Damage caused to houses in the Marina district of San Francisco during the Loma Prieta earthquake of October 17th 1989. Buildings in this area were constructed about 75 years ago over an old land- fill site topped with local sand. Many of them had timber frames so inadequately anchored to their concrete foundations that they literally slipped off during the quake (as here). Measuring 6.9 on the Richter scale, the earthquake was named after a region in the Santa Cruz Mountains close to the epicentre, about 100-km south of San Francisco. The rupture occurred, at a depth of 18 kilometres, along part of the San Andreas Fault, the boundary between the Pacific and North American Plates.