New Maps Make Aftershocks Look Scarier Than the Main Quake

United States Geological Survey

Aftershocks continue shaking the cities of Kumamoto, Japan and Muisne, Ecuador, almost a week after earthquakes rocked the two cities, frightening residents still reeling from the devastation and hampering relief efforts.

A 7.0 temblor shook the island city of Kumamoto on April 15, killing at least two people. One day later, a magnitude 7.8 quake hit the coastal town of Muisne, killing 410 people and injuring thousands. Scientists say the two quakes, separated by 9,000 miles and occurring on different faults, are not related.

Aftershocks typically follow a major earthquake, and the USGS says dozens of temblors of 4.1 or greater shook the two regions this week. That's problematic, because aftershocks can exacerbate existing damage and endangering the lives of survivors, relief workers, and first responders digging through the rubble. And an aftershock like the 6.1 that hit Muisne three days after the primary quake is especially worrisome. "Structures that were damaged could fall down, and slopes that didn't slip could slide," says US Geological Survey geophysicist Gavin Hayes.

Adding to the challenge, smaller temblors are no easier to predict than major quakes.

Foreshocks and aftershocks to Ecuador's magnitude 7.8 earthquake on April 16. USGS

Science hasn't figured out how to predict a quake, but if you're a researcher, or just an armchair seismologist, the USGS has you covered with free, data-packed maps. So many maps.

"PAGER—that stands for the Prompt Assessment of Global Earthquakes for Response—is our most useful product," says Hayes. "It helps us quickly characterize the quake." PAGER compares seismic data to population density and building vulnerability information and spits out a good estimate of the disaster scale and economic loss—often within 20 minutes of the quake happening. ("That's what we aim for, at least," Hayes says.) In Ecuador's case, PAGER predicted hundreds of shaking-related fatalities. After the latest aftershock, the death toll passed 500.

PAGER isn't always right, though. It predicted thousands of fatalities from the Kumamoto, but the toll currently stands at 48. "If you compare Japan's quake to Haiti's, which was similar, you see how valuable preparing and building structures that respond well to shaking can be," says Hayes. "Over 300,000 people died in Haiti's quake … the difference in deaths says something."

Though the USGS data can't help predict exactly when or where a quakes will occur, they show how preparedness can mitigate death tolls and infrastructure damage. So brush up on your earthquake safety and be sure to have a survival ki

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