Template:Are You Sure/April 18

San Francisco Earthquake of 1906: Ruins in vicinity of Post and Grant Avenue, looking northeast.

• ... that the 1906 San Francisco earthquake struck the coast of Northern California at 5:12 a.m. on April 18 with an estimated moment magnitude of 7.9; that devastating fires soon broke out in the city and lasted for several days; and that as a result, up to 3,000 people died and over 80% of the city of San Francisco was destroyed?

• ... that mathematician Karl Mikhailovich Peterson (nonfiction)|Karl Mikhailovich Peterson]] gave, in his graduation dissertation (1853, but not published until later), an early formulation of the fundamental equations of the surface theory, now usually known as Gauss–Codazzi equations, sometimes Peterson–Codazzi equations?