Earthquake Geology

Introduction

Earthquakes occur due to the rapid release of energy in the Earth’s lithosphere that generates seismic waves.
They typically happen as a result of tectonic forces, when rock in the Earth’s crust breaks or slips along a fault.
The location below the earth’s surface where the earthquake starts is known as the hypocentre, and directly above it on the surface, the epicentre.

The Cause and Effect of Earthquakes

Earthquakes are mainly caused by the movement of tectonic plates. When these plates move past each other, they sometimes 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 the form of waves.
These seismic waves can cause ground motion, surface rupture and other phenomena such as liquefaction and landslides.
Secondary effects are often consequential as they lead to events like flooding (from dam breaks), fires (from gas mains breaking) and disruption of services.

Types of Seismic Waves

The energy radiates outward from the fault in all directions in the form of seismic waves like P-waves (primary), S-waves (secondary) and surface waves.
P-waves are the fastest, traveling through solids, liquids and gasses, and shake the ground back and forth.
S-waves travel through solids only and have a shearing motion, shaking the ground up and down and side-to-side.
Surface waves, which move along the Earth’s outer layer, cause the majority of damage during an earthquake.

Earthquake Measurement

Earthquakes are measured using a seismometer, which produces seismic waves that appear as wiggly lines on a seismograph.
The strength of the earthquake is commonly communicated as magnitude, measured using the Richter scale.
The Mercalli scale measures the effects of an earthquake, creating an intensity rating based on the observed impact on people, buildings, and the Earth’s surface.

Earthquake Prediction and Mitigation

Even with modern technology, accurate prediction of earthquakes is not yet possible, but the likelihood of future seismic events can be assessed based on various factors.
Understanding the geology of an area, including the history and type of seismic activity, can help in creating seismic hazard maps and inform building design to better withstand seismic forces.
Furthermore, earthquake prediction could involve the monitoring of foreshocks, smaller earthquakes that precede the main event.
Public education on earthquake readiness and effective early warning systems are essential in minimizing loss of life and property damage during an earthquake.