longest known earthquake, lasted 32 years

The devastating earthquake that struck the Indonesian island of Sumatra in 1861 was for a long time the sudden rupture of the previous sleeping fault. But new research suggests that the tectonic plates beneath the island were pounding slowly and quietly against each other 32 years before the catastrophic event occurred.

This decades-long silent earthquake – also known as a “slow slip event” – is the longest earthquake chain ever discovered. It was too deep and steady to notice during his journey. However, it could have caused a massive seismic storm of at least a magnitude of 8.5 in 1861, which in turn triggered a tsunami that killed thousands of people. This is acceptable From a study in “Nature Geoscience” Shows. The results can help better monitor hazardous earthquakes.

Like earthquakes that can be felt on the earth’s surface, slow slip earthquakes occur when two parts of the earth’s crust face each other. Some faults are now monitored for slow slip using seismic instruments or GPS technology, but tracking such events over long distances is still very difficult.

Most of the moves the team learned in the past took hours, days, or weeks, some even years. So far there is evidence of a slow decline over decades. “This makes the subduction zone more diverse than we thought,” said Kevin Furlong, a geologist at Pennsylvania State University who was not involved in the new research.

Dry coral reefs show the movement of the earth

Corals cannot grow when exposed to air. So when local sea levels change due to tectonics, these changes become visible in coral growth patterns, said Rishav Malik, a doctoral student at Nanyang Technological University in Singapore and lead author of the new study. A similar case occurred on a coral reef near the Indonesian island of Simeuluë off the coast of Sumatra. They show a history of ups and downs from 1738 to 1861.

The pattern shows how Simeuluë has been declining at a steady rate of 1 to 2 millimeters per year for 90 years. Then around 1829, the fault suddenly began to sink five to seven times faster — even an inch in a few years, Malik said, suggesting that the fault began to move in slow earthquakes. “This is a very sharp change,” he said. The “fast” movement continued until the Great Earthquake of 1861.

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