Introduction The California landscape is cut by many faults capable of making earthquakes, but one of these, the San Andreas Fault, more important than all the others. It is the principal boundary between the Pacific Plate and the North American Plate, and its displacement rate is the highest of all California faults – more than one inch per year. Two of the greatest earthquakes in the history of California, the 1857 Fort Tejon Earthquake and the 1906 San Francisco Earthquake, resulted from slippage along this fault.
The San Andreas Fault that we see today however, is merely a snapshot in time, as the fault has migrated eastward. To understand this, let’s start about 30 million years ago. Three tectonic plates are involved, the North American, Pacific and Farallon Plates. Dividing the Farallon and Pacific oceanic plates was the East Pacific Rise (divergent boundary), and the Farallon was being subducted beneath the North American continental plate.
The San Andreas Fault at this time “stepped inland” to roughly its position today. The spreading center that now runs up the Gulf of California to the Salton Sea is broken into numerous short segments by long transform faults. The San Andreas Fault at this time “stepped inland” to roughly its position today. The spreading center that now runs up the Gulf of California to the Salton Sea is broken into numerous short segments by long transform faults.
Depending on which way a strike-slip fault like the San Andreas “bends”, it may be a “restraining bend”, as it is in southern California, or a “releasing bend” as it is more commonly in areas more to the north. Depending on which way a strike-slip fault like the San Andreas “bends”, it may be a “restraining bend”, as it is in southern California, or a “releasing bend” as it is more commonly in areas more to the north.
Dostları ilə paylaş: |
