MULTIFRACTAL ANALYSIS OF SEISMICITY OF KUMAON REGION (UTTARAKHAND)

Abstract

Most fractal systems in nature are heterogeneous. For such fractals, a unique fractal dimension is insufficient to characterize them and the same differs depending upon the method used to estimate it. Such fractals called multifractals and are characterized by the generalized dimension Dq.The generalized dimension Dq and Dq spectra of the special distribution of earthquake epicenters in the Kumaon region (Uttarakhand) are studied for the time series having a time window of 01.01.1980 to 31.12.2009.Multifractal analysis of earthquakes (mb>3.5) occurring during 1980 — 2009 led to the detection of a clustering pattern in the narrow time span prior to all the large earthquakes: Ms=7.0 on 19.10.1991(Uttarkashi) and Ms=6.7 on 28.03.1999 (Chamoli). The increase of Dq value shows a declustering of events before the main event and then a sudden decrease in the Dq value (clustering) prior to the release of a large amount of strain energy accumulated at an asperity. The rate of decrease (slope) of Dq spectra has been found to be associated with change in seismicity structure in the region. Steep slopes in the Dq spectra have been found to be associated with high rates of energy release and the gentle slopes correspond to low rates of energy release in the region. Based on the spatio-temporal clustering pattern of events, the potential for future large events can be assessed. Spatio-temporal clustering of events apparently indicates a highly stressed region, an asperity or weak zone from which the rupture propagation eventually nucleates, causing large earthquakes.