Premium
Anomalous early aftershock decay rate of the 2004 Mw6.0 Parkfield, California, earthquake
Author(s) -
Peng Zhigang,
Vidale John E.,
Houston Heidi
Publication year - 2006
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl026744
Subject(s) - aftershock , seismology , geology , seismogram , induced seismicity , foreshock , shock (circulatory) , medicine
We analyze the seismicity rate immediately after the 2004 Mw6.0 Parkfield, California, earthquake from near‐source seismograms. By scrutinizing high‐frequency signals, we can distinguish mainshock coda from early aftershocks occurring as soon as 30 s after the mainshock. We find, as expected, that a significant fraction of aftershocks in the first few hours after the main shock are missing in the Northern California Seismic Network catalog. We observe a steady rate of aftershocks in the first 130 s, followed by a power‐law decay of aftershock activity. Thus, there appears to be a distinct early stage of aftershock activity that does not fit the Omori's law with a constant p value, a phenomenon that we refer to as Early Aftershock Deficiency (EAD). Our observation suggests that mainshock rupture and aftershocks are distinct processes, not described by a single Omori's law. Several physical models of aftershocks can explain the EAD.