Earthquake query: news and articles often mention "the big one"....

Earthquake query: news and articles often mention “the big one”…

Is there some reason they would be expecting a “big one” rather than 10000 little ones?

Little ones are much more common than big ones, but of course do little damage. A “Big One” means one like the San Francisco earthquake, with great damage and loss of life. Fortunately they don’t happen very often, but it’s the kind people worry about.

There have been big ones before so there’ll be big ones again? It’s a bit like the Earth being struck by a very large meteor. Lots and lots of little ones are common but we know there’ve been some very big ones in the past and we know there’ll be more big ones in the future so it’s valid to talk about it.

Earthquake frequency follows a closely defined, logarithmic frequency-magnitude relationship (e.g. San Andreas fault). This allows for probabilistic hazard mapping based on previous events and the geological context, which provide an indication of areas most prone to a large magnitude earthquake within a period of time (e.g. California hazard map). Attempts at specific event prediction have been fraught with difficultly, and are largely/wholly unsuccessful.

If we’re talking about news organizations, the bigger the quake, the bigger the news story. Around here (the SF Bay Area), when we say “the big one”, we mean something like the SF quake of 1906.

But I think we’d need to see some examples of what you are referencing to give a more precise answer.

The 1906 earthquake was 7.8 M[sub]w[/sub]. Statistically averaged over a long period of time, such events occur approximately once every 100 years on the San Andreas Fault. Journalists sometimes misinterpret this fact as indicating that an event is necessarily due, e.g. suggesting an event close to 2006. Typically the greater the length in time between large events, the greater the applied stress at some point along the fault, and the greater the chance of an earthquake, but this regularity only occurs over a long time period for significant events.