Solomon Islands Earthquakes: Foreshocks, Mainshocks and Aftershocks

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Foreshocks as Precursors of Major Tremors

A year's worth of aftershocks from the Tohoku-Oki earthquake of 2012. Image credit: Pekachu

A year’s worth of aftershocks from the Tohoku-Oki earthquake of 2012. Image credit: Pekachu

With a pattern of foreshocks and aftershocks, you might ask whether it’s possible to use foreshocks to predict a major earthquake. In his book The Million Death Quake, seismologist Roger Musson describes an example from China in 1975 when a major earthquake was successfully predicted on the basis of foreshocks – but he goes on to describe how, the following year, a larger, much more devastating tremor in the same region occurred without any precursor. And in Italy, seismologists who failed to treat a tremor as the precursor of a larger earthquake (which it proved to be) ended up in jail.

The problem is twofold. Firstly, as the 1976 example from China (cited above) demonstrates, not all earthquakes have foreshocks. Secondly, because a mainshock is defined as the largest earthquake in a sequence we can’t know how big an earthquake to expect. So an M5.0 may be a foreshock to an M7.0 – or it may be the mainshock itself. We don’t know until we have the benefit of hindsight.

Patterns of Earthquakes

Although there are laws that can be applied to aftershocks in particular, earthquakes and their associated shocks (fore and after) remain difficult to quantify. And as long as it remains the case that earthquakes vary from location to location, along with the fact that we don’t fully understand the details of where and when they occur, the use of foreshocks as even a short-term tool for predicting major earthquakes remains unproven. So, will the 7.0 and greater quakes in the Solomon Islands turn out to be foreshocks or aftershocks? Only time will tell.

Sources

USGS. M7.0 Santa Cruz Islands. (2013). Accessed February 8, 2013.

USGS. Earthquake glossary. (2013). Accessed February 8, 2013.

Liu, M and Stein, S. Earthquake Aftershocks. (2011). Encyclopedia of Solid Earth Geophysics edited by Gupta, H. Springer. Accessed February 8, 2013.

Musson, R. The Million Death Quake. (2012). Macmillan.

Yeats, R. Active Faults of the World. (2012). Cambridge University Press.

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