Thursday December 5th at hours 10.44am (local time, 7.44pm in Italy), a violent earthquake occurred magnitude 7.0 off the coast of California, about 62km from the city of Oil north of San Francisco. The earthquake shock recorded a rather shallow depth just 10km but, fortunately, having occurred in the open sea did not cause any particular damage on the mainland, even if it was felt by the population.
At the same time, national authorities such as theUS Tsunami Warning Center they initially issued thetsunami warning for the adjacent stretch of coast between California and Oregon (where about 5 million people live), then returned within a few hours. This earthquake started a seismic sequence followed by dozens of tremors with magnitudes lower than 4.0. But from a geological point of view, what caused the earthquake?
The main suspect is the San Andreas fault. It’s one strike-slip fault approximately long 1280 kmdeep at least 16km and which crosses the west coast of the USA from the city of Los Angeles to that of San Franciscoall the way to the Oregon border. This enormous fracture system has been at the center of public debate for years due to the “Big One“, a journalistic term that refers to the very violent earthquake that, sooner or later, could hit California. The last major earthquake associated with the fault dates back to April 18, 1906with an earthquake of magnitude 8.3 which caused destruction and fires in the city of San Francisco.
And when will the next earthquake be? Unfortunately, it is impossible to predict this with precision.
