The Solomon Islands mainshock was probably caused by thrust faulting associated with the subduction of the Australian plate beneath the Pacific: the scale and submarine location of the earthquake generated a tsunami which killed at least five people. At the time of writing, the area continues to be shaken by periodic aftershocks which decline in size and frequency with time after the main event: to date over 120 of ≥M5.0 have been recorded.
M5.3 in North Korea: Natural or Man-Made?
Although not one of the week’s major earthquakes, the M5.3 in North Korea is worth noting for very different reasons. Described by the USGS as a “seismic event” rather than an earthquake and occurring in what is not normally a seismically active zone, this tremor has potentially more sinister origins.
Coming on the day that news reports indicate that North Korean authorities had tested an underground nuclear device, the 1km depth shock is almost certainly anthropogenic (man-made) in origin. Its location (between the sites of previous nuclear tests in October 2006 and May 2009 which triggered seismic events of M4.3 and M4.7 respectively) further supports the nuclear origin of this tremor.
Largest Earthquake in the USA: M3.7 in Utah
Against the background of significant earthquake activity elsewhere, the United States once again had a calm week. The largest tremor outside Alaska was an M3.7 which occurred in southern Utah. In the so-called “Basin and Range” province to the east of the Rockies and the west of the Great Plains, the dominant force is mainly extensional, causing normal faulting (downward movement) on a series of parallel and broadly north-south trending faults.
The Strange Ways of Man and Nature
The week’s map of earth movements demonstrates that it is unwise either to assume that earthquakes follow a pattern or to assume that any recorded seismic event is naturally-induced. With both major earthquake activity and a human-induced seismic shock, the pattern looks very different to that of previous weeks.
BBC News online. North Korea carries out biggest nuclear test. (2013). Accessed February 12, 2013.
USGS. Earthquakes in the Intermountain Seismic Belt (Southern Utah). (2013). Accessed February 12, 2013.
USGS. North Korea Seismic Event of 12 February 2013. (2013). Accessed February 12, 2013.
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