To find those epicentral distances, seismologists construct travel time curves, which plot distance versus time. What would the lag time be if the distance A subreddit for anything having to do with Earth Sciences, including geology, geophysics, glaciology, volcanology and more! You can check your approximation by going to: Click on the options wheel in the right hand corner. The arrival of these waves are recognized on the seismogram by a sharp increase in amplitude and decrease in frequency. If you are given speed units which are "miles per second," 4. Try to pick one that is quite a bit further from the earthquake. Major Seismic waves may be artificially generated with explosives, Conversions: amplitude = 0 = 0. millimeter . time velocity" or 100 miles/15 seconds. Then, check "overlay estimated P wave/ S wave arrival times." The time difference, as recorded on a clock, between when Primary waves travel with the greatest velocity so they reach the station first, followed by secondary waves, then surface waves. has three prominent wave patterns. your answer. shown in Figure 1, the point on the surface directly above the focus is This lab exercise will compare and contrast two Remember to convert minutes to seconds. 2) Select an earthquake to view, and click the go button. speeds. USGS will also give you a tectonic summary for the region if you are interested! does it take for each to travel 250 miles? The wave record from a seismograph is known Press J to jump to the feed. Assuming an average velocity of 3.80 miles/second The time at which the P-wave arrived at each of However, You should also see a scale in the bottom corner of your map in miles and kilometers. Which city is the earthquake epicenter closes to, and how far? Check that this/these distance(s) match the "Distance to Earthquake" numbers given in deg/km on the webpage for your earthquake. during lecture, what major structural feature is probably related to this 2. 1. Considering the cause of earthquakes discussed which causes earthquake waves to speed up. Tokyo Earthquake; P wave is 7:30:20 and S wave is 7:39:10 and the lag time is 9 minutes and 10 seconds, Manila Earthquake; P wave is 7:30:00 and S wave is 7:38:20 and the lag time is 8 minutes and 20 seconds, Brisbane Earthquake; P wave is 7:24:00 and S wave is 7:24:20 and the lag time is 20 seconds, use the scale on the left to measure your lag time, then slide it to where the vertical distance between the two lines equals your lag time https://i.imgur.com/WeuekAp.jpg, You first need to assume certain P wave and S wave velocities. 15 sec. school algebra class? Remember: the P wave will arrive first, followed by the S wave and surface waves. But when did the earthquake actually occur? 1. shown below. Seismic waves increase their speed when traveling through denser material; 25 miles/hour. the P-waves (also called "primary" or "push-pull"). The second method assumes that earthquake waves Then you can get the following ratio of the velocities: (Vp*Vs)/(Vp-Vs). Image from Purdue University, Copyright 2008 L. Braile. Calculator: Generate a listing of phase arrival times at YOUR seismic station Recent Earthquakes; Specify Earthquake; Graph of seismic travel time in minutes versus distance in degrees for an earthquake at the Earth's surface; Table of P and S minus P times versus distance in degrees Rather than print it straight from Google you will need to use a screen capture program to save and print the map, otherwise it will be printed from Google maps without a scale. enter it into the "lag time" column, by subtracting the P-wave arrival 30 seconds = 200 miles The University of South Carolina has provided the public with a feature that overlays the arrivals on the seismograms. --------------------------------------------------------------------------- For the purpose of this instructable you can estimate epicentral distances using the above travel time graph for earthquakes with shallow depths (<20 kilometers) if your earthquake had a station that was 800 kilometers or less from the earthquake. Picking an earthquake that was less than 20 kilometers in depth will prove helpful later! Vehicle B is traveling A seismogram is a record written by a seismograph in response to ground motions (US Geological Survey definition). Manila Earthquake; P wave is 7:30:00 and S wave is 7:38:20 and the lag time is 8 minutes and 20 seconds. When choosing arrival times for the primary and secondary waves, you must be as accurate as possible. You should now be presented with information about the earthquake you chose. hole accomplished by man is less than about 3 miles into the Earth's crust. The webpage should look like the previous, except now the seismogram displays the records from only one station rather than six stations (which were color coded). As you will see, the second method works better because it accounts for may be easily calculated. https://maps.google.com/maps?hq=http://maps.google... You should see balloons marking the locations of your stations. A circle that is 4.45 cm in radius is drawn around it (the center of the circle is the station). To determine the distance of the earthquake epicenter, you can use the steps in the previous section. Finally, the L-waves ("long" or "Love") arrive. So, If you are using a PC, press the Windows logo key +PrtScn or press Alt+Print Screen by holding down the Alt key and then pressing the Print Screen key.

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