October 5, 2009 2:06:17 pm
Earthquakes and volcanic eruption go hand-in-hand in Indonesian island Sumatra so it is wise to keep a close watch on the recurrance of quakes and following developments in the region,says a senior volcanologist. There are more than 200 volcano lines along the Sumatra fault running parallel to the subduction zone. During March 2007 earthquake,the Talang volcano showed increased volcanic activity throwing ash plumes,Dr D Chandrasekharam,a volcanologist at IIT here said.
The current series of seismic activities are lined over the active Sumatra fault close to three active volcanoes Marapi,Talang and Tandikat,he said. The entire subduction zone,extending from Java to north Andaman islands appears to be seismically very active as evident from the recurring earthquakes in the recent few weeks and it is better that the authorities in that region keep a close watch on the volcanic activities also to save lives,he said.
Considering the depth of focus of the series of earthquakes that occurred close to these volcanoes (104 km) strongly indicate melting of the deeper segment of the subducting Australian plate below these regions,the scientist said.
Krakatau between Jakarta and Sumatra and Toba towards the eastern part of Padang (the current loci of series of earthquakes) are the deadly volcanoes that erupted violently in the recent past.
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Perhaps it is wise to keep a watch on the activity of these volcanoes in the light of recurring earthquakes over Sumatra,he reiterated. The southern Sumatra region is active since December 2008 with the occurrence of 5.9 magnitude tremor followed by 7.4 magnitude quake on September 3 near Java.
These events were followed by two major earthquakes one on September 30 with magnitude of 7.6 and another on October 1 with magnitude of 6.6. The 7.6 event on September 30 was preceded by 4.7 tremor and succeeded by 5.5 magnitude tremor,he said. The most interesting thing about these earthquakes are that their origin (focus) is at different depths varying from 15 to 104 km. All these events occurred at the junction between Sunda Australian plates,with the Australian plate moving Northwest directing at a speed of 66 mm per year with respect to Sunda plate,thus giving rise to strike slip motion as well as thrust motion,he said.
Sumatra is traversed by 1900 km long northwest-southeast trending Sumatra fault running parallel to the Sumatra trench. These tectonic motions are to some extent related to the December 2004 event,although the Focus is located SE of the major earthquake that occurred in 2004. The Sumatra fault was the foci of nearly 14 earthquakes of magnitude greater than 6.6 since late 19th century,Chandrasekharam said.
The present location where 6.6 magnitude earthquake occurred on October 1,2009 was loci of two major earthquake one in 1909 with a magnitude of 7.7 and a second one in 1995 with a magnitude of 7.
Besides these events,the recent North Andaman earthquakes of magnitudes varying from 6.6 to 7.6 (August 11) clearly demonstrates that the entire region is seismically very active.
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