Large scale plate tectonic processes are observable on a human timescale by monitoring earthquakes. By collecting seismic data we can locate shifting in the Earth to help us understand what is happening on a global scale. In the four days we spent in Denali National Park we installed four seismometers in the Kantishna area.
Introduction to Earthquakes
Focus and Epicenter:
The focus of an earthquake is the point combining latitude, longitude, and depth at which an earthquake originates. The epicenter is the point on the surface directly above the focus.
S-waves and P-waves:
There are two important components of a seismic wave: P-waves and S-waves. P waves are compressional waves which are the first to show up on the seismogram while S waves travel by moving particles up and down like a rope. Both waves radiate from the epicenter. As shown in the figure above, S waves show up best on the horizontal channels (HHN/HHE) while P waves show best on the vertical channel (HHZ). By measuring the time between these two waves on multiple stations, it is possible to calculate the location of the earthquake in the earth and the time at which it occurred.
Another measurement recorded in the data is the amplitude. The amplitude is a measure of how much the ground moves as the waves propagates through it. The amplitudes recorded on these seismometers are the actual velocities at which the ground moves and not the actual ground displacement as older instruments did.
The map above shows the locations of representative earthquakes talked about in the Data section as well as the general location of the seismometers deployed as part of this project.