December 2016 Northern Sumatra Earthquake

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Posting Date: December 7, 2016, 3:52:00 AM

An M6.5 earthquake jolted the northernmost area of Sumatra, Indonesia, at 22:03 UTC on December 6 (5:03 a.m. local time on December 7). The epicenter was 19 kilometers (km) southeast of Sigli and 92.3 km east-southeast of Banda Aceh. The quake has strongly impacted Pidie Jaya district, with a population of about 150,000, in Aceh province. Shaking was felt in Banda Aceh as well as several provinces in Thailand, according to Thailand’s National Disaster Warning Center. The epicenter was originally placed undersea, and a tsunami was feared, but this quake has not generated one. There have been at least 12 aftershocks reported.

Hundreds of buildings have been damaged or destroyed in the province, mainly in Pidie Jaya. The quake had a major impact on Mereundu, the seat of Pidie Jaya’s regency government. In the affected areas, representative residential and religious buildings are unreinforced masonry. Because of the lack of seismic considerations, many of these buildings collapse during earthquakes, leading to significant casualties. The latest seismic design code in Indonesia was released in 2012; however, the code is not strictly enforced, so many buildings are not up to code.

Nearly 100 fatalities in Aceh province have been reported, as well as more than 600 injuries. These numbers will most likely rise, as rescue operations are in the early stages. President Joko Widodo has ordered all of Indonesia’s government agencies to participate in rescue efforts in Aceh province, which has a level of autonomy in Indonesia. The Red Cross has also sent emergency response teams. The chief of Pidie Jaya district has called for more equipment to help remove debris, as well as emergency supplies. Hospitals in the district have been overwhelmed, and many of the injured have been moved to Sigli.

Seismotectonics

Indonesia sits along the Pacific Ring of Fire, the seismically active fault line known for producing some of the strongest earthquakes in history. The devastating December 26, 2004, M9.1 to M9.3 Sumatra-Andaman earthquake occurred in the Sumatra subduction zone in the Sunda Trench, which roughly parallels the western side of the Indonesian island of Sumatra.

Yesterday’s earthquake near the northern segment of the Sumatra Fault (also known as the Great Sumatran Fault), which runs the length of the island of Sumatra for over 1,000 km, is one of the largest crustal faults on earth. Its principal motion is right-lateral strike-slip. This fault has been the site of many large historical earthquakes and is a significant contributor to seismicity in Sumatra.

Numerous historic earthquakes have occurred along the Sumatra Fault Zone with many having magnitudes larger than 7.0. The largest historic earthquake has a magnitude of about 7.7, which occurred in 1892. At least six earthquakes with magnitudes between 7.2 and 7.6 have occurred since 1900. However, most of the large historic earthquakes occurred in the central and southern segments of the Sumatra fault. No earthquakes larger than M7.0 have ruptured the northern segment. The epicenter of yesterday’s earthquake is about 25 km east of the main Sumatra fault, which may indicate that this earthquake may not have directly ruptured the Great Sumatra Fault.

The Sumatra subduction zone is the most active fault system in Indonesia. The In the 2004 M9.1 to M9.3 earthquake ruptured the northern part of the subduction zone fault as well as the Andaman Sea subduction zone. The resulting displacement triggered a tsunami of unprecedented scale, which quickly spread throughout the Indian Ocean. Wave heights of up to 30 meters were observed where the tsunami traveled inland in Aceh province.

Insured losses from today’s M6.5 Northern Sumatra earthquake are not expected to be significant.

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Posting Date: December 7, 2016, 3:52:00 AM