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Comments on Earthquake Storyboard (1).pptx
Slide 1: “Researchers at the Southern California…”
Slide 2: We prefer changes to two of the text boxes. For “Magnitude of Shaking”,
because this phrase combines two important but different earthquake concepts
(magnitude, intensity), we’d prefer “Intensity of Shaking”. For the San Andreas Fault
line, we’d prefer “San Andreas Fault trace”, since it is not a straight line.
For the challenge question, for earthquake science, we talk separately about the
location of the earthquake, and the locations of the shaking. For the red challenge
text, we prefer to say, “a magnitude 8 will occur during your stay.” With this change,
we hope to avoid people thinking that the location of the earthquake changes with
their choice. The location of the earthquake doesn’t change, only the location of the
shaking they will experience.
Slide 7: We recommend updating the text this way:
“Earthquakes generate seismic waves that propagate away from the fault in all
directions. Do the earthquake waves shown in this simulation of a San Andreas
earthquake propagate evenly in all directions?”
Small updates to the revealed text:
“In this simulation, the rupture is propagating south and moves down a straight
section of the San Andreas Fault. Because both the fault rupture, and some of the
generated seismic waves are moving south, the ground motions produced by the
rupture, and the front edge of the fault slip patch, add up to produce a region of
strong ground motion at the leading edge of the earthquake. Researchers identify
this area of strong ground motions as a Mach Cone, related to the effects that cause a
sonic boom. From this animation, we learn that rupture directivity can lead to lead
to strong shaking in some areas, with significantly weaker shaking in other areas for
the same earthquake.
Slide 9: For these two clips, unless the students know California geology well, it may
be difficult for them to see where the mountains are and the impact of the shaking
caused by the mountains. We think these segments might be better to make a point
about the relationship between duration of rupture and magnitude of earthquake. A
magnitude 6 rupture might take 6 seconds, a magnitude 8 rupture might take 130
seconds.
We recommend updating the text this way:
“The San Andreas fault rupture continues to moves south. It has been nearly 50
seconds since the earthquake started. Does the duration of the fault rupture have an
impact on the magnitude of the earthquake?
“The rupture slows down as it propagates into a bend in the San Andreas. Strong
shaking is spreading across a large area of southern California, and strong ground
motions are propagating across the San Gabriel Mountains, and approaching Los
Angeles. In this simulation, the San Andreas Fault has been slipping for nearly one
minute. As a fault rupture continues for a long period of time, the magnitude of the
earthquake increases. A fault that causes a magnitude 6 earthquake may slip for
only 10 seconds. A fault that cauess a magnitude 8 rupture may continue slipping for
over 2 minutes.”
Slide 11: We suggest updating the text this way.
“Observe the areas which are experiencing the strongest shaking. At 90 seconds
after the earthquake started, the strongest shaking is occuring along the San
Andreas Fault. However, there are other areas also experiencing strong shaking. Is it
safe to assume that farther away from the fault is always safer than near-by the
fault? “
The simulation shows the earthquake rupture has progressed south, past Los
Angeles, while strong ground motions are occurring throughout southern California,
including the densely populated region of Los Angeles, and San Bernardino. The
distribution of strong shaking from an earthquake can vary widely, and that it is not
safe to assume that strongest shaking happens closest to the fault.
Slide 13: We recommend the following small edits:
“Observe the Los Angeles area compared to the surrounding region. How is Los
Angeles? Is the duration of shaking similar across regions?”
“The rupture has propagated south, into the Salton Sea area, and strong shaking is
occurring near the fault. The simulation also shows strong shaking passing through
hard rock mountainous areas, while strong shaking lasts longer in some areas like
Los Angeles. Los Angeles is built on top of a sedimentary basin, and this region of
soft soil continues to shake strongly well after the initial earthquake waves pass
through. From this, we learn that the duration of shaking produced by a specific
earthquake can vary widely for different regions, with shorter duration shaking
expected in hard rock mountainous areas, and longer duration shaking expected in
sedimentary basins.”
Slide 17: We like your general conclusions. It is true that earthquake scientists need
to simulate a lot of different earthquakes so we need a lot of supercomputing time!
Thanks for your help with this. It looks very good. Please let us know if you have
questions or would like clarifications on any of this material.
[email protected]
Phil Maechling