I felt both earthquakes this past week in Palm Springs which is about 170 miles from the epicenter in Ridgecrest. It compelled me to review the chapter from Nate Silver’s Signal and the Noise discussing our inability to forecast earthquakes despite a long history of seers and scientists trying. What do we know?
- While we are confident in the statistical nature of aftershocks, when a large earthquake hits we still don’t know if it is the main event or a foreshock.
- We do not understand geological processes that cause earthquakes enough to construct models which can predict earthquakes. Without such bottoms-up simulations, we are left to rely purely on statistics of past earthquakes to predict them.
- We are able to approximate long-term averages. Enter the Gutenberg-Richter law.
If you graph earthquakes on a log scale with the Y-axis as frequency and X-axis as magnitude we see a “stunning regularity”.
Something that obeys this distribution has a highly useful property: you can forecast the number of large-scale events from the number of small-scale ones, or vice versa. In the case of earthquakes, it turns out that for every increase of one point in magnitude, an earthquake becomes about ten times less frequent. So, for example, magnitude 6 earthquakes occur ten times more frequently than magnitude 7’s, and one hundred times more often than magnitude 8’s.
But now I must let you down. Even though we can approximate the frequency of earthquakes we can’t predict when and where they might occur.
The official position of the USGS is even more emphatic: earthquakes cannot be predicted. “Neither the USGS nor Caltech nor any other scientists have ever predicted a major earthquake,” the organization’s Web site asserts. “They do not know how, and they do not expect to know how any time in the foreseeable future.”
credit: Signal and the Noise