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Rippling Rainbow Map Shows How California Earthquakes Moved The Earth

Curious how much the ground shifted after the two large earthquakes last week in Southern California? NASA has just the map for that question — and it happens to look like beautiful, psychedelic art.

On July 4, a 6.4 magnitude quake hit the town of Ridgecrest, north of Los Angeles. The next evening, the area was jolted again by a 7.1 magnitude earthquake. Luckily, there were no serious injuries or major infrastructure damage.

The map was created by the Advanced Rapid Imaging and Analysis team at NASA's Jet Propulsion Laboratory. It shows rippling rainbows forming a circular pattern around the faults of the two quakes.

Each rainbow stripes means that the ground has been displaced there by some 4.8 inches. It's the same logic as a topographic map, where lines that are closer together indicate steeper slopes. In this case, the closer together the rainbow stripes are, the more the ground was displaced by the temblor.

Eric Fielding, a geophysicist at JPL, says the parts of the map along the fault where the colors appear jumbled suggest even more dramatic movement of the ground.

He explains how they mapped the changes.

"We've taken a radar image of before the earthquake and another image after the earthquake," Fielding tells NPR. They then compared each point's change between the two images. "That allows us to measure the amounts that the ground moved either towards or away from the satellite."

The scientists used data collected by radar from the Japanese satellite ALOS-2. Fielding says the radar can detect movement as small as half an inch.

Here's another map produced by NASA that shows the same information in a different way:

This map created by NASA shows how much the ground moved during a series of earthquakes in Southern California's Ridgecrest area.
/ NASA/JPL-Caltech
This map created by NASA shows how much the ground moved during a series of earthquakes in Southern California's Ridgecrest area.

In this one, the difference in color makes it easier to see that the earth's surface moved in different directions along the fault. "We can see clearly the two sides of the fault moved in opposite directions," he said.

The long line of green circles on the map running from the northwest to the southeast is the fault that ruptured during the larger earthquake on July 5. Fields says the fault rupture measures some 30 miles long. The line of green circles cutting into that fault almost at a right angle is the rupture from the smaller earthquake on July 4.

"The 6.4 did a fault that goes almost exactly perpendicular to the 7.1," he said.

The blue area west of the largest fault moved by as much as 2.7 feet northwest during the biggest quake, while the red area moved by as much as 2 feet southeast, according to NASA.

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Merrit Kennedy
Merrit Kennedy is a reporter for NPR's News Desk. She covers a broad range of issues, from the latest developments out of the Middle East to science research news.
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