An earthquake is the sudden shaking of the Earth’s lithosphere, the outermost layer consisting of the crust and the upper mantle. It happens when energy shock waves or seismic waves pass through the solid rocks on the Earth’s crust. If you are curious to know more, our post on facts about earthquakes can be of your interest. Earthquakes can be mild that pass without anyone knowing or disastrous, leading to loss of lives, widespread destruction, and displacing or disrupting the ground (1). Keep reading for more details on earthquakes, safety measures to take, and more.
What Are Tectonic Plates And Faults?
Before we delve into how earthquakes are caused, it is important to understand tectonic plates and faults. The Earth’s crust, called the lithosphere, comprises 15 to 20 moving tectonic plates that rest on the hot, molten rock of the Earth’s mantle (2). The heat within the Earth’s interior causes the plates to move, sometimes toward and sometimes away from each other. A zone of fracture between two blocks of rock is known as a fault. Fault lines are the cracks in the Earth’s crust where tectonic plates meet. Faults can range from a few millimeters to thousands of kilometers. During an earthquake, the rock on one side of the fault slips suddenly (3). The major types of faults include dip-slip normal, dip-slip reverse, strike-slip, and oblique-slip.
What Causes An Earthquake?
The continuous motion of the tectonic plates leads to the steady build-up of stress or pressure along the faults in the Earth’s crust. When the accumulated stress is suddenly released, it results in seismic waves that travel in all directions and cause the shaking of the Earth’s surface (4) (5) (6). Let’s learn about the four main types of earthquakes in order to understand the causes of earthquakes better.
What Are Hypocenter And Epicenter?
The point of origin of an earthquake rupture within the Earth is called the hypocenter, also called the focus. It is the position where the seismic waves in the rocks are first released, marking the origin of the fault. The point on the Earth’s surface or the ground directly above the hypocenter, where the earthquake originates, is called the epicenter. Locating the epicenter is important in determining the faults that rupture and cause an earthquake. If the fault is recognized, the hazard modeling of that area can be done more effectively (12).
What Are Aftershocks And Foreshocks?
The smaller earthquakes that follow the main earthquake in an area are called aftershocks. These occur following the first hours, days, weeks, or even months after the major earthquake and can cause further damage to the already weakened structures in towns or cities. The foreshocks are earthquakes that occur before the main intense earthquake. These are comparatively less severe and might come as a warning sign of a major quake (13).
How Are Earthquakes Measured?
Earthquakes are measured using a seismograph, also called a seismometer, which monitors the seismic waves. It works on the principle of a pendulum and integrates a timing device and a recording device. Initially, the Richter scale was used to measure the magnitude of an earthquake, but today, the moment magnitude scale (MMS) is used globally (14). The larger the value of MMS, the more severe the earthquake.
At a value below 3 on the magnitude scale, one cannot feel an earthquake. At a value of 4 or 5 on the scale, your house might shake, and you may feel as though a large truck is passing close by. Some people may not notice this. At 6, things fall off, windows break, and houses might crack. At 7, buildings and other structures often collapse, and there are many casualties. At 8 and above, whole areas near the epicenter can be totally destroyed.
Safety Measures To Take During An Earthquake
Here are some safety measures to follow before, during, and after an earthquake (15) (16).
1. Before an earthquake
Have a disaster prevention plan to reduce the damage and injury caused by an earthquake. Improve the earthquake resilience of the house. Stockpile water and foodstuff. Participate in disaster training. Prepare a first aid kit.
2. During an earthquake
Drop under something sturdy, such as a table, bed, or desk, cover your head and neck with your arms, and hold on to your shelter until the shaking stops. Stay indoors and away from windows. When on the road, move to an open area and away from buildings, powerlines, poles, bridges, and trees. Avoid areas of secondary hazards, such as landslides. If you are inside a train, grip the railing/ hand strip firmly. If you are at the seashore, seek high ground. Turn on the radio for instructions and updates.
3. After an earthquake
Check for injuries and damage, and secure escape routes. Prevent fires, shut off gas valves, and unplug electrical cords. Watch out for aftershocks. Make sure your family is safe, assist neighbors, and fend for yourself. Recover things and try to get back to normal.
What Is A Tsunami?
A series of large, destructive sea waves produced by an earthquake, landslide, or volcanic eruption on the seafloor are known as tsunamis. When these giant waves approach land and shallow water areas, they build up to higher and higher heights. The speed of a tsunami depends on the depth of the ocean rather than the distance from the source of the wave. Tsunamis are not to be confused with tidal waves, which result from strong winds and the gravitational pull of the Earth, Moon, and Sun. Most tsunamis are triggered by earthquakes with a magnitude of 6.5 and above (17) (18) (19).
30 Fascinating Facts About Earthquakes For Kids
Here are some interesting facts about earthquakes (1) (6) (20) (21) (22) (23) (24) (25) (26) (27) (28).
