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Comment by rorrr | Hacker News Reader

What does depth refer to here?

    ...

    4.8M, depth: 17km 17/3/2011 00:00

    5.3M, depth: 32km 16/3/2011 23:46

    4.7M, depth: 38km 16/3/2011 23:38

    4.7M, depth: 23km 16/3/2011 23:27

    5.4M, depth: 1km 16/3/2011 22:38

    4.7M, depth: 25km 16/3/2011 21:48

    ...

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The earthquake's distance beneath the Earth's surface, which I believe starts at 0km on the ocean floor for the purposes of these measurements -- meaning, the water has nothing to do with it and the word depth is a coincidence. That confused me at first.

http://earthquake.usgs.gov/learn/topics/seismology/determini...

I could be wrong, but I think it's the depth of the rupture itself. Earthquakes don't really occur "on the surface"

via http://earthquake.usgs.gov/earthquakes/glossary.php

"The depth where the earthquake begins to rupture. This depth may be relative to mean sea-level or the average elevation of the seismic stations which provided arrival-time data for the earthquake location. The choice of reference depth is dependent on the method used to locate the earthquake. Sometimes when depth is poorly constrained by available seismic data, the location program will set the depth at a fixed value. For example, 33 km is often used as a default depth for earthquakes determined to be shallow, but whose depth is not satisfactorily determined by the data, whereas default depths of 5 or 10 km are often used in mid-continental areas and on mid-ocean ridges since earthquakes in these areas are usually shallower than 33 km."

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