March 6, 2007 Sumatra Earthquake

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Posting Date: March 6, 2007, 11:30:00 AM

Two strong earthquakes struck the Indonesian island of Sumatra on Tuesday, March 6. The mainshock, which occurred at 10:49 a.m. local time and which the US Geological Survey estimated at a magnitude of 6.4, was followed two hours later by an aftershock of M6.0. The epicenter was located about 49 km (30 miles) north northeast of Padang, 930 km (580 miles) northwest of Jakarta and about 420 km (260 miles) from Singapore. There was no immediate tsunami warning, as the quake occurred inland rather than under the sea. The region around Padang is situated south of the province of Aceh, where some 130,000 people died in the earthquake and tsunami of 2004. Many buildings in the town of Padang near the epicenter were destroyed, and preliminary reports indicate that at least 80 people have been killed. The tremors were felt as far away as Malaysia and Singapore, where some buildings were evacuated. Government officials have begun search and rescue efforts, but these have been hampered due to damage to a main road connecting Batu Sangkar and Padang. Electrical facilities have been knocked out and many other roads in the area that have become impassable. Today’s event occurred along the central segment of great Sumatra fault. The fault runs from the Sunda Strait between the islands of Java and Sumatra to the Andman Sea, for a total length of about 1600 km. This is one of the largest intra-plate strike slip faults on Earth. With an average slip rate of about 2.5 cm/yr, it absorbs part of the 6-6.5 cm/yr relative plate motion between the Indo-Australia and Sunda plates. The Sumatra fault runs parallel to the Sumatra subduction zone, which has generated some of the largest mega-thrust earthquakes in the world, including the M 9.3 mega-earthquake in December 2004 and the M9.0 earthquake in 1833. The formation of the Sumatra fault is due to the oblique convergence between the Indo-Australia plate and Sunda plate. More than 20 disastrous earthquakes have occurred along various segments of this fault since the end of the 19th century. Today’s earthquake and its M6.0 aftershock appear to have ruptured the same segment that ruptured during the 1926 M6.7 earthquake. In 1934 two events of magnitude 7.1 and 7.3 ruptured segments south of the current one. The AIR earthquake team has assembled the available information in the aftermath of this event and has run simulations based on estimates of epicentral location and magnitude using the AIR earthquake model for Indonesia. Results indicate that because take-up rates in the affected region are low, insured losses will be minimal.

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Posting Date: March 6, 2007, 11:30:00 AM