Notes 10-27-09

Notes 10-27-09 - t • aftershocks day = α(constant tells...

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GEOL 240Lxg Notes 10-27-09 Foreshocks – smaller events that precede the mainshock o Roughly in the same location (within about one fault length of the mainshock) o Close in time to mainshock (within about one month) o Only about 5% of m>6 earthquakes have foreshocks o There are only a few foreshocks (if any) o Hint that region seismicity may increase before large events Mainshocks – largest even in a cluster Aftershocks – smaller events that come after mainshock Also in same location (within about one fault length of the mainshock) Virtually all large shallow earthquakes have lots of aftershocks Omori’s Law – the number of aftershocks per day decreases as a function of 1/
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Unformatted text preview: t • # aftershocks / day = α (constant tells how active sequence is)/ t (time since mainshock) ccv+ β (constant) 6.1 Båth’s Law • For a magnitude M mainshock there is 1 aftershock with magnitude M-1 o 10 aftershocks with magnitude M-2 o 100 aftershocks with magnitude M-3 • Gutenberg Richter frequence-magnitude relation o N M (number events with magnitude M) = 10 (a- bM) o Log 10 N M = a (depends on earthquake size) - b M • Earthquakes are clustered in time • Energy released by an earthquake o Em = 10 11.8 + 1.5M ergs (cm gm sec) E8 (m) / E7 (m-1) = E 1.5 = 30 • Ergs • dynes...
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Notes 10-27-09 - t • aftershocks day = α(constant tells...

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