The Really Big One
An earthquake will destroy a sizable portion of the coastal Northwest. The question is when.
[This is a really good article, especially for people who haven’t caught wind of this. I’ve actually wanted this subject to be on a Science Friday post for years, because I used to blog on other websites that have since gone away for one reason or another, and I just didn’t get to it in time. But now, with this article, it is time. I’m going to skip the first few paragraphs about the Tohoku, Japan, earthquake and tsunami, not because it’s not interesting info, but because you really should take the time to read the article]
Most people in the United States know just one fault line by name: the San Andreas, which runs nearly the length of California and is perpetually rumored to be on the verge of unleashing “the big one.”That rumor is misleading, no matter what
the San Andreas ever does. Every fault line has an upper limit to its potency, determined by its length and width, and by how far it can slip. For the San Andreas, one of the most extensively studied and best understood fault lines in the world, that upper limit is roughly an 8.2—a powerful earthquake, but, because the Richter scale is logarithmic, only six per cent as strong as the 2011 event in Japan.
Just north of the San Andreas, however, lies another fault line. Known as the Cascadia subduction zone, it runs for seven hundred miles off the coast of the Pacific Northwest, beginning near Cape Mendocino, California, continuing along Oregon and Washington, and terminating around Vancouver Island, Canada.The “Cascadia” part of its name comes from the Cascade Range, a chain of volcanic mountains that follow the same course a hundred or so miles inland.The “subduction zone” part refers to a region of the planet where one tectonic plate is sliding underneath (subducting) another.Tectonic plates are those slabs of mantle and crust that, in their epochs-long drift, rearrange the earth’s continents and oceans. Most of the time, their movement is slow, harmless, and all but undetectable. Occasionally, at the borders where they meet, it is not.
Viewing and Understanding the Analemma
If you looked at the Sun at the same time each day, from the same place, would it appear at the same location in the sky? If the Earth were not tilted, and if its orbit around the Sun were perfectly circular, then, yes, it would. However, a combination of the Earth’s 23.5 degree tilt and its slightly elliptical orbit combine to generate this figure “8” pattern of where the Sun would appear at the same time throughout the year. The pattern is called an analemma.
The Sun will appear at its highest point in the sky, and highest point in the analemma, during summer. In the winter, the Sun is at its lowest point. The in-between times generate the rest of the analemma pattern. (See Analemma Curve.) Analemmas viewed from different Earth latitudes have slightly different shapes, as do analemmas created at different times of the day. Analemmas on the other planets have different shapes entirely!