The North American plate is drifting southeast relative to the Pacific plate, and the boundary between the two plates is the San Andreas fault, which runs inland through the Transverse Ranges at the area around Santa Barbara. This movement of the two geologic plats creates stress that is put on the rocks that make up the crust on both sides of the fault. Rocks are hard, and so take some amount of force to break, but when they do break it happens rapidly and catastrophically. This breaking is what causes earthquakes. The fact that the rocks are moving relative to each-other and are rigid also creates a lot of other faults and fractures in the area around the San Andreas fault, which is why an earthquake can occur that is not on the main fault itself (as this one was not). It was on one of these smaller faults.

Earthquakes are caused by the movement of the tectonic plates. The plates are pieces of the earth’s crust that float on the liquid mantle below them. The edges of the plates rub up against the neighboring plates as they all move around. The plates do not move smoothly because the edges are jagged, so plates are often caught on each other. Since the plates are caught on each other but are still trying to move, pressure builds until a piece of a plate breaks, allowing the stuck plates to finally move. When the rock breaks, energy is released, which propagates through the earth as a seismic wave, which we call an earthquake.

Earthquakes are caused by the movement of Earth’s tectonic plates, and they usually occur along the plates’ “fault lines” or where they overlap. The largest fault line near us is called the San Andreas fault and it runs the length of California. There are plenty of fault line traces around Santa Barbara. A small shift in the plates originated off our coast and sent movement across the surface of the land, which is what we felt as the shaking and trembling around us.