Why was the 5.6 earthquake in Indonesia so deadly?

A A 5.6 magnitude earthquake left more than 260 dead and hundreds injured as buildings collapsed and terrified residents fled for their lives on Indonesia’s main island of Java.

Bodies continued to be pulled from the wreckage Tuesday morning in the hardest-hit town of Sianjur, located in the country’s most populous province of West Java and about 217 kilometers (135 miles) south of the capital, Jakarta. A number of people are still missing.

While the magnitude is normally expected to cause little damage to buildings and other structures, experts say the proximity to fault lines, the shallowness of the earthquake and inadequate infrastructure that cannot withstand earthquakes contributed to the damage.

Here’s a closer look at the earthquake and some reasons why it caused so much destruction:

Was Monday’s earthquake considered ‘strong’?

The US Geological Survey said the earthquake late Monday afternoon had a magnitude of 5.6 and struck at a depth of 10 kilometers (6.2 miles).

Earthquakes of this size usually do not cause much damage to well-built infrastructure. But the agency points out, “There is no one magnitude above which damage will occur. It depends on other variables, such as the distance from the earthquake, what type of soil you are on, the construction of the building” and other factors.

Dozens of buildings were damaged in Indonesia, including Islamic boarding schools, a hospital and other public facilities. Roads and bridges were also damaged and parts of the region suffered power outages.

So why did the earthquake cause so much damage?

Experts said proximity to faults, the depth of the quake and buildings not built using earthquake-resistant methods were factors in the devastation.

“Even though the earthquake was of medium size, it (was) close to the surface … and it was inland, close to where people live,” said Gayatri Marliyani, an assistant professor of geology at Universitas Gadjah Mada, in Yogyakarta. Indonesia. “The energy was still great enough to cause significant shaking that resulted in damage.”

The worst-hit area is near several known faults, Marliani said.

A fault is a place with a long break in the rock that forms the surface of the earth. When an earthquake occurs on one of these faults, the rock on one side of the fault slips relative to the other.

“The area probably has the most internal faults compared to other parts of Java,” Marliani said.

She added that while there are some well-known faults in the area, there are many other active faults that are not well studied.

Many buildings in the region were also not built with earthquake-resistant designs, which further contributed to the damage, said Danny Hillman Natavijaya, an earthquake geology expert at the Indonesian Institute of Sciences’ Center for Geotechnology Research.

“That makes an earthquake of this size and depth even more destructive,” he said.

Does Indonesia usually have earthquakes like this?

The country of more than 270 million people is frequently hit by earthquakes, volcanic eruptions and tsunamis due to its location on the arc of volcanoes and fault lines in the Pacific basin known as the “Ring of Fire”. The region stretches for about 40,000 kilometers (25,000 miles) and is where most of the world’s earthquakes occur.

Many of Indonesia’s earthquakes are mild and cause little or no damage. But there have also been deadly earthquakes.

In February, a 6.2-magnitude earthquake killed at least 25 people and injured more than 460 in West Sumatra province. In January 2021, a magnitude 6.2 earthquake killed more than 100 people and injured nearly 6,500 in West Sulawesi province.

A massive earthquake and tsunami in the Indian Ocean in 2004 killed 230,000 people in a dozen countries, most of them in Indonesia.

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