Locating the Epicenter The method of triangulation This

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Locating the Epicenter The method of triangulation

Locating the Epicenter The method of triangulation

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The method of triangulation by knowing the distance to the epicenter of at least

The method of triangulation by knowing the distance to the epicenter of at least three seismic stations we can determine, or triangulate, its location. 3 seismic stations Ellensburg The relative distance of the quake from each station The intersection of the three circles gives the location of the epicenter St. Louis San Diego

How do we go from this…. …to that? Ellensburg St. Louis San Diego

How do we go from this…. …to that? Ellensburg St. Louis San Diego

We will exploit the fact that S-Waves travel a little slower than P-Waves P

We will exploit the fact that S-Waves travel a little slower than P-Waves P S

We will exploit the fact that S-Waves travel a little slower than P-Waves Start

We will exploit the fact that S-Waves travel a little slower than P-Waves Start P S Time A Time B The distance between the Withgreater time thethe distance P and Sthe waves the farther we are from between P and S waves P P the epicenter! increases! S S

The Distance between the P and S Wave The time between the arrival of

The Distance between the P and S Wave The time between the arrival of the P-Wave and the S-Wave

Three seismograms of the same quake Station 1 P-Wave S-Wave Time in seconds Station

Three seismograms of the same quake Station 1 P-Wave S-Wave Time in seconds Station 2 9. 2 sec Step 1: Identify P and S-Wave Step 2: Measure the time between their arrivals Step 3: Do this for all three station seismograms Station 3

Three seismograms of the same quake Station 1 P-Wave S-Wave Time in minutes Station

Three seismograms of the same quake Station 1 P-Wave S-Wave Time in minutes Station 2 Station 3 9. 2 seconds P-Wave S-Wave 16. 5 seconds P-Wave S-Wave 21. 2 seconds

The Travel Time Graph Helps us convert the time interval between arrival times of

The Travel Time Graph Helps us convert the time interval between arrival times of P and S waves into distances from the epicenter for each station Station #1 50 9. 2 seconds 3, 000 km 16. 5 seconds 6, 500 km Station #3 40 Time (seconds) Station #2 S Wave 30 P Wave 20 10 21. 2 seconds 8, 750 km 0 _, ___ km 2, 000 4, 000 6, 000 8, 000 10, 000 Distance between epicenter and seismograph (km)

Finding the epicenter using triangulation This circle was drawn using a compass set at

Finding the epicenter using triangulation This circle was drawn using a compass set at a radius scaled to 3000 km using the map scale. Station #1: (Seattle) 9. 2 seconds 3, 000 km Station #2 (Sudbury) 16. 5 seconds The earthquake occurred Notice 6, 500 km the scale bar! along the Alaskan Aleutian Island Chain – Station #3 (St. John’s) an active subduction zone! 21. 2 seconds 8, 750 km 1, 000 km

Determining the magnitude of the quake We need to have two pieces of data:

Determining the magnitude of the quake We need to have two pieces of data: 1) The distance to the earthquake 2) The amplitude of the biggest recorded wave 20 mm Station 1: Seattle P-Wave Highest Amplitude S-Wave R & L-Waves

The Distance-Amplitude Graph Helps us determine the magnitude of an earthquake based on the

The Distance-Amplitude Graph Helps us determine the magnitude of an earthquake based on the distance to the epicenter and the amplitude of the highest wave Station #1: (Seattle) 9 min, 20 sec 5000 4000 100 6 50 5 20 3000 3, 000 km 2000 20 mm 1000 600 Here we used only one seismogram to find magnitude – you must plot all three in your assignment! 400 200 50 4 Magnitude 5. 2 3 5 2 1 2 0. 5 1 0. 2 0. 1 0 Magnitude (M) Distance (km) 10 Amplitude (mm)