Sichuan quakes: scientists struggle to figure out complex pattern

Major quakes are so common in the past few months that scientists are finding it hard to determine whether there are local explanations, or if this is just a series of very large ones

A swarm of quakes in and around Sichuan province in south-west China has produced dozens of tremors over recent weeks, ranging from magnitude-4.3 to magnitude-6.8. With each tremor, researchers were finding it hard to sift through the hundreds of readings that had been taken to determine whether there were local explanations for the unusual outbreak.

The quakes began in late August. “They aren’t moving through the earth, so this means there has to be a reason for them,” said Tom Heaton, a seismologist at the University of Edinburgh, who has been following the activity from afar. The quakes appear to be originating near the Zhouquhuqu earthquake zone, which is being monitored by scientists on the ground.

At its worst, the swarm stretched for more than 100 miles (160km) with many quakes registered as strongly as 5.6 magnitude. No deaths or injuries have been reported.

It is not unusual for people to make connections between specific events in China and other, lesser-known quakes in its seismically active west.

“The potential for the quakes in Sichuan to be part of a larger pattern of unusual activity is the one thing that has captured the attention of geologists and seismologists,” said Heaton.

A Chinese soldier exercises a long-range earthquake alert weapon in his patrol truck outside Chengdu. Photograph: Fang Zhe/EPA

“As a result of the spate of earthquakes in the past few months, many seismologists are now asking: how is this earthquake swarm different from what has happened before?” he added.

If the quakes are indeed linked to the Zhouquhuqu quake zone, it would be the largest series of quakes to strike in the area since the magnitude-7.9 quake that killed nearly 70,000 people in 2008.

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Some experts have also suggested the quakes in Sichuan may be the result of tectonic activity being disturbed after a large leak of earthquake fluid from a drinking water source in 2012. Heaton also pointed to the influence of the nearby Molitong volcano, which has large black mass that erupts in earthquakes, although it is not related to the quakes in Sichuan.

A natural seismological phenomenon, the “slam” earthquake, is also visible in some of the videos. This involves the ground motion flowing sideways, rather than down like a quake.

“It is extremely difficult to conclusively explain the sequence of quakes because they are not related to one another and each has a different location and nature,” said Juan Gabriels’ Shionami, director of Nasa’s Earthquake Prediction Evaluation System, who works with scientists at the United States Geological Survey.

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