This volcano stopped an earthquake in its tracks, scientists say

Before they break a volcano’s heart, earthquakes must stop in the name of lava. That’s the conclusion of a new study, which reports that Japan’s 2016 Kumamoto earthquake may have been stopped in its tracks by the magma chamber underneath the active volcano Mount Aso. The study offers insight into the interplay between earthquakes and volcanoes—and it may also help explain Mount Aso’s explosive eruption this month.

As the products of slowly moving tectonic plates, large earthquakes and active volcanoes are closely related phenomena that often occur near each other. Large earthquakes can trigger volcanic eruptions—even at considerable distances—and the presence of underground bodies of magma can affect the patterns and segmentation of geological faults in volcanic regions. Despite these links, opportunities to study earthquake-volcano interactions are comparatively rare, and a lack of geological observations means that little has been known about how volcanoes might affect an earthquake rupture.

This is what made the earthquakes that hit Japan’s Kyushu Island earlier this year rather special. The shocks, which peaked with a magnitude-7.1 event on 16 April that caused widespread damage, struck only 30 kilometers southwest of Mount Aso, one of the world’s largest active volcanoes. The mountain features a caldera—a cauldronlike depression caused by a volcano collapsing into itself—about 22 kilometers in diameter.

Seizing this rare opportunity, geoscientist Aiming Lin of Kyoto University in Japan and colleagues raced to the epicenter the day after the main shock to investigate the quake’s fault ruptures and the impact on the caldera. The researchers combined satellite images from Google Earth with on-the-ground observations of broken roads and river channels to find out how much the earth had shifted near fault lines, a measurement known as displacement. They also used seismic imaging to study the structure of the crust below the ground.

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The team found that the earthquake created a 40-kilometer-long swath of surface ruptures along the pre-existing Hinagu-Futagawa fault zone, with horizontal displacements of as much as 2.45 meters and vertical shifts of up to 0.9 meters. They also found a new set of faults that cut across the Aso caldera from the southwest toward the northeast. Near the northeastern edge of the caldera, however, the surface rupturing changed. There, the ruptures were dominated by vertical movements before abruptly stopping.

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