The California Geological Survey turns 150 this year. As part of that celebration, they have released new maps revealing the state’s complex geology. One map in particular is making headlines: a map of all the known fault lines in California, including those discovered since the last fault map was put together in 1994. This fault activity map color codes fault lines based on their most recent activity. For the record, the faults in red and orange are the most active cracks to fret over.
In geology, a “fault” can refer to almost any break in a chunk of rock, as long as movement or displacement periodically occurs along that fracture. The many tectonic plates that make up Earth’s surface (go here to learn more) move past one another and collide along zones of complex fault lines, where the slow movement of the plates has caused fracturing of rock on both sides of the boundary. California is a textbook example of such a zone of fault lines. While most of the state resides on the massive North American Plate, a significant chunk (including all of coastal California south of the Bay Area) actually resides on the equally massive Pacific Plate. At California, the North American and Pacific plates are sliding past one another. The North American plate is moving south and east relative to the Pacific Plate’s north and west course. This plate boundary also extends further south, where past movements have torn lower California (the Mexican states of Baja California and Baja California Sur) away from the mainland, opening up the Gulf of California. However, plate boundary is at its most geologically troublesome as it runs through the American State of California.
The Pacific plate is on the left, while the North American plate is on the right. Image provided courtesy of the United States Geological Survey.