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Lab 11.2 -- How Seismic Waves Travel Through Earth Learning Goal You will use travel-time data from an actual earthquake recorded by several seismograph stations to construct travel-time curves for P-, S-, and surface waves. Data from five seismograph stations that recorded a magnitude-7.2 earthquake on May 6, 2019, are given in Fig. A11.2.1. The earthquake focus was ~127 km below eastern Papua New Guinea, with an epicenter location of 7.0 ° S , 146.6 ° E . Travel times for the first arrival of P-, S-, and surface waves are given in decimal minutes to make it easier to plot the data on a travel-time graph.
A.Plot the travel-time data on the graph in Fig. A11.2.1. a.Use the distance to the epicenter and the travel times to plot the first arrivals for each of the seismograph stations listed in the table. Use a pencil as you plot each point carefully, using the grid lines to assist you in interpolating the point location on the graph. (Blue = primary, Red = secondary, Purple = surface) b.Notice that the points associated with each of the seismic-wave types seem to plot along a line or curve across the graph, so there seems to be a systematic increase in travel time with increasing distance from the epicenter. Lightly sketch a line or curve through the data points you plotted for each type of seismic wave—three lines/curves in total. Be certain that your lines/curves pass through each of the data points that you plotted. When you are confident in both the location of the points you plotted and the lines/curves through those points, darken them so your teacher can see your work clearly. (Hint: Look at Fig. 11.5 for guidance.) (tried to make lines curved and straight but didn’t really work. Sorry!) c.Label the curve that represents travel times of P-wave first arrivals. Now do the same for the two lines/curves associated with S- and surface-wave first-arrivals, respectively. d.Briefly explain why these points (and all similar points from other earthquakes) occur along three discrete lines or curves.