Earthquakes: ‘Foreshock,’ ‘mainshock,’ ‘aftershock,’ ‘pre-shock’ – what’s the difference?

CALTECH – Foreshock! Who knew?
For some Southern Californians, earthquakes have been all about, well, the earthquake – the main event, the big one (little b and little o). But Caltech scientists in the days since the July 4th 6.4 earthquake in Kern County and the 7.1 magnitude just a day later on a nearby second fault have a new lesson for us — or at least a reintroduction, of sorts, to the terms pre-shocks, foreshocks and mainshocks, and yes, the ubiquitous aftershocks –