Whenever I hear of a major earthquake, I always wonder when our turn will come. I've been asking myself that question way too frequently recently. My family and I live in the San Francisco Bay Area, prime earthquake country (or so I thought until I looked at Japan...). I started playing with NOAA's earthquake data after the New Zealand earthquake. After the recent Japan quake, I thought I'd publish a few graphics.
Disclaimer: I'm no geologist, statistician, or expert on earthquakes. I don't even play one on TV. I don't think anyone can predict earthquakes with any certainty (though there is some interesting research) and I certainly won't try.
The Ring of Fire is the name given to the chain of mountains, volcanoes, and faults that ring the Pacific Ocean. Of the world's 16 largest earthquakes since 1900, 15 occurred in the Ring of Fire.
Here's an interesting graphic showing the earthquakes above 6.0 magnitude that have hit the Ring of Fire region since 1900. Earthquakes of magnitudes between 6 and 7 are in green, between 7 and 8 in blue, and 8 or higher in red.
Notice anything? Well, as a Californian, the first thing that struck me was: "we're getting off lightly!".
This movie gives you a different way to see the earthquakes. Same legend as before: magnitude 6+ green, 7+ blue, 8+ red. The video isn't the most exciting one you'll ever see. It helps to pick a point of interest on the map and imagine some elevator music in the background :-)
Let's dig deeper...
Japan, California, New Zealand, and Chile
Looking at the graph above it's clear California gets fewer earthquakes than many other parts of the Ring.
When I compare a circular area 2,000km around the center of Japan with the same size area around California (centered on San Francisco), Japan has been hit four times as often by large (i.e. 6+ magnitude) earthquakes than California (~200 vs. ~50).
Here are Japan's large earthquakes, with 6.x, 7.x, and 8+ magnitude earthquakes broken out (notice that the data for 6.x earthquakes in 1900-1950 is likely incomplete):
The equivalent map for the 2,000 km surrounding San Francisco looks like this (sorry, no, there are no 8+ earthquakes, NOAA has the 1906 one at 7.9):
Let's look at the "earthquake history" in the other recent hotspots: New Zealand and Chile.
Earthquakes from 1900-2011 in a 2,000km area centered on Christchurch, New Zealand.
And finally South America. 2,000km area centered on Santiago, Chile. (That 9.5'er in 1960 was a monster).
BTW, I've only focused on a few of the Ring of Fire hotspots. Indonesia, Central America, etc. are all very active.
So are we Californians due for an earthquake?
As I wrote earlier: Who really knows? On the one hand 110 years of data tells us that our corner of the Ring of Fire experiences 25% as many earthquakes as Japan. On the other hand... It may be about time for a big one to hit us.
Simon Winchester (an author whose many books I'd recommend, esp. The Man Who Loved China) wrote recently:
[The Chile, New Zealand, and Japan earthquakes] involved more or less the same family of circum-Pacific fault lines and plate boundaries—and though there is still no hard scientific evidence to explain why, there is little doubt now that earthquakes do tend to occur in clusters: a significant event on one side of a major tectonic plate is often—not invariably, but often enough to be noticeable—followed some weeks or months later by another on the plate’s far side. [...]
Now there have been catastrophic events at three corners of the Pacific Plate—one in the northwest, on Friday; one in the southwest, last month; one in the southeast, last year.
That leaves just one corner unaffected—the northeast.
Are earthquakes really clustered? I haven't analyzed the data for correlations. Just eyeballing the graphs above, there are enough earthquakes happening around the Pacific Rim that you could claim some correlation exists.
If you want my advice... Better safe than sorry: Be prepared.
Technical Info
All graphs were created with Mathematica 8, one of my favorite pieces of software. It's a tremendously powerful package and, though it does have a bit of a learning curve, the help system is excellent at giving lots of examples.
There's a lot more that could, and probably should, be done with this data: time-based analysis, looking for correlations, leveraging more of the data (e.g. tsunamis, impact of earthquakes, etc.).
The graphs above are pretty simple. Mathematica can create much more sophisticated ones. Here's 3D version of the Japan-area earthquakes.
