Most earthquakes last seconds to minutes, but others will rumble along slowly for days, weeks or even months, at low frequencies that may not be felt at the surface. Now, researchers in Singapore have discovered the slowest earthquake ever found, which lasted 32 years.
Earthquakes are caused by stress between two tectonic plates pushing against each other, which eventually builds to the point where the rocks can’t handle it and shift. Most of the time that shift is sudden, producing vibrations that can be felt at the surface and potentially cause destruction. But other times, the plates will slide past each other more slowly, producing vibrations that may only be detectable by extremely sensitive equipment.
These slow slip events (SSEs) typically last a few weeks, although some have been recorded to go for as long as three years. But that’s nothing compared to the marathon earthquake that researchers at Nanyang Technological University have now discovered.
The team was investigating some unusual ancient coral structures known as “microatolls” off the coast of Sumatra, Indonesia. These structures grow slowly, providing a good record of changes in sea level and land elevation in the process.
The team found signs of a normal baseline between 1738 and 1829, when the microatolls were sinking at a steady rate of 1 to 2 mm per year. But around 1829, the rate suddenly increased, sinking at up to 10 mm per year – a gear shift that has been associated with tectonics in previous studies. The faster sinking continued until about 1861, indicating a record-breaking 32-year slow slip earthquake.
Unfortunately, the drawn-out rumbling ended with the 1861 Sumatra earthquake, a devastating 8.5-magnitude event that claimed the lives of thousands of people. The researchers say that better monitoring of these long-lasting SSEs could one day provide an early warning system for these larger quakes.
The research was published in the journal Nature Geoscience.
Source: Nanyang Technological University