In 1906 a 7.8 magnitude Earthquake hit San Francisco, causing immense damage. Fires burned
for 4 days, 25,000 buildings were destroyed and an estimated 3000 lives were lost. The
stage for that disaster was set 20 million years ago two tectonic plates came together
and formed the San Andreas fault, an 800 mile long system of earthquake causing cracks in
California. In fact we are in one right now. But the question is...when are we due for
the next big one? I’m Jake and this is Extreme Science.
Let’s imagine that the surface of the Earth is an egg shell, actually, it’s more like
a broken egg shell where all of these little pieces are the surface, the tectonic plates.
And they are always shifting and moving - about 34 meters every thousand years. When they
stop moving, tension builds up, like stretching a rubber band, until it finally snaps. All
of that energy being released moves through the Earth, creating an earthquake.
It is estimated that 12,000 to 14,000 earthquakes happen every year, about 35 a day. A little
over a thousand are ever large enough to cause any structural damage.
Where we are now on the fault line the plates have collided...literally pushing the earth out of the ground.
In North America we tend to associate California with earthquakes, a movie called San Andreas
came out all about a magnitude 9 Earthquake destroying a large portion of the state, but
we’ve actually experienced one on that scale before in a place where 9 out of 10 of the
largest quakes ever recorded in US history happened, over 3500 miles away from where
we are now in California...Alaska.
The 1964 Alaska earthquake was the biggest in recorded US history coming in at 9.2 on
the richter scale. Some areas were raised 30 feet, others dropped 8ft into the ground.
Tsunamis went as far as Hawaii and Japan and effects from the quake were felt in Texas.
Now to put into perspective just how powerful a magnitude 9 would be let’s go down the
logarithmic scale to a 2, which we would hardly feel. At 6 it would be equal to 120 million
pounds of TNT - pretty powerful, at 8 we get to the 1906 San Francisco quake - it’s energy
equivalent is close to the volcanic eruption of Mount St. Helens. At 9, the Alaska Earthquake,
about 4 trillion pounds of TNT. The most powerful one we’ve ever experienced was in Chile
in 1960 coming at 9.5.
In 2004, scientists drilled 2 miles below the San Andreas fault line and discovered
some curious things. For example, the first samples they brought up to the surface were
literally boiling hot. They also observed the tiniest earthquakes ever recorded...so
small that they had negative magnitudes.
When the Richter scale was created, 0 was assigned to the smallest earthquakes measurable...at
the time. If we go to say -0.2 the energy equivalent would be that of 30 matches being
lit. Pretty tiny comparatively and we wouldn’t even feel it, but scientists have now been
able to measure it. As it turns out, we can measure earthquakes that don’t even happen
on Earth.
In the 60s and 70s, Apollo astronauts put seismometers on the moon, which revealed quakes
of up to 5.5 on the Richter scale that lasted for 10 minutes. On Earth, quakes generally
dissipate much more quickly.
That’s because unlike our natural satellite, the Earth has water. It helps absorb the vibrations,
deadening them. And as you can see around me, it looks pretty lush and that's because along the fault line
shear zones are created and through them water reaches the surface. Creating an oasis.
The fault line just doesn't run through the desert. It runs through cities and towns like this one.
And the damage it would cause would be catastrophic.
The Southern California Earthquake Center made a simulation of what an M8 earthquake would
look like on the San Andreas fault. The US Geological Survey created a video of a realistic
look at the effects of a 7.8 magnitude quake...collapsing 15,000 buildings, injuring 53,000 and costing
around 213 billion dollars.
So what do we do to stop it? Well, that’s what is so scary about Earthquakes, you can’t
stop them. We don’t even really know when they are going to happen. The last big one
in California happened in 1857, and according to scientists one happens every 150 years...but
it’s already been 158. What everyone says is to be prepared. The Southern California
Earthquake Center started the Shake Out! program, which instructs you to Drop, Cover and Hold
On. The ground beneath us is constantly moving, constantly changing, creeping and locking.
All we can do is move along with it and try to hold on. I’m Jake and this is Extreme
Science.