Compute the velocity of the Pacific plate with respect to the North America plat
ID: 106282 • Letter: C
Question
Compute the velocity of the Pacific plate with respect to the North America plate at Palmdale....
Euler Poles, Relative Rotation Rates, and Relative Velocities DeMets et al [1990] produced the following global model for present plate rotation rates, called NUVEL-1. Each Euler vector is relative to a Pacific-plate reference frame. Rotations which are counter clockwise (when looking at the Earth from space) are positive. (Notice that when we take the Pacific plate as the reference frame, all rates become rather large and all Euler poles lie in the Northern hemisphere!) Compute the velocity of the Pacific plate with respect to the North America plate at Palmdale, CA (34.5degree N, "118 degreeW" = -118 degree E. Do this by hand, and turn in all the steps of the computation. Your final answer should be a velocity-magnitude and an azimuth. Compare the results to a geologic map (measuring the azimuth of the San Andreas fault with a protractor), and discuss what type of plate boundary is expected at Palmdale today.Explanation / Answer
At any point r along the boundary between plate i and plate j, with latitude and longitude µ, the linear velocity of plate j with respect to plate i is
vji = ji × r.
r is the position vector to the point on the boundary, and ji is the angular velocity vector or Euler vector. Both vectors are defined from an origin at the center of the earth.
Given Data from the Question.
Radian r = 4.33x10 to the Power 16
Velocity = 1.15 cm/year
Magnitude V= w x r.
Magnitude V= (4.33*1.15) x 10 to the power 16
V is 4.979 8 10 to the Power 16.
The current pattern of slip1,2 within the San Andreas fault system in the San Francisco Bay area is distinctly different from the long-term slip pattern inferred from the geological record3,4. This difference is not surprising because geological data record the accumulated displacements over many earthquake cycles, whereas geodetic data reveal the present-day slip pattern. It is not known, however, what mechanism triggers the change from the 'inter-seismic' slip pattern (when the San Andreas fault is locked) to the 'co-seismic' slip pattern (when the San Andreas fault ruptures in earthquake slip). Here we use numerical simulations of the entire seismic cycle on this complex fault system to show that the San Andreas fault may be in a critical state and sensitive to small perturbations in regional compression. In particular, we find that small increases in regional compression may lock the San Andreas fault, whereas small decreases in regional compression may release the locked segment and so permit co-seismic slip. This sensitivity suggests that cyclic changes in the regional stress field resulting from plate convergence and thrust faulting in the Coast Ranges could trigger major earthquakes on the San Andreas fault. Lake Palmdale was and still is a huge sag pond made by the San Andreas Fault. A sag pond (in this case) when an underground river leaks up towards the surface of the Earth. Lake Palmdale was formed by the San Andreas Fault. As you can see there is a huge windmill on the other side of the lake. This windmill is on the North American Plate while, where you will be standing is on the Pacific Plate.
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