Silver seemed offended. Drawing himself up, he said, “I beg your pardon, sir. It

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Silver seemed offended. Drawing himself up, he said, “I beg your pardon, sir. It is   not rotten. It is shattered.” The region was a tracery of faults, like cracks in ancient paint. The mountains were divided by faults, defined by faults, and framed by them as well: on the near side, the Raymond Fault, the Sierra Madre Fault, the Cucamonga Fault; on the far side, the San Andreas Fault. The rock of the San Gabriels had been battered and broken by the earthquakes on these and related faults. In 1971, Silver had flown over the San Gabes immediately after an earthquake that reached 6.2 on the Richter scale. Like artillery shells randomly exploding, the aftershocks were sending up dust in puffs all over the landscape. Something like that would add quite a bit, he said, “to the debris potential.” Some of the rock up there had become so unstable that whole hunks of the terrain were moving like glaciers. One mountaintop was heading south like a cap tipping down on a forehead. Things like that had been going on for so long that the mountains were in many places loaded with debris from ancient landslides—prime material, prepared to flow. “The ultimate origin of the debris flows,” he said, “is the continuous tectonic front that has made this one of the steepest mountain fronts in North America and produced a wilderness situation not a hundred metres from people’s houses.”The continuous tectonic front is where the North American and Pacific Plates are sliding past each other—where Bakersfield moves toward Mexico City while Burbank heads for Alaska. Between Bakersfield and Burbank lie the San Gabriel Mountains. With the San Bernardino Mountains east of them, they trend east-west, forming a kink in the coastal ranges that come down from San Francisco and go on to Baja California. The kink conforms to a bend in the San Andreas Fault, which runs along    the inland base of the mountains. The kink looks like this: It could be a tiptoeing h. It resembles a prize-winning chair. Los Angeles is like a wad of gum stuck to the bottom of the chair. The mountains are one continuous system, but its segments are variously named. The upper stretch is called the Coast Ranges. The lower leg is called the Peninsular Ranges. The kink is called the Transverse Ranges.

1.The roles of plate tectonics and faults in this region are described on p. 226 as well as in other areas in this part of the book. Describe the tectonic factors in the region and why it contributes to the debris flow problem. (4 points)

Explanation / Answer

The role of the plate tectonics and faults in this region is explained below

Plate tectonics: in order for plates to be able to move relative to another another , plate boundary is required, Transform plate boundaries are characterized by horizontal motion , along the transform fault system, which is parallel to the plate boundary segment that separates two plates, these plate boundaries are also known as conservative plate boundaries because no crust is ls lossed( oceanic trench) aur created( mid oceanic ridges) but the crust is conserved and plates motion is in horizontal manner

Faults: when lithospheric plates slide past one another in a horizontal manner, a transform fault is created, they are special class of strike slip fault. Earthquake along such transform fault are shallow focus . This faulting occurs because some part of plate must be moving at a higher relative velocity than other part. One of the largest such transform boundaries fault occurs along the boundary of North American( nazca plate) and Pacific plates and is known as San Andreas fault, this fault is situated in state of California in USA it's is 1200km long active in nature and have dextral motion of plate relative to one another

Debris flow is a phenomenon where water laden masses of soil and fragmented rocks rush down mountain slides. San Gabriel mountain are near this dextral strike slip zone number of small faults are also found in these region because of this large area fault, this fault is active in nature and displacement in undergoing, therefore sometime it may displace a potential water laden masses and fragmented rocks a fault plane .and the driven factor of this debris flow, or faulting is the motion of transform plate boundaries (tectonic)

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