Union, Nebraska - Earthquake Faultline

The Days Nebraska Shook
Earthquakes in Nebraska? Yes, but our faults are minor.

By CURT ARENS, NEBRASKA LIFE MAGAZINE, JULY/AUGUST 2003

FOR GOD’S SAKE, let’s get out of here!” The Omaha courtroom audience was startled. An assistant to the district attorney was on his feet, shouting for everyone to leave. Then the D.A. himself shouted, ‘There’s an earthquake!”

In a third-floor courtroom on November 15, 1877, just as a judge was about to open a case for the U.S. Circuit Court, a wall clock behind him began swinging wildly. Above, chandeliers swayed. The whole building rumbled. At once, attorneys, plaintiffs, defendants and judge sprinted from the building.

At first, no one could believe that it was really an earthquake. Soon, dispatches began arriving at Union Pacific headquarters from points between Omaha and Sidney. Other cities had felt it too. The epicenter — the spot on the earth’s surface directly above the movement occurring miles underground — was probably near Garland, in northeastern Seward County.

In Columbus, a courthouse wall was cracked in nine places. In North Platte, children vacated their school building when two severe tremors lasting 40 seconds each rocked the city. Lincoln reported two short-lived tremors that gave residents a sickening sensation. In Council Bluffs, Iowa, quick shocks lasting two minutes sent the occupants of one building rushing into the street, fearing the structure would crumble around them. As far away as Yankton, S.D., and Sioux City, Iowa, similar tremor abruptly ended a church service and sent high school students into panic.

In Omaha, meanwhile, as people scurried into the streets, the quake damaged buildings under construction at the new Creighton University.

Though it lasted only a few seconds in most places, the earthquake was the largest in the state’s recorded history. It shook an estimated 140,000 square miles of Nebraska, South Dakota, Minnesota, Iowa, Missouri and Wisconsin.

In the days before seismographs or the Richter scale, quakes were described only by their effects on the surface. They were classified according to the modified Mercalli scale, which described 12 levels of intensity. Intensity I, for example, is hardly felt at all; IV feels like a heavy truck striking a building; VII can break chimney and send everyone running outdoors; X cracks the ground and destroys brick buildings; XII ripples the ground in waves and levels all buildings.

The 1877 Nebraska earthquake rated a VII. On the Richter scale which measures the actual energy of a quake based on seismographic readings, it might have registered 5.1. By comparison, the 1989 San Francisco earthquake that killed 62 people and left 12,000 homeless measured 7.1.

In other words, Nebraskans aren’t rushing to buy earthquake insurance. Even so, the state has a few known fault zones and several other unidentified lines that move occasionally, causing a quake or two each year.

Nebraska quakes are monitored by stations outside the state, up to hundreds of miles away. “Seismic waves are analogous to sound waves,” University of Nebraska geologist Malt Joeckel explained “but they can move much faster through solid material than sound waves can through the air."

“After measuring the time it takes the three different kinds of seismic waves to travel to at least three widely-distributed seismograph stations, computers can accurately calculate where a given quake was centered,” he said. The point where results from the three stations intersect is the epicenter.

Nebraskans who have experienced an earthquake never forget in Last November, a 4.3 quake rocked much of north central Nebraska. The epicenter was just southwest of Butte, near Paul and Jan Hostert’s place.

‘It was a surprise,” Jan said. “I was putting clothes in the dryer and our granddaughter was working on the computer in another room. Everything started to rattle for what seemed like a lone time maybe a minute.”

Jan heard a crash as a framed picture fell from a wall and broke a vase. Both she and her granddaughter ran through the house meeting in a hallway. Neither knew what was happening. Jan thought it might be a plane crash or a bomb. “It was so strange, she said.

Paul, meanwhile, relaxed in a chair in the living room. ‘It was an earthquake,” he said calmly. Jan laughed in disbelief. Soon, however, an O’Neill radio station confirmed that Paul was right.

That day in Butte, Donna Bernt was in her kitchen, gathering food for a daughter who was about to return to college in Kearney ‘You could hear it and feel it,” she recalled. ‘It gave you a queasy feeling. Your mind starts jumping. I thought a building exploded or it was a car wreck."

All over the area, when the ground started shaking, it seems that no one — except Paul Hostert — thought first of an earthquake. Native Boyd County residents can’t remember another.

The same day, a massive 7.9 earthquake shook the Denali Fault in Alaska. Coincidence? Maybe, but if so it’s not the first. On Good Friday, March 28, 1964, Prince William Sound suffered the strongest earthquake ever recorded in the U.S., measuring 9.2 on the Richter scale. That day in Merriman, Neb., four shocks about four minutes apart cracked roads, slumped banks of the Niobrara River, and shook dishes from tables and canned goods from shelves. The felt area was estimated at 90,000 square miles; the strength was estimated at 5.1.

It hasn’t been proven, but Roger Pabian, a 35-year veteran research geologist at the University of Nebraska, believes there could be connection between the Nebraska and Alaska quakes. “It’s happened quite a few times where a strong shock will occur almost simultaneously with a separate, weaker earthquake,” he said. Strong movement of one plate of the earth causes a smaller movernent of another. Twenty minutes after last November’s Alaskan quake, well monitors near Aurora, Neb. measured water lapping up six inches inside the wells.

We tend to think of the West Coast when we think of big earthquakes. In fact, the largest earthquake in the recorded history of the lower 48 states happened in Missouri. In 1811, New Madrid, at the southeastern tip of the state, suffered an 8.1 quake and thousands of aftershocks. The ground rolled in visible waves and large landmasses were displaced. It was felt as far away as Washington, D.C. The New Madrid Fault Zone, as it is now known, is at greater risk of earthquakes that any location east of the Rocky Mountains.

Without intending offense, Nebraska can honestly say that, compared to Missouri, its faults are relatively minor. In southeastern Nebraska, where the risk of earthquakes runs slightly higher than the rest of the state, the Humboldt Fault is part of the Nemaha tectonic Zone that extends southward to Oklahoma. “Looking across one creek valley, you can see the displacement,” Pabian said. “That’s as close as you can come in Nebraska to seeing tilted sedimentary rocks,” evidence that the Earth’s crust has moved.

The Union Fault, which runs from southeastern Lancaster County to a point east of Union and then east into Iowa, is another Nebraska fault that can be seen from the surface, in this case at an old Missouri River quarry. Normally, soil and surface sediments cover up faults. The Union Fault lies at the southern boundary of the Mid-continent Rift System, a gigantic, billion-year-old crevice hundreds of feet below the surface. It runs southwest from Lake Superior, crossing Minnesota, Iowa, southeast Nebraska, and ending in Kansas. It is at least 700 miles long and up to 40 miles wide. In places it is filled with hundreds of feet of ancient, solidified lava.

Other Nebraska faults include the LaPlatte in Sarpy and Cass counties, the Bunzhastl in Furnas County and the Bed Canyon in Frontier and Red Willow counties. In these places, the Earth shows displacement of a few hundred feet. Some places on Earth show miles of displacement.

A number of quakes have struck the more active southeast over the years, including one intensity VII quake that hit Tecumseh on March 1,1935, with two shocks about four minutes apart. That one was attributed to the Humboldt Fault line and was felt over 70,000
square miles. Another smaller quake hit Tecumseh later that same month.

“We could have a damaging earthquake,” said Joeckel. Especially in the southeastern part of the state, where ancient underground structures are relatively plentiful, there are no guarantees. But the risk is low.

That wasn’t the case a billion years ago, when the Mid-continent Rift System was active and the Earth heaved and cracked. “Most people don’t realize this,” said Joeckel, “But it is one of the fascinating parts of geology.’ Much of what we know about the internal structure of the earth comes from studying earthquakes.

“Earthquakes are part of the basis for determining that the Earth has solid, liquid and semi-solid layers,” Joeckel said. In rock formations, the atoms are so dense and close together, that if these rocks hit each other with enough force, like a hammer shattering a rock, the energy or vibrations from the collision can be felt on the other side of the world. “Vibrations from even modest earthquakes can be felt at distant stations around the globe,” he said.

But even when quakes are felt across the globe, there are “shadow zones” where a given earthquake isn’t detected. Because some earthquake waves can’t travel through liquid, geologists are certain that part of the earth’s core is molten.

Despite having a number of fault lines, earthquakes aren’t often noticeable in Nebraska. The reason, Pabian said, is that most of them are not close to the surface, but are instead buried by sand that acts as a “shock absorber.”

Silt and clay in glacial till, or loess covering the surface, may act like a liquid when subjected to sudden shock like an earthquake. “Note how ketchup becomes more liquefied as you shake the bottle,” Pabian said. The principle is the same.

Are the earthquakes becoming more frequent? Though it might seem that way, in reality they’re just being monitored more closely. Many of the severe quakes of the past happened in remote places where few people could report them. Such places are harder to find nowadays, and no place is out of reach of the world’s networks of seismographs.

In an average year, about 50,000 earthquakes of low intensity are recorded somewhere in the U.S. Most of the 20-plus quakes recorded in Nebraska since 1975 have been in the 3.5 magnitude range.

In 1976, a network of seismic recording stations was set up across the state, with seismographs located in Platte Center, Loup City, Clay Center, Beatrice, Johnson and Wahoo. The project, which lasted until 1989, recorded 91 micro-earthquakes in the state. A micro-earthquake has a magnitude of 2.5 or less and cannot be felt by humans.

The micro-earthquakes, combined with what geologists have learned about Nebraska’s subsurface over the years from earthquakes and exploratory drilling for petroleum and minerals, tell a lot about how the state was formed and how it is still reacting.

Joeckel said the network was dismantled and the state doesn’t have a research seismograph, or even one for teaching purposes, in operation today. New seismographs cost around $50,000, and Nebraska would need a couple of them to set up an accurate seismic network. He said it would be nice to have one or more in operation, not only as a way to monitor Nebraska quakes, but also to provide an educational opportunity for students of earth science. At present, the state’s nuclear power plants apparently have the
only operating equipment in the state able to detect the motion of earthquakes with a magnitude of 2.9 or greater.

Last summer, a 3.5 quake briefly shook Greeley. “It felt like a car ran into my house,” a resident told reporters. Most Nebraskans probably don’t worry much about the possibility of a stray motorist taking a short cut through the front porch. We worry even less about earthquakes. But for Joeckel and other geologists, the presence of earthquakes arouses neither fear nor disbelief. To the scientist, they have a sort of beauty, and serve a useful purpose in revealing the mysteries of our Earth’s structure and beginnings.