When you least expect it, disaster strikes like a lightning with no place to run and no place to hide.
Palu, Indonesia was caught off guard and its population of 300,000 when the city was struck with a 7.5-magnitude earthquake last September 2018. The sudden disaster took over 200,000 peoples’ lives due to the Palu earthquake and the soil liquefaction, towering tidal waves, and landslides as the aftermath.
However, the catastrophe should not have emanated from a 7.5-magnitude earthquake, most especially not in this region. A couple of researches have been published in the Nature Geosciences on Feb. 4 that points out why and what it signifies for future forecasts.
IRD and Université Côte d”Azur seismologist, Jean-Paul Ampuero coordinated with an international team to analyze the 7.5 magnitude Palu earthquake that shook the Sulawesi Island in Indonesia on September 28, 2018. The team also includes University of California Los Angeles and California Institute of Technology.
“In classical earthquake models, faults live in idealized intact rocks. But real faults are wrapped in a layer of rocks that have been fractured and softened by previous earthquakes. Steady rupture at speeds that are unexpected on intact rocks can actually happen on damaged rocks, simply because they have slower seismic wave speeds,” study author Ampuero said.
The occurrence of an earthquake is due to the developed stress in the Earth’s crust that hits the breaking point. It then made the rocks on either side of a tectonic fault to unexpectedly move in opposite directions. Shock waves, also known as shear waves usually diffuse through the crust at around 3.5 kilometers or 2.2 miles a second. It shakes the ground and causes reverberations often linked to earthquakes.
Based on the high-resolution evaluation of seismological data, the Palu earthquake came between at a rare speed of 4.1 kilometers or 2,5 miles a second. This event resulted in a “supershear” earthquake or a geological seismic blast. It advanced to the 80-kilometer-long fault line at a quicker rate compared to the shock waves it produced.
According to Ampuero, it is the first time they have steadily monitored the speed. The earthquake raced in the “prohibited” speed range and can be noted as a supershear event, given the fact that it’s not as quick as the past occurrences.
Although the earthquake might have persisted for only 35 seconds, it left a ground offset of over 5 meters throughout the district. Typically, this kind of earthquake is seldom observed and frequently occurs on “superhighways” which are faults that straight and don’t have any barriers to interrupt speeding earthquakes. Researchers discovered that the fault itself is not straight and has two bends.
The Palu earthquake could provide the primary definite test of such latest models if looked into by researches of the fault’s structure and its area of damaged rocks. Since the aftermath of an earthquake is based strongly on its speed, similar studies on other faults worldwide can better expect an earthquake.
In the upcoming decades, additional researches might likewise identify if the speed of the Palu earthquake intensified its surging effects by stimulating coastal and submarine landslides that could cause tsunamis.
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