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A powerful earthquake, measuring 8.7 on the Richter scale, hit the Indonesian island of Nias close to midnight local time.
Earthquakes had actually been predicted almost two weeks ago and scientists at the Honolulu-based Pacific Disaster Center were gathering information even before the Nias quake hit.
Channel NewsAsia spoke to Allen Clark, the Director of the Pacific Disaster Center in Honolulu who shared his expert opinion on the magnitude of the quake as compared to the December 26 quake that triggered tsunamis as far away as Africa.
Carolyn Bell from the US Geological Survey helped shed some light on why this particular earthquake did not trigger a tsunami the way the December 26 one did.
| Watch Allen Clark's interview >>> |
Allen Clark first highlighted the main difference between the two earthquakes; "This earthquake occurred about 200 miles (321 kilometres) south of the epicenter of the previous earthquake.
"And we know also that this earthquake was somewhat deeper, that is, focused deeper in the earth's crust than the previous earthquake. It was of a lesser (sic) magnitude. This one was reputed to be 8.7. The previous one was a 9.
"And the interesting part about that, even though the numbers seem very small together, the difference between 8.7 and 9.0, is about twice as much energy in the December earthquake as in this one."
Allen also shared his view on why this quake did not trigger a tsunami; "Obviously we are not exactly sure. But perhaps two things, one, it seems to be somewhat deeper and therefore it did not have as much lift on the ocean floor to cause a tsunami. The other thing is, it seems to have directed a lot of its force to the south, along the fault, and that also reduced the impact."
Questions are also now being raised about what actually triggers a tsunami.
To shed some light on this, we spoke to Carolyn Bell from the US Geological Survey; "Well unfortunately the difference is not just the magnitude of an earthquake, what creates a tsunami is of course an earthquake that is offshore like this one was, and the one in December.
But it is also determined by the geologic structures of where the plate boundary broke.
This happened on a subduction zone between the Australian plate and the Sunda plate which is about 110 miles south of where the December 26 event occurred.
That earthquake broke hundreds of miles of the plate boundary. This one was not quite as large.
Hopefully in the future, seismologists will advance the technology where we can determine which earthquakes are going to created a tsunami or not."
Carolyn also clarified that the earthquake off the Nias Island cannot be classified as an aftershock of the December quake; "This wasn't really and aftershock. We're calling it a triggered quake. It happened 110 miles south east of the December event.
"It is on the part of the plate that did not break in December. So really, it was triggered by the 9.2 earthquake but it was not an aftershock. This one itself has several aftershocks of its own." - CNA
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