Original subtitles

Powerful tremors catch millions by surprise.

There was a very violent earthquake.

NARRATOR: Collapsing buildings kill thousands.

Many are buried alive.

ANDREW OLVERA: And we're going to go ahead and have the rescue squad come in

and help extricate that victim out of the hole.

NARRATOR: It's the biggest quake to happen here in 80 years.

MICHAEL ANDREW: Major earthquake!

We've never seen anything like it!

CLIMBER: Oh, look at that, look at that, look at that!

NARRATOR: The quake triggers a huge avalanche on Mount Everest,

killing 20 people.

PAUL DEVANEY: Whoa, whoa, whoa, inside!

NARRATOR: It's the Himalayan peak's most deadly day.

DAVID BREASHEARS: It looks like what you see

when one of these tornadoes runs right through a place.

I've never seen anything come at us like that before.

NARRATOR: Millions across Nepal are homeless.

Many are cut off from the world by landslides.

SURAJ VAIDYA: They've lost all the houses that they had.

The whole village is wiped out.

NARRATOR: Even scientists are stunned by the powerful aftershocks.

Whoa, that was enormous!

ANDREW: Oh my gosh, it's like the whole mountain's coming down!

We've seen just one fraction of a second

in a 50 million year time interval

of building the Himalayas.

NARRATOR: Can they forecast when the next big one will strike?

ROGER BILHAM: You know, it's really scary.

There's no reason why one could not occur

in the next ten years or the next ten minutes.

NARRATOR: The race is on to unravel the mysteries

of the "Himalayan Megaquake," right now on NOVA.

Major funding for NOVA is provided by the following...

In this hilly terrain, almost all arable land is used.

The slopes stretch up

to eight of the world's ten highest mountains.

Each spring, hundreds of mountaineers come

to climb Mount Everest, the highest point on Earth.

The birthplace of the Buddha,

Nepal is a peaceful haven for both Buddhists and Hindus.

Ancient palaces stand side-by-side

with even older Hindu temples.

April 25, 2015, 11:56 a.m.

(shouting)

NARRATOR: The earth begins to move

and doesn't let up for a full minute.

(rumbling)

There's no safe place to run.

PAUL DEVANEY: Whoa, whoa, whoa, inside!

NARRATOR: An earthquake rips across the Himalaya...

DEVANEY: Get down, get down, get down, get down!

CLIMBER: Close the door!

DEVANEY: Close the door!

NARRATOR: ...unleashing an avalanche

upon hundreds at Everest's Base Camp.

(rumbling)

I've never seen anything come at us like that before.

Oh my God.

Oh my God!

JOST KOBUSCH: Are you okay?

CLIMBER: Yeah!

WOMAN: Are you all right?

KOBUSCH: Yeah.

NARRATOR: Survivors quickly become rescuers.

(honking)

Makeshift hospitals spring up

to deal with the nearly 18,000 injured.

Many are still buried alive.

Eight-year-old Seema Tamang was trapped under her house.

She can't walk, has a head injury,

but medical care is limited.

NARRATOR: There's a race to find anyone alive in the rubble.

NARRATOR: Since April 25, seismometers across Nepal

have recorded 400 aftershocks of magnitude four or greater.

NARRATOR: Over two million are now homeless.

NARRATOR: Shaking isn't the only threat.

Over 5,000 landslides

have left thousands of villages unreachable.

SURAJ VAIDYA: They're cut off from the rest of Nepal,

and they've lost all the houses that they had.

The whole village is wiped out.

They have supplies for about 11 days.

And she's not sure what she's going to do after 11 days,

but she's hoping that the government will come

and give some sort of rescue,

you know, drop some food up here.

So living for them is extremely, extremely difficult

at this stage.

This used to be a cow shed,

and now what you have is people actually occupying this

for their shelters, yes?

So you see there are four little children up here.

They live up here, you see they live in the middle?

That's how they're living.

NARRATOR: As the death toll rises toward 8,000,

a few miracles emerge from the dust.

Rescuers dig a baby boy out

from underneath his home on day two.

Remarkably, he's unharmed.

This earthquake came without warning.

People in the central mountain villages felt it first.

Then, just 16 seconds later, the shaking reaches the capital.

The waves rock people like a storm at sea.

The tremors take only a minute to reach Mount Everest,

150 miles away.

KOBUSCH: The ground is shaking!

Do you hear that?

NARRATOR: Irish climber Paul Devaney

picks up his camera to record what's happening.

We realized, "Wow, this is an earthquake

and the whole of the base camp is moving pretty violently."

NARRATOR: Then, up above them,

the earthquake dislodges a massive block of snow and ice,

which comes hurtling down.

But they can't see it.

BREASHEARS: I think probably if it had been a clear day,

people would've seen that avalanche much sooner.

NARRATOR: Photographer David Breashears was on the mountain that day.

They had no time by the time they turned around.

CLIMBER 1: Oh, look at that, look at that, look at that.

Oh, look straight ahead.

Ready to go in the tents, or what?

CLIMBER 2: That is immense.

CLIMBER 1: Look, look, look, look, look!

Ready to go in the tent?

NARRATOR: The climbers have a few seconds to decide where to run.

I'd say within about 50 feet of our location,

a massive avalanche was bearing down on us.

KOBUSCH: Oh, oh!

CLIMBER 3: Look, look!

DEVANEY: Whoa, whoa, whoa, inside!

At that point in time, you're just focused on,

"How can I survive this, and will I survive this?"

(panting)

KOBUSCH: Come under my jacket!

Come under my jacket!

Are you okay?

MAN: Yeah, yeah, yeah.

WOMAN: Are you all right?

MAN: Yeah.

(panting)

DEVANEY: I've never seen anything like that cloud come at us before.

Are you okay?

BREASHEARS: We started to learn, three or four hours later,

that there had been loss of life.

Many casualties, people with serious injuries,

multiple broken bones, concussions.

Then every few hours, the death count went up.

These were massive blunt force trauma injuries.

People were blown through the air into rocks.

NARRATOR: Ultimately 20 people die on Everest,

and in the rest of Nepal, the total dead nears 9,000.

News of the devastation travels faster

than the seismic waves themselves.

As the earthquake's waves ripple out,

they hit seismic stations at different times.

It takes 24 minutes for them

to reach the other side of the Earth,

in Colorado, where the U.S. Geological Survey

can compare the time they took to reach each station

and then pinpoint where the waves started--

the epicenter.

This one started 50 miles northwest of Kathmandu.

But word travels hundreds of times faster via social media.

HARLEY BENZ: We monitor for the word "earthquake" in many languages.

We saw a surge in Twitter traffic.

Realizing it was in a heavily populated area,

an area that we know large earthquakes can do damage,

I was called at home.

Within a few minutes, our seismic sensors

will start seeing this earthquake,

and then we'll locate the earthquake,

determine its magnitude.

NARRATOR: Magnitude is the size of the earthquake

at its source.

This one's 7.8-- sometimes called a "megaquake,"

an earthquake that's seven or greater.

Earthquake magnitude is not linear.

The 2010 quake in Haiti at 7.0

had the energy of 32 Hiroshima bombs.

Nepal's 7.8 is more than 15 times stronger,

but not as large as this highly active zone can produce.

Geologist Roger Bilham is a first responder

to most of the world's major earthquakes.

I immediately had a look

to see how much money we had in the bank,

and I purchased a ticket on the next flight to Kathmandu.

NARRATOR: He's especially interested in the Himalayan region

because of its unique geologic history.

The earth's crust consists of several tectonic plates.

About 50 million years ago, one of them, the Indian plate,

began colliding with Eurasia, gradually forcing it upwards,

creating a massive mountain range--

the Himalayas.

That's what builds the Himalayas.

Where you have compression of two plates,

the plates initially start to fold and fracture.

The Himalayas is probably the largest collision

that we've seen on the planet for the last 500 million years.

NARRATOR: The Indian plate continues to converge with Tibet

at the rate of 18 millimeters a year.

In some places, the plates stick,

accumulating stress,

which eventually releases all at once in an earthquake.

This is what scientists believe happened on April 25, 2015.

MAN: My god!

SEARLE: We've seen just one fraction of a second

in a 50 million year time interval

of building the Himalayas.

NARRATOR: This blip in the geological timeline

was so powerful, it wiped out thousands of villages.

Rescue has been slow to arrive.

A team of Nepalese athletes and nurses

takes matters into their own hands.

They gather tents, tarps, and food

to deliver to the cut-off villages.

NARRATOR: They're travelling to the district

with the highest death toll: Sindhupalchok.

Few vehicles have passed here since the earthquake.

NARRATOR: They want to get food and medical supplies

as far as the bus will take them.

Then, they'll set up a hospital for survivors.

All homes here are abandoned.

NARRATOR: This road was just dug out

from an earthquake-triggered landslide.

A strong aftershock could cause another.

NARRATOR: They reach the village of Thulo Bhotang.

Over 3,400 people have died in this district.

NARRATOR: They've brought 3,000 pounds of rice and lentils

to feed the villagers.

NARRATOR: Seema Tamang was literally buried alive by the earthquake,

pinned beneath the stones of her home for an entire day.

NARRATOR: Unable to walk, Seema is in a lot of pain.

The doctors believe she could have broken bones.

An x-ray is needed,

so she'll have to be evacuated to Kathmandu.

NARRATOR: 95% of the structures in this district were destroyed,

including Seema's home.

(speaking Nepali)

BHANDARI:

NARRATOR: But among the less lucky ones is this young woman,

whose mother and baby sister died.

(translated): I live in Kathmandu-- I have a job there.

My mother and sister died

in the earthquake.

I came back here, and now I live in a cow shed

with my brothers and sisters.

One brother doesn't even know that mother has passed away.

I haven't been able to tell him.

He's only seven years old.

(sobbing)

I can't stay here because I don't have land here.

Landslides have destroyed all the lands we had.

The earthquake has rendered us homeless.

Sometimes, I wish I were dead,

thinking that it would be better.

This is the house.

We dug mother out the day before.

It was a two-story house.

It went down and it became a rubble.

NARRATOR: Some of the villagers have no family left to care for them.

This man was found collapsed in his home.

BHANDARI:

NARRATOR: Many villagers will move away, for fear of landslides.

Those who stay have nowhere else to go.

NARRATOR: Ang and the nurses have raised just enough money

to call in a helicopter for Seema.

A broken leg left untreated could be fatal.

She and her father have never flown before,

and this flight, through the clouds, is a risky one.

This ambulance is one of Seema's first rides in a vehicle.

She's never been to Kathmandu, and now it's a city in crisis.

This is a military field hospital set up by the Chinese.

One of the few available x-ray machines in Nepal is here.

Surprisingly, Seema's bones are completely intact.

NARRATOR: The stones that were pinning down her leg

may have damaged a nerve.

NARRATOR: She can't move her toes, and without treatment,

she could lose the use of her leg for life.

As the aftershocks continue, everyone is afraid

another large quake will strike soon.

Earthquakes almost always follow patterns.

These photos are from the last big one here, in 1934.

It was at least an 8.0

that ruptured in an area further to the east.

Roger Bilham believes this quake

is a repeat of one that happened in 1833.

It ruptured in the same region with similar impact.

BILHAM: This earthquake enables us

to reinterpret all historical earthquakes,

and our only knowledge of these earthquakes

is how people perceived them.

NARRATOR: Since there were no seismic records in 1833,

Roger had to study newspaper accounts

and travelers' journals.

From those descriptions, he estimated the earthquake

had a magnitude of 7.8, similar to the present-day quake.

Well, suddenly we have an earthquake

that we know about numerically

which has just been felt by a million people,

and those million people have spoken to reporters

and we've now been able to make a catalogue

of hundreds of accounts for this earthquake.

And those accounts can now be translated

into a much more precise numerical evaluation

of historical earthquakes.

NARRATOR: That quake was followed by a series of aftershocks

over two years.

But since 1833, enormous stress has built up along the fault,

leading Roger to believe that the 2015 earthquake

should've been larger.

The first thing we thought was,

"Gosh, this is smaller than we expected."

NARRATOR: He expected a magnitude eight or higher,

at least double the power of the killer that just struck.

So how much energy is still stored in the fault?

Scientists know that the plates move at 18 millimeters a year.

In the 182 years since 1833,

they've moved about three meters.

But in some places, the faults are stuck,

and this lack of movement

creates a predictable amount of strain.

John Galetzka is a geodesist

who measures changes on the surface of the planet.

He can tell how much of the strain

the 2015 earthquake released.

He's flying directly to one of the places

where the two plates,

carrying India and Tibet, are stuck.

33 kilometers to Dunche!

NARRATOR: He'll determine just how much the locked plates,

20 kilometers below, lurched forward during the quake.

If they didn't move enough,

there's more stress to be released.

We'll get seismic data!

NARRATOR: GPS stations fixed solidly to the earth's surface

have the answers.

GALETZKA: I'm just going to demonstrate for you

how strong the monument is here.

So really, it's anchored into the earth here,

about a meter and a half or two meters.

Glued in.

Hi-ya!

NARRATOR: This is one of over 50 active GPS stations

placed across the Himalayan arc of Nepal

measuring minute movements of the Earth.

GPS satellites broadcast microwave signals

to stations on the ground.

The GPS stations are so sensitive,

they can detect shifts as small as a millimeter.

Data reveals the earthquake released

only half of the stress that's accumulated since 1833.

This station moved to the south about a meter and a half.

So just to demonstrate,

this station was about right here ten days ago,

and then the earthquake happened,

the earthquake happened, so seismic waves,

and then seismic waves and the tectonic movement,

the plate shifting,

and then the antenna settled to where it is right now.

NARRATOR: This GPS station and others didn't move as much as expected

because the earthquake only ruptured

the lower, deeper part of the fault.

This means a portion of the fault remains loaded

with pent-up energy for future earthquakes.

JOHN ELLIOTT: This was a very big earthquake in Nepal,

but it's not the biggest that can happen.

It hasn't relieved all the pressure

across this large faulting area.

There are other bits of the fault

that still need to break in the future.

NARRATOR: Does this mean there's more to come?

This earthquake battery didn't run all the way down.

It's still partially charged,

leaving a reservoir of stress to be tapped by future quakes.

A bigger concern is that there are places along the fault

where no stress was released by this earthquake.

Recent earthquakes have relieved built-up stress

to the east in India,

and also to the west in Pakistan.

But there's an area in between, to the west of Nepal,

that's locked.

This earthquake didn't cause it to budge even a bit.

It's a time bomb waiting to erupt,

where no movement has occurred for centuries.

SEARLE: Unfortunately,

all the strain built up has not been released

and it's still down there,

which means that there is some danger of further earthquakes

to the west of the fault, which still remains locked,

and that's a problem.

NARRATOR: Like a sleeping giant,

the west of Nepal has at least ten meters

of built-up slip stored beneath it.

It last slipped in 1505.

That's 500 years of coiled up potential energy

ready to spring.

BILHAM: You know, it's really scary.

We know earthquakes

as big as 8.6 have occurred in the Himalayas.

There is no reason why one with that magnitude

could not occur in the next ten years

or the next ten minutes.

NARRATOR: The challenge is to now prepare the people

for this potential catastrophe.

It'll be 16 times bigger than the 2015 earthquake.

Day five.

Just as rescuers are losing hope,

they discover a trapped victim still alive.

Volunteers from the Los Angeles County Fire Department

have arrived to help the local police.

ANDREW OLVERA: We were told that there's voices heard

and a void space.

We have a search reconnaissance team with us right now,

and we're going to go ahead

and have the rescue squad come in

and help extricate that victim out of the hole.

NARRATOR: Concrete rescue saws

can cut through what's left of an eight-story building.

Nepal police force inspector Laxman Bahadur Basnet

risks his life to crawl under the tons of rubble.

NARRATOR: They've found a 15-year-old boy entombed in complete darkness.

They battle for five hours to free him.

(shouting)

PEMBA LAMA (translated): I was eating,

and then the earthquake hit.

When I was trying to get out,

the walls broke into pieces and fell on top of me.

I was unconscious at first,

and then I thought it was just a nightmare.

OLVERA: It's what we call an entombment.

So, he wasn't specifically crushed,

but what he was was inside of a box,

a box with heavy concrete all around him.

(cheering)

NARRATOR: Pemba Lama has emerged

into a world dramatically altered.

Earthquakes have the power to instantly reshape the land.

Their most obvious effect is a sudden slip

to one side or another.

What's less obvious

is that the earth can move vertically, too.

Geophysicist John Elliott figures out just how much

using satellite data.

ELLIOTT: Using this data,

we can measure precisely how much

the earth has moved up and down.

Each of these is a contour,

but instead of telling you how high the mountains are,

it tells you how much higher, how much they grew,

or how much they reduced in size.

Each of these is a ten-centimeter contour--

we have ten of them--

and this area beneath Kathmandu

actually uplifted by about a meter,

whereas these high mountains north of Kathmandu

actually went down about 70 centimeters.

NARRATOR: The earthquake caused Kathmandu to rise three feet up.

Mount Everest, on the other hand, sank by about an inch.

But it was the side-to-side shaking

on a ridge above Base Camp that triggered the avalanche.

Ultimately, it killed 20 people and injured 120.

But the avalanche only deposited a couple inches of snow in camp.

NARRATOR: So what caused the death and destruction here?

BREASHEARS: This wasn't a normal avalanche.

Some of these tents have thick steel poles.

We later learned that when those things are hit

by a 300 mile-per-hour-plus wind,

they become lethal missiles.

NARRATOR: Scientists in Davos, Switzerland, simulate

the physical forces behind avalanches.

But they've never modeled one this extreme.

Yves Buhler and Perry Bartelt want to figure out

exactly how much ice was dislodged above Base Camp

by the earthquake.

David Breashears was able to get them close-up photos

of the ridgeline where the ice calved off.

BREASHEARS: I commissioned a helicopter

to fly directly above Base Camp.

And I flew back and forth with the door open.

BUHLER: Because David is doing

so high-resolution shots we can zoom in.

So this is what we identified as the main release mass.

NARRATOR: The chunks of ice that the earthquake tremors shook

off the ridge above Base Camp

were akin to 100,000 cars plummeting toward camp.

The avalanche took 60 seconds to descend nearly 3,000 feet,

reaching speeds of up to 157 miles an hour.

The impact of the ice mass hitting ground zero

detonated a force comparable to a bomb blast.

One powder cloud jet managed to push its way through

and it shot it directly towards the Base Camp.

NARRATOR: Upon impact, the avalanche kicks up an envelope,

called a "powder cloud," one percent snow and 99% air.

And that's what we observed in the video.

That it was like ejected into the air.

NARRATOR: This powder cloud reached a height of 650 feet.

And just in front of that cloud

blasts an invisible, but deadly, pressure wave.

The Swiss team determined that the force of the pressure wave,

indicated here in red,

was enough to flatten a wooden building.

Many climbers were killed by a violent blast of air

moving at more than 100 miles per hour.

The color is the pressure,

so the pressure that people experienced

when they were there.

And red means the limit where a person gets smashed

against rocks.

NARRATOR: Climber Paul Devaney photographed huge barrels

that were blown from the camp

several hundred meters across the glacier into a gully.

DEVANEY: It's a scene of pretty surreal devastation.

It's like a plane crash or something.

It's hard to imagine what's just happened here

in the last few hours.

(exhales)

NARRATOR: At the same moment, nearly 100 miles away,

a similar, and even more deadly, avalanche

hit the village of Langtang.

David Breashears photomapped the devastation.

BREASHEARS: When I flew in that helicopter up that valley

and over Langtang, I really had a hard time

getting my head around what I was seeing.

An entire village was gone.

Obliterated.

Thousands of trees, trees this big around, were flattened,

stripped of their bark and branches.

It looked like what we had seen after the volcanic eruption

of Mount Saint Helens.

NARRATOR: David stood at the place where he had taken a photo

of Langtang in 2012 and shot an exact match.

Over 400 people and 116 homes were lost in an instant.

How could such a colossal event come to pass

without a trace of warning for those below?

(shouting)

NARRATOR: In the village above Langtang, a similar event occurred.

BREASHEARS: This would've been a group of people

who would've gotten out of their buildings and said, "It's okay."

And then they would have no idea

what was coming from 10,000 feet above them.

NARRATOR: They had survived an earthquake,

but out of the clouds came something even more powerful.

MAN: Look, look, look!

WOMAN: Oh, my God!

NARRATOR: The earthquake unleashed multiple avalanches

onto Langtang Valley,

one of the most popular trekking routes in Nepal.

BARTELT: It took the avalanche about 80 seconds after release

to get down to the valley bottom.

And the avalanche reaches tremendous speeds.

And shot out almost directly into the air above Langtang

and then plummeted into the valley bottom.

NARRATOR: People just below Langtang,

in the narrow valley, suffered from pummeling rocks and debris.

Here comes more!

NARRATOR: The cloud could be seen for miles.

Everyone was running

from plummeting boulders and landslides.

AUSTIN LORD: And it was breaking everywhere,

and it was breaking in places you couldn't see.

It was in the clouds.

And you could hear it coming from 2,000, 3,000 meters above.

NARRATOR: Austin Lord captured this footage

in a village two miles below Langtang.

LORD: You weren't sure if all of a sudden something would burst

through the clouds that you couldn't run from.

Here comes another tremor!

LORD: Splinters coming from the sky,

small rock debris coming from the sky.

BARTELT: The houses that were directly

in the path of the core had absolutely no chance.

They were demolished and blown away immediately.

BREASHEARS: It looks like what you see when one of these tornadoes

of epic proportion just runs right through a place.

NARRATOR: This was a mega-avalanche.

A chunk of ice larger than the Empire State Building

fell three times farther than the Everest avalanche--

more than 10,000 vertical feet--

reaching a speed of 225 miles per hour

before hitting the village of Langtang.

That would be ten times the most extreme avalanche

we would have in Switzerland.

And that's just a very, very extreme

and unique avalanche event.

NARRATOR: Austin Lord was among over 300 survivors stranded

in Langtang Valley, unable to get out

due to landslides and avalanches blocking the way.

LORD: And then I looked upslope, where Langtang should've been,

and you could see that Langtang was just... gone.

And I was standing with two or three other people

who realized it at the same time as me,

locals whose families are located above and below

and in Langtang, and it was heartstopping.

Local people were seeing each other, realizing who was gone,

who was still there,

people coming down saying to the people coming up:

"There's no one.

This is... this is everyone."

And just people collapsing, just people breaking and melting

and children wailing.

That was the hardest part.

BREASHEARS: We were wandering down this trail

with debris on both sides of us

and we saw a man coming up the trail towards us.

And he'd come back up the valley, having evacuated it,

to look for his wife,

and along with the army search team,

he had found her body ten minutes earlier.

The earth shook.

10,000 feet above him the ice fell.

And in the blink of an eye his life had changed.

He had no home, he had no wife,

and he had only the 600 rupees in his pocket

and that was six dollars.

And that's something that I will never forget.

NARRATOR: 17 days after the main shock, huge tremors rock Nepal again.

Cameras in parliament capture the panic.

ROGER BILHAM: About a minute ago,

there was a very violent earthquake.

We don't know where it was,

probably about 20 or 30 kilometers from Kathmandu.

And it set the whole valley shaking,

just like it did in the main earthquake.

Everyone was absolutely terrified.

NARRATOR: Could this be a big aftershock, as in 1833?

Or the big one from the west of Nepal

that they've been dreading?

Rarely does a seismologist get to be part

of an earthquake he is studying.

I think it's still moving!

PATRICK GREAVES: It is still moving.

Good grief!

To see people with their arms outstretched

wondering what was going to hit them

even though there was nothing above them.

Only trees and birds.

People don't do that unless they've just recovered

from an even worse shock, which of course was 16 days ago,

the main shock.

This is what happened in 1833.

About two weeks later, there was a large aftershock

that was felt in India.

And I'm sure this one would have been, too.

NARRATOR: Roger will be able to determine if it's an aftershock

or a new earthquake in a matter of minutes.

I've dialed up the USGS earthquake page

and I'm sitting here waiting for a dot to appear on the map

to tell me how big and exactly where it was.

It takes 24 minutes for a seismic wave to cross

from one side of the Earth to the other.

And what we're waiting for are the seismic waves to hit

those distant seismometers and then for their data

to be transmitted via satellite at the speed of light.

Keep going for 1.5 kilometers.

Yeah, go down here.

And these data arrive in Golden, Colorado,

and then they're processed to find out how big

and exactly where and how deep the earthquake was.

NARRATOR: The shaking is intense enough

to send people running out of buildings,

bodies of water sloshed in waves.

Whoa!

That was enormous!

It's a 7.4.

My goodness!

So, this is only a little bit smaller

than the main shock.

No wonder people were scared.

The main shock was 7.8.

This was 7.4, which means the energy released

is four times less,

but to the terrified inhabitants of this city,

the impact was just the same.

(woman screaming, people shouting)

BILHAM: It was 83 kilometers from Kathmandu.

It was near Mount Everest.

So that will have produced an enormous amount of avalanches.

It's really tragic.

NARRATOR: Roger concludes it's an aftershock

to the east of the main shock,

a section of the fault that hadn't moved enough

and was catching up,

releasing as much energy as a 25-megaton bomb.

BILHAM: This aftershock was big enough

to be a main shock in its own right.

Let's go and talk to the survey department.

It was magnitude 7.4!

NARRATOR: When an earthquake strikes, scientists need to know

not only the magnitude at the epicenter,

but also the intensity of the shaking felt in each village.

Roger and David Breashears fly over the region.

BREASHEARS: Roger's mission was

by looking at buildings and the way that they had held up,

he could determine the shake intensity.

It's the velocity

at what the surface of the earth was moving at and the frequency.

There were no instruments in these mountain areas

to measure the shake intensity,

but Roger knows how to determine that

by what happened to buildings.

BILHAM: We needed to get out here quickly

because in the days following an earthquake,

people already start cleaning up.

You don't leave a pile of rubble in your front yard.

So, we lose some of the clues that we need

to understand why the buildings fell down.

NARRATOR: They maneuver close to villages

so David can shoot high-resolution photos.

BREASHEARS: We'll be able to zoom in on those images

and even look at such fine detail that you can just see

bricks or stacked fieldstone

and from that Roger was able to make a determination.

NARRATOR: Using a shake intensity scale,

Roger puts a value between one and ten

on the observable damage produced in each village.

If crockery falls off a shelf, it's intensity six.

Poorly made buildings will partially collapse at seven,

but they'll flatten at eight.

Total destruction would result from intensity ten.

This scale informs engineers

rebuilding for the next big quake.

Over 770,000 buildings were either damaged or flattened

by this earthquake.

Why did some collapse and others survive?

There's a clue in the heart of Kathmandu.

Durbar Square experienced intensity seven shaking.

It's a World Heritage site turned to rubble.

But the dust-laden debris,

dating back to the sixth century, holds a secret.

KAI WEISE: The big earthquakes only come every 80 to 100 years

so there's a generation gap very often

and then they have to relearn

the need to protect themselves.

After the last earthquake, I mean,

we were still reconstructing after 80 years.

Initially, it was just a shock to see on the news

all these images, and it's just unbelievable.

But then it slowly sinks in and you sort of have to accept

the fact, you know, what kind of destruction there has been.

NARRATOR: Coronations of kings have taken place here--

five acres and ten courtyards,

dominated by the white 19th century portion

of the neoclassical Hanuman Dhoka palace,

the newer wing of the original palace, built in the 1770s.

The palace presides

over some of Kathmandu's oldest living temples.

WEISE: Most of these temples are still being used

and they have religious value as well as purely cultural value.

NARRATOR: This undated stone image of Kal Bhairav,

the Hindu god of justice, has survived many quakes.

Out here, we see that two of these tiered temples

on these platforms have totally collapsed.

Very clearly these two temples sort of create

this whole space here,

which is a part of the identity of the city.

They went in with heavy machinery to clear it up

and the problem is heavy machinery impacts

all of the material that could be reused later on.

But we've tried to salvage

as much of this material as possible.

There are all these different elements

and I think they have been mixed up between the temples

and that will be a major challenge

just trying to figure out

where these different elements came from.

NARRATOR: Damage assessment of heritage buildings

requires detective work.

The skin of a centuries-old palace can hide

the true structure within.

Why is the old palace still intact,

while the newer, white palace walls must be shored up?

WIESE: So we were scared

that that would actually collapse,

and if it would, it would bring that whole corner down...

NARRATOR: The white plaster-faced building is failing.

Both are brick construction

and have suffered through past earthquakes.

Randolph Langenbach is a conservation architect.

He travels to earthquake zones to find out what makes

some traditional buildings earthquake-resistant.

NARRATOR: Randolph finds timber hidden within the brick façade.

It's not just a single timber, but it essentially is

like placing a ladder onto the wall.

In other words this cross piece is very much a part

of the system.

WIESE: So you have the beams on the inside and outside.

And then it's held together with this one, which goes through,

so that it basically ties the wall together.

You know what's interesting?

You know what I realized?

It's a frame, timberframe structure.

Yeah, yeah, yeah, you can see the woodwork

going all the way through the ground floor.

And in one corner, probably one of...

Vertical woodwork.

Yes, yes, yes!

And it's tied together.

Then it answers the question.

It answers why it behaved...

it had a different sympathetic motion.

Because this is a frame structure.

It's actually more flexible.

And it's rocking back and forth essentially as a solid unit.

So it can't travel with this

and it broke everything up around it, but it stayed intact.

NARRATOR: It's the timbers hidden within the brick masonry

that laces the older palace together, holding it firm

yet elastic enough to withstand an earthquake.

WIESE: So here the beautiful thing is

that they also started to put in ornamentation

within the latticework.

Up here you can see these beams.

They're tied with the wooden pegs.

And now that is to hold the brickwork.

This is really traditional earthquake technology.

NARRATOR: This combination of timberlacing with brick was not used

in the more recently constructed white palace,

which is on the verge of collapse.

WIESE: They had to develop this system of combining the wood

with the brickwork

and it took centuries for them to develop this

and it became the traditional system of construction,

but then later on they forgot these lessons.

NARRATOR: For the two million Nepalis faced with rebuilding

their homes, this critical lesson in protecting themselves

must be relearned.

But wood in remote villages is often not available.

So how can the millions who live in fieldstone villages

build earthquake-resistant homes?

BILHAM: The village construction practices have to use

indigenous materials.

They don't have access to cement.

Bricks are not available.

Instead they use local stones

and they do not adhere to the cement that they have to use,

which is mud.

And mud is incredibly weak.

Some of the structures that survived have wooden tie beams

around the walls that have held them together.

NARRATOR: One of the hardest-hit districts,

close to the epicenter, is Dhading.

Randolph is on a mission to rebuild a home

that is earthquake-resistant, using local materials.

The right consistency of mud, hardware wire and stone

is all that's needed for a safe home

made in the traditional style for much of Nepal.

The wire was purchased

at the nearest hardware store and carried in.

LANGENBACH: One thing they had

was wire fencing for keeping the animals in.

The idea came to my mind.

Well, why not use the wire?

NARRATOR: Randolph's idea is to install

a reinforcing element he calls "gabion bands"

right into the masonry walls,

just like the Hanuman Dhoka Palace.

Gabion is a wire cage filled with rocks.

We need 22 feet.

NARRATOR: Structural engineer Dipendra Gautam trains local stonemasons

to use gabion bands as a substitute for timber bands.

NARRATOR: The homes in this region suffered intense damage.

Ninety percent have to be rebuilt.

Add a simple band that ties the walls together,

even with bicycle tubes, and the building might hold.

LANGENBACH: They needed to have some tensile reinforcement in the walls,

and the traditional way of doing that was in the series of bands.

NARRATOR: Each wire band has a layer of stone and mud mortar

placed onto it.

This is wrapped into a cage and all four walls of the building

are tied together to form what engineers call a ring beam.

LANGENBACH: The band seemed to be something that could be hand-carried in.

It could be understood by people in a short explanation.

NARRATOR: This will be home for a man named Ram, who is a Dalit,

the lowest caste in Nepal.

His father committed suicide last year,

and the earthquake then destroyed Ram's home.

GAUTAM:

(boy laughing)

LANGENBACH: The timberlacing that we saw

in the 18th century part of the Hanuman Dhoka palace--

and those parts have survived almost entirely intact--

is a way of giving tensile strength to the wall.

And this is a basic engineering concept.

This is not distant at all from what engineers say is needed.

NARRATOR: We know another earthquake will come,

maybe in two years as an aftershock,

or maybe the big one will rupture from the west of Nepal.

But Ram is now better prepared.

This earthquake took nearly 9,000 lives, but Seema Tamang--

who was buried under the rubble of her home for 24 hours--

survived the odds.

How do you feel today?

(translator speaking)

NARRATOR: She had little hope of recovering the use of her leg.

But she wants to go back to school

and get there on her own two feet.

Having lived through a megaquake,

the first of their lifetimes,

are the people of Nepal now more prepared to face

their seismic future?

BILHAM: This earthquake acted as a kind of a Rosetta stone,

interpreting all previous earthquakes, and I'm sure

we are going to see enormous headway

as a result of this earthquake.

Not only from the seismological point of view,

but from the philanthropic point of view,

and earthquake engineering,

and what kind of buildings we need

to survive the next earthquake.

NARRATOR: The pent-up tectonic stress miles beneath the Himalayas

continues to build.

Can you lift your toe?

This one?

And now this one.

Straighten the good one.

Straight.

Oh, look at that!

They both go straight.

So that means this quadriceps muscle is working,

which is good.

NARRATOR: Living with large earthquakes

is a reality for the people of the Himalaya,

since they happen in Nepal about every hundred years.

Thankfully, the earthquake wasn't that big.

Tragic, yes.

But, let's see if we can't learn now from this earthquake

to help us get prepared for that next big one, whenever it comes.

GARDNER: This is fantastic!

Come back here, sweetie.

I'm so happy for you.

This is great!

This is really good.

NARRATOR: Nepal is a nation that will walk again,

because this earthquake not only tells a story about the past,

but about the inevitable seismic perils

that will come in the future.

The investigation continues online,

This NOVA program is available on DVD.

To order, visit shopPBS.org, or call 1-800-PLAY-PBS.

NOVA is also available for download on iTunes.