Sunday, November 17, 2013

Major Earthquake of M7.8 Strikes in the Scotia Sea, South Atlantic

November 17, 2013 by

One of the largest earthquakes of 2013 to date struck on 17 November in the south of the Atlantic Ocean. At magnitude 7.8 (M7.8) the Scotia Sea tremor is approximately the same size as the great San Francisco earthquake of 1906 (which had an estimated magnitude of around M7.9) which the United States Geological Survey describes as ‘one of the most significant earthquakes of all time.’ Was today’s Scotia Sea quake as significant?

M7.8 Scotia Sea Earthquake: Location and Tectonic Setting

While experts intensively study some of the planet’s earthquake belts, and, in consequence, understand them reasonably well, they don’t study or understand the tectonics of other areas. The Scotia plate, a microplate squeezed between the South American and Antarctic plates just off the Antarctic’s Palmer Peninsula, falls clearly into the latter category and remains largely unstudied, except for the active subduction zone to the east of the South Sandwich Islands.

The southern boundary of the fault is a conservative margin – that is, a margin at which the tectonic plates slide past one another without creating or destroying ocean crust. Data published in the USGS earthquake report suggest that the movement is relatively slow, at a rate of approximately 6mm per year. The USGS reports on the earthquake also indicate that the tremor took place to the south of this boundary as a result of lateral faulting.
The M7.8 earthquake is just the largest in an ongoing series of tremors to have struck along several hundred kilometre long section of the ridge over a period of a few days. Since 13 November, the USGS real time earthquake map records 21 earthquakes of at least M4.5 in the area – over half of these quakes have been ≥M5.0. The USGS also recorded a tremor of M6.8 along the same section of the plate boundary yesterday, on 16 November.

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