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

Saroj Kumar Mondal, Paresh Nath SinghaRoy, Joshi K Catherine, Auchitya Kumar Pandey



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 five years with a magnitude (mb ≥3.7), in order to observe a crucial information in terms of Dc value fluctuation 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 mainshock. The low value of Dc is an indicator of clustering and it shows how intermediate size events correlate with one another in the preparation 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 fluctuation 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 marked to have been 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 identified strong event is Mw 7.2 (2003) along with low Dc value prior to the event.  Thus, stress correlation measured along with these indirect statistical tools gives the clue of self-organization of long wavelength of stress, which was not measured earlier with classical approaches. This type of study may provide a very useful information for hazard mitigation.





Earthquakes, Fractal correlation dimension, clustering, seismic b-value, Coulomb stress.

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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X