USC
GEOL 240Lg -
Lecture notes
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Lecture 11 13 Largest magnitude earthquake in a sequence Foreshock An earthquake that occurs before mainshock but Is smaller in magnitude Approx the same location Within a brief period before the mainshock Not that common On average 1 20 5 of eqs in California have Omari s Law of aftershocks day decays inversely with time since the mainshock foreshocks events per day Time Every mainshock has Usually largest aftershock is 1 magnitude unit smaller 10x of aftershock 2 units smaller 100x for magnitude 3x smaller than mainshock Triggered earthquakes Relatively large Magnitude compared to mainshock Distinct enough to be considered separate events with their own aftershocks E g Mw 6 3 in big bear after 7 3 in Landers San Francisco Bay Area Eqs
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