Powerful Earthquake Off Indonesian Coast Triggers Tsunami Warning

The epicenter of the 7.9M earthquake. USGS

At 12:49 p.m. GMT on Wednesday, March 2, a magnitude 7.8 to 7.9 earthquake struck off the western coast of the Indonesian island of Sumatra, according to the U.S. Geological Survey (USGS). As is standard practice when large tremors occur within the oceans, a tsunami warning was issued.

Fortunately, as of 4 p.m. GMT, there appears to be no signs of a tsunami. In addition, there are no reports of major structural damage on the mainland or any nearby islands, nor any injuries. The tsunami warning has also been officially cancelled.

The epicenter was 808 kilometers (502 miles) southwest of Padang, a city that rapidly felt the tremors. According to the Guardian, people quickly ran outside of their houses and reached higher ground. The rupture occurred at a depth of 24 kilometers (14.9 miles), too deep and too distant from any major cities or populations to cause any serious damage.

Indonesia straddles the Pacific Ring of Fire, a complex arrangement of colliding and grinding tectonic plates. The descent (subduction) of the Indo-Australian plate beneath the Sunda plate is responsible not only for the spectacular volcanoes found in the region – including Krakatau – but also a wide range of earthquakes.

Parts of the subducting plate occasionally encounter some resistance, and this can build up immense amounts of stress. The release of this stress causes earthquakes, and although many are harmless, some can be truly devastating. It was along this plate boundary that the 2004 Indian Ocean earthquake occurred; registered as a magnitude 9.1 event, it released the energy of 23,000 Hiroshima-type atomic bombs in mere moments. The resulting gargantuan tsunami killed 200,000 people.

In this case, the tremor was caused by two parts of the Indo-Australian plate grating alongside each other. A tsunami can only occur if a large amount of water is displaced, and this type of plate movement – a strike-slip fault – is unlikely to cause this. This time around, the people of Indonesia, and the wider region, got lucky.

The magnitude of Wednesday’s earthquake is almost identical to that of the one that struck Nepal last April. Unfortunately, this extremely shallow quake occurred on land, close to Kathmandu, and 9,000 people were killed.

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