SOUNDS OF SEISMOLOGY:
Shallow and deep earthquakes

Here we compare two seismic sounds from the Andes, to illustrate the importance of the depth of an earthquake in terms of how its waves propagate, and also how we know the depth of an earthquake.


Andes, Mw 5.7, off coast of Peru, 2004/12/18, 17:57 GMT
shallow source: 24 km.
12 hrs of data, 20 sps

This earthquake is shallow, near the trench of the subduction zone. Much of its energy is converted to surface waves, which dominate the signal around the globe.

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56 k

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Argentina, Mw 6.8, 2005/03/21 12:23 GMT
Depth: 572 km (!)
12 hrs of data, 20 sps


The source of this earthquake is very deep, almost 600 km below the surface, inside a cold, rigid subducting slab. Because the source is so far from the surface, it has no surface wave energy... only body waves. For shallower earthquakes, the surface waves dominate the waveform and the sound. Here, you can hear the pinging of the body waves as they hit different stations around the globe.
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(Now watch the deep bolivia wave propagation movie again!)