Geology 100, Phil Farquharson, presiding Second Writing Assignment Spring 2017 Weathering, Sedimentary Rocks, Metamorphic Rocks, Geologic Time, Deformation, Earthquakes (Chapters 6 through 11)Page 1 of 2
The subject is Earthquakes.
1. LOCALLY… First we’ll consider the types of faulting we have in southern and central California (up to Cape Mendocino). They’re called strike-slip faults, and are found where one block of crust is sliding horizontally past another. The most famous of these is the San Andreas Fault (SAF), which runs from the corner of the Salton Sea 700 miles north-by-northwest to Cape Mendocino, The earthquakes produced by this fault can be large as 8.0+ which is rather impressive, but pale in comparison to truly “great” earthquakes like the 2011 Japan (Tohoku) earthquake and tsunami.
So for the first part of this assignment, let’s take a look at our local ‘cousin’ of the SAF, the Rose Canyon Fault (RCF).
Study the following resources:
• The web page “Significant Earthquakes and Faults” at http://scedc.caltech.edu/significant/ – note the various faults in our neighborhood, and how often each has produced earthquakes.
• The video “The Rise and Fall of San Diego” which I have posted in YouTube, with Closed Captioning (cc), at http://youtu.be/-drjJoRGfAk – thanks, Dr. Pat Abbott!
• Another Pat Abbott video “Earthquake Country Los Angeles” (note that the Newport-Inglewood Fault he talks about continues south from Newport Beach underwater, until it emerges as the Rose Canyon Fault at LaJolla and continues through Old Town, Downtown San Diego and across the bay past Coronado. It’s on my YouTube Channel (cc) at http://youtu.be/axLLD80Aa9I, again with closed captions.
• The web page “Recent Earthquakes in California and Nevada” at http://scedc.caltech.edu/recent/ – note the number at the lower left of the map (758, as I write this). That is the total number of temblors detected by seismometers in the last week. Most are too feeble to be felt, fortunately!
• From Scripps Institution of Oceanography comes a very recent (7 March 2017) study of the Newport-Inglewood/Rose Canyon Fault which suggests that an earthquake with a magnitude of up to M7.4 could happen. The link to the actual SIO study is http://news.agu.org/press-release/fault-system-off-san-diego-orange-los-angeles-counties-produce-magnitude-7-3-quake/ – if you’d like an abbreviated version, do a Google search.
Question #1:
I want you to think about earthquake preparation. You have probably been bombarded with information from all sorts of government entities
a. Which scenario should someone in San Diego be more concerned about, a magnitude 8.1 on the stretch of the San Andreas Fault from the Salton Sea to San Bernardino, Wrightwood and Palmdale, or a magnitude 7.1 on the offshore portion of the Rose Canyon / Newport-Inglewood Fault (Dana Point to LaJolla)? Explain your answer.
b. What steps should you take to lessen the effects of an earthquake to you and your loved ones? Remember, you will be responsible for taking care of yourself for three days with no power, no cell service and streets impassible. Think about your furniture, your food and water supplies, medications, etc.
c. Just for fun, think about the worst place(s) to be when a big earthquake strikes. (I know that after the Northridge quake in 1994, I neither wanted to be on top of an overpass, nor stopped under one!)
Your answer should be no less than 300 words. (25 points)
Geology 100, Phil Farquharson, presiding Second Writing Assignment Spring 2017 Weathering, Sedimentary Rocks, Metamorphic Rocks, Geologic Time, Deformation, Earthquakes (Chapters 6 through 11)Page 2 of 2
2. GLOBALLY… Let’s take a look at how many earthquakes occur in the world every hour of every day. Even discounting the tiny shakers that most people can’t feel (less than about 2.5 or so), the number is staggering – for the year 2011, there were more than 9,000 earthquakes with a magnitude of 4.5 or greater, which is quiet impressive when put into an animation like the one shown in the animation in Blackboard entitled “2011 World earthquakes Visualization map” (web link is https://youtu.be/h4SULuWS9eQ) – note the pattern of the yellow dots (epicenters) left behind. Doesn’t it look a lot like the figure in your book showing earthquake concentrations?
But note that the really big quakes are only at convergent plate boundaries, especially where subduction is involved. The biggest earthquake ever recorded happened in 1960, off the coast of Chile. It was a magnitude 9.5, and created an ocean-crossing, devastating tsunami. All of the really big tsunami-creating earthquakes have been on the so-called Ring of Fire, plus one off the northwest edge of Sumatra. I’ve already mentioned the San Andreas Fault, which is NOT capable of generating tsunami (in spite of the really bad 2015 Hollywood movie “San Andreas” (starring Dwayne “The Rock” Johnson)). But where the San Andreas ends, at Cape Mendocino the Cascadia Fault begins. It stretches from just south of Eureka, California more than 700 miles to the north end of Vancouver Island, California, and generated a M9.0 earthquake on January 26th, 1700, with a tsunami that crossed the Pacific Ocean and washed on shore in Japan.
Study the following resources:
• The previously-mentioned video entitled “2011 World earthquakes Visualization map” (web link is https://youtu.be/h4SULuWS9eQ) It appears that the total amount of energy released by earthquakes on a year-by-year basis is relatively steady.
• A video entitled “Tsunamis Generated by Megathrust Earthquakes” at https://youtu.be/VJIdMvL9KcA – a ‘megathrust’ fault is the kind found at a subduction margin. In this animation we explore different tsunami-producing mechanisms by examining three famous earthquakes: Japan 2011, Chile 2010, and Alaska 1964 (text on YouTube says 2014, but no…).
• Another video, “Tectonic Earthquakes of the Pacific Northwest” at https://youtu.be/_belQwGNolY, shows the different types of earthquakes that can be expected in the Pacific Northwest.
• Brian Atwater gave a talk at a U.S. Geological Survey in 2015 about the solving of a mystery that had been vexing Japanese scientists since 1700 AD. The talk was entitled “Cascadia Earthquake of January 26, 1700 – Detective Stories from North America and Japan” and can be found at https://youtu.be/AiojgMBQPBM – the study is an Open-File Report, and can be downloaded from http://pubs.usgs.gov/pp/pp1707/. It’s another case that shows how the Scientific Method in action.
• Check out the San Diego County Office of Emergency Services “Tsunami Facts and Preparedness” web page at http://www.sandiegocounty.gov/oes/disaster_preparedness/oes_jl_tsunami.html – check out the brochures and inundation maps to see how you might be affected.
Question #2:
I live in Point Loma, at an altitude of 17 feet above sea level, 240 meters from Point Loma Sportfishing. Should I be concerned about preparations in the event of a tsunami generated by an earthquake off the coast of Chile (like the one in 2010)? The answer is, yes I am ‘concerned’ although in 2010 the tsunami did considerable damage in both San Diego Bay and Mission Bay, but did not rise up over the sidewalk. My questions to you, though:
a. What is the altitude above sea level at you residence? Where you work? Along your customary route of travel? Have you considered those ‘Tsunami Evacuation Route’ signs you may have seen along the coast?
b. Please explain the different ways a great earthquake like Tohoku 2011, Alaska 1964 or Cascadia 1700 can generate an ocean-crossing tsunami.
Your answer should be no less than 300 words. (25 points)