Rocking In Socal

A few days ago I turned 77. It was not exactly an earth shaking event, but several days thereafter I was rocking and rolling along with millions of other southern Californians. It was an earthquake. It was 6.4 in magnitude and what seismologists later called a foreshock. It was a surprise only in the sense that no one can predict when or precisely where such a temblor will strike. Historically such events are frequent in a region as seismically active as southern California is. Yet here we had people who said they grew up here exclaiming that they had never experienced anything like this quake. How can that be? It is not like the television networks have people stationed in desert towns such as Ridgecrest, which is where the quake took place. So the people who told reporters they had never experienced anything like this earthquake were at least one hundred miles away from the epicenter. As someone who was also one hundred miles from Ridgecrest when the shaking started I can tell you that the intensity was great enough to get your attention by shaking your dwelling and rattling your windows, but it was not strong enough to knock things off your selves. Not strong enough to knock things off the shelves seems rather tame, doesn't it? So why did those Californians say they have never experienced an earthquake that was this strong?

As I was pondering that question Cal Tech seismologist Lucy Jones appeared on the news coverage I was watching. She said this was the largest earthquake we have had in over twenty years. But, she added, it is not surprising that we just had an earthquake of that magnitude. What is surprising is that we went so long without one. She explained that earthquakes with a magnitude of 6 or above occur roughly every ten years and that it is usually twenty years between earthquakes with a magnitude of or greater than 7. So a Californian approaching my age has been through a hell of a lot of earthquakes; whereas a Californian younger than 35 probably would not remember any significant temblor that struck prior to this one. All right, but that is not where this story ends; it is not a wrap. We were soon rocking again because the quake I have been writing about was the foreshock and the mainshock that followed it had a magnitude of 7.1. Where I live the intensity of this mainshock seemed to be as great as the intensity of the 1992 Landers earthquake, and that is not just a window rattler even a hundred miles from the epicenter.

Welcome to the club my young friends! The odds of a foreshock being followed by such a large mainshock is only around 5%, but the odds greatly favor you experiencing another earthquake of 7 or greater during your lifetime!