ing. Doors rattle, buildings creak and groan, things fall to the floor.

You wonder how long the quake will last. The thunder turns into a freight train. You shout, turn quiet, grab onto something. After it stops, you take a deep breath and think how strange it is when the world becomes a giant, beating drum.

In Northwest Montana, that giant drumbeat is rarely heard. While small earthquakes take place here regularly, most are imperceptible. It’s entirely possible for someone to spend their whole life in the area and never feel the stampede coming.

Over geological time, however, a veritable tympanic symphony has played across this region. Some of the biggest faults in Montana crisscross the landscape here, shaping rivers and defining mountain belts. Huge blocks of crust have shifted and moved, some as much as 60 miles from their original location.

“Over the last 20 million years or so, major down-dropping has occurred along the east side of all the major valleys here, including the North Fork, South Fork and Flathead Valley,” Kalispell geologist Lex Blood said. “The amount of vertical displacement along these boundary faults has been up to 10,000 feet, or about two miles.”

Some of that displacement came in incremental jumps, an inch or two at a time, in the type of small-to-moderate earthquakes that leave people feeling excited and queasy.

And some of it took place in monster events, with violent bucking and heaving that wrenched the earth apart.

Seismic images from Flathead Lake, for example, show individual fault scarps several feet high in lake bed sediments that were laid down after the last Ice Age.

“Flathead Lake exists where it does because of structural downdrops along the Mission Fault,” said University of Montana geologist Marc Hendrix, during a 2004 interview. “Some of these fault segments were quite active. Based on the offsets we see, a few of the quakes probably had magnitudes greater than 7.0.”

The last earthquake of that scale in Montana — and the only one to take place here during historical times — was the 1959 Hebgen Lake quake near West Yellowstone.

Outside of Alaska or California, Hebgen Lake was the largest earthquake in the United States in the last century. With a magnitude of 7.3, it created fault scarps as high as 18 feet, ruptured the surface for 22 miles and caused a massive landslide that dumped about 30 million cubic yards of rock into the Madison River.

A slide of similar proportions happened near the mouth of Bad Rock Canyon about 12,000 years ago, according to geologist Larry Smith with the Montana Bureau of Mines and Geology.

Since that time, additional fractures have developed on Columbia Mountain “indicating that many feet of hilltop spreading has occurred,” Smith said during a 1999 conference in Calgary. “If these cracks define the outer limits of a detached rock slab, up to 37 million cubic yards of rock could be shed from the mountain” during another major earthquake.

A disaster of that magnitude “is a worst-case scenario and is very unlikely,” he added, “but there is some hazard of [smaller] continued rockfall at that location.”

Although northwest Montana is the northern terminus of the Intermountain Seismic Belt — a 1,000-mile-long fault zone that’s rooted in southern California — there’s no clear consensus on how at-risk the Flathead is for a large earthquake.

The Montana Multi-Hazard Mitigation Plan and Statewide Hazard Assessment, which was completed in 2004, estimated that the recurrence interval for events with a magnitude of 7.0 or higher in Western Montana was about 133 years.

Since 1900, however, there have only been about two dozen earthquakes in the entire state with magnitudes of 5.5 or higher, and Hebgen Lake was the only one to exceed 7.0.

Moreover, a 2005 report from the Bureau of Mines and Geology indicated there’s just a 1 percent chance that Flathead or Lake County will be hit by a 7.0 to 7.5 event in the next 50 years (although the report also emphasized that “there are large uncertainties associated with earthquake predictions in Montana, due to limited information.”)

Whatever the recurrence interval, though, Kalispell Fire Chief Randy Brodehl said quakes and major floods are the most likely catastrophic events for which the valley needs to prepare.

“With an earthquake, every day you don’t have one you’re that much closer,” Brodehl said. “They don’t just go away.”

Preparation occurs in a variety of ways. One of the more common methods is to hold periodic “tabletop” exercises — basically indoor drills in which the people responsible for a particular issue or area sit around a table and simulate handling a disaster.

The drills help familiarize local officials and emergency responders with the communications procedures and command structure that would be used in a real event.

“All of Kalispell’s firefighters and police officers are familiar with this system,” said Brodehl, who also is a liaison officer for one of the nation’s elite Type 1 incident management teams. “We use it for emergencies and non-emergencies. It helps keep things simple. We’re also developing a relationship with the county and [Office of Emergency Services Director] Mark Peck that will be very good for the community.”

Various local organizations do their own disaster mitigation planning and training, too.

Flathead Electric Cooperative, for example, backs up its entire computer system every night to a location in Mandan, N.D., so critical data won’t be lost.

Co-op officials also hold monthly tabletop exercises. They haven’t simulated an earthquake yet, but they’ve practiced such issues as what happens if they have to evacuate their headquarters building on U.S. 2, or how to take care of employees’ families so their people can focus on keeping the power system up and running.

“Our industry is inundated with this whole [disaster planning] concept,” said Ed Mahlum, Flathead Electric’s information technology manager. “Just to borrow money from a major lender, we have to have a recovery plan.”

To some extent, the reaction to a major earthquake would just be a bigger version of what people here do all the time: Go out, evaluate a situation, fix the problem.

Co-op crews, for example, fix power outages every day. Similarly, the doctors and nurses at Kalispell Regional Medical Center respond to emergencies constantly.

“Whether it’s the typical ‘Friday night mayhem’ or something different, our employees are very adaptable,” said Bill Boyd, Kalispell Regional’s safety officer. “Hospitals are notoriously ingenious. The people who work here are creative and skilled; that’s how they get through every day.”

The hospital has its own disaster mitigation plan and procedures as well, and over the last few years it has taken steps specifically to prepare for an earthquake. Support columns and beams, for example, have been added to several older structures to reinforce them. It also has three electrical generators with enough diesel fuel available to run critical equipment for seven days.

Just recently, “the hospital board approved drilling our own water well,” Boyd said. “For most things, we’re trying to have some level of independence.”

No matter how well-prepared organizations think they are, though, a major quake will test everyone’s ability to make order out of chaos.

“The water mains will be gone, so we won’t have any water pressure,” Brodehl said. “Geographically, the area might be isolated. Mutual aid will be rare, because every department will be dealing with their own emergencies. There’s even the possibility of rivers changing locations, and because of its age we don’t know how well Hungry Horse Dam will do. We could get floods and a quake within hours of each other.”

Lex Blood said prehistoric earthquakes generated waves hundreds of feet high in the Lake Tahoe region. A similar event could produce an inland tsunami that might devastate areas surrounding Flathead Lake.

“That scenario is not unrealistic to consider here, if there’s substantial displacement along the Mission Fault,” Blood said.

Given the uncertainty of what will happen and how bad the damage will be, Brodehl said people have to be ready to take care of themselves.

“Don’t plan on calling 911 and getting a response,” he said. “The alpha and bravo [minor to moderate injury] ambulance responses will probably go away. So will some critical patient responses; if death is imminent, we’ll look at providing comfort in place. That’s the reality. There will be people lining up at the hospital, so if we have no way to transport someone to a place where they can be treated and get better, then we have to function in the areas where we can make a difference.”

Brodehl recommended that people have a two-week emergency supply of water, food and critical medication on hand, and make sure everyone in the family knows where it’s stored.

“People need to plan on being self-sufficient,” he said. “We’ll help, but people need to do what they can to mitigate the problem. I could say we have a plan that will fix everything, but I’d be lying. We can prepare and train to manage a disaster, but for the first 48 hours there’s going to be a lot of scrambling.”

Reporter Bill Spence may be reached at 758-4459 or by e-mail at bspence@dailyinterlake.com