May 13, 2008
by Frank James
Baltimore Sun
As we view the images of the aftermath of the earthquake in China's Sichuan Province and the reports of an estimated 12,000 dead, it's impossible to escape the sense that not only could it happen here but it will.
And it's not just California that we should be concerned about. While the Golden State obviously has had the most experience with earthquakes because of the very active San Andreas Fault, which is overdue for the Big One, the Midwest is at risk too.
That's largely because of the New Madrid Fault, although that quake zone isn't the only one in the central part of the country to worry about. It was the Wabash Valley Fault, after all, that caused an earthquake measuring 5.2 on the Richter Scale in Southern Illinois.
The combination of April's Midwest earthquake and this week's calamity in Sichuan Province should remind federal, state and local officials, as well as individuals themselves, to do more to prepare for and respond to the inevitable earth shaking that most scientists say is only a matter of time.
Even before the devastating China earthquake FEMA, which since Hurricane Katrina has been working, with some success, on a self-improvement plan, was working with states in the New Madrid region on response plans to a major earthquake. They've been holding workshops, working towards the ultimate goal of a a full-scale, mock earthquake exercise in fiscal year 2011.
Given the importance of the situation, that seems a little far off. Maybe the Sichaun quake will get officials to move that up a bit.
What many people don't realize is that a large 7.8 or more quake in the Midwest could be substantially more destructive than the San Andreas since, scientists say, the energy from such a quake would travel farther than a West Coast quake because of the older, colder earth crust in the eastern part of the country.
The east also has more sediment over the earth's crust than does the west, which would worsen the shaking from a major New Madrid quake compared with a similar-sized San Andreas event.
At a December Senate hearing on the New Madrid Fault, Jack Hayes, an earthquake expert at the National Institute of Standards and Technology, testified that many more people and much more property is at risk from earthquakes than is commonly believed.
A 2006 National Research Council report noted that 75 million people and half of the nation's buildings worth $8.6 trillion in 2003 dollars are located in areas of the U.S. that are prone to damaging earthquakes. The U.S. has been fortunate not to have experienced recent, severely damaging earthquakes, but considering our significant urbanization and societal interconnectivity, the consequences of earthquakes include significant injury and loss of life, in addition to potentially severe economic and national security consequences. Experts consistently estimate that a big one that strikes a major U.S. urban area may cause over $100 billion in losses.
Another expert at the December hearing, David Applegate from the U.S. Geological Survey said:
This is a very important topic. From today's perspective, the three magnitude 7-1/2 to 8 earthquakes that struck the Mississippi Valley back in the winter of 1811 and '12 seem quite distant, but infrequent events nevertheless represent very real risks, and if those earthquakes were to recur today, significant damage to buildings, transportation, and critical infrastructure would occur in at least eight states...
Now why are there earthquakes in the central U.S.? Although the large majority of earthquakes occur along the edges of the brittle tectonic plates that make up the earth's outer skin, earthquakes do occur far from present-day plate boundaries as the stresses from those boundary zones are translated into the more stable interiors, as is the case in the central and eastern U.S.
Such earthquakes are less frequent than in California or Alaska, but an earthquake in the Mid-Continent affects a much larger area than the same size earthquake in California, and that's reflected in both of the diagrams up here -- the one on the dais showing comparison of a damaging earthquake, the Northridge Earthquake in 1994, with the Marked Tree event in 1895 -- that's sort of a moderate-size quake -- and the one over here to my left comparing the 1811 New Madrid events to the 1906 earthquake that destroyed the San Francisco area.
And you can see that the damage zones and the zones over which it was felt are much broader, and that's because, in the central U.S., the crust is older and it's colder, and it translates the energy from seismic waves much more efficiently. And in the Mississippi Valley in particular, you also have amplification of that shaking because of the very thick sediment. So the communities there are more intensely affected.
Now geologic research shows that similar sequences of major earthquakes to those in 1811 and 1812 have happened at least twice before, in about 1450 AD and 900 AD. We estimate that there is a 7 to 10 percent chance of an earthquake the size of those in 1811 and 1812 striking the region in the next 50 years. However, the occurrence of even a moderate-size earthquake like the 1895 event, close to urban centers like Memphis could be locally devastating. And the chances of a magnitude 6 earthquake occurring in this region in the next 50 years are 25 to 40 percent.
There is some good news. Scientists are developing systems that will let them inform government, emergency-response officials and the public, soon after an earthquake occurs, where the most shaking, and thus, greatest damage happened.
Applegate said:
Now turning to response, knowing where shaking is most intense immediately after an earthquake can save lives by providing emergency responders with the situational awareness that they need to concentrate their efforts where they matter most. For that reason, USGS has been building the Advance National Seismic System to modernize the nation's seismic monitoring infrastructure and provide the most rapid information we can about strong shaking.
Through ANSS, the USGS sends rapid reports of potentially damaging earthquakes to over 100,000 users, including the Departments of Defense, Homeland Security, state and local emergency managers, the news media, and the public. USGS monitors earthquakes in the central U.S. in cooperation with the University of Memphis, St. Louis University, and the University of Kentucky.
Now, within five minutes after a potentially damaging earthquake in the central U.S., notifications are sent to local, state, and federal officials with the epicenter and preliminary magnitude. Within 20 minutes, an initial ShakeMap is released, and that's shown here. It's on the left.
This is a scenario ShakeMap of the views for the recent SONS exercise for an 1811-type New Madrid event, with the strongest shaking shown in red. That's available in about 20 minutes, and then the products are refined as more data arrive, helping to prioritize response.
Now, three months ago, USGS began delivering a new product known as PAGER, the Prompt Assessment of Global Earthquakes for Response, which provides rapid estimates of population exposure to shaking, giving emergency responders and aid agencies a quick estimate of the extent of the likely response required, and that's what's shown on the right.
In addition to shaking that would cause significant damage to today's buildings and lifelines, the 1811 and 1812 earthquakes also caused landslides along the bluffs from Mississippi to Kentucky. A type of ground failure called liquefaction caused soils to flow and may make roadways in the Mississippi Valley, such as I-55, impassable. It also can disrupt agriculture and cause levee failures.
The citizens of this region need to be aware of the likely consequences of earthquakes. Through the Central U.S. Earthquake Consortium testifying in the next panel, the USGS and FEMA have partnered with state emergency management agencies in geological surveys to provide information that they can use in their planning efforts and to educate the public.
http://weblogs.baltimoresun.com/news/politics/blog/2008/05/china_quake_should_wakeup_us.html