Original subtitles

Little can prepare you for the horror

of the deadly disaster we focus on in this episode.

When the earth shakes, buildings collapse

and the ground quite literally opens up under your feet.

There’s absolutely no way

we can prevent an earthquake happening.

The earthquake

is one of nature’s most terrifying phenomena.

Throughout history,

there has been a serious earthquake

almost every year,

and they have caused the death of millions of people.

In this episode,

we feature the Northridge earthquake

that struck Southern California in 1994.

And the quake that devastated Christchurch, New Zealand

in 2010 and 2011.

As well as the 2009 earthquake

that destroyed much of the beautiful medieval city

of L’Aquila in Italy,

killing 300 and leaving 60,000 homeless.

With eyewitness accounts and expert contributions,

we dig deep into the fascinating science

and show the effects

of this destructive and deadly disaster.

An earthquake is categorized by any shaking of the ground

due to the action of seismic waves in the earth’s crust.

So when an earthquake happens,

you get vibrations sent out through the ground

in two different ways.

The first one,

which is felt at the surface is called a P wave,

and that’s energy traveling back and forth

from the earthquake’s source

to the surface in this kind of orientation.

But the most damaging type of seismic wave,

the one that causes damage to buildings,

is called the S wave.

And that causes, sort of--

Um, that causes vibrations to occur

in this sort of up-and-down and side-to-side motion,

which really strongly shakes the ground.

But what exactly causes the powerful shock waves

that create so much mayhem?

An earthquake occurs when stresses build up

over time on a fault.

And when that fault slips,

when one side of a fault moves past the other side,

then that radiates seismic energy.

It radiates waves and the ground shakes.

An earthquake is the very rapid movement,

wavelike movement, of the earth’s surface.

And that can be caused by, for example,

an undersea landslide.

It can be caused by a volcanic eruption.

It can be caused by tectonic plates moving past each other.

But essentially, it’s the very rapid release of energy

that’s being felt on the earth’s surface.

The part of the earth that we live on is called the crust.

It’s as little as 5 kilometers thick under the ocean

and between 45 to 50 kilometers thick on the continents.

This crust is floating on a soft mantle of molten rock.

And far from being solid, the crust is actually made up

of vast, separate tectonic plates

that are moved around by the currents

in the molten rock beneath them.

Where the plates meet,

they slide past each other

at the rate of 3 to 5 centimeters a year--

About the same speed as your fingernails grow.

But the movement is not steady.

Earth’s plates are shuffling around.

And as they interact with one another,

you develop what are called fault lines.

That’s where the earthquake happens is on the fault line.

The plates may be locked against each other

for many years until the strain becomes too great,

and they suddenly slip along a fault line,

sometimes for several meters all at once.

The cracking rock sends out shocks of seismic waves

in all directions, which are felt as earthquakes.

Every year there are about 50,000 earthquakes

that are powerful enough to be felt by anyone in the vicinity.

Around 100 are so violent

that they will damage any nearby structures.

The shaking that is caused by an earthquake

is not just dependent on the magnitude of an earthquake,

but is also dependent on how close you are

to a fault that failed.

When such a violent earthquake

occurs in the vicinity of a village, town or city,

it is almost certain to result in death and injury.

Earthquakes were largely a mystery

until the emergence of the science of seismology

at the start of the 20th century.

Since then, we have gradually begun to understand

why and how earthquakes occur.

It had long been noticed that earthquakes tended to occur

along clearly defined bands

that crisscrossed the world’s surface.

Then came the discovery

that the surface was not actually solid

but consisted of moving sheets of rock

which were named as tectonic plates.

The areas where these vast plates

rubbed against each other

were seen to coincide with the belts

where earthquakes most often took place.

So the largest earthquakes worldwide

happen in subduction zones.

So these are at the boundaries

where tectonic oceanic plate meets a continental plate.

And essentially, the oceanic plate

is pushed down underneath the continents.

These faults are very, very big,

and the earthquakes that happen on them can be very large.

The largest earthquakes

can be magnitude 8 to magnitude 9 earthquakes,

such as the 2004 Sumatra earthquake

or the 2011 Tohoku earthquake in Japan.

One of the most notable belts of activity

is one that goes around the edge of the Pacific Ocean.

This is where nine out of every 10 earthquakes occur.

It accounts for earthquakes in many Pacific nations,

including New Zealand, Japan, Alaska,

and along the vast coastline

of both North and South America.

The area along this belt is also known

for its volcanic activity,

giving rise to its popular name: the Ring of Fire.

Another belt of seismic activity

is the Alpine-Himalayan Orogenic belt.

This stretches from the Mediterranean through Asia

all the way to the East Indies.

As its name suggests,

the Alpine-Himalayan belt was responsible for the formation

of many mighty mountain ranges,

from the Atlas in North Africa,

the Alps and the Caucuses,

all the way to the Himalayas in Asia,

which includes Mount Everest, the highest peak in the world.

An earthquake is fundamentally movement on a fault,

or a line of weakness within the crust.

And that movement, it happens many, many times

over thousands of years, millions of years.

That can generate changes in the ground’s surface.

If this is your ground surface,

a normal fault will mean that the ground

will move steadily like this over time.

So, what that means, is you’ll get mountains being generated

on this side and flat plains being generated on this side.

The earthquakes from this belt

release around 15 percent of the world’s seismic energy.

The earthquakes in the continental regions

are generally smaller, so magnitude 6 to magnitude 8.

But actually, they, paradoxically,

they lead to a greater number of deaths worldwide.

The type of earthquakes

that release the huge amounts of energy

that cause major tremors

are called tectonic earthquakes.

In 1906, San Francisco was rocked

by such an earthquake

after a rupture in the San Andreas Fault,

which forms part of the Ring of Fire.

The ground shifted horizontally

by as much as 6 meters along a 430-kilometer stretch,

releasing a colossal amount of energy.

Study of this earthquake

gave rise to the Elastic Rebound Theory.

It states that these earthquakes

occur when a mass of rock

is no longer strong enough to hold the strain it is under,

and suddenly gives way along a fault line.

As the two masses of rock rip in opposite directions,

they may stick together for a moment

before sliding apart again.

This irregular coming apart

is what causes the waves of vibration

that can be seen in the shaking of buildings

during an earthquake.

Similar seismic waves can be set off by human activity

such as mining, fracking for gas

and the underground testing of nuclear devices.

Research carried out

in order to discover when a country had run a nuclear test,

helped expand our ability to detect seismic activity.

Earthquakes give rise

to some of the most dramatic effects

to occur in the natural world.

They cause extraordinary shifts in the ground,

which may rise, fall and open up,

leading to landslides and mudflows.

Buildings, bridges, pipelines and other infrastructure

may be damaged or destroyed.

Anything can be damaged in an earthquake.

That can cause a whole host of problems after the earthquake.

Devastation is often amplified

when buildings are built on soft soils, sand or mud,

as this is easier for seismic waves to travel through.

Compared to other natural disasters,

earthquakes are particularly dangerous.

Per event, we have more people killed in earthquakes

than we have in a flood or in a fire.

That is per number of people affected by an event.

And the simple reason for this

is they’re very difficult to predict,

but also there are other reasons

because earthquakes can trigger other natural disasters.

They can trigger flooding. They can trigger landslides.

They can trigger tsunamis.

Before the invention of the seismograph,

earthquakes were measured

simply by the amount of shaking of the ground.

With the invention of the seismograph in 1875,

it became possible to measure

the intensity of movement against a time scale,

so you could tell when an earthquake had occurred

and how strong it was.

Then, in 1935,

a scale was developed by Charles Richter,

which became known as the Richter Scale.

For the first time, scientists were able

to accurately compare different earthquakes.

However, the Richter Scale was found to be less precise

when measuring the most powerful earthquakes,

and so a new system was developed.

This new system measured the distance a fault moved

and multiplied it by the force required to cause this movement

and was called the Moment Magnitude Scale.

On this scale, a magnitude 1 earthquake

releases as much energy as 170 grams of TNT.

That’s a very small tremor.

In fact, you would not be able to feel

anything under 2.5 on the Moment Magnitude Scale.

By comparison, a magnitude 8 is the equivalent

of exploding 5.4 billion kilograms of TNT.

That magnitude of earthquake

would completely destroy anything near its source.

The magnitude scale is logarithmic.

So for every unit of magnitude,

you release 30 times more energy.

Plus two units of magnitude,

you release a thousand times more energy.

The most powerful earthquake ever to hit the United States

occurred in Alaska in 1964--

A magnitude 9.2.

Alaska is the area most prone to earthquakes.

It endures a magnitude 7 earthquake almost every year.

The largest measured earthquake anywhere in the world

was a magnitude 9.5 that struck Chile in 1960.

It killed thousands of people

and left millions homeless.

Most earthquakes occur in areas that are known danger zones.

But sometimes, earthquakes can be triggered

by hidden fault lines

lurking beneath the surface

on which people have built their homes,

offices, hospitals and schools.

Each individual fault might only fail every hundred years,

every thousand years.

But it could still actually be very hazardous.

So there are lots of faults

that are located, you know, right next to a city,

but we actually don’t even know that they exist.

Just such a concealed fault

ruptured in Los Angeles on the 17th of January 1994.

It was 4:31 in the morning on Martin Luther King Junior Day.

The San Fernando Valley

lies just over 30 kilometers from downtown Los Angeles.

In the predawn darkness,

many in the densely populated community of Northridge

were no doubt planning to use the federal holiday

to catch up on some sleep.

But their calm was shattered

by a powerful magnitude 6.7 quake.

It shook the ground for a terrifying 40 seconds.

The amount of energy a magnitude 6.7 earthquake releases

is around equivalent to what was released

during the Hiroshima atomic bomb.

Um, so that amount of energy

directly beneath a large city at relatively shallow depth

can actually cause quite significant ground shaking

and result in damage.

Most earthquakes

occur less than 80 kilometers under the surface,

but the hypocenter of the Northridge quake

was just 20 kilometers underground,

making this a very shallow earthquake,

which released a colossal amount of energy

onto the nearby surface.

The shocks were so powerful

they were even felt 440 kilometers away in Las Vegas.

The earthquake shook the ground violently from side to side,

as well as up and down, causing catastrophic damage.

That fault moved in what we call a thrust movement.

So we have a geological fault like this:

And then one side of that fault moved upwards.

I mean, the earthquake lasted, what, 10, 15, 30 seconds.

Well, it lasted four years for me and my mother.

She’s 80 now, and I don’t know how many...

In the immediate aftermath,

20 people were reported dead and 1000 injured.

But with many unaccounted for

and feared trapped under debris,

it soon became apparent that the death toll would rise.

Most people die in earthquakes

because of building collapse.

It’s not the earthquake that kills people.

It’s the building.

Rescuers began pulling people

out of the rubble,

and they were quickly joined

by the emergency services.

We couldn’t get out.

You couldn’t get out?

We couldn’t get out.

If we hadn’t been dragged out of there,

we’d have never got out.

They told us when we moved in

it was an earthquake-safe building.

Several apartment buildings caved in,

including the Northridge Meadows apartment complex

where 16 people lost their lives

when their homes caved in on top of them as they slept.

They all lived on the first floor

of the stucco building,

which collapsed into the open void

of the car parking area below them.

This apartment building went up 2 feet, over 2 feet

and dropped down 12, and the rest of it was gone.

When the earthquake hit, I knew immediately

it was different than all the others I’ve been in.

Very strong. At one point, I was thrown down.

I think that’s when the two top floors came down the first.

The quake caused catastrophic damage

to the city’s infrastructure.

Electricity failed,

plunging the city into blackout.

Water mains burst, flooding the streets.

Gas from ruptured mains was set alight, causing fires.

All the airports, including Los Angeles International

were immediately closed.

Eight hospitals were so severely damaged

they had to be evacuated.

Doctors were forced to perform lifesaving surgery

in triage centers out in the open.

The area worst hit was the San Fernando Valley

where 3 million people were affected by the quake.

The emergency services performed heroically

but were under tremendous strain.

They brought in sensitive listening devices

to locate survivors amongst the rubble.

By sheer luck,

the earthquake occurred at night,

limiting the casualties

which could have been greater had it occurred in the day.

I know there was this large scoreboard

at a sports stadium which collapsed.

Because it was 4:30 in the morning,

there was nobody in the stadium,

but if there’d been a sports event going on,

a lot of people would have been injured or killed.

A parking lot in the local shopping center

was completely destroyed,

but as it was empty, no one was hurt.

There was extensive damage to the highways.

Seven major freeway bridges collapsed.

A policeman was killed

when his motorbike pitched off the edge of an overpass.

Another factor limiting the number of casualties

was that buildings had been constructed

to strict safety codes

following the Sylmar earthquake of 1971.

Although every building constructed since that time

survived this latest earthquake intact,

much of Northridge did not.

Mayor Richard Riordan declared a state of emergency

and imposed an evening curfew.

However, there were reports of looting

and warnings that the earthquake

might not even be over.

When an earthquake occurs,

it may not release all its energy at once.

We have now had more than 6000 aftershocks.

This is because faults may rupture

both before and after.

And these aftershocks

are sometimes almost as severe

as the original earthquake.

Aftershocks can occur over quite a protracted period of time,

partly because aftershocks can trigger

aftershocks of their own,

but also because there are other processes operating.

For example, fluids might be moving through the subsurface

driven by the first earthquake

that then might, in turn, put stress on smaller faults

and trigger extra earthquakes.

Despite the fear of aftershocks,

people were told that wherever possible,

by far the best thing to do was to stay in their homes.

Damage from the earthquake was widespread.

The Santa Monica beach community

was particularly badly affected.

It is built on much less stable ground

and although it was relatively far

from the epicenter of the quake,

it suffered violent ground tremors.

There’s always earthquakes around here

but nothing like as bad as this one.

I didn’t expect anything like this.

The Santa Monica Freeway collapsed,

fouling up Los Angeles traffic for months.

Because we can’t get out, we can’t get in,

and so we have to go way east to go west

and way west to go east.

You have to go around so many different areas,

and you don’t know where you’re going half the time.

Many had to struggle through the ravaged city

for four hours in order to find hospitals and medical care.

The death toll of the Northridge earthquake

was approximately 60 and 9000 people were injured.

Eighty-two thousand buildings were damaged or destroyed,

while over 20,000 people had to leave their homes.

California dreaming is dead.

The earthquake occurred on a fault

that had been previously unknown--

A so-called "blind thrust fault"

that was hidden under the uppermost layers of rock.

This is in no way a part of the San Andreas Fault system.

This is part of the--

A completely different set of plate movements

that are peculiar to Southern California.

Experts have since found other such buried faults,

including one that lies right beneath downtown Los Angeles,

underlining the vulnerability of the millions of people

who live and work in the area.

So there’s lots of faults that are particularly quite small

in the continents

that may only have an earthquake every thousand years

or tens of thousands of years.

So this means that there’s lots of faults

that won’t necessarily have had an earthquake in living memory,

but actually still pose a very significant hazard.

President Clinton visited Northridge

to survey the aftermath of the quake.

Having witnessed the devastation himself,

he requested Congress release $6.6 billion U.S. dollars

in relief aid.

Unfortunately, it’s going to take a while.

It’s probably going to take as much as a year.

It doesn’t take very long to demolish

a structurally damaged portion,

but to replace it can take as much as a year, we hope less.

Overall, it cost in the region

of $42 billion U.S. dollars to repair the city,

making this one of the most expensive disasters

ever to hit America.

So if you had a similar earthquake

in a similar area right now,

when there are even more buildings in the area,

the damage will be many orders of magnitude higher.

At the time of the Northridge quake,

Southern California had few systems

monitoring the tectonic plates

responsible for causing earthquakes.

Since the disaster,

several agencies, including NASA,

have set up an integrated network

of over 250 GPS stations across California and Mexico,

with the aim of developing

an earthquake early warning system.

However, earthquake early warning

is really a misleading term.

Current systems only kick in

when an earthquake is already taking place.

But they do enable you to know

how strong an earthquake is in real time

and then assess how far the effects will be felt

in order to warn communities within the danger zone.

In 2018, the U.S. Geological Survey

readied a new early warning system.

This can detect the very early phase of an earthquake

and give warnings of up to a minute

before the major tremors strike.

That’s enough time to slow down or stop trains,

shut down dangerous industrial operations

and give people a chance of getting to places of safety.

For earthquakes, if you have just a few seconds of warning

before that strong ground shaking occurs,

you might be able to protect yourself

by getting under a table or a desk or a doorway

and that can actually be the difference

between life and death.

In 2019,

technology took another leap forward

with the development of a mobile app

to alert Los Angeles county residents

of earthquakes of a magnitude 5.0 or more.

And there is no doubt that early warning is needed.

The whole of California

straddles the infamous San Andreas Fault,

which runs for 1200 kilometers

along the entire length of the state.

It was 1857

when the southern part of the fault last ruptured.

San Francisco, which lies further north on the fault,

burned for three days after the big earthquake of 1906.

With such an active fault line running through California,

it isn’t a question of if there will be another earthquake,

but when.

Another New World city,

Christchurch in New Zealand,

is similar to San Francisco in many ways.

Christchurch had its first contact with Europeans

when Captain Cook landed there in 1770,

just a year after the Spanish

first sighted San Francisco Bay.

Both cities are situated on fine natural harbors.

And both are in areas prone to violent seismic activity.

But as with San Francisco and so many other cities,

located in places known

for the dangers of deadly disasters,

the advantages of its location

outweighed the risks posed by frequent earthquakes.

Now, Christchurch, situated on the south island,

is New Zealand’s third-largest city

with a population of nearly 400,000.

Christchurch is a lovely city.

It’s on the east coast of the south island of New Zealand,

um, a great, vibrant place to be.

It’s an important industrial center

as well as a mecca for tourists with its surf beaches,

modern architecture,

heritage buildings,

museums and galleries.

Despite lying on a major fault line,

for most of the 20th century

through to the first decade of the 21st,

Christchurch enjoyed a long period of calm.

On the 16th of November, 1901,

the city suffered an estimated magnitude 7 earthquake.

After this,

there was relatively little seismic activity

for more than a hundred years.

But that calm was shattered when,

on the 4th of September, 2010,

at just after 4:30 in the morning,

Christchurch was rocked by a magnitude 7.1 earthquake.

It occurred 10 kilometers below the surface

in a previously unknown fault

some 40 kilometers west of the city.

People were jolted awake as the first phase of the quake

caused the ground to shake violently.

People checked on loved ones

and tried to get out of buildings

to the safety of open ground.

As aftershocks continued,

parts of the ground liquefied.

Some were badly injured.

Buildings and infrastructure were seriously damaged.

But thankfully, there were no fatalities.

The hazard in that region thought to be smaller

than it actually was.

As residents worked to repair their battered city

they were hampered by frequent aftershocks.

New Zealand is quite an interesting place tectonically.

So in the north part of the north island,

we’ve got subduction,

where you’ve got the Pacific plate sinking into--

Sinking beneath the land of New Zealand.

But you’ve also got subduction in the south.

But that happens in the opposite direction,

so the Australian plate is sinking there.

And so you’ve got these two regions,

which are basically doing this:

And so in the middle,

you have to have some sort of fault to accommodate,

to absorb that opposite motion.

The population heaved a collective sigh of relief.

It seemed as if they had escaped the full fury

of what an earthquake could unleash.

But the relief was short lived.

One Tuesday afternoon just over five months later,

as the people of Christchurch were busy at work,

attending school or college,

going about their shopping, or having lunch,

one of those aftershocks struck close to the city

at a depth of only 5 kilometers.

The 2010 Darfield earthquake

released 10 times the amount of energy

as the magnitude 6.3 Christchurch earthquake.

But the Christchurch earthquake was so much more damaging,

because it happened right underneath

the city of Christchurch.

Many of the buildings that had been damaged

in the previous earthquake

collapsed completely.

The damage that’s been done to our infrastructure,

I’ve got to say, it’s massive.

This has taken us, not just back

to the minutes after the earthquake

of the 4th of September last year,

it’s taken us further back than that.

Buildings were severely damaged or demolished

but there were not many serious injuries.

People in the downtown business district of the city

were not so fortunate.

The Canterbury television building,

a six-story office block full of workers,

completely collapsed.

One hundred and fifteen of them lost their lives--

More than two-thirds of the 185 people

that were killed in the earthquake.

Around the city and in the suburbs,

people were injured and killed by toppling bricks,

masonry and rockfalls.

Two city buses were buried beneath falling walls,

killing eight people,

while some were killed

by boulders tumbling away from cliffs,

triggered by aftershocks.

Tragic stories to be told about Christchurch at the moment.

We’ve only lost a house,

but people have lost their lives,

so, you know, we’re lucky.

Children attending school,

who had been repeatedly drilled

on how to react to an earthquake,

quickly adopted the "Turtle--"

Dropping to the ground and covering their heads.

Thankfully, no children were seriously hurt or killed

in any school building.

New Zealand is really good at earthquake preparation.

They have excellent building standards.

People are drilled in school and at home.

And everyone is kind of ready for an earthquake.

But here, they weren’t ready

for an earthquake that happened directly under the city.

In the immediate aftermath of the quake,

people rushed to find friends or loved ones.

Others stayed where they were most needed.

The complication is...

we have to go really, really slowly and carefully.

So every single step of the way, we are conscious

that there could be somebody literally behind a desk

or a chair or whatever else.

Many gathered around

the stricken Canterbury television building

where the majority of casualties occurred.

As well as the Pyne Gould building

where 18 people had died.

They helped the survivors,

many of them badly injured.

In total, some 16,000 properties

were left severely damaged by the violent shaking.

The Christchurch earthquake

may have also caused more damage,

because buildings would have been weakened

by the shaking from the Darfield earthquake.

The Christchurch earthquake

also caused a terrifying phenomenon

known as liquefaction.

What happens to buildings during an earthquake

depends very much on what they’re built.

If you built on solid rock,

the ground doesn’t shake so strongly

as if it’s built on sandy or muddy ground.

Parts of Christchurch were built on a drained coastal swamp

and that shook particularly violently

during the 2011 earthquake.

And the ground actually liquefied.

Mud oozed up between cracks in the pavement

and buildings sagged because of the uneven nature

of the liquefaction beneath them.

One of the worst examples of this effect

occurred during the 1976 Tangshan earthquake in China

when an area of more than 2400 square kilometers

was subject to liquefaction,

causing terrible damage to the southern part of the city.

In the Mexico earthquake of 1985,

the ground beneath the center of the city liquefied,

even though the epicenter of the earthquake

was over 350 kilometers away.

Liquefaction can even

induce soil to spew out of the ground in sand volcanoes

and cause landslides.

In a 1964 earthquake in Anchorage,

liquefaction resulted in a landslide

that destroyed 75 homes.

Christchurch was a really devastating earthquake,

because we really did not know

about the location of a fault underneath the city.

Christchurch is built to be very seismically resistant

to the most likely culprit.

So the most likely earthquake

is going to come from the New Zealand Alps

and they’re quite far away.

The type of shaking that we would expect from those faults

is very different from the type of shaking that they did get

in the Christchurch earthquake.

In Christchurch,

the fatal combination of ground shake,

liquefaction and landslide

resulted in damage to a huge proportion of all properties

in the greater Christchurch area.

Older brick and mortar constructions,

were especially vulnerable to shaking.

Many of the city’s iconic heritage buildings

were either damaged or destroyed.

Both the Anglican and the Catholic cathedrals

suffered extensive damage.

And the clock in the famous Victoria Tower

was frozen at 12:51,

bearing lasting testament

to the very moment the quake struck.

The cost to put right the devastated city

was estimated to be upwards

of $20 billion New Zealand dollars.

Following the earthquake,

even five years after the event,

the city has not really recovered.

After the disaster,

the New Zealand government set up a commission

to investigate the buildings that were damaged

in the Christchurch earthquakes.

Following months of inquiries,

the then-Prime Minister, John Key,

stated that 175 out of the 185 deaths

had been caused by structural failures.

The design and construction of the CTV building,

where 115 lost their lives,

came under severe criticism.

If a modern city, like Christchurch,

had been left shockingly vulnerable

to the threat posed by earthquakes,

what chance would a city built 800 ago have?

That’s exactly what is revealed in our next case study.

Many regard the beauty and historical importance

of the 13th-century city of L’Aquila

to be on a par with Florence and Salzburg.

The city is situated on a hill in the Apennine mountains,

about 130 kilometers northeast of Rome,

overlooking the Alterno River.

Behind it’s medieval walls

lie a host of baroque and renaissance churches,

with narrow streets giving out onto magnificent piazzas.

L’Aquila itself sits a fairly wide, flat mountain basin,

and it’s surrounded by mountains on most sides.

And that difference in the topography--

The mountainous regions versus the flat regions,

in Italy and many places worldwide.

is directly due to the movement on the faults

that results in-in earthquakes.

L’Aquila is no stranger to seismic disaster,

having been largely destroyed by two previous earthquakes

in 1461 and again in 1703.

And a more recent, but relatively minor quake,

in 1958.

Historical data on earthquakes can be extremely useful,

because where we’ve had earthquakes in the past,

we’re very likely to have earthquakes again in future.

Then, on the 6th of April, 2009,

at 3:32 in the morning,

the city was rocked by a magnitude 6.3 earthquake.

It lasted for 20 seconds, causing terrible damage

as well as death and injury to the terrified inhabitants.

Much of Italy lies on the cusp

between the giant European and African tectonic plates,

and has suffered many earthquakes.

In such a seismically active area

there are frequent, smaller tremors.

This was the case in the months leading up

to the devastating earthquake in L’Aquila.

In October 2008, the year before the disaster,

dozens of tremors were felt in the city

and the surrounding areas.

Ninety-nine out of 100 times a small sequence of earthquakes

is not going to result in something big.

During the beginning of 2009,

these "seismic swarms," as they are called,

continued to plague the city.

Aftershocks are commonly smaller

than the earthquake that triggered them,

but they can actually also be larger.

And that’s expected for some smaller amount of earthquakes.

This is actually likely the case in L’Aquila

where there was a swarm of smaller seismicity

in the weeks, months before the L’Aquila earthquake.

It was not surprising

that many of the medieval buildings disintegrated.

What did startle and stun experts

was the damage to modern buildings,

even those like the new San Salvatore hospital.

It was lauded as being earthquake proof

when it first opened in 2000--

Just nine years later, it lay in ruins.

Doctors had to treat victims of the earthquake

along with their regular patients in a courtyard.

In L’Aquila, most of the modern buildings collapsed

and were later found not to have been built

to the regulations in place.

Many young people lost their lives.

University students were killed

when a dormitory they were housed in collapsed.

Significant damage in L’Aquila

happened on buildings that were built in the ’70s and ’80s,

after a good code for earthquake resilient buildings

had been established.

So those buildings that were built later,

and should have been resilient,

should have been reinforced concrete

and had much more resistance to shaking, they fell.

And they caused many deaths.

In Onna, which was one of the small villages

right on top of a fault,

the death toll there was around 12 percent.

So about 12 percent of people

living in that town unfortunately died.

The damage to the cultural heritage of the city

was said to be incalculable.

Part of the basilica of Santa Maria di Collemaggio,

caved in completely.

Later, in June,

the European Commission

proposed granting 494 million euros

to fund the repairs and recovery of the region.

Aftershocks continued to be felt throughout central Italy,

a constant reminder to the whole nation

of the terrible situation being endured

by their fellow citizens in L’Aquila.

Many who had lost their homes had been rehoused,

although thousands were forced to remain in temporary camps.

It’s difficult.

We have a tent, and we stay--

We don’t know how long.

Next week, maybe one month.

The city’s historic center

including the Basilica of St. Bernardino

as well as the city hall remained closed to the public

long after the earthquake,

shut behind a sealed off "Red Zone,"

while they were first made safe and then painstakingly rebuilt,

a process which appeared later

to have been hampered by corruption

in the awarding of public contracts.

So I visited L’Aquila about five years after the earthquake

and actually, it was really shocking to see

that there was still extensive damage in the city center.

That really was a loss of identity

to many L’Aquilans and people that lived there,

to have such damage to their historical city center.

In the aftermath of the disaster,

survivors began to question

why they had not been warned of the impending catastrophe.

The prediction of earthquakes

has long been the holy grail of seismology.

Predicting earthquakes is currently impossible

and may always be impossible.

While early warning systems

are capable of giving people vital seconds

to get out of buildings or assume safe positions,

longer-term warnings that would enable mass evacuation,

such as have been possible for disasters such as hurricanes,

have proved elusive.

There is no way to know exactly when and where

an earthquake may happen.

Um, we can do a fairly decent forecast

of where earthquakes might happen.

So we can say, "Yeah, this place

is very likely to have some earthquakes,"

but we can’t say when it’s going to happen.

So the word prediction just doesn’t apply, unfortunately.

The whole issue of scientist’s ability to raise the alarm

about earthquakes was brought into sharp focus

after the L’Aquila quake.

Six scientists,

all internationally respected seismologists

and geological experts,

along with a government official,

were charged with multiple manslaughter.

They were all members of a national commission

for the forecast and prevention of major risks.

Prosecution alleged that they had underestimated the risks

posed by tremors that had been felt

in the months before the devastating earthquake

and given "inaccurate, incomplete and contradictory"

information to the public.

Their advice was that there had been this background

swarm of very small earthquakes

and what they said was that

whilst that could lead to a larger earthquake,

and they certainly couldn’t rule that out,

in most cases,

those swarms don’t normally lead to a larger event.

The accused all vigorously protested

the contentions of the prosecution.

The trial of the L’Aquila scientists was controversial

because the earthquake experts,

who met at the meeting six days before the L’Aquila event,

actually gave very clear, measured,

reasonable and scientifically accurate advice.

One of the defendants, Bernardo de Bernardinis said:

"I believe myself to be innocent before God and men."

When they were found guilty

and sentenced to six years in prison,

scientists from around the world were horrified.

They felt that the trial set a shocking precedent

which would deter experts from sharing important knowledge,

ultimately leaving the public less safe.

I think the trial sets a dangerous precedent

and in particular, has the potential to create

quite a strong chilling effect that discourage scientists

from engaging with policymakers, from engaging with the media

on these really important humanitarian issues.

Enzo Boschi, one of those found guilty,

said that he did not understand what he had been convicted of.

Scientists maintained that it had not been possible

to predict what would happen in L’Aquila.

This opinion was validated

when the defendants successfully appealed,

and their sentences were quashed.

It’s hugely important

that scientists engage with policymakers

and with the general public

to help feed into preparations for emergencies

and building codes

and to make sure that the actions

that take place at a government level

are actually based on a solid foundation of science.

Earthquakes kill and destroy by causing fires,

ruptures in the ground, landslides and tsunamis.

But more individuals die

as a result of the collapse of buildings

and other man-made structures.

The most important thing that could be done worldwide

to reduce earthquake deaths

would be for governments to enforce building codes.

So by far the most effective action that can be taken

to protect people from this type of deadly disaster

is to construct buildings

capable of withstanding the vicious ground movements

that occur during a quake.

Huge advances in this field have been achieved.

Shock absorbers made of rubber

can be incorporated into the building’s foundation

to soak up the violent tremors.

Steel frames within buildings are now designed

to allow the whole construction to sway during an earthquake.

Open areas in the immediate vicinity of buildings

have been factored into planning

so that people who can evacuate

have safe spaces to congregate in.

The chance to live in an earthquake-proof building

would be some comfort for the millions of people

that live near the world’s fault lines.

Without the ability to accurately predict earthquakes,

it represents the best chance we have

of surviving this particular kind of deadly disaster.