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The Science of Earthquakes

Technical University of Munich_031422A
[Technical University of Munich]

- Overview

Earthquakes occur when two blocks of Earth suddenly slide past each other. The surfaces on which they slide are called faults or fault planes. The location below the earth's surface where an earthquake occurs is called the source, and the location directly above the earth's surface is called the epicenter.


Sometimes earthquakes have foreshocks. These smaller earthquakes occur in the same locations as subsequent larger earthquakes. Scientists cannot tell whether an earthquake is a foreshock until a larger earthquake occurs. 

The largest major earthquake is called a mainshock. Mainshocks are always followed by aftershocks. These are subsequent smaller earthquakes that occur at the same location as the main shock. 

Depending on the size of the main shock, aftershocks can continue for weeks, months, or even years after the main shock!


- Seismology

The scientific study of earthquakes is called seismology. Seismologists study earthquakes by observing the damage they cause and using seismometers to record the shaking on the Earth's surface. The information recorded by seismometers is called a seismogram, which scientists use to determine the size of earthquakes. 

Seismologists study earthquakes by observing the damage they cause and using seismometers. A seismograph is an instrument that records the vibrations on the earth's surface caused by seismic waves. The term seismograph usually refers to a combination of seismometer and recording device.


- Seismograph

Most seismometers today are electronic, but the basic design and components remain the same: a drum with paper on top, a rod or spring with a hinge at one or both ends, a weight, and a pen. One end of the rod or spring is bolted to a rod or gold box fixed to the ground. Place a weight on the other end of the rod and attach the pen to the weight. The paper tube is pressed against the pen and rotates continuously. 

When an earthquake occurs, everything in the seismometer moves with the earth except the weight on the pen. As the drum and paper swayed beside the pen, the pen drew wavy lines on the paper, recording the earthquake. The records made by seismometers are called seismograms.

By studying seismograms, seismologists can determine how far away an earthquake is and how strong it is. This record does not tell seismologists exactly where the epicenter was, only that the earthquake occurred many miles or kilometers away from the seismometer. To find the exact epicenter, you need to know what was recorded by at least two seismometers in other parts of the country or world.


- What Causes Earthquakes?

Earthquakes happen every day, but most are so small that humans cannot feel them. Nonetheless, over the past 50 years, earthquakes and the tsunamis and landslides that resulted from them have contributed to millions of injuries and deaths and more than $1 trillion in damage.

Earthquakes are the result of sudden movement along faults within the Earth. The movement releases stored-up 'elastic strain' energy in the form of seismic waves, which propagate through the Earth and cause the ground surface to shake. 

Earthquakes occur when the pressure between tectonic plates becomes so great that they break apart. This happens along fault lines, which are cracks in the Earth's crust where tectonic plates meet.

Here are some reasons why earthquakes occur:
  • Tectonic plate movement: The movement of tectonic plates causes pressure to build up in the rock strata on either side of a fault. When the pressure becomes great enough, it is released in a sudden movement.
  • Volcanic eruptions: Volcanic eruptions can cause minor earthquakes.
  • Underground explosions: Underground explosions can cause minor earthquakes.
  • Collapse of rock formations: The collapse of rock formations on the Earth's surface can cause minor earthquakes.
  • Human activities: Human activities can cause earthquakes.
Some warning signs of an impending earthquake include: unusual animal behavior, small tremors or foreshocks, ground uplift or subsidence.
[Split, Croatia]

- Methods for Predicting Earthquakes

Many different avenues of prediction have been explored, such as using observations of warning foreshocks, changes in magnetic fields, seismic tremor, changing groundwater levels, strange animal behaviour, observed periodicity, stress transfer considerations, and others.

While there are no reliable methods to predict earthquakes, scientists use a variety of methods to forecast them:
  • Study past earthquakes: Scientists analyze observations of past earthquake activity, including the frequency of large earthquakes in a specific area. They also study the rate at which strain accumulates in the rock.
  • Use radon detectors: A network of radon detectors can act as an early detection system for earthquakes. Radon is a radioactive gas that fissures in rocks emit before an earthquake.
  • Monitor the ionosphere: The Laboratory project QuakeCast uses machine learning to monitor the Earth's ionosphere for electron activity that may precede an earthquake.
  • Use GSI sensor technology: GSI sensor units include sensors for temperature, pressure, conductivity, and other physical parameters. These units can be operated autonomously using artificial intelligence (AI) methods.

Other methods for predicting earthquakes include:
  • Observations of warning foreshocks
  • Changes in magnetic fields
  • Seismic tremor
  • Changing groundwater levels
  • Strange animal behavior
  • Observed periodicity
  • Stress transfer considerations

- AI-driven Tool Predicts Earthquakes

Machine learning (ML) algorithms can analyze patterns in seismic activity, geological data, and other factors to identify the probability of an earthquake occurring. 

Here's how one AI-driven tool predicts earthquakes:

  • The AI is given a set of statistical features based on the team's knowledge of earthquake physics.
  • The AI is trained to detect statistical bumps in real-time seismic data that researchers have paired with previous earthquakes.
  • The AI is trained on a five-year database of seismic recordings.
  • The AI gives its forecast by listening for signs of incoming earthquakes among the background rumblings in the Earth.
In a trial in China, an AI-driven tool developed by scientists at The University of Texas was 70% accurate in predicting earthquakes a week in advance.

[More to come ...]


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