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Seismic Tomography_1stArrival-480.mov

Science

iriseno

Aug 14, 2009

2459 views

The Seismic Tomography

By using the arrival times from worldwide earthquakes, seismologists were able to define layers in the earth, later they expanded the method to look at smaller areas. Let's look at how this is done by using a highly simplified model of a uniform crust for simplicity we will use straight-line ray paths so the seismic waves won't get deflected and bent by different layers as they do in reality. And evenly spaced grid of seismometers records earthquake arrival times. 

Seismic waves travel through different materials at different speeds by measuring the time it takes seismic waves to travel from an earthquake to different seismic stations, scientists deduce velocity variations within the earth. Late arrival times for the slower ray paths in the shaded red area, indicate slowing his occurred somewhere along the way. We won't actually know where the slowing is occurred until the data have been analyzed. By using what we know about how seismic waves travel through different materials, we can infer what the structure might look like. 

What does this tell us geologically? What are these anomalies? Well, they could be regions that have different compositions, temperatures, or fluid contents, including water, steam, or magma. In order to know which, seismologists work with other earth scientists such as geologists and Duke chemists to combine independent observation to solve ambiguities

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