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0:01
NARRATOR: 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 city,
0:49
building up stress to strike once again.
0:56
The San Andreas Fault is one of the most dangerous geological features on Earth.
1:13
California's greatest cities and millions of our citizens live in constant peril.
1:23
Since records began, there have been 13 large earthquakes along the San Andreas Fault. And now America's geologists, her rock detectives, are warning of a potential disaster.
1:46
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. NARRATOR: The definitive scientific report presented to politicians was codenamed Shakeout. It forecasts thousands of deaths and billions of dollars of damage in the city of Los Angeles, which
2:22
makes it crucial to investigate the most important question. When will the next big earthquake hit the San Andreas Fault?
2:36
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.
3:00
The ground shook violently for 45 seconds, igniting fires that raged unchecked for the next four days.
3:12
28,000 buildings, a tenth of the entire city, were destroyed. And more than 3,000 people, one in every 100 of the population, were killed. With a magnitude of 7.8, it's in the top 20 of North America's strongest ever earthquakes.
3:32
The scale of the great San Francisco earthquake shocked the nation. But no one understood what had made the city shake.
3:47
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.
4:10
300 years later and science has still made little progress. Refugees in the ruins of San Francisco still blamed earthquakes on mysterious underground explosions.
4:25
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.
4:40
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,
5:17
Lawson realized that the land had jolted apart and torn the fence in two.
5:25
Plotting the evidence on a map around San Francisco revealed a surprising pattern.
5:33
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.
5:53
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.
6:32
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 that's near the present day shoreline. And it is just inboard of the San Andreas Fault.
7:07
The San Andreas Fault is about a quarter of a mile offshore here. And of course that's one of the major crustal junctions on this side of North America.
7:20
NARRATOR: Modern computers can now trace how damage waves spread out across the city. And that pinpoints where the quake originated along the San Andreas.
7:35
It was offshore, about two miles out to sea from the Golden Gate Bridge.
7:41
So to continue tracking the fault, the investigation must head out to sea. Marine geologists use remote operating vehicles, mini submarines to map the seafloor. What you would see is subtle variations in the topography 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. NARRATOR: Running south across the seabed,
8:16
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. And 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.
8:46
NARRATOR: This Pacific coastline where cliffs crumble slowly into the sea is the boundary between two of the Earth's massive continental plates.
8:58
Separated by the San Andreas Fault, two vast separate blocks of the Earth's crust lie directly alongside each other.
9:09
Here, the continent of North America lies slightly on top of the adjacent section of crust which holds the Pacific Ocean.
9:23
The join can be seen where these lower darker rocks are overlaid by light colored sedimentary rocks. CHARLES PAULL: These rock types differ by more than 100 million years in age. Two rock bodies that are not similar in any way have been brought together. NARRATOR: 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.
9:58
Until around 40 years ago, when the answer was finally revealed by the theory of plate tectonics.
10:09
The theory showed that the Earth's crust consists of separate moving plates on which the oceans and continents sit.
10:18
Around 200 million years ago, the heavy Pacific Ocean plate collided with North America and started sinking underneath the lighter continent.
10:30
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 that process went on for well over 100 million years. So a tremendous amount of activity was occurring. NARRATOR: As the unstoppable force of one plate met the immovable object of the other,
11:04
they were forced to change direction. MARK ZOBACK: 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, the principal motion is this sliding process between the two plates. And 20 million years ago, the San Andreas Fault was born. NARRATOR: It was the moving plates that crushed different types of rock together, just as here at Mussel Rock.
11:37
At last, the investigation knows what it is dealing with.
11:44
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.
11:57
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.
12:35
It might help them answer the all important question-- when will the San Andreas strike again?
12:49
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.
13:01
But there's an immediate problem. Here in California, it's a particular challenge. 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. NARRATOR: The investigation moves 350 miles south of San Francisco to a desert where the San Andreas may have been active for thousands of years.
13:31
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.
14:00
NARRATOR: 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. NARRATOR: 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. KEN HUDNUT: So this layer was originally flat and then,
14:34
in a subsequent earthquake, it was broken like this along this tiny fracture strand of the San Andreas Fault. NARRATOR: 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. KEN HUDNUT: Here, a bush was burned by a prehistoric wildfire.
15:05
And that remnant of carbon is why you see this black stain on the side of the trench wall. NARRATOR: 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 radioactivity 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
15:40
in which the carbon is found. And through this, we can reconstruct the evidence of the past earthquakes. NARRATOR: 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.
16:15
The investigation moved 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.
16:29
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.
16:45
The creek crossed the line of the San Andreas Fault. But early geologists were mystified. Why did it bend in this way?
16:59
The scientific pioneers were limited to studies on the ground. Nowadays Hudnut has an advantage, he can take to the air.
17:13
The San Andreas Fault, where it cuts through the Carrizo Plain, it almost looks like a scar. And it was caused by repeated earthquakes in the past. NARRATOR: Along the long line of hills marking the course of the San Andreas, Hudnut spots the puzzling bends that he's seeking.
17:32
KEN HUDNUT: If we could swoop along the fault through here, that would be awesome. Oh, there's a great angle. See that right angle offset channel with the elbow in it right there? That's a classic one right there. NARRATOR: Hudnut's aerial view of the creek bed shows that the river once flowed straight on across the fault. But little by little, a series of earthquakes along the San Andreas dragged the creek away from its original course.
18:04
Recreating how the land had moved showed Hudnut that the two parts of the creek had traveled more than 300 feet apart. KEN HUDNUT: 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. NARRATOR: Earlier investigators had already radiocarbon dated the land on each side of the fault
18:34
here, revealing that it took 3,000 years to change the creek's position.
18:42
So knowing the distance and the time it took to do it let's Hudnut calculate the average speed with which the two landmasses are moving past each other.
18:54
300 feet in 3,000 years, 1 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.
19:44
The San Andreas Fault is giving up its secrets. Clues from a long dried up pond revealed 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.
20:11
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.
20:30
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 part 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.
21:11
Hollister has a population of 37,000 and nothing here is quite the way it should be.
21:24
There are plenty of clues suggesting that the land must be moving here--
21:34
sidewalks with cracks in, curb stones way out of line, and walls that have bent out of shape. CHARLES PAULL: 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. And it's a progressive thing. NARRATOR: 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
22:06
still slides imperceptibly slowly and effortlessly along. In one sense, the damage that you see here associated with the creeping 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. NARRATOR: For many years, the creeping ground that moved without earthquakes remained an unsolved mystery.
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But then the investigation moved 100 miles south to another small community where the land also creeps along.
22:50
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 right now on the Pacific plate on the west side of the San Andreas Fault. And 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
23:29
of that building or that fence post, and then on off to Middle Mountain. NARRATOR: 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.
24:02
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.
24:21
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
25:04
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.
25:25
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.
25:57
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.
26:11
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 the first time that team leader geologist Mark Zoback had ever seen rocks from the center of the San Andreas. MARK ZOBACK: What we're looking at here are cores from the active San Andreas Fault
26:47
from a depth of about two miles. So for the Earth science community, these are like moon rocks. As we are trying to exhume these cores, we had a great deal of drilling difficulty. The San Andreas Fault was literally fighting back. After nine weeks of attempting to recover the cores, in the middle of a huge lightning storm, almost a scene directly out of Hollywood, with the thunder and lightning these cores came to the surface. And so it was a tremendous feeling of satisfaction.
27:19
The lightning and thunder just made it that much more dramatic. And we're all wearing gloves. We didn't want the 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 it was just such a remarkable thing to be actually looking at the San Andreas Fault for the very first time that we all got to touch it a little bit.
27:54
NARRATOR: 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 at the base in 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. Talcum powder is very slippery. NARRATOR: Talc's crystalline structure
28:29
of soft sliding flat plates makes it one of the slipperiest rocks known to science.
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So talc could well be a key mineral in deciding how the fault is actually working in central California. We see that the secret of the slipping San Andreas Fault is actually the rocks themselves. NARRATOR: 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 wall show the land creeps in Hollister. And a bend in the bridge reveals the same creeping ground
29:15
in a nearby town. Rock cores extracted from the fault contain serpentinite, leading investigators to the softest and slippieriest 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?
29:48
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.
30:05
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.
30:17
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 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.
30:47
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. NARRATOR: Predictions are most crucial where the San Andreas runs to the south of LA. Here in the Coachella Valley Desert, geological evidence of earthquakes stretches back 1,500 years and more. And they follow a regular pattern. Major earthquake strike here with monotonous regularity every 200 years.
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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.
31:41
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.
31:57
He lines up his GPS equipment precisely over a series of metal pegs fixed into the ground.
32:07
YURI FIALKO: This information is crucial for estimating how fast the fault slips at depths 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 depths. NARRATOR: 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. YURI FIALKO: The fault is launching
32:37
at depths at fairly high speed. And this deformation is growing and growing and growing with time. NARRATOR: 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.
33:18
YURI FIALKO: And one example is this type of rock, which is called granite. Or this is, in fact, the rock out of which most of the Earth's crust is made.
33:32
NARRATOR: 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, it is able to crack and be sheared on the fault surface. And the brittle behavior of these rocks is what lies behind the physics of earthquakes. NARRATOR: Granite rocks underlie all of the San Andreas Fault.
34:04
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 the strain, the modest strain that has been accumulating on the fault at this point, is very close to the maximum strain that this fault has ever seen through its geologic record. And this is a fault that is capable of generating great destructive earthquakes. NARRATOR: Fialko believes the coming quake could
34:37
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.
34:59
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, few things moving in your house. But it's really actually kind of fun. There is no major destruction. People just go on with their life. Much bigger events, on the other hand, are quite a bit different story.
35:30
NARRATOR: 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.
35:57
All the evidence points towards a potentially huge earthquake building up in southern California.
36:06
And new experiments suggest the coming quake could be far worse than anyone had ever imagined.
36:25
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.
36:45
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 LA 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.
37:14
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.
37:36
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.
37:51
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.
38:21
He creates his own mini earthquakes representing the San Andreas Fault by a hairline crack in a thick transparent block.
38:32
This special material shows up internal stress lines when it's lit by a laser.
38:39
And the earthquake is triggered by a tiny explosion. 3 2 1 zero. A node has dropped. And the explosion was big enough that we even have a crack. NARRATOR: An ultra high speed camera capturing 10 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.
39:16
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. NARRATOR: And just like a sonic boom it can be dangerous.
39:48
In the same sense that we hear the sonic boom from the Concorde, you're going to feel the sonic boom from the rupture. NARRATOR: 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, you'll shake one way. You will accumulate some damage. And very soon after that, you'll get very strong ground shaking because of other types of waves coming also.
40:25
NARRATOR: The high speed ruptures that Rosakis calls super shear 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.
40:49
The overwhelming damage in San Francisco has long seemed surprisingly out of proportion to the 7.8 magnitude of the quake. And there is 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 super shear speed.
41:19
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 super shear earthquake develops on that line, then the consequences could be disastrous.
41:43
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. ARNOLD SCHWARZENEGGER: If this earthquake would have happened in reality, those would have been buildings coming down. We know that there would be no water now in certain areas. So that's what this exercise is all about. NARRATOR: But what are the real chances of Los Angeles soon being hit by a massive earthquake? Frightening.
42:12
The best scientific consensus now warns that there's a 99% chance of a major quake in southern California within the next 30 years. To better understand the threat to LA, 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.
42:42
The shaking is going to be severe for two to three minutes.
42:49
And then it's going to stop. And then you're going to have that moment of silence that often happens before you start hearing the car alarms and all those other sounds that you have in a disaster like this. NARRATOR: The study estimates that a major earthquake in the LA Metro area would cause 2,000 deaths, 50,000 injuries, and $200 billion of damage. You're going to have conflagrations developing, tens of blocks will be on fire.
43:22
That's the kind of nightmare scenario that we're looking at.
43:29
NARRATOR: 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 riverbed is proof how fast the land is moving. The mineral talc explains why some parts slip without major quakes.
44:07
The brittle granite rocks reveal a threat to Los Angeles. And recent lab experiments uncover new and more dangerous earthquake shock waves.
44:22
But one goal has eluded the rock detectives who study the greatest fault line on Earth.
44:32
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.
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