M 7.7 - Scotia Sea

Tectonic Summary

The November 17, 2013, M 7.7 earthquake in the Scotia Sea, to the northwest of the South Orkney Islands, occurred as the result of either left-lateral strike-slip faulting on an east-west oriented plane, or right-lateral faulting on a north-south-oriented plane. The location of the event adjacent to the east-west-oriented plate boundary between the Antarctica and Scotia plates implies that the left-lateral faulting scenario is most likely. Finite-fault modeling of globally recorded seismic data is also more consistent with slip on the east-striking (left-lateral) fault. At the location of this earthquake, the Antarctica plate moves eastward with respect to to the Scotia plate at a velocity of about 6 mm/yr.

The November 17th earthquake is the latest in a series of moderate to large earthquakes to strike the same region over the previous several days. The sequence began with a M 6.1 event on November 13 approximately 50 km to the west of the November 17th quake. On November 15, a M 6.8 earthquake struck very close to the preceding M 6.1 event. Since then, nine aftershocks were recorded in the area, ranging from M 4.7 to M 5.4, near the previous earthquakes and in the same approximate location as the November 17th event.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Strike-slip events of the size of the November 17, 2013, earthquake are typically about 160x20 km (length x width); modeling of this earthquake implies dimensions of about 280x40 km, predominantly surrounding and southeast of the hypocenter.

Though the region surrounding the Scotia Sea frequently experiences earthquakes, the majority occur around the subduction zone adjacent to the South Sandwich Islands, to the east of the November 17th earthquake. Only two events of M 6+ have occurred within 250 km of this earthquake over the past 40 years—a M 6.0 earthquake 230 km to the west in September 1979 and a M 7.6 earthquake 160 km to the east in August 2003. These two events involved normal and oblique normal faulting, respectively, associated with the same plate boundary. Neither is known to have caused damage or fatalities.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)