waves continued racing outward to the east, high frequencies getting stifled with every additional kilometer, until they began rocking Sacramento and the Central Valley, many minutes after they’d wreaked their havoc in SF.
Rocking from this earthquake was felt as far away as Nevada and Los Angeles, but it was a relatively modest event when compared with the earthquakes northern California’s major faults are capable of.
"Did You Feel It?" survey results for the 1989 quake
This earthquake–named Loma Prieta after the hills nearest its epicenter–was a truly remarkable event made famous by a still rather unbelievable coincidence of conditions: Hitting the urban population of northern California alone would have made it remarkable, but it did so during live nationwide TV coverage of a major sporting event; that would have been remarkable in itself, but the baseball game in question was between both of the Major League teams from the region, and deeply involved all of their local fans.
Failure of the Bay Bridge during a 6.9 earthquake 70 miles away... Image courtesy USGS
Gradually (surely aided by the wealth of attention already focused on the Bay Area for the World Series game) information started to spread about the extent of this quake’s effects. The waves had bounced around, slowed down, sloshed, and churned in the poorly consolidated sediments and made-land beneath San Francisco’s Marina District and the industrial coastal stretches of Oakland and the east bay, collapsing houses and double-decker roadways, and igniting fires that for a while brought back visions of 1906.
The eastern span of the Bay Bridge had wriggled and stretched, and during a particularly tensile yank, a segment of the upper deck was pried away and flopped down onto the eastbound deck below.
These details may describe familiar sights to many people. Certainly some of the footage from the Loma Prieta earthquake is the quintessential earthquake footage for many Americans far from significant seismic hazard and exposed to earthquakes only through their interest in baseball.
As you re-live that moment through some of this footage, the most important thing to note is that this was not San Francisco’s earthquake. It was largely Santa Cruz’s. The quake was far south of the peninsula, and had a relatively modest magnitude of 6.9, about an order of magnitude smaller than the real Big One in 1906. The havoc wreaked in 1989 doesn’t come close to illustrating the real effects of a large rupture on one of the faults bounding the Bay Area. Fortunately we can use modern instruments and computing power to compare the Loma Prieta earthquake with simulations of potential earthquakes on both the Hayward and San Andreas faults. We have maps showing the shaking hazard as well as other associated hazards, including landsliding and liquefaction. The USGS has a neat zoomable map of liquefaction susceptibility in the Bay Area–check out where your house stands:
The 1989 failure of the Bay Bridge spurred the construction of an entirely new bridge span that is soon to be completed, and implements some excellent (and super cool) earthquake-savvy devices. (Watch the video at the link below)
As is the nature of earthquake science, earthquakes that occur are our primary way about learning what to expect and what to do in the future. San Francisco is likely to have bigger and closer earthquakes than this one, so it’s best to be prepared and know what you’ll be dealing with. Try ShakeOut!
This Thursday (October 20), the fourth annual California ShakeOut drill will take place at 10am. What that means for you in California is that companies, agencies, and organizations all around you (hopefully including yours!) will be preparing and practicing their emergency procedures and reviewing their plans for the inevitable occurrence of an earthquake.
Emergency management and response agencies and school districts throughout the state have implemented educational campaigns spurred by the ShakeOut drill, and individuals are encouraged to play along. If climbing under the nearest desk while you’re sitting at work at 10am to practice what you would do in a real earthquake seems a little too basic, consider using the drill and the wealth of materials prepared for it to contemplate the real danger of earthquakes, and to think concretely about how you will cope when one does happen. Think of it this way: if a major earthquake happened 30 minutes from now–which is entirely possible–what would you do? Would you be ready?
The brutal truth of it is that earthquakes are an inevitability in California. We average around one M7 and several ~M6 quakes each decade, whether they hit densely populated areas or not. Of course the San Andreas is capable of unleashing a Big One–a M8–on us soon, but there are plenty of other faults throughout the region that present a great hazard. We don’t know which one will hit us next, so the best we can do is be prepared.
Map showing where specified peak ground accelerations (PGA) have a 2% probability of being exceeded within 50 years
Take the opportunity of the ShakeOut drill not simply to await a prescribed time to drop, cover, and hold on, but to pause during each different activity of your day and consider what you would do if a strong earthquake hit at that moment. Are you prepared? In some places you will be much less prepared and much less safe than in others, but this is somewhat out of your control. Make sure the places you spend most of your day–your office, your couch, your bed–will be relatively safe during extreme shaking. We have plenty of little quakes, so we know how some jostling feels, but consider a truly large earthquake. Consider ground motion akin to that captured during the Kobe and Haiti earthquakes (still the most intense ground motion I’ve witnessed on film…). Stuff won’t just fall off shelves; it will be thrown across the room, along with the furniture that holds it.
This imagination exercise is scary. It should be; the major earthquake(s) in our future will be. Thinking seriously about this very real hazard can help you protect yourself during and after the quake. Most people survive major earthquakes. The better prepared you are, the more confidently you can handle the risk of a major temblor. Register with ShakeOut, or “like” it on facebook, where they post practical daily tips that you probably haven’t thought of.
I won’t bother replicating the wealth of advice these resources offer, but I will seriously encourage you to visit www.shakeout.org and www.daretoprepare.org to get some inspiration about how to deal with the earthquakes you’ll inevitably face.
To lighten the tone a little but keep you thinking about how to be prepared, I’ll guide you to www.totallyunprepared.com where you can watch a collection of Discovery-Channel-style clips (“Will It Shake?“) and a series of videos exploring “Where Will You Be?”
Like I said, don’t just Drop, Cover, and Hold On at 10am. Stop once an hour and re-assess what you’d do. What if a major quake happened right now?
After three months of field work, weddings, and conferences, I finally have a settled, relatively stationary schedule ahead of me, during which time I can get back into the routine of posting the interesting things I find and various seismological musings. I have bunches to talk about, so you can expect plenty o’ earthquake discussion in the future, which, as I will discuss and try to convince you, is very important because the best way to protect yourself is to be prepared, and that requires thinking about earthquakes.
Over the summer you all probably (hopefully?) realized the importance of being earthquake-aware, when a sizable earthquake jiggled the tops off the National Cathedral’s cornices and cracked the top of the Washington Monument. It seems to have been about as harrowing inside as you would expect an earthquake to be at the top of an enclosed 555-foot obelisk. The surprising and quite unexpected quake caught the nation’s attention, and despite a sassy (if recycled) repartee between the coasts trivializing its occurrence, it was a rather fearsome reminder of our vulnerability to the unpredictable forces beneath our feet. More on that quake later.
If it can happen in the Hamptons, it can happen to you.
In the meantime, I’ll leave you with a friendly reminder that the ShakeOut drill is coming up in a week (!) and no matter how lame you think participating in a voluntary preparedness drill sounds, you would be well served by registering on the website and browsing their thorough, practical earthquake tips.
In the near future you can expect posts from me on field work, lessons from recent conferences, discussion of how to deal with the threat of earthquakes, updates on my quake-related presentation at the AGU conference, and of course literally phenomenal videos of quakes happening from around the world; or, more specifically, the following:
A recap of field work in China!
Earthquake risk to CA’s nuclear power plants!
Why the 8/23 Virginia quake happened, and why a third of the continent felt it!
How we deal with rare/unpredictable but devastating natural disasters!
What scientists discuss about the riskiest quakes facing California!
Figures from my upcoming American Geophysical Union presentation on the 2010 Baja quake!
…and so forth. Those are just the ones I have drafts of saved already. I have to pace myself.
I'm a Ph.D. student in earthquake geology, using topographic and stratigraphic investigation to unravel the seismic history and dynamic behavior of continental faults. I get excited about all things seismological, and I bring them to you here.
Big quakes in the past week
The Trembling Earth 