A magnitude-5.6 earthquake ruptured about 10 kilometers below the surface in West Java’s Cianjur region, with shaking felt in Indonesia’s capital city of Jakarta.
By Temblor Editorial Team, (@temblor)
This is a developing story; updated 11/22/22 at 10:20 a.m. Pacific time.
At 1:21 p.m. local time on Nov. 21 (06:21 UTC Nov. 21), a shallow magnitude-5.6 earthquake shook the Cianjur region in West Java, Indonesia, which lies about 80 kilometers (50 miles) southeast of Jakarta. News reports suggest 268 people have already been reported dead, 151 missing, more than 1,000 injured and thousands more displaced. The missing may still be trapped in collapsed buildings. Hospitals have been treating victims in parking lots because of damages and loss of power, and for fear of further collapse.
The quake was particularly damaging because it ruptured a mere 10 kilometers (about 6 miles) below the surface. Severe shaking (VIII on the Modified Mercalli Intensity Scale) occurred nearest the epicenter, affecting some 232,000 people. Some 514,000 were expected to have felt very strong shaking, with an additional 3-plus million people likely feeling moderate to strong shaking, according to the U.S. Geological Survey (USGS). “Significant casualties and damage are likely and the disaster is potentially widespread,” according to the USGS. Damaged roads and landslides are hampering disaster relief efforts.
“Earthquakes like this are such a marker of a nation’s wealth and resolve,” says geophysicist Ross Stein, CEO of Temblor (publisher of TEN). “A quake of the same size struck the Southern California city of Claremont in 1990. Some 30 people were injured and there was $12 million in damage. But on Java — the most populated island on Earth — yesterday’s quake, at the same depth, was devastating for families, buildings, and the fabric of the the community.”
The quake appears to be the result of strike-slip faulting (the same kind as occurs on the San Andreas) within the crust of the Sunda Plate in Indonesia, based on the USGS moment tensor solution. (Confused about moment tensor solutions? See this video for more information.) About 260 kilometers (about 160 miles) southwest of the epicenter of this quake lies the Sunda Trench, a subduction zone where the Australian Plate dives beneath the Sunda Plate; far larger quakes can occur on subduction zones than typically occur on strike-slip faults, a prime example being the 2004 Sumatra-Andaman magnitude-9.1 quake.
This region is no stranger to strong earthquakes. On Feb. 9, a magnitude-6.6 quake struck offshore West Java, but didn’t cause much damage (see “Intraslab earthquake shakes (half of) Java, Indonesia, again” for more on that event). It was offshore and deeper than today’s quake, which struck on land.
Since 2007, four earthquake larger than magnitude-6.5 have struck within a couple hundred kilometers of today’s quake. Some occur on the Sunda Plate, some on the Australian, and some at the boundary between the two.
Aftershocks are still rocking the region and are expected to continue.
If you were in the region and felt shaking (or even if you didn’t), consider reporting it to the USGS’s “Did You Feel It?” citizen science project.
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