Assignment: Earth Structures, Earthquakes& River Systems
1) Annotate this photograph (taken earlier this semester near the Ohio River in West Virginia) by labeling the hanging wall "HW" and the footwall "FW" and marking the fault highlighted in red with shear sense arrows.
a. What kind of fault is this?
b. Would this fault accommodate horizontal shortening, horizontal extension, or transform motion?
c. This fault formed during the time period when Alfred Wegener argued Pangea was being assembled, about 300 million years ago - what kind of plate boundary characterized eastern North America at this time?
2) What is Elastic Rebound Theory and how does it related to the concept of the earthquake cycle and earthquake forecasting?
3) List and briefly describe 3 strategies or principles that have been or could be applied to avoid or minimize risks associated with earthquake hazards:
Locating and Interpreting a South American Earthquake.
For this exercise, you will locate a South American earthquake just as you did for the earthquake homework. The earthquake waveform records follow the questions below, and the seismic stations are located in the Google Earth .kmz file attached to this exam. Open the Test 2 folder in the sidebar and double click on the "Earthquake Exercise" folder to navigate to the relevant seismic stations in Google Earth.
4) Open the attached Google .kmz file and open the EQ exercise folder where you should see the three seisimicstations listed in the table below: LCO - Las Campanas Astronomical Observatory, Chile; TRQA - Tornquist, Argentina, and LVC - Limon Verde, Chile. Complete the table just as you did for the homework assignment and locate the earthquake in Google Earth. Note that there is a Travel-Time graph following the three seismic records to help you determine the epicentral distances. Drag your three location circles and your earthquake epicenter marker into the folder with the seismic stations and make sure to save your work in a new kmz file with your name in it and attach it to your test submission. (20 pts, including location circles plotted in Google Earth)
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Station
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P-arrival
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S-arrival
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S-P lag
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Epicentral Distance
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P-travel time
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Time of Quake
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LCO
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TRQA
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LVC
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Latitude:
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Longitude:
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Est. time earthquake occurred (average time of quake):
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5) Based on your earthquake location, briefly describe what tectonic setting and type of fault you would expect for this earthquake.
6) According to the U.S. Geological Survey, this earthquake registered a Magnitude 8.3, and the depth was 22.4 km.
a. How much more energy would a MW 8.3 earthquake release than a MW 6.3 earthquake?
b. Given the size of the earthquake, its tectonic setting, and the fact that most of its energy was concentrated beneath the seafloor, what would you expect was the biggest hazard that may have raised concern for this quake?
c. Only 11 fatalities were reported, most modern buildings survived the quake with relatively minor structural damage, but as illustrated in the video linked below, some buildingsin the most affected city of Illapel, Chile were severely damaged:
https://www.youtube.com/watch?v=HGAwXCWQrzc
After viewing this video, comment on what kinds of structures seem to have been most severely impacted and whether or not this is surprising based on what we learned in class. In addition, what do you think the intensity was at Illapel, and why? (seeMercalli Intensity scale appended after the seismic station records; you may also comment on what additional information would enable you to make a more confident Intensity ranking)
d. Search the Pacific Tsunami Warning Center message archive for the date of this quake (9/16/2015): https://ptwc.weather.gov/ptwc/archive.php?basin=pacific. Did they issue a tsunami warning for this quake? If so, what area did they predict would be most severely affected, and what wave height did they forecast?
Analyzing River Erosion and Flood Risk.
For this exercise, you will evaluate river erosion patterns and flood frequency relationships. After the first question below, most of the questions relate to the Le Sueur River in Minnesota, and there are related materials in the Google Earth .kmz file attached to the test.
7) Label the following features in the photograph below by filling in the call-out boxes provided:
Point Bar Cutbank Oxbow Lake Stream Cutoff
8) In the above image, which stretch of stream would you expect to have the fastest average velocity, the stretch between points A and B or the stretch between points B and C. Why? (Explain).
9) Go to the attached Google Earth file and double click on the "Le Sueur River Problem." Read the linked article in the Mankato Free Press (https://www.mankatofreepress.com/news/river-erosion-threatening-more-area-homes/article_c105d680-a77a-11e6-a7c6-db3646db71ee.html). The boss of your geotechnical consulting firm based in Mankato Minnesota read the attached story in the Mankato Free Press and thinks he smells some potential business. He has asked you to review the historical imagery in Google Earth for the area outlined in the red box. Place a red marker on top of any house you believe is at future risk from river erosion, and use the "path" tool to highlight with a red line at least two stretches of road that you believe are also at future risk from river erosion. Also use the red path tool to highlight bluffs that you believe are especially at risk of continued erosion in the future. Finally write up a brief (<250 word) executive summary explaining to your boss what the fundamental processes of stream migration are that are driving erosion in this neighborhood.Be sure to submit your Google Earth kmz file along with your test.
10) The article in the Mankato Free Press suggested that climate change may have something to do with the increase in flood frequency and increased rates of stream erosion along the Le Sueur River. In this exercise we will evaluatewhether it is possible that climate change may have led to an increase in flood frequency in this basin. There is a gauging station on the Le Sueur Riverat Rapidan Dam, USGS Station 05320500. In the pop-up box for Rapidan Dam I have included two links, one to information on the dam, and the other to the peak streamflow data for this gauging station.
a. First, review the information sheet on the dam. When was the dam built?
b. Also, characterize the landscape around the Le Sueur River in this area (i.e., Is it mostly forested, agricultural, urban or suburban?).
c. Note that Minnesota has been settled and farmed since the late 1800's. Given the age of the dam and the nature of the historical and present land use, is there any reason to think that any aspects of human development of this drainage basin since 1935 would have substantially affected flood peaks in the subsequent time period? (I.E., Is it likely that explanations other than climate change could explain changes in flood frequency in this basin?)
d. Open the tab-separated file of peak annual flood peaks and copy and paste it into an Excel Spreadsheet using the Paste Special (Text) command. To evaluate the possibility flood peaks have been increasing over time, first create a plot of the flood date vs. peak discharge (this should be similar to the plot that first appeared in the pop-up box). Add a linear trendline to the data. Based on this analysis, does the peak annual flood appear to have increased today vs. 1940? How much?
e. Now, use the data set to compare flood recurrence intervals between two eras - 1935-1975 and 1976 to Present. Climate scientists generally infer that the modern era of global climate change began to become discernible between the mid-1970s and the mid-1980s. Create Recurrence Interval plots for each era and title them appropriately. Find a best-fit trend for each era, and compare your best estimates for the discharges for the 2-year, 5-year, 10-year, 20-year, and 50-year floods in the table below. Is the hypothesis that flooding is becoming more prevalent in the Le Sueur valley supported by these data or not?
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Recurrence Interval
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1935 - 1975 Discharge
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1975 - Present Discharge
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2-year
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5-year
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10-year
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20-year
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50-year
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Be sure to append your spreadsheet to your test when you turn it in.
https://www.dropbox.com/s/0awep3sc9da5hri/Assignment.rar?dl=0