CN's+Post-Assessment

LIGO Questions


 >>>Using Google Earth, I plugged in the latitude and longitude of the earthquake, 34.5390 73.5880, and the coordinates for LIGO 46°27'18.76"N, 119°24'27.51"W. From there I used the ruler and determined that the distance between the earthquake and LIGO is 10,940.03 kilometers.

**2. Calculate the seismic wave speed twice, once for each of the LIGO plots shown.**
 >>>You would calculate the speed of the wave using distance/time=speed.

1. __Using the Seismic Y Graph:__ You would use the distance 10,940.03 km divided by the time. I have approximated the time the earthquake started for the Y Graph to be about 4:12. The difference in time of the actual starting of the earthquake, 3:50:40.80, and the LIGO time, 4:12, is 21 minutes and 20 seconds. The total seconds would be 1,280 seconds.

(10,940.03km) / (1,280sec) = 8.55km/sec

2. __Using the Seismic Z Graph:__ You would use the distance 10,940.03 km divided by the time. I have approximated the time the earthquake started for the Z Graph to be about 4:08. The difference in time of the actual starting of the earthquake, 3:50:40.80, and the LIGO time, 4:08, is 17 minutes and 20 seconds. The total seconds would be 1040 seconds.

(10,940.03km) / (1040sec) = 10.52km/sec

**3. Comment on any difference you see between the LIGO plots, and between the wave speed estimates obtained using each plot.**
 >>>The two graphs are different in that there waves coming in on the graph vary. For the Seismic Y Graph, the graph shoots up at about the time of 4:12, while on the Z Graph, the graph shoots up a little early at around 4:08. This would change the wave speeds for each of the graphs. This would happen because e ach seismometer, tiltmeter and magnetometer actually has three sensors for the three independent directions, x, y, and z.([|Data Channel]) The Y Graph would seem more like an earthquake because of the fact that the speed of the earthquake is just slightly faster than a normal earthquake speed. But the graph still seems unlikely in that the earthquake had to travel to the other side of the earth. For the Z Graph, doesn't seem like a plausible earthquake graph thought. The Z Graph gives you an earthquake speed of 10.52km/s making it 2-3km/s faster than an average earthquake. It is unlikely for an earthquake to travel that fast to the other side of the world. S and P waves "spread through the planet in a series of expanding spheres. Some of the wave energy reflects off the boundary between the mantle and core." ([|P and S Waves]) "P and S waves are often called body waves because they propagate outward in all directions from a source (such as an earthquake) and travel through the interior of the Earth " ([|S&P Waves, Purdue University]) "S-waves do not travel through fluids, so do not exist in Earth's outer core (inferred to be primarily liquid iron) or in air or water or molten rock (magma). S waves travel slower than P waves in a solid and, therefore, arrive after the P wave"  ([|S&P Waves, Purdue University]). "P wav es shake the ground in the direction they are propagating, while S waves shake perpendicularly or **transverse** to the direction of propagation" ([|Seismic Waves]). So according to this information, the P-wave would be the only one that would be able to reach LIGO because S-Waves are unable to travel through liquids and would not be able to travel that fast because according to the [|S&P Waves, Purdue University] site, S-Waves can only typically travel 3-4km/sec. On the Y Graph, the graph seems a little more clear cut and shows the earthquake hitting and it decreasing in strength. On the Z Graph, there seems to be more waves causing it to have more disturbance on the graph.