When Was The Last Time The San Andreas Fault Moved? Constantly, Actually, But It's Been A While Since A Big Shift

At least a dozen earthquakes have occurred in California in May alone. This is par for the course in a state that boasts a "simplified fault line map" that's so complex, reading it looks like deciphering a failed connect the dots drawing. According to the National Earthquake Information Center, as many as 50 earthquakes occur throughout the world each day, totaling nearly 20,000 earthquakes per year. The smaller earthquakes that go unobserved or fail to register occur an average of 1.3 million times per year. When it comes to the most notorious fault of all — San Andreas — earthquakes are just as constant on its over 800 mile expanse. The most recent movement on the San Andreas fault occurred earlier Wednesday near the southernmost point of the fault, near the Salton Sea.

The last major earthquake to occur along the San Andreas fault was in the highly seismically active Parkfield area, located in Central California. Parkfield is an unincorporated community spanning just 18 residents. It's perhaps best known for its rich seismic data, which seismologists have been studying for years. The 6.0 earthquake that occurred in 2004 marked the biggest development in Parkfield since seismologists had been studying the area. The town is so seismically sensitive that large earthquakes regularly occur there just about every 22 years. Studying Parkfield puts seismologists as close to predicting earthquakes as current science allows.

Little damage occurred when the 2004 Parkfield earthquake hit because of its desolate location. It did, however, provide seismologists with a 3D map of the fault line borehole that scientists had created to observe seismic activity as well as show the diversity of the San Andreas fault line. Within Parkfield lies a section of fault that is constantly shivering and moving, while just down the fault a mere 100 yards lies a completely still section within the boundaries of the town itself.

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Prior to the 2004 Parkfield earthquake, nothing had come close to rocking the San Andreas fault like the 1989 Loma Prieta earthquake, a 6.9 magnitude earthquake that killed 63, injured thousands, and became the first major earthquake broadcast live thanks to the 1989 World Series aptly dubbed the Battle of the Bay between the San Francisco Giants and the Oakland A's. Its epicenter was located to the north in the Santa Cruz mountains, affecting a far more populated area. The 2004 Parkfield earthquake could nonetheless be felt from as far as 200 miles away in the state capital of Sacramento.

Images: USGS (1); Getty Images (1)