Scientists who study earthquakes have identified several factors that could have contributed to the tragic death toll. The epicenter was shallow, about six miles below the surface, so seismic energy did not have to travel very far before striking people and buildings. As it happened on the densely populated island of Java, in a region of the world where not many structures were built to withstand earthquakes.
A 5.6 [earthquake], in the scheme of things, not just a massive earthquake. There are too many faults that could produce an earthquake of this magnitude, said Susan Hough, a seismologist with the US Geological Survey (USGS) in Pasadena, California. do not remember.
“Unfortunately, if you put an earthquake like this in the wrong place, it can cause damage,” Hogg said. “It’s kind of the perfect storm, in terms of damage relative to its size.”
Indonesia is located in a region known for its activity in the world called the Ring of Fire, where the Pacific Plate collides with several other tectonic plates in a semi-circular region surrounding the Pacific Ocean. As these plates oscillate past or sink under each other, seismic stresses build up until energy such as earthquakes, volcanic eruptions, and other activities are released along the plate boundaries.
In 2004, a 9.1-magnitude earthquake occurred under the Indian Ocean off the coast of Sumatra, causing a devastating tsunami. This type of earthquake occurs in a subduction zone, where one tectonic plate sinks under another.
By contrast, Monday’s quake was a slip-hit earthquake, the same type of quake that occurs along the San Andreas Fault in California. In a slip-strike earthquake, energy accumulates like Two tectonic plates are grinding against each other.
USGS scientists have located the epicenter of the latest underland earthquake in Java, close to the capital, Jakarta. This is part of the reason why tsunamis do not occur. Scientists also say it struck about six miles below the surface. This may sound deep, but earthquakes can originate from hundreds of miles underground, and depth can be a factor in how the surface feels.
Think of it like throwing a rock into the middle of a pond, said Don Blackman, a seismic analyst with the USGS. The ripples radiate downward from the point where the rock fell, and become weaker until they dissipate.
“If you have an earthquake like this near the surface, it’s close to people and buildings,” Blackman said. “If it was 500 miles deep, you’d be 500 miles away from where it happened.”
Blackman added that much of the destruction caused by an earthquake depends not only on the amount of shaking, but also on how strict building codes force people to create earthquake-resistant structures.
Hogg said that although the devastation it caused was realistic, from a scientific perspective this was in many ways an earthquake of the garden variety. But, she added, seismologists will closely analyze the data from the event, because quakes of similar magnitude can sometimes generate different levels of shaking — something that appears to have happened in this case because of the level of destruction.
“The vibration level seems high,” said Hough. He was down to earth. She was close to people. There’s a chance it actually generated more vibration than average.”