Taiwan Earthquake, Magnitude, Causes and Impact

The most recent major earthquake in Taiwan struck on March 27th, 2024, making it the strongest in nearly 25 years. Check here Causes and Impact of recent Taiwan Earthquake.

Table of Contents

Taiwan Earthquake

A 7.2 magnitude earthquake (7.4 as per US Geological Survey) struck Taiwan’s eastern coast. The epicentre was about 25 km southeast of Hualien.

Taiwan Earthquake was reported between 7.2 and 7.4 on the Richter scale struck on March 27th, 2024.
It was the strongest quake to hit the island in 25 years.
- A 7.6-magnitude quake struck in Taiwan in September 1999.

Impact of Taiwan Earthquake

Tragically, at least 9 people were killed.
Over 1,000 people were injured.
There was widespread damage to buildings and infrastructure, with areas hit by landslides and road closures.
Rescue efforts focused on those trapped in damaged buildings and remote locations.

Earthquakes: An Overview

An earthquake is an intense shaking of the Earth’s surface caused by the seismic waves or earthquake waves that are generated due to a sudden movement (sudden release of energy)

Note

Most earthquakes take place near plate boundaries—but not necessarily right on a boundary—and not necessarily even on a pre-existing fault.

Focus, Epicentre And Types of Waves

Focus or the Hypocentre: The point where the energy is released.
Epicentre: The point on the surface directly above the focus
- The first surface point to experience the earthquake waves.

Isoseismal line

A line connecting all points on the surface where the intensity is the same.

Types of Waves

Body Waves: These travel through Earth’s interior, originating from the earthquake’s source (focus).
- P-Waves (Primary Waves): Fastest waves, travel through all materials (solids, liquids, gases) and are like sound waves, causing pushing and pulling motions.
- S-Waves (Secondary Waves): Slower than P-waves, can only travel through solids (not liquids or gases). This helps scientists understand Earth’s internal structure.

Wave Movement

P-Waves: Vibrate back and forth in the same direction they travel, causing pressure changes in the medium.
S-Waves: Move particles up and down (perpendicular) to the direction they travel, creating wave-like troughs and crests.

Surface Waves

These waves are generated when body waves interact with Earth’s surface.
They are the slowest waves and recorded last on instruments but cause the most destruction due to their large shaking motions.

Causes Of Earthquake

Fault Zones

A fault is a sharp break in the crustal rocks.
Cause: Sudden release of stress along a fault rupture.
Rock movement: Constant change in volume and density due to high temperature and pressure within Earth.

Fault size and earthquake magnitude: A longer length and wider width of the faulted area results in larger magnitude.
- Thrust faults (convergent boundary): Thrust faults are reverse faults where the hanging wall (upper block) has moved upward relative to the footwall (lower block) due to compressional forces.
  - It have the longest ruptures (up to 1,000 km)
- Strike-slip faults (transform fault): Strike-slip faults involve horizontal movement where rock masses slide past each other parallel to the fault plane.
  - Half to one-third as long as thrust faults.
- Normal faults(divergent boundary): Normal faults occur due to extensional forces, causing the hanging wall to move downward relative to the footwall.
  - Have the shortest ruptures.

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Plate Tectonics

Tectonic Plates and Movement

Earth’s crust is divided into large, moving plates on the semi-fluid asthenosphere.
Heat from Earth’s core drives convection currents in the mantle, causing plate movement.
Plate interactions at boundaries create earthquakes and other geological phenomena.

Types of Plate Boundaries

Divergent Boundaries: Plates move apart, magma rises to fill the gap, forming a new crust (Mid-Atlantic Ridge). This can cause minor earthquakes and volcanic activity.
Convergent Boundaries: Plates move towards each other.
- Oceanic-continental convergence: Oceanic plate subducts under the continental plate, creating earthquakes and volcanoes (Andes mountains).
- Oceanic-oceanic convergence: One plate subducts under the other, forming trenches and island arcs (Mariana Trench).
- Continental-continental convergence: Plates collide, forming mountain ranges (Himalayas).
Transform Boundaries: Plates slide past each other horizontally. Friction causes occasional sticking and sudden release, generating earthquakes (San Andreas Fault).

Volcanic Activity

Volcano-tectonic earthquakes are caused by the movement of magma within the crust.
As magma forces its way upwards through the mantle and crust towards the Earth’s surface, it encounters resistance from the surrounding rock.
This can lead to:
- Fracturing of Rock: The pressure exerted by ascending magma can fracture surrounding rock, leading to earthquakes.
- Inflation and Deflation: The swelling (inflation) or shrinking (deflation) of a magma chamber as magma fills or drains can also produce seismic activity.
- Fault Activation: The movement of magma can change stress distributions in the Earth’s crust, potentially activating faults near or beneath a volcano.

Human-Induced Earthquakes

Human-induced earthquakes, often minor, arise from human activities such as mining, large-scale petroleum extraction, the creation of artificial lakes (reservoirs), and nuclear tests.

Reservoir-Induced Seismicity

Water Column Pressure: The pressure from the water column in a large, deep artificial lake alters the stresses along existing faults or fractures.
Soil Structure Weakening: Water percolation weakens the soil structure and lubricates the faults.
Stress Changes from Water Load: The loading and unloading of water in reservoirs can significantly alter stress levels.
Fault Movement and Earthquakes: These stress changes can cause sudden movements along faults or fractures, triggering earthquakes.
Examples
- 1967 Koynanagar Earthquake: Near the Koyna Dam reservoir in Maharashtra, a magnitude 6.3 earthquake resulted in over 150 deaths, with subsequent smaller quakes observed. This is attributed to reservoir-triggered seismic activity by some geologists.
- 2008 Sichuan Earthquake: Approximately 68,000 deaths were caused by this quake, possibly triggered by the construction and filling of the Zipingpu Dam, illustrating another case of reservoir-induced seismicity.

Swarms

Definition: Earthquake swarms are sequences of many small earthquakes striking a region over a period, which could last for months without leading to a major earthquake.
Characteristics: Unlike traditional earthquake sequences that typically feature a mainshock followed by aftershocks, swarms consist of many small tremors without a single, distinct main event.
Association with Volcanic Activity: Swarms are often linked to volcanic activity, indicating the movement of magma beneath the surface.
Significance: They can act as indicators for the location and movement of magma within or beneath volcanoes, providing valuable information for volcanic monitoring and prediction efforts.

Ring Of Fire

The Ring of Fire, also referred to as the Circum-Pacific Belt, is a path along the Pacific Ocean characterised by active volcanoes and frequent earthquakes.
Roughly 90% of all earthquakes occur along the Ring of Fire (the 2004 Indian Ocean Earthquake or Northern Sumatra earthquake, the Alaska earthquake of 1964, and the Japan earthquake of 2011), and the ring is dotted with 75% of all active volcanoes on Earth.
Many volcanoes in the Ring of Fire were created through a process of subduction.