Earthquake in Illinois could portend an emerging threat

The concern of Douglas Wiens, Ph.D., and Michael Wysession, Ph.D., seismologists at Washington University in St. Louis, is that the New Madrid Fault may have seen its day and the Wabash Fault is the new kid on the block.

The earthquake registered 5.2 on the Richter scale and hit at 4:40 a.m. with a strong aftershock occurring at approximately 10:15 a.m. that morning, followed by lesser ones in subsequent days. The initial earthquake was felt in parts of 16 states.

"I think everyone's interested in the Wabash Valley Fault because a lot of the attention has been on the New Madrid Fault, but the Wabash Valley Fault could be the more dangerous one, at least for St. Louis and Illinois," said Wiens, professor of earth and planetary sciences in Arts & Sciences. "The strongest earthquakes in the last few years have come from the Wabash Valley Fault, which needs more investigation."

Wiens said that seismologist Robert Hermann of Saint Louis University, Gary Pavils of Indiana University, and several geologists including Steven Obermeir of the U.S. Geological Survey (USGS), have made studies of the Wabash Valley Fault. Pavils also has run a dense local array of stations and recorded many very small earthquakes at the Wabash Valley Fault. Hermann has studied the 1968 magnitude 5.5 earthquake, the largest ever recorded there. Obermeir and others have found disturbed sediments from previous earthquakes along the fault with estimated magnitudes of about 7 on the Richter scale over the past several thousand years.

According to Wysession, there are 200,000 earthquakes recorded every year, with a magnitude 6 earthquake happening every three days somewhere in the world.

"There hasn't been a magnitude 6 earthquake on the New Madrid zone in more than 100 years, yet in 20 years there have been three magnitude 5 or better earthquakes on the Wabash Valley Fault," said Wyssession, associate professor of earth and planetary sciences. "There is evidence that sometime in the past the Wabash Valley Fault has produced as strong as magnitude 7 earthquakes. On the other hand, the New Madrid Fault has been very quiet for a long time now. Clearly, the Wabash Valley Fault has gotten our deserved attention."

Wysession said a recent re-analysis of data by USGS shows that the New Madrid fault risk is much less than was thought three decades ago. The three notable earthquakes that occurred at the end of 1811 and the beginning of 1812 were not magnitude 8s, rather magnitude 7s. A magnitude 8 is 30 times more explosive than a magnitude 7.

"The damage to the region by those earthquakes has been exaggerated," Wysession said. "St. Louis was here at the time, and all that happened was some chimneys fell in East St. Louis. The little village of St. Genevieve, closer to the fault zone, had no damage at all. But, let's face it, St. Louis is the biggest city in the region of both faults, and the Wabash Valley Fault is closer to us. If the big one does occur, it's looking more like it will come out of Illinois."

Wysession said that the North American Earth's crust is filled with cracks and faults, and that an earthquake can occur anywhere on the continent. Many of the faults are undetected.

"As the continents bang into each other, sometimes they pull apart, and the crust cracks and ruptures, causing earthquakes," he explained. "This whole region of New Madrid and the Wabash Valley seismic zone became a rift zone about 750 million years ago when the continent almost broke apart. There was a lot of volcanic activity, a lot of seismic activity. The crust got stretched and thinned. By looking at seismometers, we can actually see many of these faults in the thinning of crusts underground."

Wysession said that an earthquake in the Midwest will be felt ten times farther away than one occurring in the western United States because the crust beneath the Midwest is very old, stiff and cold. The rock is about 1.7 billion years old and the seismic waves can travel very long distances through this type of crust. It can be felt hundreds of miles away, even if it was a smaller earthquake. In the western United States, the rock is hotter, and thus it dampens the shock waves and they are not felt as far away.

Despite the fact that most seismologists, including Wysession and Wiens, don't think it likely that earthquakes ever will be predicted — which inevitably dredges up memories of the 1990 Midwest earthquake scare sparked by Iben Browning — Wysession says that there are some precursory phenomena that have been observed right before some earthquakes. Radon or helium gas may leak out of the ground as the ground cracks. Sometimes water well pressure changes, or there's a change in the magnetic field. Electrical resistivity changes have been noted, too.

"These are changes we can measure with instruments, but we can't sense them as humans," he said. "Many people think that animals sense atmospheric changes. You always get stories about Rover going bananas right before an earthquake. But until Rover learns to tell us what he's barking about, we won't be able to employ animals in any predictive way. "

Source: Washington University in St. Louis

Stalagmites may predict next Big One along the New Madrid Seismic Zone
Small white stalagmites lining caves in the Midwest may help scientists chronicle the history of the New Madrid Seismic Zone (NMSZ) – and even predict when the next big earthquake may strike, say researchers at the Illinois State Geological Survey and the University of Illinois at Urbana-Champaign.
May 2008 earthquake in China could be followed by another significant rupture
Researchers analyzing the May 2008 Wenchuan earthquake in China's Sichuan province have found that geological stress has significantly increased on three major fault systems in the region. The magnitude 7.9 quake on May 12 has brought several nearby faults closer to failure and could trigger another major earthquake in the region.
Major flooding risk could span decades after Chinese earthquake
Up to 20 million people, thousands of whom are already displaced from their homes following the devastating Chinese earthquake, are at increased risk from flooding and major power shortages in the massive Sichuan Basin over the next few decades and possibly centuries.
Not enough space: The dicey game of storing, backing up files
About five years ago, a technical disaster struck Fernando Santos: His computer hard drive failed. The San Francisco resident lost everything on it and had to reformat his drive. "I lost a lot of nice pictures," said Santos, 20.

Magmatically triggered slow earthquake discovered at Kilauea Volcano, Hawaii
From June 17-19th 2007, Kilauea experienced a new dike intrusion, where magma rapidly moved from a storage reservoir beneath the summit into the east rift zone and extended the rift zone by as much as 1 meter.
New analysis of earthquake zone raises questions
Oregon State University scientists have completed a new analysis of an earthquake fault line that extends some 200 miles off the southern and central Oregon coast that they say is more active than the San Andreas Fault in California.
Earthquakes may endanger New York more than formerly believed
A study by a group of prominent seismologists suggests that a pattern of subtle but active faults makes the risk of earthquakes to the New York City area substantially greater than formerly believed. Among other things, they say that the controversial Indian Point nuclear power plants, 24 miles north of the city, sit astride the previously unidentified intersection of two active seismic zones. The paper appears in the current issue of the Bulletin of the Seismological Society of America.
Scientists explore Sichuan fault
Durham University expert, Alex Densmore, is to explore the fault lines that caused the May 12th earthquake in China that killed 69,000 people.

Earthquake in Illinois could portend an emerging threat

Related stories:

News discussion: