In 1861, the slow quake, which was the longest ever recorded, ended in horror. Experts are frantically searching for modern-day equivalents of this earthquake that lasted for 32 years!

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8.5 Mega-Earthquake

In February 1861, a magnitude 8.5 mega-earthquake hit off the Indonesian island of Sumatra, causing the ground to tremble and releasing a wall of water that smashed on adjacent coasts, killing thousands of people.

Long assumed to be a sudden rupture of a previously dormant fault, a severe earthquake struck the Indonesian island of Sumatra in 1861. However, a recent study indicates that the tectonic plates under the island had been rumbling against one other for 32 years prior to the catastrophic occurrence.

32 Year Earthquake

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Now it appears that the unfortunate tragedy was not an isolated occurrence: It really marked the conclusion of the world's longest earthquake, which had been rumbling beneath the surface for 32 years. These kinds of quakes, known as slow-slip events, have been seen unfold over days, months, or even years. However, scientists reveal in Nature Geoscience that the newly recorded event lasted more than twice as long as the previous record-holder.

Related Article: What Exactly Causes Mysterious Deep Earth Earthquakes?

Slow-Slip Event

This quiet, decades-long earthquake, termed a "slow-slip event," was the longest of its kind ever observed. Although it was too faint and slow to be recognized throughout its course, a recent analysis suggests it may have produced the huge 1861 temblor, which generated a tsunami that killed thousands of people. The new research might aid today's scientists in better detecting hazardous earthquakes.

The finding of a slow-moving earthquake will aid scientists in understanding the amazing range of ways our restless planet moves-as well as the catastrophic potential for these quiet occurrences to trigger far more powerful quakes.

Slow-motion earthquakes, like their high-speed relatives, unleash energy stored in tectonic plate changes. On the other hand, slow quakes release strain slowly over time rather than in a ground-shaking explosion and hence are not risks on their own. Still, small subsurface adjustments might put a strain on neighboring zones along a fault, thereby increasing the danger of a larger temblor nearby.

Slow Quakes

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Slow earthquakes have only been detected in the Pacific Northwest of North America and the Nankai area off the coast of Japan since the late 1990s. Because of their slow energy release, they produce little surface movements, and they weren't detected until GPS technology had advanced sufficiently to track such minute changes.

The more areas geologists have investigated since then, the more slow earthquakes they've discovered, from New Zealand's beaches to Costa Rica and even Alaska. "We find aseismic slip everywhere," says Lucile Bruhat, a geophysicist at Paris' Ecole Normale Supérieure (ENS).

Sensitive Information

Researchers may miscalculate where the stress is on a fault-and how large a quake that fault may possibly produce-if slow-slip motion is overlooked. "We can better characterize the magnitude of an earthquake that can occur once we properly characterize the locked region," Furlong adds.

Also Read: Experts Worried as 61 Earthquakes Recorded 24 Hours After Volcanic Eruption in Congo

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