What Made Indonesia’s Recent Earthquake So Deadly?

Last week, an earthquake struck the Indonesian island of Java, leaving at least 321 people dead and roughly 2,000 others injured.

The disaster damaged over 62,000 homes and displaced more than 73,000 people, per the Agence France-Presse.

But all this catastrophic damage occurred despite the disaster only registering at a magnitude of 5.6—which, “in the scheme of things, is just not a huge earthquake,” Susan Hough, a seismologist with the United States Geological Survey, tells the Washington Post’s Carolyn Y. Johnson. “There’s lots of faults that can produce an earthquake that big.”

Indonesia is no stranger to earthquakes of this size. It lies in the Pacific Ocean’s Ring of Fire, where several tectonic plates collide. Where moving tectonic plates grind together, pressure can build up. An earthquake occurs when the rocks break or slip by each other, releasing energy that shakes the surface.

Two magnitude 6.2 earthquakes—stronger than the recent one—struck Indonesia in February 2022 and in January 2021. They killed about 25 and 100 people, respectively, writes Victoria Milko of the Associated Press (AP).

One reason why the recent earthquake was so damaging has to do with its location. Its epicenter was just over 6 miles from the surface, writes CNN’s Masrur Jamaluddin and Rhea Mogul.

“Even though the earthquake was medium-sized, it [was] close to the surface… and located inland, close to where people live,” Gayatri Marliyani, a geologist at Universitas Gadjah Mada in Indonesia, tells the AP. “The energy was still large enough to cause significant shaking that led to damage.”

Authorities said soft and loose soil on the area’s hills also led to more destruction, per the Agence France-Presse. Landslides buried entire villages near the town of Cianjur, according to the BBC’s Valdya Bara and Frances Mao.

The damage was compounded by the area’s infrastructure—many buildings are not designed to survive earthquakes, Danny Hilman Natawidjaja, an earthquake geologist at the Indonesian Institute of Sciences, says to the AP. “This makes a quake of this size and depth even more destructive,” he tells the publication.

According to Dwikorita Karnawati, head of Indonesia’s Meteorological, Climatological and Geophysical Agency, hundreds of aftershocks have been recorded in the area since the earthquake, causing additional damage, per ABC News’ Randy Mulyanto, Kevin Shalvey, Jon Haworth and Morgan Winsor.

Due to the risk of aftershocks, a hospital in Cianjur treated people for injuries outside, a senior government official said in a televised interview, per the Wall Street Journal’s Dave Sebastian and Fadiyah Alaidrus.

Karnawati said Wednesday that the frequency and intensity of aftershocks have been decreasing, according to ABC News.

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.