Understanding Earthquakes: Causes, Effects, and Preparedness

What Causes Earthquakes?

Earthquakes are caused by the sudden release of energy within a limited region of Earth’s rocks. This energy can be released by elastic strain, gravity, chemical reactions, or the motion of massive bodies. The tectonic plates of the Earth are always moving slowly, but they become stuck at their edges owing to friction. When the stress on the edge overcomes friction, there is an earthquake that releases energy in waves that travel through the earth’s crust and cause shaking. Most earthquakes occur in fault zones, where tectonic plates —giant rock slabs that make up Earth’s upper layer—collide or slide against each other. These impacts are usually gradual and unnoticeable on the surface; however, immense stress can build up between plates. When this stress is released quickly, it sends massive vibrations, called seismic waves, often hundreds of miles, through the rock and up to the surface. Other quakes can occur far from fault zones when the plates are stretched or squeezed.

Tectonic plates are large pieces of Earth’s crust and uppermost mantle, together referred to as the lithosphere. These plates are constantly moving, albeit very slowly, owing to convective forces in the underlying semi-fluid asthenosphere. The movements can be divergent (moving apart), convergent (moving towards each other), or transform (sliding past each other).

The boundaries at which these plates interact are often sites of intense geological activity, including earthquakes. When plates move past each other at transform boundaries, they sometimes get stuck owing to friction, even though the rest of the plate continues to move. This causes stress to build up at the point where the plates become stuck. When stress accumulation exceeds the strength of the rocks, it is released in the form of seismic waves, which is an earthquake. The earthquake’s focus is the point inside the Earth where the stress is first released, whereas the point directly above it on the surface is the epicenter. The release of stress and subsequent earthquakes can also cause plates to bounce back in a process known as elastic rebound, which can further generate seismic waves. This cycle of stress accumulation and release is continuous along the plate boundaries, leading to frequent seismic activity in these regions.

Types of Earthquakes Based on Their Causes

Depending on the cause, different types of earthquakes can occur.

• Tectonic Earthquakes: These are the most common types of earthquakes caused by tectonic plate movement. They occur when the stress accumulated in rocks along geological faults is released suddenly.
• Volcanic Earthquakes: These are associated with volcanic activity and are caused by the movement of magma beneath Earth’s crust.
• Collapse Earthquakes: These small earthquakes occur in regions with extensive underground caves or mines. These are caused by the collapse of caves or mine roofs.
• Explosion Earthquakes: These are a result of the explosion of nuclear and chemical devices. They are man-made and not a natural phenomenon.

Explanation of the Earthquake Waves

• Primary Waves (P Waves): These are the fastest seismic waves and are the first to be detected by seismographs. They can travel through solids, liquids, and gases and cause particles to move in the same direction as waves.
• Secondary Waves (S Waves): These waves are slower than P-waves and arrive second. They can only move through solids and cause particles to move perpendicular to the direction of the wave.
• Surface Waves: These waves move along Earth’s surface and cause the most destruction. There are two types of surface waves: Love waves move the ground from side to side, whereas Rayleigh waves shake the ground up and down and side-to-side.

Understanding these different types of earthquakes and seismic waves is crucial for seismologists to predict their potential impacts and prepare for future seismic events.

Earthquakes can be classified based on various factors.

• Location:
  • Interplate Earthquakes: Occur at the boundaries between tectonic plates.
  • Intraplate Earthquakes: Occur within the interior of a tectonic plate.
• Epicentral Distance:
  • Local Earthquakes: Epicentral distance of less than 1 °
  • Regional Earthquakes: Epicentral distance between 1 and 10 °
  • Teleseismic Earthquakes: Epicentral distance greater than 10 °
• Focal Depth:
  • Shallow Earthquakes: Focal depths between 0 and 70 km.
  • Intermediate Earthquakes: Focal depths between 71 and 300 km.
  • Deep Earthquakes: Focal depths greater than 300 km.
• Magnitude:
  • Earthquakes are classified based on their magnitude, which is a measure of the energy released. The Richter scale and moment magnitude scale are commonly used to measure the magnitude of earthquakes.

Each of these classifications provides valuable information about earthquakes, helping scientists to understand their causes, effects, and potential risks.

How are earthquakes being measured?

Earthquakes are measured using a device called a seismometer, which records the ground’s movement during an earthquake. The record from a seismometer provides information regarding the time, location, and intensity of an earthquake.

Two common measures were used to quantify earthquakes.

1. Magnitude: This is a measure of the size of the earthquake at its source and is the same number regardless of where you are or what the shaking feels like. The most common measure of an earthquake’s magnitude is its magnitude. The Richter scale, an outdated method, measures the largest wiggle (amplitude) in the recording. Today, the moment magnitude scale (MMS) is preferred because it works over a wider range of earthquake sizes and is applicable globally. The moment-magnitude scale was based on the total moment release of the earthquake.
2. Intensity: This is a measure of the shaking and damage caused by an earthquake, and this value changes from location to location.

These measurements provide meaningful data that can help scientists understand the characteristics of earthquakes and their potential impacts.

Richter Scale: The Richter scale, developed in 1935 by American seismologists Charles F. Richter and Beno Gutenberg, is a logarithmic scale used to measure the magnitude of an earthquake. The magnitude was determined using the logarithm of the amplitude (height) of the largest seismic wave calibrated to a scale using a seismograph. Each increase in magnitude represents a tenfold increase in the measured amplitude.

Moment Magnitude Scale (MMS): The moment magnitude scale (MMS), denoted as M or Mw, is a measure of an earthquake’s magnitude based on its seismic moment. It was defined in a 1979 paper by Thomas C. Hanks, and Hiroo Kanamori. The seismic moment was calculated by multiplying the area of the fault that ruptured by the average amount of slip and rigidity of the rock. The MMS is considered to be more accurate than the Richter scale because it provides a more direct relation to the energy released by an earthquake.

Seismographs: A seismograph is a device for measuring the movement of the earth and consists of a ground-motion detection sensor, called a seismometer, coupled with a recording system. It operates on the basis of the principle of inertia. The 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 records the relative motion between itself and the rest of the instrument, thus recording the ground motion. Modern research seismometers are electronic, and instead of using a pen and drum, the relative motion between the weight and frame generates an electrical voltage that is recorded by a computer.

Effects of Earthquakes

Earthquakes can have a wide range of immediate and long-term effects. The severity of these effects depends on the magnitude of the earthquake, depth of focus, population density of the area, and resilience of the local infrastructure.

• Landslides: Earthquakes can trigger landslides, particularly in hilly or mountainous areas. Shaking can destabilize slopes, leading to rapid rock and soil downhill movement. Landslides can bury homes and roads, causing further damage beyond the initial earthquake damage.
• Tsunamis: Underwater earthquakes can displace large amounts of water, creating a series of waves known as tsunamis. Tsunamis travel vast distances across the ocean and cause extensive damage when they reach the land.
• Fires: Shaking due to earthquakes can rupture gas lines and electrical cables and spark fires. These fires can be particularly devastating if the earthquake has caused damage to waterlines, hampering firefighting efforts.

Impact on Infrastructure and Human Life

The impacts of earthquakes on infrastructure can be catastrophic. Buildings, bridges, roads, power lines, and other structures may suffer severe damage, particularly if they are not designed considering seismic activity. This can lead to significant economic losses and disrupt essential services such as healthcare and transportation.

The human costs of earthquakes can also be immense. In addition to the immediate danger posed by collapsing buildings and other structures, earthquakes can lead to long-term health issues owing to displacement, lack of clean water and sanitation, and psychological trauma.

Understanding these potential effects underscores the importance of earthquake preparedness and the development of building codes that consider seismic activity. It also highlights the need for effective emergency response plans to mitigate the impact of earthquakes when they do occur.

Earthquake Preparedness

Preparing for an earthquake involves understanding the risks, planning, and having the necessary supplies. Here are some tips:

• Understand the risks: I know if you live in an earthquake-prone area. Understand the types of buildings and infrastructure that are more likely to withstand earthquakes.
• Make a Plan: Have a family emergency plan that includes evacuation routes and safe places in your home. Know how to communicate with family members during and after an earthquake.
• Prepare an Emergency Kit: This includes food, water, medication, and other necessities for at least 72 hours. It also includes important documents, cash, and a battery-powered or hand-crank radio.
• Secure Your Home: Secure heavy items that can fall and cause injury. This includes bookcases, mirrors, and light fixtures.

Importance of Building Structures That Can Withstand Earthquakes.

Building structures that can withstand earthquakes are crucial to minimize damage and save lives. This involves the use of specific construction techniques and materials that absorb and dissipate seismic energy. For example, buildings can be designed to sway with ground motion rather than resist it, thereby reducing the likelihood of collapse.

In many earthquake-prone areas, building codes require structures to be designed to withstand a certain level of seismic activity. Engineers and architects use these codes as guidelines when designing and constructing new buildings or retrofitting existing buildings.

However, it is important to note that no structure is entirely earthquake-proof. The goal is to make buildings earthquake-resistant so that they can withstand shaking with minimal damage. This is a key aspect of earthquake preparedness and plays a significant role in reducing the impact of earthquakes on our lives and infrastructure.