Geography10 Abraham Lincoln The 1906 San Francisco Earthquake Report This is a geography assignment. Need a geography major.Need to answer all questions.I)

Geography10 Abraham Lincoln The 1906 San Francisco Earthquake Report This is a geography assignment. Need a geography major.Need to answer all questions.I) The 1906 San Francisco Earthquake After the 1906 San Francisco earthquake, Henry Fielding Reid, Professor of Geology at Johns Hopkins University, spent months surveying and filling notebooks with information on the aftermath of the quake. When the results were plotted, it looked something like what is shown on Figure 1, and Reid deduced what the earthquake was from this figure.Figure 1: The dashed line shows where the ground ruptured. Each white (or red) dot represents where a benchmark was before the earthquake, and the arrow shows where it ended up after the earthquake. You can find the scale for benchmark location on the bottom of the map. For instance, the red dot is about 3 km West from the rupture. The scale on the right is for the movement of the benchmarks. For instance, after the earthquake, the benchmark indicated with the red dot had moved about 1.5 meters North. The motion of the benchmark has been greatly amplified in this figure. 1) From the motion of the points plotted on the map, extrapolate what the ground motion would be for the imaginary benchmarks shown in yellow (3 points). 2) What is the relative displacement from one side of the rupture to the other? How does the intensity of the displacement evolve away from the rupture, on each side? What are Name : __________________________________
Score:
/20
Lab #6:
I) The 1906 San Francisco Earthquake
After the 1906 San Francisco earthquake, Henry Fielding Reid, Professor of Geology at
Johns Hopkins University, spent months surveying and filling notebooks with information
on the aftermath of the quake. When the results were plotted, it looked something like what
is shown on Figure 1, and Reid deduced what the earthquake was from this figure.
Figure 1: The dashed line shows where the ground ruptured. Each white (or red) dot represents
where a benchmark was before the earthquake, and the arrow shows where it ended up after
the earthquake. You can find the scale for benchmark location on the bottom of the map. For
instance, the red dot is about 3 km West from the rupture. The scale on the right is for the
movement of the benchmarks. For instance, after the earthquake, the benchmark indicated with
the red dot had moved about 1.5 meters North. The motion of the benchmark has been greatly
amplified in this figure.
1) From the motion of the points plotted on the map, extrapolate what the ground motion
would be for the imaginary benchmarks shown in yellow (3 points).
2) What is the relative displacement from one side of the rupture to the other? How does
the intensity of the displacement evolve away from the rupture, on each side? What are
your thoughts about the earthquake, based on the results of question 1? (3 points)
If you were to plot the motion of the benchmarks for the 2 years leading up to the
earthquake, you would see something like what is shown in Figure 2.
Figure 2: Notice, benchmark motions on this map are measured in centimeters (see scale on right
side). That is, the benchmark motion is amplified even more than in Figure 1, so that these small
motions can be visualized.
3) With this information, extrapolate and plot what the ground motion would be for the
imaginary benchmarks shown in yellow using the motions of the points on the map (3
points).
4) How does this slow movement relate to the fast, large movement in the first figure? Try
to explain what caused the San Francisco earthquake using this information (4 points).
II) Elasticity
Examples of elastic material include springs, erasers, foam rubber, and perhaps
surprisingly, the Earth’s crust. The concept of elasticity implies:
– Recovery (the original shape is restored when forces are removed as in releasing a spring)
– Deformation = force / a constant. So, a force that pulls a spring twice as hard will deform
the spring twice as much. The constant in the equation is the material’s stiffness. Therefore,
if a material is twice as stiff as another one, you will need twice the force to achieve the
same deformation. Or, put it another way, if you use the same force, the deformation will be
twice smaller. The goal of this part of the lab is to understand:
A. Analog material and scaling: applying large-scale concepts on human scales to allow us
to make an analog representation (a physical model) that makes interpretation easier. For
example, here we will use an eraser (i.e., analog material) to “mimic” the Earth’s crust. Of
course, the eraser does not have the same stiffness as the Earth’s crust and obviously
deforms more easily than rock, but it behaves elastically, the same way the crust does.
B. Quantification: using the power of math to tackle larger problems by scaling
calculations we first make on an analog representation. For example, if we know how much
stiffer the Earth’s crust is compared to an eraser, we can do some experiments on the eraser
and then scale our results to the Earth’s crust, using some simple math.
Imagine an eraser that is 5 cm long, 1 cm wide and 2 cm thick (Figure 3). Some experiments
have been made on this eraser and they showed that to shear that eraser by 2 mm takes 1
kg of force (Figure 3). Using the equation deformation = force / constant, if we were to
shear the eraser by 4 mm, it would take 2 kg of force.
Figure 3
5) We can consider that the crust (oceanic or continental) is also an elastic material, but an
elastic material that has a much greater stiffness than the eraser. In fact, crustal rock is
30,000 (3 x 105) times stiffer than the eraser. If you wanted to get a displacement of 2 mm
on a piece of crust that has the exact same size as the eraser, what force would you need to
apply? Explain how you got this number. (4 points)
6) Now consider a case where your rock is 1 km thick (instead of 1 cm thick). Then, how
much force would you need to apply to the side to get 2 mm of displacement? (1 km is
100,000 times larger than 1 cm). (3 points)

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