Why a relatively small earthquake caused so much destruction in Indonesia

Java, one of the islands of Indonesia was struck by an earthquake last week and it left 321 people dead while grievously injuring 2,000 others. That is not all as it caused destruction of 62,000 homes and displaced more than 73,000 people.

As per a report in smithsonianmag.com, what was astonishing is that this huge quantum of damage was caused by a tremor which was 5.6 in magnitude. This quake as per Susan Hough, a United States Geological Survey seismologist “in the scheme of things, is just not a huge earthquake”. Talking to Washington Post she observed: “There’s lots of faults that can produce an earthquake that big.”

In February 2022 and January 2021, two earthquakes of 6.2 magnitude struck the country. The casualty in the former was 25 while in the latter it was 100.

Those wondering as to how a magnitude of 5.6 could struck such havoc the reason is the location of its epicentre which was just 9.65 kilometres from the surface.

Speaking about this aspect to news agency Associated Press, Gayatri Marliyani who is a geologist at Indonesia’s Universitas Gadjah Mada said: “Even though the earthquake was medium-sized, it [was] close to the surface… and located inland, close to where people live. The energy was still large enough to cause significant shaking that led to damage.”

The area’s hilly terrain which has loose and soft soil also increased the quantum of destruction. Villages located near the Cianjur town were buried under landslides.

Infrastructure in the region added to the woes of the people as a number of the buildings were not designed and constructed to withstand earthquakes. Commenting on this, Danny Hilman Natawidjaja, Indonesian Institute of Sciences’ earthquake geologist told AP: “This makes a quake of this size and depth even more destructive.”

Following the quake, the aftershocks numbering in hundreds caused additional destruction. In fear of these aftershocks, a hospital in Cianjur treated injured patients outside.

Located in the Pacific Ocean’s Ring of Fire where many tectonic plates collide, Indonesia is continuously jolted by quakes. Pressure builds up when tectonic plates in motion grind together. The quake takes place when the rocks break or slip by each other leading to freeing of energy that shakes the surface.