GeologicalProcessesActivity3Earthquakes

Student Exploration: Earthquakes 1 – Recording Station Vocabulary: body wave, earthquake, epicenter, fault, focus, P-wave, S-wave, seismic wave, seismogram, seismograph Prior Knowledge Questions (Do these BEFORE using the Gizmo.) (2 marks) 1.Have you ever experienced an earthquake? If so, what did it feel like? My mom did. Firstly she felt Inaudible sound around the entire building, Entire building once. 2.Earthquakes are usually caused by the sudden movement of rocks along a fault, or fracture, in Earth’s crust. The most famous fault in the U.S. is the San Andreas Fault in California. What major cities are located near the San Andreas Fault? San Francisco and San Bernardino. Gizmo Warm-up The Earthquakes 1 – Recording Station Gizmo simulates the seismic waves released by an earthquake. To begin, look at the key on the bottom left side of the Gizmo. 1.The epicenter of the earthquake is the point on Earth’s surface closest to the focus, or origin, of the earthquake. (2 marks) A.What symbol represents the epicenter? B.What symbol represents the recording station? 2.Click Play () and observe the seismic waves leaving the epicenter of the earthquake. (2 marks) A.What types of seismic waves are released? P-wave and S-wave. B.Look at the Recording station detector on the upper left side of the Gizmo. What happens when the seismic waves hit the recording station? A small amplitude wave was recorded when the purple wave passed, and a large wave was recorded when the green wave passed. Activity A: Reading a seismogram Get the Gizmo ready: Click Reset (). Check that the Distance from the station to the center of earthquake is 860 km. Introduction: An earthquake releases an enormous amount of energy, which passes through Earth’s interior in the form of body waves. There are two types of body waves: P-waves (primary waves) and S-waves (secondary waves). Scientists study earthquakes with the aid of an instrument called a seismograph. When seismic waves reach the seismograph, a graphical record, or seismogram, is produced. Question: How are P- and S-waves shown on a seismogram? 1.Observe: Click Play, and then click Pause () after the purple P-wave hits the station. (2 marks) A.Look at the upper right corner of the seismogram. At what time did the P-wave hit? At around the 154s. B.What is shown on the seismogram at this time? The purple wave hit the station. 2.Observe: Click Play, and then click Pause after the green S-wave hits the station. (2 marks) A.At what time did the S-wave hit? At around the 250s. B.What is shown on the seismogram at this time? The green wave hit the station. 3.Describe: Click Play and wait for the vibrations to stop. Suppose you were at the recording station when the earthquake hit. Based on the pattern of waves on the seismogram, what did you experience during the earthquake? (1 mark) I experienced a slight vibration (from P-wave) about 154 seconds after the earthquake, and after about 96 seconds I experienced relatively severe fluctuations (from S-wave), and relatively severe fluctuations continued two hundred seconds or so, then the vibration gradually returned to calm. 4.Explore: Click Reset, and drag the recording station closer to the epicenter. Click Play. A.How does this seismogram differ from the one you first investigated? (1 mark) Both kinds of fluctuations come faster and more intense. B. What would this earthquake feel like? (1 mark) C. Such an earthquake makes people feel more violent. Activity B: Distance to the epicenter Get the Gizmo ready: Click Reset. Place the recording station 300 km from the epicenter. (Does not have to be exact.) Question: How can you determine how far you are from the center of an earthquake? 1.Observe: Click Play, and observe the P- and S-waves. Which waves are faster? P-wave. (1 mark) 2.Measure: Wait until the seismogram is complete. Turn on Show time probe. Place the left (green) probe on the first P-wave, and the right (blue) probe on the first S-wave. (See example at right.) (1 mark) What is the Time difference (∆t) between the P- and S-waves? 100 seconds. 3.Predict: How do you think the time difference between the first P-wave and the first S-wave will change as the distance to the epicenter increases? (1 mark) The closer the station is to the earthquake center, the smaller the time difference. On the contrary, the time difference is greater. 4.Gather data: Place the recording station at each of the following distances to the epicenter. (Does not need to be exact.) Measure the P- and S-wave time difference (∆t) on the seismogram at each distance, and record the values in the table on the left. (3 marks) 5.Make a graph: Plot your data on the graph to the right of the data table. Draw a line to connect the points in order. What does this graph show? (3 marks) The time difference increases with distance (almost linear growth).