Have you ever experienced an earthquake? If yes, how often? Have you ever asked yourself the following questions:
- What causes an earthquake?
- What areas are more susceptible to earthquakes?
- Can earthquakes be prevented?
- Can earthquakes be predicted?
- Is there a way to put the occurrence of earthquakes to an end.
- Do earthquakes have any positive impact on the environment
Information about Earthquakes for Projects and Students
What is an earthquake?
Earthquake is the sudden movement of the earth caused by a powerful release of energy beneath the earth. Earthquakes occur along fault lines. The most common earthquake is the one that occurs when two points move along fault lines due to tectonic movement. A tremendous amount of energy is released in form of tremors and vibrations called tectonic earthquakes.
The point of origin of an earthquake is the focus. The point of the focus directly above the earth surface is the epicenter. Earthquake damage is greater around the epicenter.
Occurrence and Measurement
There are three types of seismic waves around the focus
- Primary waves or P waves. The primary waves cause rock particles to move in the direction of the focus.
- Secondary waves or S waves. They are waves that cause rock particles to move in right angle to the direction of the waves. Shocks and damages are caused by the right angle waves.
- Deep focus earthquake that occurs at depths below 300Km/s
- Intermediate focus earthquake that occurs at depths between 55Km/s and 300Km/s
- Shallow focus earthquake that occurs at depths less than 55Km/s.
The branch of science that studies about earthquake and other seismic activities is known as seismology. Earthquakes are measured using the Richter scale.
The Richter scale rates magnitude or the energy released. There are twelve different levels in the scale. On level one, the earthquake cannot be felt and on level ten, there is change in landscape.
What are the Causes of Earthquakes?
Earthquakes occur naturally.. However, they can be induced by certain anthropogenic activities.
Earthquakes are caused by sudden release of energy within some limited regions of the earth crust. The energy can be released by elastic strain, gravity, chemical reactions or even the motion of massive bodies. Elastic strain is the most significant cause because it is the only form of energy that can be stored in sufficient quantity in the earth.
Volcanic activity is another natural cause of earthquakes. Volcanic earthquakes can be attributed to sudden slip of rock masses close to volcanoes and the consequent release of elastic strain energy. This is obvious in the clear relationship between the geographic distribution of volcanoes and major earthquakes.
Anthropogenic causes of earthquakes
The United States Geological Society estimates that more than 3 million earthquakes occur every year (8,000 per day). A good number of these earthquakes occur as a result of certain human activities.
Some British scientists in 2017 decided to catalog some human activities that can trigger an earthquake. More than half of the causes were due to the extraction of mining products, groundwater and oil.
These activities involve the withdrawal of volume of subsurface material from the earth crust which cause instability leading to sudden earthquake.
Oil and gas-induced earthquakes have raided areas like Germany, Middle East, Netherlands and USA.
Another quarter of the human causes of earthquakes as outlined by those British scientists is loading of the earth surface where it was not loaded before. A very good example is reservoirs held behind dams.
When the valley behind a dam is filled, the crust below the water experiences a massive change in stress load. An example is the earthquake that occurred in Western India in 1967. Following the completion of the 103 metres high Koyna dam in 1964.
In a meeting of the American Geophysical Union in San Francisco, Klose argued that the pile-up of water at the reservoir might have overstressed the fault thereby accelerating natural tectonic pressure by hundreds of years.
Quater 3 is caused by the injection of fluids produced by the earth back into underground formations in the earth. The mechanism involved in the injection of water into wells weakens an already existing fault by elevating the fluid pressure.
Especially wells that dispose of large volumes of water and those that put pressure directly into basement faults. If the pore pressure increases enough, the weakened fault will slip, releasing stored tectonic stress in the form of an earthquake.
Understand that faults that have not moved in millions of years can be made to slip and cause an earthquake.
What Areas are most Susceptible to Earthquakes?
Earthquakes can occur in any part of the earth. However, they occur most frequently in 3 large zones of the earth. Namely:
- The Circum Pacific Seismic Belt: This belt is also known as the Rim of Fire or the Ring of Fire. 81 percent of the world’s dangerous earthquakes occur here. The belt is found along the rim of the Pacific ocean where oceanic crusts are subducted under plates. Its earthquakes occur as a result of a rupture in a plate and slip between plates. Examples of countries within this belt are
- The Alpide Earthquake Belt: This belt accounts for 17 percent of the world’s largest earthquakes. The Alpide belt extends from Sumatra through the Himalaya, the Mediterranean and into the Atlantic.
- The Mid-Atlantic Ridge: The ridge is formed where two tectonic plates diverge. A major part of this ridge sits underwater where humans don’t live in. Iceland is the only island that exists here.