The earthquake - known as the Big Shake - struck the coast of Northern California at 3:00pm on September 12 2017 with the epicenter in East San Jose (37.3382° N, 121.8863° W). The reported magnitude of the earthquake was 8.1 in the Richter magnitude scale, which makes it the strongest earthquake in the history of this region. The area affected by severe shakings extended from Santa Rosa and Sacramento in the North all the way Monterey and Salinas in the South, however, according to the local authorities, the most severe damages were reported in the South and East part of the Bay Area. The quake resulted in the destruction of 60% of the city of San Jose and 50% of the nearest towns (including Santa Clara, Sunnyvale, Milpitas and Saratoga). Nearly 300 people died and another 1,000 were injured as a result of the collapse of several buildings in the area of the epicenter. According to the American Geological Institute, it has been the deadliest earthquake since the San Francisco Earthquake in 1906.
Tectonic setting and intensity
The Big Shake was caused by the motion of the Pacific Tectonic Plate and North American Plate which created the tectonic boundary known as the San Andreas Fault. The crucial characteristic of the intensity of the earthquake - reported by the Journal of Geophysical Research, in their annual report - was ‘the clear correlation of intensity with underlying geologic conditions’.The movements in the region are well-known to geologists, however, according to Richard Allen - the seismologist from UC Berkeley - 'the process got stronger in the last century and soon we will see its consequences'. The Big Shake was preceded by a series of minor shakings of the magnitude of 3.1 to 3.4 on the Richter scale in the East San Jose on September 9 and 10.
As noted by NBC, the impact of the earthquake covered the area of over 6,900 square feet of land. On September 14 2017, the members of San Jose City council were briefed on the status of damages caused by the earthquake. According to the report, at least 30% of the buildings in Santa Clara County showed signs of external damage. Based on the estimate provided by the USGS, the damages caused by the quake reached $ 634 million.