5 January, 2006 News stories

While many people were still getting over their new year celebrations, a large earthquake in the Southern Ocean sent shock waves around the world. The quake occurred at 6.10am on 2 January, its epicentre lying more than 400km southeast of the South Sandwich Islands, a UK Dependency in the southernmost Atlantic Ocean. With a magnitude of 7.3, the quake was the largest in the world since the one that devastated parts of Pakistan and India on 8 October. In contrast, the recent earthquake in the Southern Ocean caused no casualties or damage due to the fact that its epicentre was more than 400km from the nearest island (Bristol Island, South Sandwich Islands) and 1,100km from the nearest settlement (Grytviken, South Georgia). The epicentre of the earthquake was located 10km below the seabed, near the eastern end of a 400km-long ‘transform’ fault called the South Sandwich Fracture Zone. The fault forms part of the boundary between the South American and Antarctic Plates, and links a mid-ocean ridge (the South American–Antarctic Ridge) to a deep ocean trench east of the South Sandwich Islands. The earthquake was the third largest in the South Atlantic sector of the Southern Ocean since a worldwide network of seismographs was first established about 40 years ago. The epicentre of one of the two previous larger earthquakes in the region was also located on the South Sandwich Fracture zone, less than 5km from the calculated epicentre of this quake.

Alison Dean, Base Commander of the King Edward Point Research Station, South Georgia, said the scientists there had not felt the earthquake and did not notice anything unusual. “We never felt a thing,” she said by telephone. “I raced to the Internet for information. If anything was to happen, it would be around this way as far as a tsunami goes.” However, despite its magnitude the earthquake did not generate a tsunami because the fault displacement was horizontal, with the South American Plate moving westwards with respect to the Antarctic Plate, however, officials reported that news of the event prompted thousands of residents along the coast of Sri Lanka, over 7,500 miles away, to flee inland.

The first seismic station to detect the earthquake was at Hope Point on South Georgia, about 1,100km from the epicentre, which is jointly maintained by the British Antarctic Survey and the Incorporated Research Institutions for Seismology Project International Deployment of Accelerometers (IRIS/IDA) based at the University of San Diego, California. Earthquakes in this region are of particular interest to scientists studying the Earth’s core. To study the core, seismologists need to examine seismograms recorded at seismic stations on the opposite side of the globe from the earthquakes that produced them. The South Sandwich Islands region happens to be on the opposite side of the globe from Japan, which has an exceptionally good network of seismic stations.

Due to the immediate area being virtually unpopulated there were no reports of injuries or damage from Monday’s earthquake, though some people reported shaking as far west as Santiago, Chile.

 

1. Map of the region showing the location of the earthquake epicentre (yellow square).

 

2. Seismic traces recorded at Hope Point, South Georgia, at the moment the earthquake struck.