Fractal and Morlet-wavelet Analyses of M≥6 Earthquakes in the South-North Seismic Belt, China

  • Author(s): Jeen-Hwa Wang, Kou-Cheng Chen, and Kao-Hao Chang
  • DOI: 10.3319/TAO.2017.01.25.01
  • Keywords: Multifractal dimension, earthquake sequence, epicenter, inter-event time, Morlet wavelet technique, dominant period
  • To evaluate the multifractal dimensions of epicentral distributions
  • To evaluate the multifractal dimensions of earthquake sequences
  • To evaluate the dominant periods of sequences of M≥6 earthquakes
Abstract

The M≥6 earthquakes occurred in the South-North Seismic Belt, Mainland China (longitudes from 98oE to 107oE and latitudes from 21oN to 41oN) during 1900–2016 are taken to measure the multifractal dimensions of spatial distribution and time sequence of events and the dominant periods. The multifractal dimensions, Dq, are measured from the log-log plots of Cq(r) versus r and Cq(t) versus t, where Cq(r) and Cq(t) are the generalized correlation integrals for the epicentral distribution and time sequence of events, respectively, and r and t are the epicentral distance and inter-event time, respectively, at positive q. The log-log plot of Cq(r) versus r shows a linear portion when log(rl)≤log(r)≤log(ru). The values of rl and ru are, respectively, 120 km and 560 km for M≥6 events, 100 km and 560 km for M≥6.5 events, and 63 km and 560 km for M≥7 events. The value of rl decreases with the lower-bound magnitude. Dq monotonically decreases with increasing q. The values of Dq are between 1.618 and 1.426 for M≥6 events, between 1.562 and 1.108 for M≥6.5 events, and between 1.365 and 0.841 for M≥7 events. The log-log plot of Cq(t) versus t show a linear distribution when log(tl)≤log(t)≤ log(tu), where tl and tu are, respectively, 5 and 50.1 years for M≥6 events, 5 and 50.1 years for M≥6.5 events, and 16 years and 63.1 years for M≥7 event, thus suggesting that the time sequences of earthquakes in the study region are multifractal. The values of Dq are between 0.830 and 0.703 for M≥6 events, between 0.835 and 0.820 for M≥6.5 events, and between 0.786 and 0.685 for M≥7 events. The Morlet wavelet technique is applied to analyze the dominant periods of temporal variations in numbers of yearly earthquakes for the three magnitude ranges, i.e., M≥6, M≥6.5, and M≥7. The resultant dominant period is 2.94 years for M≥6 events and cannot be evaluated for M≥6.5 and M≥7 events.

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