It was a Tuesday exactly half a century ago, just after 6 a.m., and most of Los Angeles was dozing. The wake-up call lasted 12 seconds, registered 6.6 on the Richter scale, buckled buildings and killed 64 people. Those who recall what is known as the Sylmar or San Fernando earthquake of 1971 describe the experience as if the ground is still shaking, with specific markers seared into their memories. “Lots of broken glass in the kitchen, and the five-gallon Sparkletts bottle exploded on impact,” says Howard Cohen, who was 8 at the time and living in Lakeview Terrace. He recalls his bed moving during the initial quake and the aftershocks in the bedroom he shared with his grandmother.