JOHN YANG: This week's 4.4 magnitude tremor in Los Angeles didn't do much damage, but it was along a fault that runs through a densely populated area, and scientists warn that that fault has the potential of producing a devastating 7.5 magnitude quake.

It's again raised the question of earthquake preparedness in Southern California.

But it's not just the west coast that ought to be thinking about that.

JOHN YANG (voice-over): October 17, 1989, a 6.9 magnitude quake in the San Francisco Bay Area collapses elevated highways in a section of the Bay Bridge.

Candlestick Park is evacuated as the World Series is postponed.

Broken gas mains fuel fires that destroy buildings.

63 people die.

Damages total more than $6 billion.

February 9, 1971.

MAN: A state of emergency in California following the earthquake which disrupted the entire state.

JOHN YANG (voice-over): A 6.6 magnitude earthquake in California's San Fernando Valley leaves 65 people dead, some in the partial collapse of a Veterans Administration Hospital.

Damage is estimated at $500 million.

Quakes many still vividly remember but a less well known seismic event reshaped an area in the middle of the country more than two centuries ago.

For two months at the end of 1811 and the start of 1812 a series of quakes and smaller tremors shook the area around the tiny frontier town of New Madrid, Missouri.

The initial shock is estimated to have been about magnitude 7.5.

Witnesses said houses collapsed and the earth opened up.

Some said the Mississippi river ran backwards for a short time, trees snapped and geysers of water and sand shot up from deep underground.

KENT MORAN, Earthquake Historian: The effects were in the Epicentral Area Catastrophic.

You had landslides.

You had liquefaction.

JOHN YANG (voice-over): Earthquake historian Kent Moran at the University of Memphis studies the event.

KENT MORAN: The buildings literally being shaken apart at New Madrid, the river sloshing back and forth, the people screaming in panic, the ground opening up all concurrently at same time.

The effects were apocalyptic.

JOHN YANG (voice-over): It was felt as far away as Louisville, Kentucky in Cincinnati, it rang church bells in Charleston, South Carolina.

KENT MORAN: They were all puzzled by it's like, why is the ground moving?

Why are objects in my house or a cabin swinging back and forth for no apparent reason?

Why is the water sloshing back and forth in the stream or pond by my house.

It's not supposed to be doing this.

JOHN YANG (voice-over): About three and a half million acres of the Mississippi and Ohio River valleys were reshaped.

Hills and lakes appeared on previously flat, dry terrain.

Two centuries later, the effects are still visible.

Stretches of sand that the pressure of the shifting Earth forced to the surface, a phenomenon known as sand blows.

KENT MORAN: It depopulated it and depressed the population that area for years afterwards.

JOHN YANG (voice-over): But now the area is home to millions of people in at least five states, including major cities like Memphis, Tennessee, Little Rock, Arkansas and St Louis.

JOHN YANG: The U.S. Geological Survey estimates that in the next 50 years, there's a 25 to 40 percent chance of an earthquake of at least magnitude 6.0 in the area, and about a seven to 10 percent probability of a repeat of the 1811, 1812 earthquakes.

Brian Houston is Chair of the University of Missouri's Department of Public Health and director of the school's Disaster and Community Crisis Center.

Mr. Houston, this was, of course, the frontier when this happened in the 1810s but if there were a repeat, what would the results be now in that area?

BRIAN HOUSTON, University of Missouri Disaster and Community Crisis Center: Yeah, I think that's one of the big issues that you bring up is that the last time this happened almost 200 years ago, there weren't a lot of people in the area.

And now there are many more, many more millions of people that live in the area, a lot of transportation infrastructure, highways that cross the Mississippi River and other rivers.

And so the impact of an event as strong as what was experienced in the early 1800s would really impact a lot of homes, a lot of businesses, a lot of transportation.

And so would have a significant human toll and also economic impact in the area.

JOHN YANG: And you talk about spans across the Mississippi, but the Mississippi has become now an important economic pipeline, bringing coal and agricultural products to the world.

What would be the effect of having that disrupted?

BRIAN HOUSTON: We know that some of the rivers were redirected as a result of these large earthquakes.

And so you could imagine if something like that were to happen.

Now, the shipping and the transportation that occurs up those rivers could be completely unpassable and not even doable.

And of course, as I already mentioned, just getting over those rivers is a big conduit between the, you know, the eastern half and the western half of the country, and so at least in that region, that could be dramatically reduced.

JOHN YANG: So the estimates of the possibilities of this happen are relatively low, 25 to 40 percent but in the Midwest, you do have every year, you have flooding, you have severe weather, tornadoes.

How do you prioritize taking care of preparing for things you know are going to come because they come every year, versus preparing for something like this?

BRIAN HOUSTON: Yeah, that's the big challenge.

You know, we've conducted focus groups and collected survey data throughout the new mattered region and that's what we hear from people, is that there are all sorts of other day to day risks that seem very possible and are quite salient.

So flooding for sure severe storms.

And so when you put something like an earthquake risk on top of that, when there, you know, doesn't seem to be a huge chance that it's going to happen tomorrow, say, even if it could be quite severe, that in the people we've talked to really falls to the bottom of the list in terms of risks they're thinking about, or planning for, or even concerned about overall well.

JOHN YANG: Those people who are thinking about that risk, what should they be doing?

What should they be thinking about?

BRIAN HOUSTON: Yeah, there's sort of a range of activities that individuals and families can take to prepare for an event like this.

Kind of the most basic end.

There's things like prepare a disaster kit and have some water and some food and some important medications and documents in a place that if an event like this happens and there's damage to your home or you're displaced, you've got those emergency supplies that you need.

And the nice thing about something like that is it can help with an earthquake, but can also help, you know, if there's some flooding or a severe storm or that sort of thing.

And then on the higher end, there's sort of more complex ways to more specifically prepare for earthquakes.

So one of the things we recommend is to make sure heavy objects are bolted to the wall, like water heaters and heavy shells and things like that, so if an earthquake occurs, those things don't fall down and cause more injury or damage.

And then maybe I kind of the highest end of preparation is something we talk a lot about with people, which is getting earthquake insurance.

So homeowners insurance does not cover damage to a home from an earthquake, and so for people living in this region, even though it may be a small percentage chance that it's going to happen tomorrow, when you imagine a major event that could significantly damage or even destroy your home.

Having something like earthquake insurance might be something that you want to consider doing.

JOHN YANG: What about state and local emergency preparedness officials?

Are they worrying about this?

BRIAN HOUSTON: Definitely, and one of the things they really work on is just making sure people know that this risks exist, because, you know, you don't get a lot of big earthquakes in the area.

You talk about earthquakes in the U.S., and you think about California, Washington, you don't usually think about Missouri.

So they're very active in getting the word out that this is a risk, and then doing things like community drills, so people know what to do, right when an earthquake occurs, to stay safe.

But again, people have a lot on their minds and a lot on their plates.

So even though this may be one risk, it doesn't always seem like the most obvious and likely to occur risk this week.

JOHN YANG: And on the west coast in California, a lot of attention to building codes for new construction and trying to retrofit existing buildings.

Is anything like that going on in the new management area?

BRIAN HOUSTON: Not nearly as much as you see on the West Coast, for sure, because not as many people are aware of this risk.

I don't think that there's quite as much emphasis and support on building codes.

There are definitely some efforts in some areas, but you don't see a lot of statewide policy in places like Missouri or Tennessee in this area.

So, there's definitely a lot of opportunity for improvement in terms of helping prepare communities relative to building codes, but not a lot going on and not a lot has been done so far.

JOHN YANG: Brian Houston of University of Missouri, thank you very much.

BRIAN HOUSTON: Thank you, John.