HR: 0800h
AN: S11C-0717    [Abstracts]
TI: Towards a Logical Distinction Between Swarms and Aftershock Sequences
AU: Gardine, M
EM: mgardine@gi.alaska.edu
AF: University of Alaska-Fairbanks/Geophysical Institute, 903 Koyukuk Dr., Fairbanks, AK 99775, United States
AU: * Burris, L
EM: leab@giseis.alaska.edu
AF: University of Alaska-Fairbanks/Geophysical Institute, 903 Koyukuk Dr., Fairbanks, AK 99775, United States
AU: McNutt, S
EM: steve@giseis.alaska.edu
AF: Alaska Volcano Observatory/University of Alaska-Fairbanks, 903 Koyukuk Dr., Fairbanks, AK 99775, United States
AB: The distinction between swarms and aftershock sequences has, up to this point, been fairly arbitrary and non- uniform. Typically 0.5 to 1 order of magnitude difference between the mainshock and largest aftershock has been a traditional choice, but there are many exceptions. Seismologists have generally assumed that the mainshock carries most of the energy, but this is only true if it is sufficiently large compared to the size and numbers of aftershocks. Here we present a systematic division based on energy of the aftershock sequence compared to the energy of the largest event of the sequence. It is possible to calculate the amount of aftershock energy assumed to be in the sequence using the b-value of the frequency-magnitude relation with a fixed choice of magnitude separation (M-mainshock minus M-largest aftershock). Assuming that the energy of an aftershock sequence is less than the energy of the mainshock, the b-value at which the aftershock energy exceeds that of the mainshock energy determines the boundary between aftershock sequences and swarms. The amount of energy for various choices of b-value is also calculated using different values of magnitude separation. When the minimum b-value at which the sequence energy exceeds that of the largest event/mainshock is plotted against the magnitude separation, a linear trend emerges. Values plotting above this line represent swarms and values plotting below it represent aftershock sequences. This scheme has the advantage that it represents a physical quantity - energy - rather than only statistical features of earthquake distributions. As such it may be useful to help distinguish swarms from mainshock/aftershock sequences and to better determine the underlying causes of earthquake swarms.
DE: 7200 SEISMOLOGY
DE: 7280 Volcano seismology (8419)
SC: Seismology [S]
MN: 2007 Fall Meeting