In this blog post, we’ll explore the scientific principles behind earthquakes and the steps we can take to minimize the damage they cause.
The powerful magnitude 9.0 earthquake that struck Japan in 2011 sent shockwaves across the entire country and triggered a tsunami, resulting in massive loss of life and property damage. This massive earthquake was also linked to the Fukushima nuclear power plant accident, causing significant international repercussions. A similar massive earthquake occurred in Chile in 2010. That earthquake measured 9.5 on the Richter scale and is considered one of the most powerful earthquakes in recorded history. As such, earthquakes go beyond being mere natural disasters; they are among the most difficult disasters for humanity to prepare for. So, what exactly is an earthquake, and why do they occur? To understand this, we need to examine the structure of the Earth’s interior and how it works.
An earthquake is, literally, a natural phenomenon where “the ground shakes.” More precisely, an earthquake occurs when rock formations deep underground suddenly fracture due to forces within the Earth, causing the ground to shake. The energy generated is transmitted as seismic waves, and as these waves travel to the surface, people feel the earthquake. There are two main scales used to measure the strength of an earthquake: magnitude and intensity. While many people frequently encounter the terms “magnitude” and “intensity” when reading news or articles about earthquakes, it is easy to confuse these two concepts.
Magnitude is a scale that indicates the absolute strength of an earthquake. Generally, scales such as the Richter scale or the moment magnitude scale are used. The magnitude of earthquakes we commonly hear about in the news is mostly based on this scale. On the other hand, intensity refers to the relative strength of an earthquake as it is actually felt at a specific location. Even for the same earthquake, it feels stronger the closer you are to the epicenter and weaker the farther away you are. This is similar to the ripples that spread out when a stone is thrown into water.
Why do earthquakes occur? To answer this question, we need to understand the Earth’s plate tectonics. The ground we stand on is not fixed; rather, the massive plates that make up the Earth’s surface are constantly moving. These plates float on the upper mantle and move very slowly but steadily in response to the mantle’s movements. When plates collide or push against one another, a shock is generated, which causes an earthquake. Because the movement of the plates occurs very slowly, people do not feel it; however, when this movement accumulates over a long period and is suddenly released, a powerful natural phenomenon known as an earthquake occurs.
The shock generated when plates move is transmitted through seismic waves, which are classified into four types: P-waves, S-waves, L-waves, and R-waves. Among these, P-waves are the first to arrive; while they generally do not cause significant damage, detection systems can use them to quickly alert us to an impending earthquake. S-waves arrive next, and it is at this point that significant damage begins to occur. In the case of particularly powerful major earthquakes, a phenomenon called liquefaction—where the ground behaves like liquid—can occur, weakening building foundations and increasing the likelihood of collapse.
An earthquake does not end in a single event but unfolds in several stages. It can generally be divided into three stages: foreshocks that occur before the mainshock, the mainshock itself, which delivers the most powerful impact, and aftershocks that follow the mainshock. Hundreds of aftershocks may follow the mainshock, and these can also cause additional damage, so caution is necessary.
Many people claim that precursory phenomena may appear before an earthquake, but there are no scientifically verified precursors.
For example, phenomena such as animals suddenly moving in herds or unusual cloud formations are often cited as earthquake precursors, but these claims lack scientific basis. To date, there is no reliable method for predicting earthquakes, and even in countries like Japan where earthquakes occur frequently, the best they can do is issue warnings as quickly as possible after detecting P-waves through an emergency earthquake early warning system.
So, how should we respond when an earthquake strikes? The most important thing is to protect yourself from falling objects. If you are inside a building, your first priority is to take cover under a table and protect your head. Especially in countries like Korea, where most buildings are constructed of concrete, there is a high risk of collapse, so you might think it is more dangerous to stay inside. However, since there is a high risk of falling objects hitting your head if you try to leave the building while the earthquake is still active, it is safer to remain in a safe location until the shaking subsides. Outside a building, it is important to move to the widest, most open space possible. During an earthquake, do not move rashly; instead, protect your head and wait until the shaking stops.
Earthquakes are one of the natural disasters that humans cannot control, and the destructive power of a major earthquake increases with its magnitude. No matter how thorough the seismic design, it is difficult to prevent building collapse during an earthquake of magnitude 8.5 or higher. While it is impossible to be completely safe from such disasters, advance preparation and education to minimize damage are essential. Living in a seismically designed building and familiarizing yourself with earthquake response procedures in advance are the most important ways to protect your life during an earthquake.
