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.
Why the M7.8 Scotia Sea Earthquake May Go Unnoticed
Despite its size, the Scotia Sea earthquake has attracted little media attention and is unlikely to do so. What makes earthquakes newsworthy is their human impact. This quake took place in a remote area (the closest inhabited land is almost 1500 km distant) which means that there is no immediate direct impact on human populations.
Scotia Sea Quake – Tsunami?
A secondary impact of major submarine earthquakes is, of course, tsunamis: but at the time of writing no agency has reported a tsunami, and we don’t expect any reports of a tsunami as the result of this quake due to the nature of the faulting. Geological phenomena generate tsunamis when they displace large volumes of seawater laterally, or in a side-to-side motion. Earthquakes are the primary cause of tsunamis, but other mechanisms such as landslides could have the same effect. In this case, because there was no vertical movement, the quake could generate no large-scale tsunami, and any local tsunami would have disappeared before reaching land.
USGS. M7.8 Scotia Sea. (2013). Accessed November 17, 2013.
USGS. The Great 1906 San Francisco Earthquake. (2012). Accessed November 17, 2013.
Yeats, R. Active Faults of the World. (2012). Cambridge University Press.