CH221 Week 3 Lab_Earthquake Epicenter and Liquefaction Experiment (1)

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May 8, 2024

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Locating and Epicenter and Recreating Liquefaction Mr. John Misenheimer, 2019 Reading Assignment: Review Chapter 6.3 to understand how earthquakes can be located using 3 seismometers. Background: Approximately 26,000 seismometer stations constantly monitor the crust for seismic activity. Many readings are very minor earthquakes which go unrecognized by the general population. However, these seismometers become very useful when large earthquakes occur. As discussed in lecture slides, to locate the focus/ epicenter of an earthquake, it takes at least 3 seismometers to triangulate where the quake occurred. Scientists used seismogram data to back calculate where an earthquake may have occurred and plot their findings on a Travel-Time Graph. Therefore, understanding how to read a seismograph and Travel-Time Graph is important part in understanding seismology. As you know, large earthquakes can devastate cities and regions without much warning. They destroy buildings and roads and underground pipes by violent shaking, or which can move the ground many meters or even it into a moving material akin to a liquid. This unique effect from earthquakes is called liquefaction. Today you will learn more about this process. Purpose: The purpose of this lab is two-fold. One is to locate the epicenter of an earthquake using the attached handout. Secondly, you will demonstrate the process of liquefaction and interpret what damages can result from these events. Two small

heavy objects will act as an urban structure and you will simulate the effects of liquefaction often observed during large earthquakes. Materials: Attached handout: Locating an Earthquake Epicenter A small plastic tray, plastic bin approximately 8 in. x 6 in. x 3 in. Sand Water 2 Small heavy object (a small can of tomato paste represents a good size to mass ratio, but use whatever you can obtain from home) https://www.youtube.com/watch?v=b_aIm5oi5eA Part 1 Procedures and Exercises: Your first objective is to follow the questions in the worksheet. I will summarize here: 1) Examine the first seismogram that you see on page 1. Noting that each vertical line represents 1 minute, determine the time that the p and s waves are separated. Put your answer in question #2. 2) On page 3, observe the Travel Time Graph. Your objective is to use the data from Question 1 to determine how far apart the p and s waves must be on a seismogram. You start by using the miles given to you and find that number on the x (bottom) axes. Once you find your miles, go straight up and note the time that the p-wave and s-wave show.

For example, at 3000 miles, the p-wave time is approximately 8.5 minutes (look at the y-axes at the point 3000 miles hits the p-wave curve). I continue up until I hit the S-wave curve. This time shows to be 15.2 minutes (my estimate). I then subtract the P-wave from S-wave times to get the time difference. My answer is 6.7 minutes different. This means that my S-wave arrived 6.7 minutes after my first P-wave on the seismogram. 3) Use the information from Figure 1 to answer Question 3. 4) Complete Table 1 by studying the 3 seismograms from Los Angeles, Houston and St. Louis. First, determine the distance between the P and S-waves for each seismogram and record it in the table. Next, find the location on the Travel Time Graph that shows a gap between the curves that matches the time you found from the seismogram. For example, at about 280 miles there is a time difference between P and S of 1 minute. You have to look at both curves and subtract to show the difference at any specified miles. 5) Once you completed your table, begin to draw your circles on your map. Using the bottom scale to measure how to draw your circle, take one of the three miles you found and find its length. For example, if you said that the epicenter of the earthquake was 2500 miles from Houston, you would measure the entire scale using a ruler. You found that the length of 0 to 2500 miles on the scale was 5.2 inches. 6) Ideally you would use a compass to draw your circle, set at your measured distance. As a replacement, you can place multiple dots around Houston in all directions (exactly 5.2 inches in all directions) until an incomplete circle appears. Connect the dots to complete your circle. Do the same for your measured distance for St. Louis and Los Angeles. 7) Somewhere on your map your three circles should intersect at one point. Place a star where the three circles meet. This is your earthquake epicenter. Response  Answer the following questions.

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