Why Earthquakes Occur Frequently in Japan?

Japan is one of the most earthquake-prone countries in the world. The location of Japan is such that it witnesses natural disasters like earthquakes, volcanic eruptions, and tsunamis on regular basis. Geographically, Japan is situated along the Pacific Ring of Fire or Circum Pacific Belt, at the junction of four major tectonic plates. These tectonic plates are the Eurasian Plate, the North American Plate, the Pacific Plate, and the Philippine Plate.

Pacific Ring of Fire is an active zone where these tectonic plates interact with each other.  These plates either collide, move apart or slide past one another. The movement of these tectonic plates causes tension resulting in phenomenons like earthquakes, volcanic eruptions, and deep ocean trenches.

Earthquakes are observed most frequently along the Pacific Coast of Japan.  It is usually around the two plate boundaries where Pacific Plate collides with the Eurasian Plate and where the Philippine Sea Plate meets the Eurasian Plate.

What is the earthquake frequency in Japan?

Earthquakes are very frequent in Japan. In numerical terms, Japan experiences over 100,000 earthquakes in a year.  Yes, you heard that right! But worry not, most of these earthquakes are so minor that they hardly gets any notice.  Only those earthquakes which are assigned intensity level-1 or above on the Seismic Intensity Scale are actually felt or noticed. Nevertheless, even the number of earthquakes that are actually felt is huge.

Around 20 percent of major earthquakes in the world are centered in and around Japan. It accounts for nearly 10 percent of the total energy released in earthquakes each year. The Japanese Archipelago has experienced 31 major earthquakes and aftershocks since 2000 as of May 2021.

Japan Meteorological Agency Seismic Intensity Scale

Japan uses the Japan Meteorological Agency (JMA) Seismic Intensity Scale to measure an earthquake. The scale ranges between intensity levels 0 to 7. It is also known as the Shindo scale.

Explanation of Shindo Scale

Earthquake Intensity	Effect(s)
Scale 0	Most people would be unable to feel the tremor. It will have no impact on objects kept indoors.
Scale 1	Some people in the upper storey of the multistorey buildings may feel slight tremors. Indoor objects may sway or rattle.
Scale 2	Many people indoors will feel the tremor. Light sleeper will be awakened. Hanging objects such as lights may shake without any damage
Scale 3	Most people indoors will feel the earthquake. The quake may frighten some people. Indoor objects may rattle prominently and the likelihood of objects falling off from raised surfaces. The tremors will also be felt by people outdoors. Overhead powerlines may sway.
Scale 4	It will frighten most people and awaken most sleepers. Hanging objects will start swinging and dishes kept in the cupboard will start rattling.
Scale 5- Lower	Most people will run outside in order to escape the danger. It may get difficult for some people to move. Furniture will start moving/getting displaced. Books will start falling off from shelves. Windows may break or fall off. Roads may get damaged.
Scale 5- Upper	Many people will find it difficult to move. They will be considerably frightened. most dishes from the cupboard will fall off. Most bookshelves will also fall. Unreinforced concrete-block walls may collapse. Less earthquake-resistant homes may suffer significant damage. Gas pipelines and water mains will get damaged. Cracks can appear on the ground and landslides may take place.
Scale 6- Lower	It would be difficult for a person to stand. Many heavy and unanchored furniture will start moving and falling. All objects will start shaking violently. Not possible to open the door in many cases. The tremors will be strongly felt even outdoors. Electric poles can fall down, cause a fire.
Scale 6- Upper	Impossible for any person to stand. No one can move without crawling. Most heavy and unanchored furniture will move and displace. Trees will fall down due to violent shaking. Bridges and roads will suffer moderate to severe damage. The less earthquake-resistant houses will collapse and get severely damaged.
Scale 7	A person will be thrown off due to violent shaking. It will impossible for anyone to move at his/her will. In most buildings, wall tiles and windowpanes are damaged. Most or maybe all residences collapse or receive severe damage despite being earthquake-resistant.

Difference between magnitude scale and seismic intensity scale

The magnitude scale and seismic intensity scale measure two different aspects of earthquakes. The magnitude scale measures the amount of energy released at the source of the earthquake. On the other hand, the seismic intensity scale measures the strength of shaking produced by the earthquake at a certain location. In simple words, the magnitude scale relies on the measurements on seismograph while the seismic intensity scale relies on the effect of earthquakes on people, infrastructure, and the surroundings.

How Japan has prepared and adapted itself for earthquakes?

Over the years, Japan has prepared itself for earthquakes in the most efficient ways. From earthquake-resistant buildings to frequent drills and training, significant measures have been taken to lessen casualties and infrastructural damages. From school children to the people in their old age, all are mentally prepared at regular intervals to face the disaster.

Best practices followed by Japan to lessen the impact of the earthquake are as follows:

• Earthquake-resistant infrastructural design
• Emergency mock drills at regular interval
• Earthquake expeditions
• Awareness campaigns
• Efficient disaster management techniques in place

Most Powerful Earthquakes in Japan

Earthquakes have shaken Japan time and again. Here is a list of some of the most powerful and destructive earthquakes witnessed by Japan.

The Tohuku Earthquake (2011)

Date: 11 March 2011

Location: Tohuku Region (Japan)

Details: It was the single most powerful disaster in Japan’s recent history.  The earthquake triggered tsunami waves at the Pacific Coastline of Japan. The earthquake and following tsunami led to a major energy accident at the Fukushima Daichii Nuclear Power Plant.  The three disasters together were later referred to as  “triple catastrophe” and it killed more than 18,000 people. The measurement of the earthquake on the Richter magnitude scale was 9.1.

The Great Kanto Earthquake (1923)

Date: 01 September 1923

Location: Kanto, Honshu (Japan)

Details: It is considered the most destructive earthquake of Japan n the recent past.  While the intensity of this earthquake was low in comparison to the Tohuku Earthquake, but the time period was such that the disaster and related fire aftermath ended up taking the lives of more than 140,000 people.