Earthquakes occur along fault lines. What is a fault line? Read what the California State Department of Conservation has to say on the subject in order to gain a greater perspective on California’s relationship to earthquakes:
“A fault is a fracture in the crust along which one side has moved relative to the other side. Faults can be very small or hundreds of miles long. The earth’s crust is composed of huge plates that are in slow but nearly constant motion. Part of California is on the Pacific Plate, and part is on the North American Plate. The San Andreas Fault, which runs from the Salton Sea in Imperial County to Cape Mendocino in Humboldt County, is the boundary between these plates. Sometimes one block of the crust moves up while the other moves down, sometimes they move horizontally in opposite directions (that’s what’s happening with the San Andreas Fault; Los Angeles is creeping closer to San Francisco). Some faults are well known and easy to spot, such as the San Andreas. Others are underground, with nothing on the surface revealing their presence (a blind thrust fault). The 1994 Northridge earthquake was caused by a blind thrust fault.” [vii]
When two faults slip against each other, they create friction. Sometimes, this friction goes unnoticed, and is harmless. Other times, the friction creates a release of seismic energy which comes up through the fault line, where the two plates crack, causing what we call an earthquake. This process is extremely volatile and can cause billions of dollars in damage if it hits a busy residential area such as Los Angeles, or San Francisco. However, over time, the more pressure builds up, the more it increases the risk of an earthquake happening in the future.
So now that we know what an earthquake is, there is a bigger question we must ask. Why is California such a prime target for such devastating earthquakes? We all know about the winds of the Great Plains that make up Tornado Alley, but what about the earth’s crust makes California so vulnerable to these destructive natural forces? According to the Department of Conservation’s website (cited above,) Alaska has the most earthquakes, however California feels the brunt of it because “more than 70 percent of [California’s] population resides within 30 miles of a fault.” Meaning, that any type of shifting of the plates could cause catastrophic harm, not only to property, buildings, and other material possessions—but more importantly—to the people residing within those areas as well. Because so much of the state’s geography runs alongside or next to fault lines, it’s very important that buildings in California be made as safe as possible—something that businesses and contractors have taken very seriously in recent years.
However, there’s another key ingredient to the California equation: The San Andreas Fault Line. This major fault line is nearly 750 miles in length, all of which runs through California. This separates two major tectonic plates, the Pacific Plate and the North American Plate, due to the convergence of multiple plates along this fault line, it’s a prime target for making California susceptible to major earthquakes.