Earthquake | Why earthquake happens | Why are earthquakes so hard to predict? | TCS - The CBSE Solver
Early Story:-
In 132 CE, Chinese polymath Zhang
Heng presented the Han court with his latest invention. This large vase, he
claimed, could tell them whenever an earthquake occurred in their kingdom– including
the direction they should send aid.
The court was somewhat skeptical, especially
when the device triggered on a seemingly quiet afternoon. But when messengers
came for help days later, their doubts turned to gratitude. Today, we no longer
rely on pots to identify seismic events, but earthquakes still offer a unique
challenge to those trying to track them. So why are earthquakes so hard to
anticipate, and how could we get better at predicting them?
Earth’s structure:
To answer that, we need to understand
some theories behind how earthquakes occur. Earth’s crust is made from several
vast, jagged slabs of rock called tectonic plates, each riding on a hot,
partially molten layer of Earth’s mantle. This causes the plates to spread
very slowly, at anywhere from 1 to 20 centimeters per year. But these tiny movements
are powerful enough to cause deep cracks in the interacting plates. And in
unstable zones, the intensifying pressure may ultimately trigger an earthquake.
It’s hard enough to monitor these miniscule movements, but the factors that
turn shifts into seismic events are far more varied.
Pressure and Friction:
Different fault lines juxtapose different
rocks– some of which are stronger–or weaker– under pressure. Diverse rocks also
react differently to friction and high temperatures. Some partially
melt, and can release lubricating fluids made of superheated minerals that
reduce fault line friction. But some are left dry, prone to dangerous build-ups
of pressure. And all these faults are subject to varying gravitational forces, as
well as the currents of hot rocks moving throughout Earth’s mantle.
So which of these hidden variables should
we be analyzing, and how do they fit into our growing prediction toolkit? Because
some of these forces occur at largely constant rates, the behavior of the
plates is somewhat cyclical. Today, many of our most reliable clues come from
long-term forecasting, related to when and where earthquakes have previously
occurred. At the scale of millennia, this allows us to make predictions about
when highly active faults, like the San Andreas, are overdue for a
massive earthquake. But due to the many variables involved, this method can
only predict very loose time frames.
Prediction:-
To predict more imminent events, researchers
have investigated the vibrations Earth elicits before a quake. Geologists have
long used seismometers to track and map these tiny shifts in the earth’s crust.
And today, most smart phones are also capable of recording primary seismic
waves. With a network of phones around the globe, scientists could potentially crowd
source a rich, detailed warning system that alerts people to incoming quakes. Unfortunately,
phones might not be able to provide the advance notice needed to enact safety
protocols. But such detailed readings would still be useful for prediction
tools like NASA’s Quakesim software, which can use a rigorous blend of geological
data to identify regions at risk.
However, recent studies indicate the
most telling signs of a quake might be invisible to all these sensors. In 2011,
just before an earthquake struck the east coast of Japan, nearby researchers
recorded surprisingly high concentrations of the radioactive isotope pair: radon
and thoron. As stress builds up in the crust right before an earthquake, micro fractures
allow these gases to escape to the surface.
Radon-thoron detectors:-)
These scientists think that if we
built a vast network of radon-thoron detectors in earthquake-prone areas, it
could become a promising warning system– potentially predicting quakes a week
in advance. Of course, none of these technologies would be as helpful as simply
looking deep inside the earth itself. With a deeper view we might be able to
track and predict large-scale geological changes in real time, possibly saving
tens of thousands of lives a year. But for now, these technologies can help us
prepare and respond quickly to areas in need– without waiting for directions from
a vase.
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