Quake Points Out the Potential for Midwest Disaster

An earthquake that rumbled through 16 states from the Eastern Seaboard to the Mississippi River on Wednesday evening demonstrated that even moderate quakes are capable of doing far more damage there than comparable quakes in the Far West, experts said Thursday.

The quake was centered in southern Illinois and measured 5 on the Richter scale, making it a modest temblor by West Coast standards, but it was noticeable as far away as Canada.

The fact that the earthquake was felt over such a wide area shows that a quake that might be little more than intimidating in California could be catastrophic to the Midwest because of the geological nature of that part of the continent, according to Thomas Heaton, scientist in charge of the U.S. Geological Survey’s field office in Pasadena.

Suspected Center

“There is considerable fear that a large quake could affect a large region” in the Midwest, Heaton said. The result, according to various government studies, could be catastrophic with the loss of thousands of lives.

Wednesday’s earthquake is believed to have been centered on the Wabash Valley Fault near Lawrenceville, Ill.

News service accounts reveal that the impact of the quake far exceeded what might have been expected from such a mild temblor.

The quake broke windows, toppled chimneys and triggered alarms at nuclear power plants in nearby states, and residents from Kansas to the East Coast, and from South Carolina to Canada, reported feeling the quake.

Only one minor injury was reported, and damage was considered slight, but that was hardly reassuring to scientists who see great peril from earthquakes in that region of the country despite a popular belief that devastating earthquakes belong in California, not Illinois.

Scientists who have studied the Midwest say the geological nature of the area is poorly understood, but it is clear that the deadly energy from an earthquake can propagate far more easily through the soil there than it does in many areas of the Western United States.

“Comparable-sized quakes are felt over a much larger area” in the Central and Eastern regions than in the West, Heaton said.

Flat Topography

Throughout much of that area the Earth’s crust is flat and regular, leaving little to interfere with the shock waves as they ripple through the soil, Heaton said. That allows the earthquake to transmit its energy over much greater distances, and that, in turn, means that a major quake could make its presence known over a much larger area.

Hard, irregular rock formations in the West tend to break up the waves, thus limiting the effect of an earthquake to nearby regions.

No seismologist is particularly comfortable discussing all of that, however, because earthquakes are fairly rare in the Central and Eastern parts of the country, so the historical record is seriously inadequate. Even in the West, where quakes occur far more frequently, there is much confusion and debate over the cause and predictability of earthquakes.

It is not even entirely clear why the Middle West should have any earthquakes at all.

The fault systems along the West Coast are caused by the slippage of two tectonic plates--the giant chunks of the Earth’s crust on which the oceans and continents float. The Pacific plate offshore grinds slowly northward while the North American plate slips slowly south, creating the San Andreas Fault.

Scientific Puzzle

But the great plains of the Mississippi Valley are half a continent away from the dynamic regions where the tectonic plates crunch against each other, and there is much uncertainty over why that area has earthquakes at all.

“Presumably earthquakes in that area are due to slippage on faults, just like in the West, but the question is why are those faults active,” Heaton said.

One possible explanation is “glacial rebound,” he said. During an ice age, giant glaciers crept down out of Canada, depressing the surface of the ground by about half a mile, Heaton said. Over eons of time, the Earth’s crust rebounds, releasing energy in the form of earthquakes as the ground strives to ease tensions.

A more likely explanation, Heaton said, is that millions of years ago the North American Plate was trying to split itself in two with a great rift zone running up what is now the Central United States. Had it succeeded, New York and California might today be on separate continents.

Mysterious Action

But for reasons no one clearly understands, the North American Plate did not split after all, and it has been burying its rift zone beneath miles and miles of fill. Many of the stresses are still there in deeply buried rock formations, releasing tension from time to time through earthquakes, Heaton theorized.

Usually, that release comes in the form of a small to moderate quake, like the one that struck Wednesday at 6:49 p.m., Central time.

History shows, however, that sometimes the release of energy is monumental.

Three powerful earthquakes struck what is now southern Missouri in 1811 and 1812, destroying the hamlet of New Madrid and creating dams of debris so high that the Mississippi River is said to have temporarily reversed its direction.

Records from that area, then sparsely populated, are grossly inadequate but estimates of the size of those quakes range from 7.5 to well over 8 on the Richter scale, making them among the most powerful earthquakes to have hit this continent since people began taking note of such things.

Warning From Experts

The severity of those quakes, which reportedly rang bells as far away as Washington, D.C., has prompted many experts to warn that the Midwest has at least as much to fear from catastrophic earthquakes as has the West.

But the scarcity of earthquakes has left many officials in that region fearful that they have grown lax in building code requirements and are not prepared for the kind of earthquake that some geologists believe is inevitable.

Recognizing a need for that area to catch up with the West in earthquake preparedness, the Federal Emergency Management Agency has financed planning programs for much of the region.

The agency estimated that a major quake could cause damage of up to $60 billion over a 200,000-square-mile area. The agency has warned that if the region does not upgrade its building codes and emergency planning, deaths and injuries could number in the thousands.