Writer: Dhakshayini Suresh
What are Earthquakes and What Causes Them?
An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust. The crust may either be being compressed, pulled apart, moving sideways or a combination of these. The hazards caused by earthquakes include:
Shaking, which is measured by the Modified Mercalli intensity scale that assesses the severity of an earthquake using a descriptive scale that incorporates the earthquake's effects on people and the degree of damage caused to the environment. This intensity depends on three factors: magnitude of earthquake, distance from the fault, and soil conditions.
Landslides, which are destabilized slopes caused by earthquakes. This is what is felt as the ground shaking. Landslides can cause significant damage to roads and other infrastructure and rockfall and debris can dam rivers causing lakes to form.
Liquefaction- During an earthquake, the seismic waves cause the water molecules in saturated soil to become pressurised and the soil particles begin to flow, behaving like a liquid. This liquefied soil is forced up and out of any available crack, weakness or fissure to the surface. The purging of the liquefied soil at the surface creates sand volcanoes and large cracks filled with silt rivers.
Subsidence–During earthquakes the ground may lower due to land subsidence caused by vertical or horizontal ground movements or a combination of both. Large areas of land may sink and become flooded.
Fire–Fires can be triggered by earthquake damage to gas mains and electrical wiring, heat sources or reactions from spilled chemicals.
Tsunamis– a series of waves caused by the rapid displacement of water that can occur during shallow earthquakes, volcanic eruptions or landslides.
Types of Earthquakes?
The type of earthquake depends on the region where it occurs and the geological make-up of that region. There are four major types of earthquakes.
The earth crust is made up of unevenly shaped slabs of rocks called tectonic plates. The energy stored here causes the tectonic plates to move towards or push against each other. With time the stored energy and the movement of the tectonic plates build up the enormous pressure within the region between two plates. That intense pressure becomes the cause of the fault line, and plates move over against or apart from each other. From the epicenter of an earthquake, the energy waves traveled in a different direction on the earth's surface causes vigorous movement on the surface of the earth which is known as an earthquake.
Earthquake-related to volcanic activity are called volcanic earthquakes. The tremors happen due to injection or withdrawal of Magma between the stressed rocks is called a volcano-tectonic earthquake. The movements of the molten magma cause mostly volcanic earthquakes directly underneath a volcano. In these types of the earthquake, magma exerts the pressure on the tectonic plates until this magma breaks the rocks.
Explosive earthquakes mostly happen during the testing of nuclear weapons. During detonation of nuclear weapons, a big blast occurs and a vast amount of energy releases. Sometimes these blasts become the cause of the earthquakes.
These earthquakes are of weak magnitude earthquakes that happen in the caverns and mines. Sometimes, underground blasts (Rock breaking) in the mines become the cause of the collapsing of mines and collapsing of mines produces seismic waves. The P and S- waves produced during the explosion of rocks on or under the surface of the earth cause this type of earthquakes.
Method of Detecting Earthquakes
Seismographs are instruments used to record the motion of the ground during an earthquake. They are installed in the ground throughout the world and operated as part of a seismographic network. A seismograph is securely mounted onto the surface of the earth so that when the earth shakes, the entire unit shakes with it EXCEPT for the mass on the spring, which has inertia and remains in the same place. As the seismograph shakes under the mass, the recording device on the mass records the relative motion between itself and the rest of the instrument, thus recording the ground motion.
New Invention That Detects Earthquakes
The new technology was invented by Mostafa Mousavi, a research scientist at Stanford's School of Earth, Energy & Environmental Sciences. Big quakes are easily detectable but they are also not as common. But, small quakes occur all the time. Occurring on the same faults as bigger earthquakes, with the same physics and mechanisms, these "microquakes" represent a cache of untapped information about how earthquakes evolve. These microquakes have been difficult to discover due to their lack of much of a consequence. The research, that was published in Nature Communications, discusses a new method using artificial intelligence to identify these subtle shifts. It is a new model that detects very small earthquakes with weak signals that current methods usually overlook. It picks out the precise timing of the seismic phases using earthquake data from around the world. They call it the Earthquake Transformer. The exact function, as stated by the researchers: To determine an earthquake's location and magnitude, existing algorithms and human experts alike look for the arrival time of two types of waves. The first set, known as primary or P waves, advance quickly -- pushing, pulling and compressing the ground like a Slinky as they move through it. Next come shear or S waves, which travel more slowly but can be more destructive as they move the Earth side to side or up and down.
Ongoing Areas of Research in Earthquakes:
Crustal deformation, ground motion, ground failure, and the effects of earthquakes.
Seismic Structure of Upper-Mantle
Seismic Data Recovered from Microformats
Several scientists, including those mentioned in the study, are attempting to find ways that are far more effective in finding hidden earthquakes. This new discovery is an imperative advancement in this field of study and brings us one step closer to understanding this natural phenomenon.
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