EQ Lab (2)

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Georgia State University *

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1121

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Geology

Date

Oct 30, 2023

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pptx

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Uploaded by ConstableHawk4507

Earthquakes Lab Earthquake seismology methods Name: GEOL 1121K Earthquakes are a fact of life on Earth and mark distinct moments in history especially when there are devasting effects on communities around the world. Not only do they result in casualties, but they can cause damage to vital infrastructure, housing, and other basic services. The earthquakes that make the news are usually the big ones. For example, the magnitude of the 2004 Indian Ocean earthquake that resulted in a quarter million casualties was a 9.2 magnitude. The 1906 San Francisco earthquake was a magnitude 7.9. The catastrophic 2010 Haiti earthquake was a magnitude 7.0.. Oklahoma experienced human-induced earthquakes as large as magnitude 5.8; this caused building damage and much public dismay. But below magnitude 3, few people are likely to feel an earthquake, even in populated areas. One would think, given our knowledge of earthquakes, that humans would avoid these locations – however, the very faults of the Earth also create its greatest advantages. It is extremely common to find human settlement along fault lines where earthquakes occur most frequently. Recent studies have revealed that there may be more to the pattern than previously thought. Tectonically active plates may have produced greater biodiversity, more food, and water for our human predecessors. Certain landscape features formed by tectonic processes such as cliffs, river gorges, and sedimentary valleys create environments that support access to drinking water, shelter, and an abundant food supply. Lab Outline • Part 1: Time-Travel Curves • Part 2: Nomograph, Seismographs, and Time-Distance chart • Part 3: Earthquake Triangulation • Lab Guide Deliverables • Powerpoint document • Triangulation map It is not known when exactly earthquakes will occur, but as scientists, we can estimate where they will happen, and roughly how big they will be. This laboratory exercise introduces you to some of the basic procedures used to estimate earthquake time and source locations. After the completion of this lab, you will have learned how to read seismograms to estimate P- and S-wave arrival times, determine magnitude energy, use a travel-time curve to obtain distances from the seismometers to the epicenter, and be able to map epicenters using Google Maps. Volcanoes and earthquakes are not randomly distributed around the globe. Instead they tend to occur along limited zones or belts. With the understanding of plate tectonics, scientists recognized that these belts occur along plate boundaries.

Some food for thought…

1. How long would it take a P-wave to travel 8,000 km? Approximately 11 minutes and 20 seconds. PART 1 : Be sure to read the Lab Guide packet first before starting the lab. It contains useful literature and examples to help you complete the lab. Answer the following questions by using the time travel curve charts below. Show your work by using the lines provided to mark the graph. Move and resize the lines (horizontally and vertically) as needed.

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2. How far can an S-wave travel in 9 minutes? 22 minutes and 20 seconds

3. If an earthquake occurs at 02:11:20, at what time do you expect the S-wave to arrive at a seismic station that is 9,000 km away? Show your work by typing out your calculations. Distance from station= 9000 km 2:11:20 + 0:22:20 = 2:33:40 Time of occurrence = 2:11:20 pm it will arrive at 2:33:40 wave = 00:22:20

4. If an S-wave arrives at a station 4,400 km away at 07:45:00, what time did the earthquake originate? 13 minutes and 40 seconds

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5. A P-wave arrived at a seismic station 3,200 km away at 06:10:00. What time did the first S-wave arrive at this station? Graph tip: Resize the bar to where the two black ticks are aligned (with either the S and P-wave curves or the y-axis, depending on the question), then copy and paste the scrap paper which will create a new one with the same measurement. Move the pasted scrap paper to the final position. 4 mins and 40 secs

6. The first P-wave arrived at a seismic station at 06:32:20. The first S-wave arrived at the same seismic station at 06:34:20. How far is this seismic station from the epicenter? Graph tip: Resize the bar to where the two black ticks are aligned (with either the S and P-wave curves or the y-axis, depending on the question), then copy and paste the scrap paper which will create a new one with the same measurement. Move the pasted scrap paper to the final position. 70.59 km

1) Imagine that we have already examined several seismograms and calculated the lag time and amplitude of waves. Use the following nomograph to find the magnitude of different earthquakes. To use the Nomograph, move and resize use the colored lines (to the left of the table) to connect the provided S-P time and amplitude. Where it crosses over on the Richter scale indicates the magnitude. Be sure to place the lines precisely and record the magnitude on the table. Line A has been drawn as an example. Once the table is complete, answer the two questions to the right. LAG TIME (S-P) MAGNITUDE AMPLITUDE (in mm) A 2 seconds 0.6 0.1 millimeters B 2 seconds 4 200 millimeters C 4 seconds 1 0.05 millimeters D 20 seconds 3 0.5 millimeters E 50 seconds 6 20 millimeters F 50 seconds 6.75 200 millimeters G 60 seconds 4.8 1 millimeter Which of the above events was the most significant (largest)? ____F_ ___ Which of the above events was the least significant (smallest effect)? ___A _____ PART 2 : Determining the epicenter location Step 1: Nomograph

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A Richter 3.0 earthquake occurred in the New Madrid region around 3:46 AM on June 19, 1987. Three different locations provided their seismograph recordings below. Follow the four steps to find location of the earthquake. 2) Determine the arrival times of P and S waves using the seismographs below. First, move/resize the colored lines onto the seismograph to precisely measure the P and S arrival times. The P and S arrivals for Station LTN have been marked for you as an example. Write these times in the table below. Then, calculate the lag time by subtracting the two times from each other. Write this in the third column in the chart below. Distance will be calculated on the next slide. Step 2: Seismographs Station ID P arrival time S arrival time Lag time (S – P) Distance (in km) (for example: 03:47:20.2) LTN 03.46.45 03.46.50 0.0.05 33 km GOIL 03.47.00 03.47.17 0.0.17 140 km POW 03.47.02 03.47.20 0.0.18 152 km 03:46:45.6 03:46:50. 0

3) Next, you will be plotting your calculated lag times (from above) onto this chart to determine distance from the earthquake. Move/resize the lines (vertically and horizontally) onto the graph to help precisely read the distance from earthquake on this graph. Provide your answers in fifth column of the previous data table.

4) In this exercise, you will be using IRIS’s Earthquake Triangulation Interactive Map to pinpoint the epicenter of the earthquake using your previous data. First, you will need to determine the latitude and longitude for each station in the map below to the nearest tenth degree. It may be helpful to draw gridlines for accuracy. The orange lines are drawn as an example for you. NOTE : • Latitude : Positive values are north of the equator (0° – 90°), and negative values are south of the equator (0° – -90°). • Longitude : Positive values go east from 0° – 180° (i.e., the prime meridian), and negative values go west from 0° – -180°. Record your coordinates in the table below. They must be to the nearest tenth degree (for example: 32.14, -88.50). Circle radius is the distance value that you recorded on the table in Part 2, Step 2. Continue to the next page. Name Latitude Longitude Circle_radius LTN 36 N -89.5 W 33 km GOIL 37.25 N -88.6 W 140 km POW 36.15 N -91.2 W 152 km Latitude = 36.15 Longitude = -91.20

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Follow these instructions: A. At the top right corner, click on the button. B. A station will randomly appear on the map and will be listed at the bottom of the window. Enter the name of the station as listed in the previous table. C. Type in the correct Latitude and Longitude of your station, which will automatically relocate. D. Then, type in the distance from your station to the earthquake as calculated using P and S arrival times on your seismogram, which will adjust the circle on the map to have a diameter equal to the distance to the earthquake. The circle size can also be changed on the map by clicking on the circle and moving it. E. Click on to add the next station. Do this until you’ve entered all 3 seismic stations. F. Click on button to see all your stations and make sure that your coordinates are correct. G. The three distance circles should nearly overlap at one location. H. Click on the left-hand menu button , then click on User Event and Show Marker. ZOOM OUT on the map and find the epicenter marker . You can then move the marker to the intersection point of your three circles, which will give you the Latitude and Longitude of the earthquake epicenter here. Once you’ve moved the marker to the epicenter location, go back to “User Event.” Record the exact coordinates of the June 19th quake below (to the nearest tenth of degree):  Latitude: 36.26  Longitude: - 89.54 Part 3: Earthquake Triangulation Next, go to https://www.iris.edu/hq/inclass/software-web-app/earthquake_triangulation . This interactive Google Maps website by IRIS allows you to easily plot stations and distance circles to demonstrate how earthquakes can be located using the time difference in the arrivals of P and S waves at a set of seismic stations. Click the green “Open Resource” button which will open up the interactive map viewer. Click on the map’s menu button and scroll down to . Adjust the zoom so that your three circles fit within most of the ”print” screen, and that the epicenter marker is visible. Print it as a “PDF file .” Save it on your computer and submit on iCollege with this lab. This is your second deliverable.