physics learning outcomes in earthquakes

1. 1. Earthquakes can be a dangerous phenomenon that can ravage the lives of many
individuals. But did you know that earthquakes can occur without us even feeling it? In
fact the last earthquake occurred in Victoria, British Columbia on February 5th at 12:42!
As we learned in the pre readings there are two main types of waves that are associated
with earthquakes: P and S waves. Which type of wave is more dangerous and why?
Given that in solids, longitudinal waves travel almost twice as fast as transverse waves.
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A. Similar to a slinky put on its side and pushing the end forward and back, waves
that travel through the ground. The longitudinal waves are faster (360km/hr) through
water and will push and pull, and compress the earth in the direction of travel. The waves
have a smaller amplitude than P waves. On the other hand S waves are transvers, and
therefore travel slower through the earth. They move the earth perpendicularly to the
direction of the wave. Therefore the S waves would have larger amplitudes and could do
more damage to buildings on top of the focal damage area.
2. Are seismic waves travelling waves or are they standing waves?
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A. Travelling waves. These waves have high points known as crests and low
points known as troughs that travel through the medium. There is no end point to the
medium that exists because seismic waves travel throughout the atmospheric
environment. There is also dampening that exists and that is why the farther you are
from the wave the less you will feel the effects.
3. Surprisingly there was a huge earthquake that originated from Wreck Beach,
(pretending don’t worry!) and among the buildings the physics building: HEBB, was seen
swaying violently back and forth before crumbling. What does this tell us about the
intrinsic damping about the building (is it low or high?), and how can the future builders
fix the present problem?
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2. A. All vibrating objects, such as buildings, will have a reduced amount of
vibrating over time. The damping occurs because the amplitude of the vibration will
decrease. If a building does not have a significant damping constant the more it will
continue to vibrate. In this case the physics building does not have high intrinsic damping
as it continued to sway due to the seismic waves before collapsing. Other buildings have
a higher damping constant due to friction and the absorption of the energy of the
earthquake. One way to fix this issue is to increase the intrinsic damping, for example by
adding shock absorbers to approve its performance during an earthquake in absorbing
seismic waves.
4. With all that has been explained of earthquakes, imagine that the model of the
earthquakes could be likened to that of the wave speed on a string. How could you
explain the wave speed in S waves. Why would this idea not work with P waves?
𝑉 = √
𝑇𝑠
𝜇
𝜇 =
𝑀
𝐿
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A. The S waves would travel at a larger velocity, which could indicate that the
tension, or restoring force of the ground in the longitudinal direction is larger, otherwise
it could be that the linear mass density of the ground is smaller. Relatively it would mean
that the length of the “string” or ground level would increase the relationship by
decreasing. This idea would not work in P waves because P waves are longitudinal
whereas S waves are transverse and this “wave speed on a string” theory works with
transverse waves.