One of the key differences between Oklahoma & California earthquakes is the relative depth of quakes of significant magnitude. Quakes caused by tectonic plate

One of the key differences between Oklahoma & California earthquakes is the relative depth of quakes of significant magnitude. Quakes caused by tectonic plate interaction and those possibly caused by fluid injection may not be usefully comparable - but ask a seismologist, or at least a geologist, not a journalist, or a random internet commenter. There's a nice interactive quake map at: http://earthquake.usgs.gov/earthquakes/map http://earthquake.usgs.gov/earthquakes/map edit: Pasting a long (512+ chars) URL did not work well, but use the settings sprocket and the checkboxes for US Faults & Hazards. BTW, the hot spot in the Missouri/Arkansas area is the "New Madrid" fault, locally pronounced with the stress on the first syllable: "Mad-rid" not "Mu-drid". It makes emergency preparedness folks nervous because it had a big quake in the early 1800s, very little since, and now has lot of brick construction - sigh.