A Crack In The Edge Of The World

Just finished reading A Crack In The Edge Of The World, Simon Winchester's new book about the 1906 San Francisco earthquake. It was really good, although a little repetitive of Winchester's last book about Krakatoa in that it is about, at its root, plate tectonics and their effects. In places, it also is a little repetitive of Assembling California, John McPhee's book about how California came together geologically, although Winchester does acknowledge the debt.

The book mostly describes the plate tectonics associated with the North American Plate, which starts in the east at the Mid-Atlantic Ridge, which is as far out as Iceland, and ends in the west at the San Andreas fault and in Alaska. (In Oregon and Washington, a small plate named the Juan de Fuca Plate is subducting under the North American Plate, which creates the volcanoes in those states. Subducting plates are one of the most common reasons why volcanoes occur. Krakatoa existed and exists due to a subducting plate.)

There's a pretty substantial discussion of mid-plate events like the 1880's earthquake under Charleston, South Carolina, and the three 8.0+ earthquakes that occurred in 1811 and 1812 under New Madrid, Missouri. The New Madrid quakes were so big that they were felt in New York and Chicago and made the Mississippi River -- a mile wide -- run backwards. These things really shouldn't have been happening in the middle of the plate, rather than at its edge, where people expect earthquakes. Apparently, because the plates move around due to the convection currents in the Earth's magma, there are some scientists who think that the New Madrid and Charleston quakes and other mid-plate events indicate that the North American Plate is in the process of splitting up. Great.

Of course, as a California native and junkie, the parts of the book about the San Andreas fault and the San Francisco earthquake were the ones that most interested me. I wasn't aware that the San Andreas basically has three parts: (1) from Cape Mendocino to somewhere around San Juan Batista; (2) from San Juan Batista down to the Tehachapis; and (3) from the Tehachapis down to the Salton Sea. The northern and southern parts are locked. They don't really move much, except with big earthquakes. The middle part, however, is pretty continuously moving north, which is why Parkfield gets so many earthquakes. (Got to get to Parkfield at some point. Barely anyone lives in that part of the world -- Parkfield, Cholame, the Carriza Plain -- but it not only features the San Andreas fault, but also the place where James Dean was killed. L. Ron Hubbard lived out there at some point, too. As a kid, I knew that we were driving past the James Dean spot every time my family drove from Lemoore to Pismo Beach, but I didn't know that we were crossing the San Andreas Fault every time too. I would have complained until my dad pulled off to look at the Fault at some point if I had known. Instead, I complained about getting lunch at the Black Oak in Paso Robles.) This movement causes the tension in the northern and southern parts of the fault that cause earthquakes in the Bay Area and LA. Accordingly, it's basically statistically certain that California will get more large earthquakes.

I also didn't realize what the geologic reason for the Tehachapis is. Generally, the Pacific Plate slides past the North American Plate. California's big bend to the east that begins around Lompoc and the Tehachapis are caused because, beginning at the bend and running down to about LA, the Pacific Plate pushes north into the North American Plate. This northern push pushed up the Tehachapis and causes earthquakes in the middle part of the fault, like the great big Tejon earthquake in 1857 and the big Tehachapi quake in the 1950's that my mom remembers.

It's quite a place where we live here. Of course, the book ends with a discussion of Yellowstone that describes how it exists because it sits on top of a volcanic hot spot (like Hawaii) and has been the site of two absolutely gigantic eruptions in the last few million years. Apparently, there'll be another one at some point. So, between Florida getting several hurricanes every single year and Yellowstone being bound to erupt gigantically at some point in the next couple of million years, California's issues may be a decent compromise. Plus you can wear shorts in October and even in November, at least this year.