Fuzzy logic approach to control the magnetization level in the magnetic 2
Lab 2. Magnetic Anomalies Please write out your answers on ......Magnetic isochrones correspond to...
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OCEAN/ESS 410 1 Lab 2. Magnetic Anomalies Please write out your answers on a separate sheet of paper. In this exercise you are going to be modeling a magnetic anomaly profile using a Matlab program and interpreting magnetic anomalies on the Juan de Fuca plate off the coast of the Pacific Northwest. Figure 1 and 2 show location and magnetic anomaly maps for the Juan de Fuca and Gorda spreading centers off the coast of the Pacific Northwest. (a) First you are going to be working with Matlab to model a magnetic profile on the Southeast Indian Ridge. To do this you will 1. On the class web site the Labs tab of the class web site right click on link “Zip file for Lab Computers for Lab02”, select “Save Target As” and save to c:\courses\OCN410\YOURNAME. You may need to create this folder. 2. With Windows Explorer navigate to the directory with the zip file (c:\courses\OCN410\YOURNAME), right click on the lab02.zip file and select “Extract All”. 3. Start Matlab on the lab computer from the Start Menu. 4. In Matlab type execute “cd c:\courses\OCN410\YOURNAME\lab02”. 5. Type ‘warning off’ in the Matlab command window to suppress some annoying warning messages during step 6 6. Type ‘Modmag’ in the Matlab command window and press enter to run the program. You should get a new window with a fill in menu options for running Modmag. If you ever crash the program (i.e., it stops working), you will have to repeat this step. 7. To load the data and the initial parameters click the folder icon under ‘Parameter file’ on the top of the menu and open the file “swir.dat”. This loads the data and sets the model up to run with a spreading rate of 20 km/Myr = 20 mm/yr. Click Run to calculate an initial model. A Synthetic Model window will pop up with the data in blue and the model in red. It will not fit the data well because the spreading rate is wrong 8. Your objective is to fit the data by adjusting the spreading rate and the level of spreading rate asymmetry in 4 Myr increments. Note that a positive asymmetry implies faster spreading to south of the ridge axis (i.e., to the right in your plots). You can adjust the parameters manually and then click Run to compute a new model in a new Synthetic model window. a. Start by trying to fit the profile with a constant spreading rate. The easiest thing to do is focus on matching the width of the central high at the ridge axis and then when that is about right make small adjustments to match the other highs. b. Once this is accomplished work with each 4 Myr increments making fine scale adjustments to the spreading rate and asymmetry to match the location of the lows and highs.
Transcript of Lab 2. Magnetic Anomalies Please write out your answers on ......Magnetic isochrones correspond to...
OCEAN/ESS 410
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Lab 2. Magnetic Anomalies Please write out your answers on a separate sheet of paper. In this exercise you are going to be modeling a magnetic anomaly profile using a Matlab program and interpreting magnetic anomalies on the Juan de Fuca plate off the coast of the Pacific Northwest. Figure 1 and 2 show location and magnetic anomaly maps for the Juan de Fuca and Gorda spreading centers off the coast of the Pacific Northwest. (a) First you are going to be working with Matlab to model a magnetic profile on the Southeast Indian Ridge. To do this you will
1. On the class web site the Labs tab of the class web site right click on link “Zip file for Lab Computers for Lab02”, select “Save Target As” and save to c:\courses\OCN410\YOURNAME. You may need to create this folder.
2. With Windows Explorer navigate to the directory with the zip file (c:\courses\OCN410\YOURNAME), right click on the lab02.zip file and select “Extract All”.
3. Start Matlab on the lab computer from the Start Menu. 4. In Matlab type execute “cd c:\courses\OCN410\YOURNAME\lab02”. 5. Type ‘warning off’ in the Matlab command window to suppress some annoying
warning messages during step 6 6. Type ‘Modmag’ in the Matlab command window and press enter to run the program.
You should get a new window with a fill in menu options for running Modmag. If you ever crash the program (i.e., it stops working), you will have to repeat this step.
7. To load the data and the initial parameters click the folder icon under ‘Parameter file’ on the top of the menu and open the file “swir.dat”. This loads the data and sets the model up to run with a spreading rate of 20 km/Myr = 20 mm/yr. Click Run to calculate an initial model. A Synthetic Model window will pop up with the data in blue and the model in red. It will not fit the data well because the spreading rate is wrong
8. Your objective is to fit the data by adjusting the spreading rate and the level of spreading rate asymmetry in 4 Myr increments. Note that a positive asymmetry implies faster spreading to south of the ridge axis (i.e., to the right in your plots). You can adjust the parameters manually and then click Run to compute a new model in a new Synthetic model window.
a. Start by trying to fit the profile with a constant spreading rate. The easiest thing to do is focus on matching the width of the central high at the ridge axis and then when that is about right make small adjustments to match the other highs.
b. Once this is accomplished work with each 4 Myr increments making fine scale adjustments to the spreading rate and asymmetry to match the location of the lows and highs.
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9. At any time you can save your current parameters for reloading later using the Save→Parameter File option from the menu on the preferred Synthetic Model window. Save with a different name from swir.dat since you do not want to overwrite the starting configuration
(i) Print out your best fitting model to the lab printer using the print→printer menu option in the Synthetic Model window. One copy per student. (ii) Write down your final choices of spreading rate and spreading rate asymmetry. (iii) Using the anomaly key on Figure 2 which shows magnetic isochrons 1, 2, 2A etc. as a function of age, label the magnetic isochrons you can see on your profile. Magnetic isochrones correspond to peaks in the magnetic anomaly (or times of normal as opposed to reverse crustal magnetization).
(b) Working with the magnetic anomaly map of the Juan de Fuca plate.
(i) Calculate a scale for the magnetic anomaly map (i.e., X cm on the map = Y km on the earth). Note: 1 degree of latitude equals 111 km. (ii) On the west side of the Gorda ridge near 42ºN, calculate the average spreading rate (in units of kilometers per million years, km/Myr) between isochron 5 and the present. Show your working with lines on the map and a clearly written out calculation on a separate sheet of paper. (Note that since you are working on one side of the ridge you will be calculating what is known as the half-spreading rate (or speed) since it measures the speed at which one plate is created. The full-spreading rate is twice this and measures how quickly the two plates are moving apart) (ii) The magnetic anomaly map shows a number of V-shaped discontinuities that look like faults. They are not faults but are the result of small offsets in the spreading ridge (look at the northward pointing V near 48ºN). What can you say about the history of the ridge offsets that produced these discontinuities? This is a hard question - we will discuss the answer in class.
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Figure 2. Magnetic isochron and fracture zone map of the Juan de Fuca region. Dots show individual crossings of isochrons. The age scale is at the left in Ma (million years) and shows the selected isochrons.
