assignment2_2024

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Cornell University *

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Electrical Engineering

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Apr 3, 2024

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Assignment#2 EAS 3880: Global Geophysics: Due Feb. 2, 11:59pm This exercise has two goals: 1) learn about plate boundaries and current plate motions; and 2) learn how to download and manipulate GNSS data in matlab. In class we talked about how to get access to matlab. If you haven’t used matlab before, check out the online resources and videos at: https://www.mathworks.com/help/matlab/getting-started-with-matlab.html Generate the plots (numbered) and answer the questions (numbered with #) below. Turn this in as a single file with text and figures merged together instead of sending multiple files. Step 1: Make plate boundary and motion maps Go to: https://www.unavco.org/software/visualization/GPS-Velocity-Viewer/GPS-Velocity- Viewer.html  click on “Display volcanic centers” and “Display plate boundaries”  click on the green button to “Draw Map”  Zoom in on Western North America spanning from Baja California to the Aleutian Islands. Make plot 1 as a screen shot. Label the three tectonic plates and use the colors of the plate boundaries (see legend below) to label the different types of plate boundaries as “Divergent”, “Convergent” and “Transform”  Make plot 2 by changing the GNSS data source to “Modeled, North American, GSRM” and “How many markers displayed” to “Show one in five”  click on the green button to “Draw Map”  Take a screen shot that shows the motion of the Pacific plate relative to North America from Vancouver Island, Canada to Kamchatka. Answer question #1: How does the angle of convergence between the Pacific and North American plates relative to the plate boundary change from easternmost (Juneau) to westernmost Alaska (Attu Station)? In your own words describe why relative plate velocity (magnitude and direction) is important for potential earthquakes. Step 2: Download data from UNAVCO for station ALBH •Click on GNSS Data source: “N. America, NAM14, UNAVCO” Click “Draw map” •Zoom into Seattle Washington and make plot 3 as a screenshot showing the GNSS measurements. #3 Briefly describe what is NAM14 and how these stations are moving in this reference frame. Speculate as to why these stations are moving in this direction. Hint: https://www.unavco.org/software/visualization/GPS-Velocity-Viewer/GPS-Velocity-Viewer-frames.html •Click on “Station labels and data download” Click “draw map” •Double click on the green box that is the ALBH station near Victoria, Canada •Once the data opens up, click on “Download data file [csv]” [Note: if the csv file doesn't download, right click on the "Download data file" and select open link in a new tab] You will have to make an account to download data but this is fast.

• You should now have “ALBH.cwu.nam14.csv” Put it in a directory with the matlab files you downloaded from canvas. Step 3: load into MATLAB using the program load_data_pbo.m, editing hw2.m as necessary. Step 4: Create plots of E, N, and U displacement at ALBH (with titles and axes labeled – plots 4-6), modifying hw2.m as necessary. #4 What is the value for the slope of each line? #5 What is the physical significance of this value? Step 5: Find and plot (plot 7) the dates of the slow earthquakes as red lines on the E displacement time series between 1/1/2013 and 1/1/2019 (see example in hw2.m). Concentrate on the E displacement. You may find this easier to do if you zoom in and first remove the linear trend (or not) – see example in hw2.m . You can also look at the raw data file for offsets. #6 How many slow earthquakes did you find? #7 How frequently do they happen? Are they periodic? Why or why not? Step 6: Test your picks of the slow earthquakes by comparing your red lines to the U and N time series for ALBH (plots 8 and 9). #8 How do they compare – do the slow earthquakes show up on the U and N components? Do the times match the E component? #9 Why or why not? What other processes besides slow earthquakes could impact the vertical velocities? Use the UNAVCO tool to download at least one other GPS time series from a station near ALBH. Plot your red lines on the E component for the new station, plot 10 (be sure to label the station name). #10 How do the time picks for the slow earthquakes from ALBH compare with your selected station? #11 Speculate on why the timing or ease of detection of events might be similar or different. Zoom into ALBH E component from 1/1/2019-2024 (plot 10) #12 Describe how the characteristics of slow earthquakes in the last few years are different from the ones you looked at from 1/1/2013-1/1/2019. Specifically mention the duration, offset, inter-event timing, and whether the onset of the slow earthquakes is abrupt or gradual.

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