104 Lab3 _ Earthquakes (3)

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Apr 3, 2024

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104 Lab - Earthquakes Page 1 104 Lab– Earthquakes and Earthquake Hazards Name: Date: Part 1 - Stress and Strain: After watching the video on stress and strain, take a few minutes to make some observations. For example, do the blocks move at the same time? Do the yellow strings stretch at the same time? What happens to the amount of strain (on the top graph) when a block moves? What else do you notice? Jot your ideas down. Part 2 - Seismic Waves: All waves are an expression of energy. The energy causes the ground to move and that movement can happen in many ways—so there are several types of waves. Seismographs record three types of seismic waves generated by earthquakes: Primary (P) Waves and Secondary (S) Waves and Surface Waves that travel along the Earth's surface. Study the four diagrams and the videos that accompany them. Pay close attention to the movement of the boxes and the shape of the boxes. 1a. What happens to the boxes (e.g. the ground) when a P-wave passes? 1b. What happens when an S-wave passes? 1c. Although S waves and Rayleigh waves look similar at first, there is one big difference. What is it? 2. Which waves have the lowest amplitude and which have the highest amplitude according to the seismogram? Which do you think might cause the most damage?

104 Lab - Earthquakes Page 2 Part 3 - Seismic Waves and Different Types of Substrates: Different types of ground experience very different kinds of shaking. Damage caused by earthquakes is cause by four factors: earthquake magnitude (size), distance to the fault (how far you away you are), ground type (substrate), and engineering (how well a building is made). 3.a. In the video, which waves caused the most damage? The least? 3b. Which building (by color and location) was damaged the most? The next slide shows seismograms for an earthquake for three locations in San Francisco. They are also below. 3c. In the seismograph, circle the surface waves. 3d. Comparing the seismograms to the city locations, where is the safest place to be? Why do you think that is? In ground that contains a lot of water (near lakes, rivers and especially the oceans), shaking can cause the water to move in a process known as liquefaction. 4a. Find both your house and CSULB on the liquefaction map for LA Basin (green area). These zones are prone to liquefaction and heavy damage. Is your home in an area likely to experience liquefaction? What about the campus? 4b. Watch the demonstration. Describe what happens to the ground, the house and the cars.

104 Lab - Earthquakes Page 3 Part 4 - Determine the Location of an Earthquake: 5. Locating the Epicenter of an Earthquake ( Part 1 ). Complete the Table 1 . Use the Seismographs ( Figure E ) to determine the S-P Time Interval at each of the three recording stations. Also, measure the amplitude of the highest seismic wave at each recording station. To determine the location of an earthquake’s epicenter, a seismologist requires at least three seismograph locations. Once a seismologist knows how far each seismograph station was from an earthquake’s epicenter, circles for each seismograph can be drawn on a map, Where the three circles intersect marks the location of the earthquake’s epicenter. Use the Time verses Distance Graph ( Figure F ) to determine the distance from the recording station to the epicenter. Place a piece of paper along the axis and mark off the amount of time for each station on the edge of the paper. Keeping the straight edge of the paper perpendicular to the X-axis move the marked paper edge along between the S-wave cure and the P-wave curve until the distance separating the two curves is equal to the distance (time) you just marked off. Draw a line straight down to the X-axis. This is the distance. Use a drawing compass and the distance, in km ( Table 1 ) to draw circles centered on the respective cities on Figure G . Use the distance scale at the bottom of the Figure G to approximate the radius of each circle. When an earthquake occurs, the S waves travels more slowly away from the earthquake’s focus than the P waves, causing the S waves to lag further behind the P waves as they move through the Earth. So, the further from an earthquakes’ focus/epicenter, the greater will be the difference in the arrival time of the first P and first S wave at the seismic station. To determine when an earthquake occurred, you must first know the how much time elapsed between the arrival of the first P and first S wave. For the earthquake that was detected in Bellingham, WA (Table 1). The elapse S-P wave arrival time: Seconds Use Figure F to determine the P-wave travel time. Using your “piece of paper” described above, place the piece of paper where the “zero” minutes mark aligns with the P-wave curve and the S-P-wave elapsed time mark aligns with the S-wave curve. Where the “zero” mark aligns on the P-wave curve, look horizontal across to the time axis to determine how many minutes it the P-wave to arrive at the seismic station. P-wave travel time: Seconds Subtract the P-wave travel time from the actual time of the first P wave arrival at Bellingham, WA seismograph station to determine when the earthquake occurred. Earthquake occurred at: Table 1 - Data from Time verses Distance Graph and Seismogrphs Recording Station Arrival Time of P Wave Arrival Time of S Wave S-P Time Interval (Seconds) Distance (Kilometers) Amplitude (millimeters) Bellingham, WA Ellensburg, WA Portland, OR

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