Tuesday, February 10, 2009
"San Andreas Fault", "How the Earth Was Made", on History Channel
Tonight, Tuesday Feb 10, 2009, the History Channel started its “How the Earth Was Made”, with “The San Andreas Fault,” directed by Robert Stanges. The strike page is here.
The program started by reviewing the 1906 San Francisco earthquake and noted that the damage was much greater than normally explained by a 7.8 magnitude quake. 1% of the population died and 10% of the city was utterly destroyed, before the fire. The show then shows the geography of the fault, moving toward the southeast from the Pacific Ocean, coming ashore in pristine country about 15 miles south of San Francisco at Muscle Point, where the two colors of unrelated, crumpled rock show that the North American Plate lies on top of the Pacific Plate.
In 20 million years Los Angeles would have moved up to occupy a position east of San Francisco. A major quake in the straight line part of the fault south of Los Angeles occurs every 200 years and is overdue by a hundred years.
The town of Hollister, CA rarely feels quakes because of the serpentine rock (like talc) absorbs the shear. On the other hand, Parkfield has a mild quake every 22 years.
Various portions of the fault are shown, including one areas where a creek moves 300 feet at a right angle. After the San Francisco quake in 1906, a fence in Marin County moved eight feet.
Experiments at UCLA show that a major quake along a straight line sends out triangular “super shear” shock waves about a minute after the quake. The shock wave resembles a sonic boom generated by a supersonic airplane. These secondary shockwaves could topple highrise buildings previously thought to be able to survive even major earthquakes.
When a company I worked for, Chilton in Dallas, was taken over by TRW in southern California in 1988, people wondered if they would keep the Dallas data center as insurance against "the Big One". They didn't. But the sequel to the company, Experian, is back in the Dallas area. Good idea.