An earthquake is the shaking of the Earth’s surface due to a sudden release of energy in the lithosphere that creates seismic waves. It is also called a quake, tremor, or temblor. Earthquakes can be classified as per their range in intensity from weak to violent, causing significant damage to infrastructure and lives.
Earthquakes may be natural due to moving of tectonic plates or human-induced, such as due to mining, fracking, and nuclear tests. The initial point of rupture is called the hypocentre or focus, while the ground level directly above it is the epicentre.
The cases of earthquakes are increasing day by day. A 7.2-magnitude earthquake struck Taiwan on April 3, 2024, resulting in at least nine deaths and around 800 injured people. The Japanese Meteorological Agency (JMA) recorded a 7.6-magnitude earthquake near the northern coast of the Noto Peninsula in Honshu, Japan on January 01, 2024. On October 7, 2023, a 6.3-magnitude earthquake struck Western Afghanistan, following multiple earthquakes in the month that killed more than two thousand people in the Herat province of the country. An earthquake of 6.8-magnitude earthquake struck Morocco on September 8, 2023, marking the most powerful earthquake ever recorded in the country.
Let us discuss each of these earthquakes one by one.
On average, magnitude 2 and smaller earthquakes occur several hundred times a day worldwide. Major earthquakes, exceeding magnitude 7, occur more than once a month, while great earthquakes of magnitude 8 and higher occur about once a year. On average, there are fifteen earthquakes with a magnitude of 7 or greater each year.
Measurement of Earthquakes
Earthquakes are measured on a scale, called the Richter scale, devised by Charles Francis Richter in 1935. It is a logarithmic scale, where each step-represents a ten-fold increase in magnitude. However, Richter scale is generally effective for regional earthquakes; not greater than magnitude 5.
Therefore, scientists have developed a far-more sensitive seismometer, called Moment Magnitude scale (Mw), which is more effective for large earthquakes using more variables to calculate the energy released. Seismic moment indicates what occurs during an earthquake, and defines how much force is needed to generate the recorded waves. The number attributed to an earthquake represents a combination of the distance the fault line has moved and the force that moved it.
Usually, tremors of 2.5 or less are not felt; however, could be detected by instruments. Earthquakes up to five are felt and might cause minor damages.
Taiwan Earthquake
Taiwan is an island nation in the western Pacific Ocean, located approximately 100 miles off the coast of southeastern China. Taiwan is prone to earthquakes because of being located along the Ring of Fire, where most of the world’s quakes occur. Therefore, the island is no stranger to powerful temblors. However, Taiwan’s advanced technology and disaster response have significantly reduced the death toll. Since 1980, Taiwan and its surrounding waters have experienced approximately 2,000 earthquakes with a magnitude of 4.0 or greater, as per the United States Geological Survey. The 1999 Earthquake in Taiwan prompted officials to enhance their emergency response and disaster reduction efforts. The 7.6-magnitude earthquake in central Taiwan resulted in the deaths of nearly 2,500 people and left around 10,000 injured. Moreover, some 50,000 buildings were destroyed or damaged. As a result, Taiwan’s government implemented the Disaster Prevention and Protection Act and established two national centres for earthquake coordination and training, resulting in one of the world’s most advanced earthquake preparedness.
The long horseshoe-shaped ring around the Pacific Ocean is nearly 40,000 km long and is particularly prone to earthquakes. Frequent earthquakes are caused by tension accumulated from the interactions of the Philippine Sea Plate and the Eurasian Plate, resulting in sudden releases of energy in the form of earthquakes.
Japan Earthquake
On January 1, 2024, the US Geological Survey’s (USGS) National Earthquake Information Center detected a 7.5-magnitude earthquake in Honshu, Japan; whereas, the JMA recorded it as a 7.6-magnitude earthquake. As per the USGS reports, measurements from various agencies can vary due to different sensors and methods. Dozens of aftershocks were also recorded. The earthquake caused significant shaking in Nanao, while Tokyo experienced light shaking. The quake also prompted a tsunami of nearly three feet in Japan. JMA initially issued a major tsunami warning, the first since Japan’s 2011 earthquake and tsunami, but later reduced it to an advisory. Two reactors at the Shika nuclear power plant on the Noto peninsula survived but experienced temporary power outages due to damage. Wajima, a city in Ishikawa Prefecture, was among the areas most severely impacted by the earthquake. A government estimate suggests that the damage from the earthquake is expected to cost between US$ 7.4–17.6 billion. Over 60,614 houses were damaged, as reported by the Japanese Red Cross. This earthquake was distinct from others as it was not caused by subduction but was rather part of an ‘earthquake swarm’.
An earthquake swarm is a series of seismic events occurring in a local area within a short period. The time frame used to describe a swarm might be days, months, or years. The energy released is different from normal earthquakes where a major earthquake (main shock) is followed by a series of aftershocks. In case of an earthquake swarm, there is no specific main shock. In other words, earthquake swarms are clusters of moderate earthquakes that occur over a period of hours to days without a distinct mainshock.
Afghanistan Earthquake
Three powerful earthquakes struck near Herat, Afghanistan in October 2023. A 6.3-magnitude earthquake struck western Afghanistan, with its epicentre located in Zinda Jan, 40 km northwest of Herat on October 7. The second earthquake occurred 14 km southeast of the epicentre on October 11, while the third one occurred on October 15.
About 2,445 individuals were killed and over 9,420 injured across eleven villages of Zinda Jan district.
The earthquake was triggered by a rupture along the Harirud Fault System. The Harirud Fault System is a major tectonic fault in Afghanistan, characterised by right-lateral strike-slip system, meaning that the two sides of the fault move horizontally past each other in opposite directions. The northwestern fault system is a right-lateral strike-slip fault, while the western section is a thrust fault. The inferred thrust faulting occurred at the left step in the fault system, where the two sections meet. Thrust faulting is a type of faulting where two tectonic plates collide, causing one to slide over the other, leading to large earthquakes, particularly when they rupture along their entire length.
Earlier, many more earthquakes took place in Afghanistan over the years. For instance, in March 2023, a 6.5-magnitude earthquake hit Badakhshan, killing at least 13 people in Afghanistan and Pakistan. In September 2022, tremors hit Kunar province, killing eight. In June 2022, a 6.1-magnitude earthquake killed 1,036 people in Paktika, causing widespread damage and forcing Afghanistan to appeal for international aid. In 2015, a 7.5-magnitude earthquake, one of the largest in Afghanistan’s recorded history, killed 399 people in Afghanistan, Pakistan, and India. The Hindu Kush earthquake in 2002 killed 1,100 people, while the 1997 Earthquake in Qayen on the border between Afghanistan and Iran killed over 1,500 people and destroyed over 10,000 homes. The 1998 Earthquake in Takhar, a remote northeastern province, killed at least 2,300 people, with estimates ranging as high as 4,000.
The reason for frequent earthquake in the country is its location. Afghanistan, located on multiple fault lines where the Indian and Eurasian tectonic plates meet, experiences frequent plate collisions, causing significant tectonic activity. Afghanistan lies on the Eurasian plate. In western Afghanistan, the Arabian plate subducts northwards under Eurasia, while the Indian plate does the same towards eastern Afghanistan. The Arabian and Indian plates in southern Afghanistan are adjacent and subduct northwards under the Eurasian plate.
Thus, Afghanistan is surrounded by various active fault systems such as the Chaman Fault and the Main Pamir Thrust.
The Hindu Kush mountain range and the Pamir Knot are geologically complex regions where tectonic plates intersect. The collision and convergence of the Indian and Eurasian plates leads to the folding and faulting of the Earth’s crust which leads to earthquake in the region.
The ongoing Indian Plates northward movement towards the Eurasian Plate results in compression, causing the Himalayas to uplift and transmit tectonic stress across the entire region, including Afghanistan. The compression causes crust to deform, leading to faults and fractures that can slip and trigger earthquakes.
Morocco Earthquake
The US Geological Survey reported a 6.8-magnitude earthquake with its epicentre in the Al-Haouz province, in the Atlas Mountains of the historic city of Marrakesh on September 8, 2023. The USGS reported that the earthquake’s epicentre was 18.5 km below the Earth’s surface, while Morocco’s agency pegged the depth at 11 km, either way indicating a shallow quake. Swallow quakes are more dangerous because they carry higher energy when they emerge to the surface compared to those occurring deeper below the surface. Deeper quakes do spread farther because as seismic waves move radially upwards to the surface, they lose energy as they cover greater distances. The magnitude of an earthquake, in addition to its depth, is also an indicator of how destructive a quake could be. For instance, the seismic waves produced by a 6-magnitude earthquake have 10 times higher amplitude than those from a 5-magnitude earthquake, and the energy differential is even higher by 32 times for every 1 magnitude change.
The 2023 Morocco Earthquake was caused by the movement of the African and Eurasian plates, which are converging at a rate of 4.9 mm per year. The earthquake occurred along the Azores-Gibraltar Transform Fault, a major fault line marking the boundary between the two plates. The earthquake was caused by a geological phenomenon known as a ‘reverse fault’. The term ‘reverse’ refers to a situation where the upper block above the fault plane moves up and over the lower block. This type of faulting is common in areas of compression, where one tectonic plate is converging into another. This happens when tectonic plates collide, making the Earth’s crust thicker. The stress along these fault lines can cause earthquakes when rocks move abruptly to relieve stored stress. The region has not experienced major earthquakes before, indicating that the stress from plates colliding has been accumulating underground for a considerable period. When the stress gets too much for the fault to handle, it causes an earthquake.
As earthquakes are very rare in the North African region, Morocco was not adequately prepared for such a calamity. The 1960 Earthquake in Morocco, known as the Agadir Earthquake, led to changes in construction rules, but most Moroccan buildings, particularly in rural and older cities, are not designed to withstand strong tremors. Therefore, the collapse of numerous houses in the old city Marrakech!
Other Major Earthquakes of the World
In 1960, the largest ever earthquake was registered with a 9.5 magnitude in Chile. It is only broadly true that the magnitude of earthquakes corresponds to death and devastation. The 1960 Earthquake was probably right around the upper limit for what the planet could generate as the chances of a much larger quake are low. Chile has a long history of devastating earthquakes (over 9), and is considered to be a model for earthquake preparedness.
In 1993, a 6.2-magnitude earthquake struck at Latur and Osmanabad, Maharashtra in which approximately 10,000 people died and more than 30,000 were injured. The quake is considered as the deadliest one in the stable continental crust to have ever occurred.
The Bhuj earthquake, that occurred on January 26, 2001 in Gujarat, had a magnitude of 6.9, killing more than 20,000 people. The tremors of the quake were felt in most of the parts of north-western India and in some parts of Pakistan.
In December 2004, a 9.1-magnitude earthquake had struck off the coast of Indonesia, leading to a tsunami, which swept away entire communities around the Indian Ocean.
In 2011, a 9-magnitude earthquake struck off the coast of Japan, and caused widespread damage on land and caused a tsunami. It also caused a major accident at the Fukushima nuclear plant along the coast.
On April 25, 2015, an earthquake of magnitude 7.8 struck near Kathmandu in Nepal, killing more than 9,000 people as well as destroying, several buildings and renowned structures, such as Darbar Square and Dharohar Tower. However, the famous Pashupatinath Temple remained unharmed.
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