Australia: The Land Where Time Began

A biography of the Australian continent 

Most Large Interplate Earthquakes Have a Long Precursory Phase

According to the authors¹ many earthquakes are preceded by foreshocks (Jones & Molnar, 1976; Jones & Molnar, 1979). The reason they occur before some earthquakes and not others, and the mechanisms generating the foreshocks, is unknown (3,8). In this study the authors¹ used seismic catalogues from the best instrumented areas of the North Pacific and analysed the foreshock sequences that preceded all earthquakes that occurred 1999-2011, with a magnitude greater than 6.5 and shallower than 50 km. They used a dataset comprising 31 interplate, occurring at plate boundaries, earthquakes and 31 intraplate, earthquakes occurring within the same plate. The authors¹ found a much strong correlation between foreshock sequences and interplate quakes than between  foreshock sequences and intraplate quakes. In the North Pacific most large interplate earthquakes were preceded by accelerating seismic activity over the months to days leading up to the main shock, though foreshocks are much less common before intraplate earthquakes. The authors¹ suggest that the interface between plate boundaries begins slipping slowly before the rupture that results in a large earthquake. They also suggest that in the case of interplate earthquakes the precursory phase, that is relatively long, could help mitigate risk associated with interplate earthquakes.

Sources & Further reading

1. Bouchon, Michel, Virginie Durand, David Marsan, Hayrullah Karabulut, and Jean Schmittbuhl. "The Long Precursory Phase of Most Large Interplate Earthquakes." Nature Geosci 6, no. 4 (04//print 2013): 299-302.