Why Was Indonesia’s Earthquake So Deadly?

shallow quake killed hundreds

By Jonny Lupsha, Wondrium Staff Writer

Earthquakes are always dangerous, but we’ve learned from the past. Improved engineering has led to buildings that are meant to absorb tremors. What happened in Indonesia?

Demolished home due to earthquake
Improved engineering of buildings is now purposed in places like California in the United States to mitigate earthquake damage, to avoid building rubble as seen in this photo. Photo by nando_uno / Shutterstock

One of the deadliest earthquakes in modern history occurred in San Francisco in 1906. This quake and a related fire destroyed about 80% of the city, but, thankfully, we learned some hard lessons about disaster preparedness. These lessons included where and how to construct buildings, among other things. Compared to this example, Indonesia’s recent quake was relatively mild, but it still killed more than 300 people. Why was Indonesia’s earthquake so deadly?

The solution lies in geographic location, building construction, and other factors. In his video series The Nature of Earth: An Introduction to Geology, Dr. John J. Renton, Professor of Geology at West Virginia University, analyzes earthquakes and what we learn from them.

Subduction Zones

Zones of subduction, or subduction zones, are points of collision between two of Earth’s tectonic plates, where one dives back into Earth’s mantle.

“Enormous amounts of energy can be stored during that collision between those two plates,” Dr. Renton said. “When it finally breaks and forms […] thrust faults or reverse faults in what we call the zone of subduction, you’ve already stored enormous amounts of energy. That energy is released, and—as a result—you have a potential killer earthquake.”

Indonesia sits atop a subduction zone, hence, its frequent earthquakes. Its proximity to these fault lines is part of the reason this most recent earthquake was so damaging.

Up to Code

Indonesia also has geological features of sloping terrain and unstable soil, both of which contributed to the death toll of the recent earthquake.

“[We] have found out a long, long time ago, for example, that buildings that have foundations anchored in bedrock will survive much better than those that are not,” Dr. Renton said. “If you think about the damage that was reported in San Francisco [in 1989’s Loma Pietra earthquake], the only real damage in the city […] was to an area called the Marina.”

The Marina is mostly loosely packed debris that was put into the East Bay as a result of, ironically, the 1906 earthquake. However, California is probably the best state for engineering buildings to withstand earthquakes due to the lessons learned from the past. Dr. Renton said that 90% of earthquake damage in the mainland United States happens in California.

“If you go to California, the law says that if you build a building—even a one-family building for a home—you’ve got to bolt it to the foundation,” he said. “In the larger buildings, what they actually do, they have between the building itself and the foundation, shock absorbers.”

Why do California buildings have shock absorbers? The shock wave traveling from the Earth to the building has to pass through the foundation first. The shock absorbers do the same thing that shocks or springs do for a car or a bicycle: They absorb the energy of the impacts with the road.

If California’s hard-earned lessons about earthquake damage mitigation were to be adopted by Indonesia, more lives could be saved in the future.

The Nature of Earth: An Introduction to Geology is now available to stream on Wondrium.

Edited by Angela Shoemaker, Wondrium Daily