Significance of fractal correlation dimension and seismic b-value variation due to 15th July 2009, New Zealand earthquake of Mw 7.8

Abstract

New Zealand earthquake that occurred on 15th July 2009 (Mw 7.8) was analysed using fractal correlation dimension (Dc) and seismic b-VALUE. We have analysed the earthquakes catalog of thirty- ve years with a magnitude (mb ≥3.7), in order to observe a crucial in- formation in terms of Dc value uctuation for the event. The event is preceded by fall and anomalous change in Dc value in the year 2007 about two years prior to the mainshock. A sudden decrease in Dc value with highly clustered events is observed before the main- shock. The low value of Dc is an indicator of clustering and it shows how intermediate size events correlate with one another in the pre- paration process of this event. Here the low Dc value may be the indicator for high stress developer along the fault to produce large size earthquake. Moreover, we also observed abnormal uctuation in b-VALUE from 2003. The fractal clustering and scaling of earthquakes are indicated by b-VALUE change prior to strong earthquake as a harbinger of stress correlation in various scales. The event is also mar- ked for that occurred in the periphery of the positive Coulomb stress development, as obtained from three low Dc time windows' events. The drop in Dc value is not a single observation prior to this large event, but such pattern is also seen for other strong events in the study zone. One such well identi ed strong event is Mw 7.2 (2003) along with low Dc value prior to the event. Thus, stress correlation mea- sured along with these indirect statistical tools gives the clue of self-organization of long wavelength of stress, which was not measu- red earlier with classical approaches. This type of study may provide a very useful information for hazard mitigation.