Seismic scaling relations and aftershock activity from the sequences of the 2004 mid Niigata and the 2005 west off Fukuoka earthquakes (M_W 6.6) in Japan

Abstract

[1] We investigate seismic scaling relations and seismic activity using two Japanese earthquake sequences, the 2004 mid Niigata prefecture earthquake (MNPE) and the 2005 west off Fukuoka prefecture earthquake (WOFE) sequences. Although the mainshocks of the two sequences have the same M W of 6.6, the aftershock activities are different from each other in term of moment release. The MNPE produced a large number of aftershocks including six events with M W ! 5.5 over a period of about two weeks. On the other hand, the WOFE sequence did not produce aftershocks that exceeded M W 5.5. In the scaling relationship of seismic moment (M 0 ) versus corner frequency ( f c ) obtained from the MNPE sequence, the f c 's tend to decrease with decreasing M 0 between M W 3.5 and 6.6 and the best fit line determined in a least squares sense is M 0 / f c À3.41 . In the WOFE sequence, the best fit line is M 0 / f c À3.06 in the same M W range. The f c range of small aftershocks is lower in the MNPE sequence than in the WOFE sequence. Moreover, the M 0 À f c relations for small events (3.5 M W 4.0) in the MNPE sequence are different between the events on the main faults (M 0 / f c À3.53 ) and the off-main fault events (M 0 / f c À4.44 ). These results suggest that there is difference (or variation) in the scaling relation even in the same M W range, probably reflecting different tectonic or seismogenic conditions.

Seismic scaling relation of the 2007 Off Mid Niigata, Japan, earthquake (Mw 6.6) sequence in comparison with two other earthquake (Mw 6.6) sequences

“…The best-fit line determined in a least-squares sense is M 0 ∝ f −3.87 c in the M w range from 3.4 to 6.6. The M 0 -f c relations of the MNE and WOFE sequences (3.5 ≤ M w ≤ 6.6) derived by Tajima and Tajima (2007) are compared with that of the OMNE (Fig. 3(b, c)).…”

“…The M 0 -f c relation estimated for the OMNE sequence in the range of 3.4 ≤ M w ≤ 6.6 is Blue and pink open circles that correspond to the M w s denote the earthquake epicenters that occurred during two weeks after the MNE and OMNE mainshocks, respectively. (b) Aftershock distribution of the MNE sequence analyzed by Tajima and Tajima (2007). This area corresponds to that enclosed by dashed rectangle in (a).…”

“…On the other hand, the moment rate function of the WOFE is approximated by a simple triangle with a duration of ∼4 s (Horikawa, 2006). The characteristics of the source time functions as well as the different M 0 -f c relations may be interpreted in terms of the relative fault maturity, as suggested by Tajima and Tajima (2007). The model of relative fault maturity is inferred from the E R and rupture speed of the main shocks (Choy and Kirby, 2004;Choy et al, 2006).…”

“…However, the source spectra sometimes become more complex than those expected from a typical omega-square (ω −2 ) model (Brune, 1970) in the vicinity of f c (Mayeda and Walter, 1996). Tajima and Tajima (2007) report the different M 0 -f c relations between the MNE and the 2005 West Off Fukuoka prefecture earthquake (WOFE) (M w 6.6) sequences (3.5 ≤ M w ≤ 6.6) and suggest the variability of scaling relations in individual earthquake sequences.…”

“…Izutani (2005) and Tajima and Tajima (2007) indicate that the scaling relationship between seismic moment (M 0 ) and corner frequency ( f c ) of the MNE sequence deviates from M 0 ∝ f −3 c . In general, the f c in the source spectrum is essential for estimating the radiated seismic energy (E R ) that characterizes the dynamic rupture properties of an earthquake.…”