Abstract
Seismically active fault zones are complex natural systems and they exhibit multifractal correlation between earthquakes in space and time. In this paper, the seismicity of the Taiwan seismic region was studied through the multifractal characteristics of the spatial-temporal distribution of earthquakes from 1st January 1995 to 1st January 2019. We quantified the multifractal characteristics of Taiwan at different scales and defined them as ΔD values. Furthermore, we studied the relationship between the ΔD and b values, which signifies the average size distribution of those earthquakes. The results are as follows. (1) The temporal multifractal curve changes substantially before and after the strong earthquakes. (2) The maximum ΔD value of the seismic region in Taiwan occurs at depths of 0~9 km, indicating that geological structures and focal mechanisms is the most complex at these depths compared with other depths. (3) ΔD values for different regions range from 0.2~1.5, and b values range from 0.65~1.3, with a significant positive correlation between them (ΔD = 1.5 × b − 0.68). For this purpose, a statistical relationship is developed between b and ΔD values, and regional and temporal changes of these parameters are analyzed in order to reveal the potential of future earthquakes in the study region.
Highlights
Earthquakes are among the most serious natural disasters and cause great losses to humanity
(2) The maximum ∆D value of the seismic region in Taiwan occurs at depths of 0~9 km, indicating that geological structures and focal mechanisms is the most complex at these depths compared with other depths. (3) ∆D values for different regions range from 0.2~1.5, and b values range from 0.65~1.3, with a significant positive correlation between them (∆D = 1.5 × b − 0.68)
Different seismic parameters can be used to analyze the characteristic of seismicity in these models, including the (1) magnitude of completeness (MC), which is the lowest magnitude at which all earthquakes in a space-time volume are credibly detected [5]; (2) b value, which defines the frequency-magnitude distribution of earthquakes, and (3) D value, which indicates the number of objects greater than a specified size with a power law dependent on size [6]
Summary
Earthquakes are among the most serious natural disasters and cause great losses to humanity. Balcerak [10] analyzed the seismic time series of the 2003 Tokachi-Oki earthquake in Japan and noted that the multifractal dimension of the seismic activity would have outliers before the large earthquake Another fundamental parameter in seismology is the b value from the Gutenberg–Richter frequency-magnitude relation. A region with a low b value is implied to exhibit a large differential stress, suggesting its being toward the end of the seismic cycle [14] Such a relationship can be used as a kind of precursory information for earthquake forecasting [16,20]. The study area was divided into different scales (i.e., regions) and the depths of the regions are divided according to the results of the latest geological structure research, thereby providing the three-dimensional characteristics of the b value and D value of the Taiwan earthquake area. The results of this study are expected to be helpful in quantitatively describing the material composition of the crust and the degree of heterogeneity of geological structures, that is, the complexity of the geological structure environment and the determination of the PSHA
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