Indianapolis, Little Rock, Cairo, Illinois. All within a three-or four-hour drive. Then there’s Paducah, Kentucky, Cape Girardeau in Missouri, and a couple hundred smaller towns that are a lot closer.”
The two headed back toward their cars, rubbing their arms to keep warm in the cold air. The wind had dropped off. Jacobs smiled and said, “Depending on whether the New Madrid system connects with two or three other faults, you might want to throw Chicago into the mix.”
Atkins tried to let all that register. How many people were affected? Several million at a minimum. The San Andreas Fault simply didn’t compare. A large expanse of Southern California west of the San Bernardino Mountains was sparsely populated. If a bad one hit, the quake would affect only one city at a time. Seismic waves triggered by earthquakes along the San Andreas Fault just didn’t travel that far. The rock out there was too soft, too fractured.
The great San Francisco quake of 1906 was a good example. It was only a little less powerful than the largest of the New Madrid quakes, but the damage was limited almost exclusively to a 200-mile radius around San Francisco.
It was a different story out here in the Mississippi River Valley, where seismic waves traveled much farther and where cities and towns were more numerous. The shock waves from the famous quakes rang church bells in Richmond, Virginia, and Charleston, South Carolina. Windows had broken in Philadelphia. It was felt as far away as Montreal. The deep rock in this part of the country was older and harder, which meant the shock waves traveled farther. A big one could send perceptible seismic waves radiating for more than a thousand miles.
Jacobs handed him another map. He’d seen this before, but it was still a shocker. It showed how midwestern quakes dramatically differed from those on the West Coast. Earthquakes of similar magnitude were far more damaging in the heartland and their destructive range far greater.
“How many tremors did you say you get on average every week?” Atkins asked, studying the map.
“Of a magnitude 1 or better, at least three or four. Sometimes they come in clusters of five or six. Lately, the intensities are getting higher. Fact is, I’m getting a little worried.”
Jacobs wasn’t sure he was doing the right thing in sharing his concerns with his friend. When it came to trying to predict an earthquake, candor was risky and usually best avoided. But after meeting Atkins, sizing him up, he decided to get it all out in the open.
“I’ve been here going on twenty years, and I’ve never seen so many things pile up,” Jacobs said. He was carefully watching Atkins, trying to read him.
“You mean precursors?”
Jacobs nodded. “I wouldn’t be so concerned if it was just one or two events. But, hell, we’ve got a swarm. For starters dilatant strain levels are way, way up.”
“How much?”
Dilatancy was a measure of increased pressure on rocks as they swelled or dilated with water. Specifically, it was found that water-saturated rocks placed under strain increased in volume during deformation. There was evidence that as the pressure on the rock increased, cracks began to develop and multiply within the rock, the fractures increasing in number as the pressure built toward the breaking point. Laboratory tests were done, squeezing rocks to high pressure using special hydraulic presses. It hadn’t been understood until fairly recently that this microcracking occurred in wet, saturated rocks before they’d break under stress. Delicate instruments could measure the expansion or “volumetric strain” of the cracks. There was some evidence that dilatancy increased before a quake.
“Eight, ten percent. We’ve also got increases in the magnetic fields.” Rocks cracking under pressure and then closing again just before a quake sometimes altered magnetic fields.
Atkins asked about radon emissions. The odorless, radioactive gas was trapped within all rocks. When they started to fracture under stress, as just before an earthquake, greater quantities of gas were sometimes released.
“We’ve got gauges on ten deep wells scattered along the fault line,” Jacobs said. “The readings are all up. A few are way up.”
“What about P velocities?” Atkins asked.
The idea behind P, or primary, wave velocities was deceptively simple. Earthquake damage is usually caused by three different kinds of elastic waves. Two of them move within the rock itself: the fast-moving primary, or P, wave and the slower-moving secondary, or S, wave. S waves resemble ripples of water moving near the ground surface, ripples that can hit harder the farther out they travel.
The P wave resembles a sound wave and can penetrate both liquid and solids—volcanic magma, mountain granite, or the ocean. When they reach the atmosphere, P waves become sound waves that can be heard by humans and animals, especially dogs. The sound is often likened to a loud, long crack of thunder.
As an earthquake indicator, P waves were important. If rock properties changed before a quake, then the speed or velocity of the seismic waves passing through them also changes. Measurements from previous quakes suggested that P velocities changed by about ten to fifteen percent before a quake.
“The fluctuations are in the twenty percent range,” Jacobs said matter-of-factly.
“What kind of uplift are you getting?”
“Over the last three years, four to five centimeters in places. We’re running another GPS survey right now.” The Global Positioning System was a complex satellite network operated by the Department of Defense. It allowed precise measurements of the earth’s topography. By comparing how the ground had changed over time, where it had risen or shifted, geologists could calculate whether stress was building along a fault. An uplift of four or five centimeters was significant.
“Is this what you brought me out here to talk about?” Atkins asked.
“I didn’t want to be too direct,” Jacobs admitted. “I thought I’d just show you the data, tell you what we’ve got. Keep the rockets to a minimum.”
Atkins understood perfectly. Any talk about earthquake precursors tended to make seismologists nervous in a hurry. It was professionally risky even to bring up the subject. And yet he had to admit that all of these indicators pointed to something going on.
They climbed into the Jimmy, the stiff wind off the lake pushing hard at their backs.
“So what do we do about the animals?” Atkins asked.
Carefully weighing his words, Jacobs said, “I’m just as skeptical about that as you are, John. But there’s been so much of it lately. A lot of animals seem to be doing weird things.”
“What about that sheriff you mentioned?” Atkins said. “The guy back in Kentucky who had the friend who raised cattle.” The sheriff had called Jacobs two days earlier and described the man’s problems with his herd. They’d been going on for nearly two weeks.
“He just said they were acting crazy as hell,” Jacobs said. “It sounds like more of the same. Your rats and frogs. His cows.”
“I wouldn’t mind visiting him and trying to hit a couple of the others on that list you gave me,” Atkins said. He grinned. “Who knows, there might be a paper we can write about it later.”
“Only if there’s an earthquake,” Jacobs said. “And I’m not sure about that.”
“Right, you’re just worried as hell,” Atkins said.
His friend nodded slowly and pulled his snap-brimmed cap lower on his head. “You’ve got that right, John. I don’t like any of this. I’m a scientist. I’m supposed to rely on facts and nothing but the facts. But I don’t like the way this feels.”
Before they left the lake, Jacobs said he’d check out some of the names on the list himself. They’d meet back in Memphis late the next day and compare notes.
NEAR MAYFIELD, KENTUCKY
JANUARY 9
4:20 A.M.
AT WALTER JACOBS’ SUGGESTION, JOHN ATKINS drove up to meet the Graves County sheriff in Mayfield, Kentucky. It was a short trip from Reelfoot Lake, about thirty miles. The sheriff—his name was Lou Hessel—had
