Open AccessStress drops and radiated energies of aftershocks of the 1994 Northridge, California, earthquake
Author(s) -
Mori Jim,
Abercrombie Rachel E.,
Kanamori Hiroo
Publication year - 2003
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001jb000474
Subject(s) - aftershock , seismology , dynamic stress , geology , scaling , seismic moment , stress (linguistics) , magnitude (astronomy) , physics , dynamic loading , structural engineering , engineering , mathematics , fault (geology) , geometry , linguistics , philosophy , astronomy
We study stress levels and radiated energy to infer the rupture characteristics and scaling relationships of aftershocks and other southern California earthquakes. We use empirical Green functions to obtain source time functions for 47 of the larger ( M ≥ 4.0) aftershocks of the 1994 Northridge, California earthquake ( M 6.7). We estimate static and dynamic stress drops from the source time functions and compare them to well‐calibrated estimates of the radiated energy. Our measurements of radiated energy are relatively low compared to the static stress drops, indicating that the static and dynamic stress drops are of similar magnitude. This is confirmed by our direct estimates of the dynamic stress drops. Combining our results for the Northridge aftershocks with data from other southern California earthquakes appears to show an increase in the ratio of radiated energy to moment, with increasing moment. There is no corresponding increase in the static stress drop. This systematic change in earthquake scaling from smaller to larger ( M 3 to M 7) earthquakes suggests differences in rupture properties that may be attributed to differences of dynamic friction or stress levels on the faults.