Original subtitles

>> Earth, a 4.5-billion-year-

old planet, still evolving.

As continents shift and clash,

volcanoes erupt, and glaciers

grow and recede, the Earth's

crust is carved in numerous

and fascinating ways, leaving

a trail of geological

mysteries behind.

In this episode, an

investigation into

California's San Andreas

Fault, the greatest fault line

on Earth. 800 miles long, this

ugly scar on the landscape has

spawned Earthquake after

Earthquake.

But, for now, it waits

quietly, deep under our

cities, building up stress to

strike once again.

The San Andreas Fault is one of

the most dangerous geological

features on Earth.

S01x01 San Andreas Fault Original Air Date on February 10, 2009

California's greatest cities

and millions of her citizens

live in constant peril.

Since records began, there

have been 13 large Earthquakes

along the San Andreas Fault.

>> Reporter: The water lines

have ruptured, there is no

water coming out of the fire

hydrants.

>> And now, America's

geologists, her rock

detectives, are warning of

a potential disaster.

>> Reporter: The major damage

has been done.

>> In the fall of 2008, more

than 300 scientists calculated

what a major Earthquake would do

to Southern California.

>> We've been conducting a

special study of a magnitude

7.8 Earthquake on the southern

San Andreas Fault, large

enough to potentially damage

tall buildings. Fire will be

very significant.

>> The definitive scientific

report presented to

politicians was codenamed

Shakeout. It forecast

thousands of deaths and

nillions of dollars of damage

in the city of Los Angeles,

which makes it crucial to

investigate the most important

question--when will the next

big Earthquake hit the San

Andreas Fault?

The latest preparations for

disaster are the climax of an

investigation that started

more than 100 years ago, in

the aftermath of the great San

Francisco Earthquake of 1906.

The Earthquake struck on a

wednesday, just before dawn.

The ground shook violently for

45 seconds, igniting fires

that raged unchecked for the

next four days.

28,000 buildings, a tenth of

the entire city, were

destroyed, and more than 3,000

people, one in every hundred

of the population, were

killed. With a magnitude of

7.8, it's in the top 20 of

North America's strongest ever

Earthquakes.

The scale of the great San

Francisco Earthquake shocked

the nation. But no one

understood what had made the

city shake.

Native American myths

explained Earthquakes as

shocks from a battle between

warring spirits. Latter-day

explorers couldn't understand

the shocks that destroyed

their mission buildings.

One spanish missionary wrote--

>>

>> "The Earth shook around me

from explosions under the

ground."

300 years later, and science

has still made little

progress. Refugees in the

ruins of San Francisco still

blamed Earthquake on

mysterious underground

explosions.

So, just three days after the

Earthquake, the state of

California asked one of the

world's most famous

Geologists, Andrew Lawson from

California State University,

to investigate what had

destroyed the city.

He and a team of 25 scientists

began collecting damage

evidence in the city and

surrounding countryside.

There were roads that had

buckled. Rail tracks that had

twisted the most startling

evidence of all? That came

near the town of Bolinas in

Marin county, to the

North of San Francisco. This

picket fence had an eight-foot

gap in the middle. Before the

earthquake, it was a solid

boundary fence, dividing

two fields. But, when he

recreated what had happened,

Lawson realized that the land

had jolted apart and torn the

fence in two.

Plotting the evidence on a map

around San Francisco revealed

a surprising pattern, because

connecting the dots drew a

straight line, and, at every

point, the Earth moved in the

same way. On the coast to the

North, inland to the South.

This line of weakness was the

culprit they were searching for.

South of San Francisco,

the suspect line ran

underneath a lake, the Laguna

De San Andreas. So now, the

earthquake perpetrator at last

had a name. Professor Lawson,

who, a decade earlier, had

identified cracks in the Earth

here as a harmless rift, now

rechristened it the San

Andreas Fault.

In modern-day San Francisco,

the buildings, the roads and

the railways have long since

been repaired. But, if you

know where to look, evidence

of the 1906 quake can still be

found.

Geologist Charlie Paull

follows in the footsteps of

Lawson's team, seeking signs

of the havoc from 1906.

He finds it on the cliffs at

Mussel rock, 12 miles south of

San Francisco.

>> The cliff is not here by

accident, there's a very good

reason why this cliff is here.

Half a mile or so of the shore

face apparently fell off in

the 1906 Earthquake, and if you

look down below us, there's a

big rotated block, um, that's

near the present-day shoreline,

and it is just inboard

of the San Andreas Fault, the

San Andreas Fault is, uh,

about a quarter of a mile

offshore here, and of course,

that's one of the major

crustal junctions, um, on

this side of North America.

>> Modern computers can now

trace how damage waves spread

out across the city. And that

pinpoints where the quake

originated along the San

Andreas.

It was offshore, about two

miles out to sea from the

Golden Gate Bridge.

So, to continue tracking the

fault, the investigation must

head out to sea. Marine

Geologists use remote

operating vehicles,

mini-submarines, to map the

sea floor.

>> What you would see is

subtle variations in the

topgraphy, or topography that

would not naturally line up.

So there might be a line on

the ocean floor that is higher

or lower on one side, and you

can use various techniques to

determine that this actually

is a fault, instead of some

other process.

>> Running south across the

seabed, the San Andreas

finally runs out of ocean, and

hits the land. This broken

line of rocks, stretching in

from the sea, marks where the

San Andreas hits land, 12

miles south of San Francisco.

>> We're here at Mussel Rock

and we're essentially standing

on the San Andreas Fault right

now. And if there was an

earthquake, I don't know what

would happen right here, but I

wouldn't want to be here.

>> This Pacific coastline,

where cliffs crumble slowly

into the sea, is the boundary

between two of the Earth's

massive continental plates.

Separated by the San Andreas

Fault, two vast, separate

blocks of the Earth's crust

lie directly alongside each

other.

Here, the continent of North

America lies slightly on top

of the adjacent section of

crust which holds the Pacific

Ocean.

The join can be seen where

these lower, darker rocks are

overlaid by light-colored

sedimentary rocks.

>> These rock types differ

by--by, uh, more than 100

million years in age. Two rock

bodies that, uh, are

not similar in any way have

been brought together.

>> The fault line was exposed

to geologists when the cliffs

collapsed here in the 1906

Earthquake. But, back then,

nobody understood how and why

the two different types of

rock were next to each other,

until around 40 years ago,

when the answer was finally

revealed by the theory of

Plate Tectonics.

The theory showed that the

Earth's crust consists of

separate, moving plates on

which the oceans and

Continents sit.

Around 200 million years ago,

the heavy Pacific Ocean plate

collided with North America,

and started sinking underneath

the lighter Continent.

Professor of Geophysics, Mark

Zoback, studies that process,

called subduction, in his

laboratory at Stanford

University.

>> For many millions of years

prior to the existence of the

San Andreas Fault, the Pacific

Plate was subducting beneath

North America, the Oceanic

Plate was diving down, and,

uh, that process went on for

well over a hundred million

years, so a tremendous amount

of activity was occurring.

>> As the unstoppable force of

one plate met the immovable

object of the other, they were

forced to change direction.

>> About 20 million years ago,

the plate motions were such

that the Pacific Plate had to

start sliding north with

respect to North America,

and now, you know, the--the

principal motion is this

sliding process between the

two plates. And 20 million

years ago, the San Andreas

Fault was born.

>> It was the moving plates

that crushed different types

of rock together, just as here

at Mussel Rock.

At last, the investigation

knows what it is dealing with.

The San Andreas Fault is 800

miles long, emerging from the

seabed north of Point Arena

in Northern California and

running down to the Salton Sea

in the south.

The evidence is coming

together. Clues from the 1906

Earthquake, such as the picket

fence that was torn apart,

prove that the land was

moving. Connecting the dots

identifies the straight line

of the San Andreas Fault.

And Mussel Rock uncovers

different plates of the

Earth's crust on either side

of the fault line.

But investigators still need

more information about how

often the San Andreas has

spawned Earthquakes in the

past.

It might help them answer the

all-important question--when

will the San Andreas strike

again?

To discover when the San

Andreas Fault will strike

again the investigation needs

to know about ancient

earthquakes that have struck

along the fault line.

But there's an immediate

problem.

>> Here in California, it's a

particular challenge, and

some of the earliest written

records were from the missions

and from the early explorers,

So only dating back into the

18th century here. Other

parts of the world, we have an

earthquake history going back

millennia.

>> The investigation moves 350

miles south of San Francisco

to a desert where the San

Andreas may have been active

for thousands of years.

There's crucial evidence here

about earthquakes from ancient

times.

>> This creek used to flow

straight across the San

Andreas Fault here, but

several earthquakes formed a

natural dam where the San

Andreas Fault wedges up here

in front of me. That created a

small pond, and now we're

looking at the dry sediments

of that pond that record the

history of earthquakes, and

that tells us quite a great

deal about the past behavior of

the San Andreas Fault.

>> Some of the clues are so

small that Hudnut's detective

work gets him down and dusty

among tiny cracks inside the

fault.

>> Sometimes we can find out

about the past behavior of

the San Andreas Fault by

looking at the tiniest

details.

>> At the bottom of this small

ancient pond, mud sediments

collected above a fine line of

pebbles. Then an earthquake

shifted the land upwards on

one side of the vertical fault

line.

>> So this layer was

originally flat, and then, in

a subsequent Earthquake, it

was broken like this along

this tiny fracture strand of

the San Andreas Fault.

>> But finding proof that this

is the site of an ancient

earthquake is only part of the

story. Hudnut needs to know

how long ago it happened.

The bare rock layers are no

help in dating his find, but

just above the fracture line

of the rocks he has found the

evidence he needs.

>> Here, a bush was burned by

a prehistoric wildfire, and

that remnant of carbon is why

you see this black stain on

the side of the trench wall.

>> The key to unlocking the

age of the rocks is carbon-14,

known as radiocarbon.

Its molecular structure

means that carbon-14 is a

more unstable isotope than

other forms of carbon.

It's absorbed by growing

plants, then radioactively

decays at a known rate, after

the plant dies. So measuring

carbon-14 in vegetation burned

in a wildfire reveals how long

ago those plants died, and

dates the rock in which the

carbon is found.

>> And through this, we can

reconstruct the evidence of

the past earthquakes.

>> Radiocarbon dating has

proved that earthquakes have

been happening along the line

of the San Andreas for

thousands of years. The

particular small earthquake

investigated by Hudnut, for

example, is around 3,500 years

old. It happened at a time

when the last Woolly Mammoths

were dying out in North America.

The investigation moves to an

even more remote desert spot.

The Carrizo Plain, 160 miles

north of Los Angeles. Here

lies a dried-up riverbed,

which takes an unusual

course. Coming down off the

hills, the creek bed takes a

sudden, sharp turn to its

right. A few hundred feet

later, it makes an equally

odd, 90-degree turn to the

left.

The creek crossed the line of

the San Andreas Fault, but

early geologists were

mystified. Why did it bend in

this way?

The scientific pioneers were

limited to studies on the

ground. Nowadays, Hudnut has an

advantage. He can take to the

air.

>> the San Andreas Fault,

Where it cuts though the

Carrizo plain, it almost looks

Like a scar, and it was caused

by repeated earthquakes in the

past.

>> Along the long line of

hills marking the course of

the San Andreas, Hudnut spots

the puzzling bends that he's

seeking.

>> Hudnut: Oh! If we could

woop along the fault through

here, that would be awesome.

Oh, there's a great angle, see

that right angle, uh, offset

channel with the elbow in it

right there? That's a classic

one right there.

>> Hudnut's aerial view of

the creek bed shows that the

river once flowed straight on

cross the fault. But, little

By little, a series of

Earthquakes along the San

Andreas dragged the creek away

from its original course.

Recreating how the land had

moved showed Hudnut that the

two parts of the creek had

traveled more than 300 feet

apart.

>> So if you imagine the North

American plate is fixed and

the Pacific Plate is moving to

the northwest, the Wallace

Creek site records that offset

because the channel is

straight across the fault,

but it's been offset through

time.

>> Earlier investigators had

already radiocarbon-dated the

land on each side of the fault

here, revealing that it took

3,000 years to change the

creek's position.

So, knowing the distance and

the time it took to do it lets

Hudnut calculate the average

speed with which the two land

masses are moving past each

other.

300 feet in 3,000 years,

one foot per decade,

just over an inch a year.

But this was never a steady,

sliding, one-inch-a-year

movement. The reality was a

series of sudden small jumps

whenever tension built up

enough between the two

moving plates to overcome

friction between the rocks and

rip the land apart with an

earthquake.

It's an important moment for

the investigation. Knowing how

fast the land is moving not

only reveals the stress that's

building up, but also the risk

of an earthquake.

The San Andreas Fault is

giving up its secrets. Clues

from a long dried-up pond

reveal the site of ancient

earthquakes. Carbon from a

prehistoric fire provides the

dates. And bends in a riverbed

prove how fast the plates are

moving along the San Andreas.

But now, the investigation has

a new mystery to solve. If the

land along the San Andreas is

moving one inch every year,

causing earthquakes, then why

has one small town along the

fault line never had any?

The investigation has

discovered how fast the land

is stretching and straining

along each side of the San

Andreas Fault, which should

help establish when that

ever-increasing stress will

snap the land apart in the

next major earthquake.

But there's a problem. One

oart of the fault line just

doesn't fit the pattern.

The small town of Hollister is

unique along the San Andreas

Fault system. It's never had

an earthquake. And the

investigation is going to find

out why.

Hollister has a population of

37,000, and nothing here is

quite the way it should be.

There are plenty of clues

suggesting that the land must

be moving here.

Sidewalks with cracks in,

curbstones way out of line and

walls that are bent out of

shape.

>> Walking through Hollister,

we can see anything that man

has built that was laid out in

a straight line may have a jog

in it. Every year it changes a

little bit, it's a progressive

thing.

>> The clues add up to one

clear conclusion. Even without

any earthquakes, the Earth in

this town in the heart of the

San Andreas system still

slides imperceptibly slowly

and effortlessly along.

>> In one sense, the damage

that you see here associated

with the creeping is, uh, is

clearly sort of under control.

But as a geologist, if you start

playing that out for tens of

thousands or hundreds of

thousands or millions of

years, the consequences of

that become enormous.

>> For many years, the

creeping ground that moved

without earthquakes remained

an unsolved mystery.

But then, the investigation

moved 100 miles south, to

another small community, where

the land also creeps along.

The village of Parkfield has a

population of just 37 people,

and a bridge which spans right

across the San Andreas Fault.

The bridge separates the

Pacific Plate on one side from

the North American Plate on

the other. And the bridge

railings have started to bend.

>> I'm, uh, right now on the

Pacific Plate on the west side

of the San Andreas Fault, and

you know, the--the San Andreas

comes off the flank of that

hill and right across that

field, right under the bridge,

and then, right over by the

corner of that building or

that fence post and then on

off to Middle Mountain.

>> The movement here around

the bridge is strikingly

similar to the slow creeping

ground of Hollister.

But there is one important

difference here in Parkfield.

Every couple of decades or so,

this village does have

earthquakes. They're just

little tremors, but they're

big enough to be recorded on

earthquake monitoring

seismographs.

That's why the village proudly

boasts of being the earthquake

capital of the world. But it's

perhaps more accurately called

the earthquake study capital

because scientists are

fascinated by the fact that

earthquakes here follow a

predictable pattern.

Elsewhere, earthquakes always

strike without warning, the

toll of death and destruction

made worse because nobody knew

they were coming. So

scientists are desperate for

any clues that might help

predict when an earthquake

could happen. And here in

Parkfield, the earthquakes

happen with astonishing

regularity, on average, every

couple of decades or so. Minor

quakes happened here in 1857,

1881, 1901, 1922, 1934 and

1966.

After the '66 Earthquake,

investigators set up a network

of monitoring instruments to

see if the fault gave any

warning before the next

earthquake arrived.

They expected it sometime

between 1988 and 1993, but it

was late. And months of

waiting stretched into years.

But still the scientists

waited, until finally, in

December 2004, the

long-awaited earthquake

arrived and was caught on

film, from a now slightly worn

and damaged camera.

The Earthquake movie may not

have seemed that impressive,

but the instruments collected

a mass of information.

The data didn't, after all,

help with earthquake

prediction, but it did

pinpoint where the earthquake

started underground, which

told investigators where to

look next, deep down under the

Parkfield countryside.

Starting slightly to one side

of the fault, the aim was to

angle in and stab into the

very heart of the San Andreas.

After three years of drilling,

long cores of rock were

extracted from the exact spot

where the Earthquake occurred.

This was first time the team leader

geologist Mark Zoback had ever

seen rocks from the center

of the San Andreas.

What we're looking at here

are cores from the

active San Andreas Fault,

from a depth of about 2 miles.

So for the Earth science community

these are like Moon rocks.

As we were trying to exhume

these cores, we had a great

deal of drilling difficulty.

The San Andreas Fault was

literally fighting back.

After 9 weeks of attempting

to recover the cores in the middle

of a huge lightening storm

almost a scene directly

out of Hollywood,

with the thunder and lightening,

these cores came to the surface.

And so it was a tremendous

feeling of satisfaction.

The lightening and thunder

just made it that much more

dramatic.

And we're all wearing gloves

we didn't want any oil

from our fingers to affect the core.

And the rule was

that you touched the core

as little as possible.

Obviously.

>> I'm not going to wait for

you guys. Oh, look at this

beautiful rock.

>> The reality was we couldn't

help ourselves, and, uh, um,

it was just such a remarkable

thing to be actually looking

at the San Andreas Fault, uh,

for the very first time

that--that we all got to touch

it a little bit.

>> Buried within the rock

cores, they found a vital

clue about the way that land

slips along the San Andreas.

They found serpentinite.

>> Serpentinite is an unusual

rock type, it was originally

formed, uh, at the base of the

Ocean crust and exhumed up

onto the continent, but the

reason that serpentinite is so

interesting is that

serpentinite is very easily

altered to talc. It allows the

rock to slide at very low

force levels, it's--talcum

powder is very slippery.

>> Talc's crystalline

structure of soft, sliding,

flat plates makes it one of

the slipperiest rocks known to

science.

>> So talc could well be, um,

a key mineral in--in deciding

how the fault is--is actually

working in--in central

California. We see that the

secret of the slipping San

Andreas Fault is actually the

rocks themselves.

>> The talc explains the tiny

earthquakes of Parkfield.

Nobody's yet drilled to

investigate the rocks at

Hollister, but scientists

suspect the talc is present

there too. Cracks in the walls

show the land creeps in

Hollister. And a bend in the

bridge reveals the same

creeping ground in a

nearby town. Rock cores,

extracted from the fault,

contain serpentinite,

leading investigators to the

softest and slipperiest

mineral, talc, which

lubricates some parts of the

Fault. The investigation is

having success, but one

crucial question remains to be

answered. What will the San

Andreas Fault do next?

The investigation into the San

Andreas Fault is trying to

predict when and where its

next major Earthquake will

strike. So far, the only

certain prediction is the far

distant future of the San

Andreas.

Look 20 million years ahead.

If the plate movements

continue to follow their

pattern, Los Angeles will end

up becoming a suburb of San

Francisco.

But predictions on a shorter

timescale are more difficult.

>> If you were to ask the

question, "can we predict

Earthquakes?" my answer would

be, "no, because I know what

your question really meant,

is, you know, 'can we predict

that an Earthquake is going to

occur on a certain fault at a

certain time that we can

specify in the future?'"

And we cannot do that. But

there are many things we can

predict. We can predict which

faults are likely to produce

the big earthquakes, we can

predict how big the

earthquakes are likely to be,

and we can even predict the

probability of the earthquake

occurrence over some period of

several decades.

>> Predictions are most

crucial where the San Andreas

runs to the south of L.A.

Here in the Coachella Valley

Desert, geological evidence of

earthquakes stretches back

1500 years and more.

And they follow a regular

pattern. Major Earthquakes

strike here with monotonous

regularity, every 200 years.

But the latest one is long

overdue. There hasn't been an

earthquake here for more than

300 years. That's a concern,

because parts of the San

Andreas Fault system run

straight from here towards the

city of Los Angeles.

The faults will transmit

earthquake shocks in a

straight line towards

California's biggest city.

Geologist Yuri Fialko

regularly monitors how the

ground moves on either side of

the fault line.

He lines up his gps equipment

precisely over a series of

metal pegs fixed into the

ground.

>> This information is crucial

for estimating how fast the

Fault slips at depth and what

is the rate of accumulation of

strain in the crust. In other

words, how close the crust is

brought to failure by a slip

of the fault at depth.

>> The repeated, ultra-precise

measurements reveal that land

here, on the surface, hardly

moves at all. This is a

problem, because deep

underground, the stresses and

strains are still building up.

>> The fault is moving, at

depth, at a fairly high speed,

and this deformation is

growing and growing and

growing with time.

>> Miles underground, the deep

fault is moving at more than

an inch a year, which tells

Fialko that in the centuries

since the last quake, the

surface should have shifted

300 inches, 25 feet or more.

But it hasn't, so sooner or

later, something's got to

give. And Fialko knows what

that something will be.

The rocks themselves.

>> And one example is this

type of rock, which is called,

uh, granite, and this is in

fact the rock out of which

most of the Earth's crust is

made.

>> A microscope reveals the

crystalline structure of the

granite. The crystals make the

rocks tough, but they have a

hidden weakness. The bonds

between them may suddenly

crack under stress.

>> Basically, once this

material solidifies, uh, it is

able to, uh, um, crack and be,

uh, sheared on the fault

surface, and the brittle

behavior of these rocks is

what lies behind the physics

of Earthquakes.

>> Granite rocks underlie all

of the San Andreas Fault, but

right here, the rock's under

greater stress than anywhere

else, because it's so many

centuries since a major quake

occurred.

>> And now we're over the

300-year limit, and so it means

that, uh, the strain, the

amount of strain that has been

accumulated on the fault at

this point is very close to

the maximum strain that this

Fault has ever seen through

its, uh, geologic record.

And this is a fault that is

capable of generating great

destructive Earthquakes.

>> Fialko believes the coming

quake could be "the big one"

that people have been talking

about for years. And the

effects could be horrific

because of the population

density of southern

California. When the last huge

quake occurred 300 years ago,

Los Angeles was just a tiny

Spanish mission community with

fewer than 100 people.

Now, it's America's

second-largest city, with

almost 11 million people living

in the Earthquake-vulnerable

Metropolitan area.

>> People who live in

California probably experience

a small or a moderate size

earthquake every year, a few

things moving in your house,

but it's really actually kind

of fun, there is no major

destruction. Um, people just

go on with their life. Uh,

much bigger events, on the

other hand, are quite a bit

different story.

>> With the threat to Los

Angeles becoming ever clearer,

the investigation is nearing

its conclusion. Data from

repeated gps measurements in

the desert reveal evidence

that stress is building up,

while examination of the rocks

of the crust show they may not

take the strain for much

longer.

All the evidence points

towards a potentially huge

earthquake building up in

Southern California.

And new experiments suggest

the coming quake could be far

worse than anyone had ever

imagined.

There is new urgency in the

investigation into the San

Andreas Fault as revealed by

recent evidence compiled by

300 of America's most

respected scientists.

They warn that Los Angeles

will be devastated if a major

quake strikes along the

Southern section of the

Fault line.

While there hasn't been a

major quake for hundreds of

years, even small ones can

still be deadly, like the

Northridge Earthquake, which

struck this L.A. suburb in 1994.

Rupturing along an offshoot of

the main San Andreas Fault,

the quake was only a magnitude

6.7, considered moderate on

the scale of Earthquake

Measurement.

But it still killed 72 people

and injured 12,000 more.

And new evidence suggests

Mother nature might have a lot

more in store for Los Angeles.

Scientists have long known

that Earthquakes generate

several distinct sets of

waves. They travel at

different speeds, each

spreading damage and

destruction out from the

epicenter.

Modern city buildings in

earthquake-prone areas like

California are engineered to

cope with such waves.

Now, new research by

Geophysicist professor Ares

Rosakis suggests that the San

Andreas may offer a new and

even more deadly threat.

Rosakis researches how

earthquakes rupture along

straight-line faults, just

like the San Andreas where it

approaches Los Angeles.

He creates his own

mini-earthquakes, representing

the San Andreas Fault by a

hairline crack in a thick,

transparent block.

This special material shows up

internal stress lines when

It's lit by a laser.

And the Earthquake is

triggered by a tiny explosion.

>> Three, two, one, zero.

The node has dropped, and the

explosion was big enough that

we even have a crack.

>> An ultra-high-speed camera

capturing ten million frames a

second, reveals a startling

and newly discovered

phenomenon.

This frozen picture reveals

stress lines speeding along the

mini San Andreas in the

milliseconds after the

explosion.

The cone to the left of this

frame is a previously

unrecognized type of shockwave

racing along the rupture line

from the Earthquake center.

On a microscopic scale, it

looks and moves exactly like

the sonic boom produced when a

supersonic aircraft, such as

Concorde, breaks the sound

barrier.

>> Because we also see mach

cones, lines that are emitted

from the rupture tips, as from

the tips of moving airplanes.

>> And, just like a sonic

boom, it can be dangerous.

>> In the same sense that we

hear the sonic boom, uh, from

the Concorde, you are going to

feel the sonic boom from the

rupture.

>> The danger comes because

many high rises just aren't

built to cope with extra

stress from this newly

discovered type of shockwave.

>> So if you are an old

building, for example, uh,

you'll shake one way, you will

accumulate some damage, and,

uh, very soon after that, you

will get very strong ground

shaking because of other types

of waves coming also.

>> The high-speed ruptures

that Rosakis calls supershear

happen where faults run in a

straight line...

which might help explain a

100-year-old mystery

surrounding the great

San Francisco quake, the

natural disaster which

launched the entire San

Andreas investigation.

The overwhelming damage in San

Francisco has long seemed

surprisingly out of proportion

to the 7.8 magnitude of the

quake. And there's a

particularly straight section

of the San Andreas approaching

San Francisco. So, many

scientists now believe that

the damage was greater than

expected because the 1906 quake

had traveled at supershear

speed.

Of greater concern to modern

emergency services is not what

happened a century ago, but

what could happen tomorrow,

because there is a similar

straight section of faulted

ground heading straight

towards Los Angeles, and if a

supershear Earthquake develops

on that line, then the

consequences could be

disastrous.

>> Here we go.

>> All of the investigation's

warnings about the San Andreas

came together in the fall of

2008, with the biggest

earthquake drill ever held in

California.

>> If this Earthquake would

have happened in reality,

there--there would have been

buildings coming down, we know

that there would be no water

now in certain areas, that's

what this exercise is all

about.

>> But what are the real

chances of Los Angeles soon

being hit by a massive

earthquake? Frighteningly, the

best scientific consensus now

warns that there's a 99 per

cent chance of a major quake

in Southern California within

the next 30 years. To better

understand the threat to L.A.,

the geologists produced their

study jointly with experts in

charge of the city's disaster

planning. And none of them

doubt that the big quake is

coming.

>> It really isn't even a

question of if anymore.

The shaking is going to be

severe for two to three

minutes.

And then it's gonna stop,

and then you're gonna have that

moment of silence that often

happens before you start

hearing the car alarms, all

those other sounds that you

have in a disaster like this.

>> The study estimates that a

major Earthquake in the L.A.

Metro area would cause 2,000

deaths, 50,000 injuries and

200 billion dollars of damage.

>> You're going to have

conflagrations developing,

tens of blocks will be on fire.

>> Reporter: The water lines

have ruptured, there is no

water coming out of the fire

hydrants.

>> That's the kind of nightmare

scenario that we're looking at.

>> This specter of disaster to

California's people and cities

motivates the search to

unravel the secrets of the San

Andreas Fault. All the

evidence is finally in.

The damage reports from the

1906 disaster show the fault's

800-mile path. The different

types of rock at Mussel Rock

provide clues to how the fault

was created 20 million years

ago. The river bends prove how

fast the land is moving. The

mineral talc explains why some

parts slip without major

quakes. The brittle granite

rocks reveal a threat to Los

Angeles, and recent lab

experiments uncover new and

more dangerous Earthquake

Shockwaves.

But one goal has eluded the

rock detectives who study

the greatest fault line on

Earth.

When will the sleeping San

Andreas come to life once

again? It could be any time.

The only certainty is that

nothing is certain in the

ever-evolving story of how the

Earth was made.