Several earthquakes in California’s history have been suspected or proven to reach supershear speeds, including the 1992 Landers earthquake and the 1979 Imperial Valley earthquake. Simulations of the great 1906 San Francisco earthquake (shown here) suggest that it was also most likely a supershear event (Song et al., 2008). With many faults capable of producing strike-slip earthquakes large enough to reach supershear rupture speeds, understanding how supershear rupture will enhance shaking will be crucial for future disaster planning in the region. Photo: San Francisco in the aftermath of the 1906 earthquake and subsequent fires. Credit: US National Archives.