New Sumatra Quake Takes Seismologists by Surprise 1 October 2009
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New Sumatra quake takes seismologists by surprise 1 October 2009 Scientists had long feared a major earthquake would occur on the part of the trench near Padang. They considered it vulnerable to a so-called quake "cascade" that began with the notorious 9.1 quake of December 26, 2004 that unleashed the Indian Ocean tsunami. "Cascade" events can occur in long, badly-stressed faults. The stress of a large earthquake causes the next section of a fault to weaken and then rupture, in a domino-like effect. An Indonesian woman cycles past a destroyed home after a 7.6-magnitude earthquake in Padang, Sumatra. A But Sandy Steacy, a professor at the seismologist told AFP that the huge earthquake that hit Environmental Sciences Research Institute at the Sumatra occurred at a deep, unexpected location, University of Ulster in Northern Ireland, said illustrating the dangerously complex geological mosaic in Wednesday's quake was not part of this chain this area. reaction. "The event yesterday was kind of strange, it wasn't what we would have expected," she said. The huge earthquake that hit Sumatra occurred at a deep, unexpected location, illustrating the "It appears if the most recent earthquake didn't dangerously complex geological mosaic in this occur on the interface of the subduction zone. It area, a seismologist told AFP on Thursday. occurred within the plate that is being subducted, the part that's going down beneath the interface." The 7.6 magnitude quake struck on Wednesday 80 kilometers (50 miles) beneath the sea, 45 Steacy said that seismologists were working hard kilometers northwest of the city of Padang, to calculate what had happened, but her bet was according to US Geological Survey (USGS) data. that the quake had occurred deep below the seabed on the tongue of the Australian plate, The fault line where this happened runs parallel to contorting as it was forced under the Sunda plate. Sumatra and is called the Sunda Trench. "Clearly you are going to get faults in that kind of It marks a "subduction" zone, where one plate of situation, because you're taking a slab, you're Earth's crust rides on top of the other. bending it, you're pushing it down, so you're going to get material breakage there," she said. To the west is the Australia plate, which is moving northeast at about five centimetres (two inches) a "I think once calculations are done, they will show year). that the stress had increased along that structure," she said. The Australia plate is being forced under, or subducted, by the Sunda plate, which lies to the "I suspect that structure, nobody even knew it was east. there. We don't have any way of mapping the faults 1 / 2 in the subducting slab because it's so deep. It's only by having earthquakes on it that gives you an indication." French expert Robin Lacassin, of the Institute of the Physics of the Globe in Paris, agreed that an "as- yet unknown mechanism" had unleashed Wednesday's quake. "It happened at some depth, around 80 kilometres. It appears to have occurred in the subducted plate, beneath the face where the two plates meet," he said. (c) 2009 AFP APA citation: New Sumatra quake takes seismologists by surprise (2009, October 1) retrieved 28 September 2021 from https://phys.org/news/2009-10-sumatra-quake-seismologists.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. 2 / 2 Powered by TCPDF (www.tcpdf.org).