Morlet Wavelet Analysis of ML ≥ 3 Earthquakes in the Taipei Metropolitan Area


ML ≥ 3 earthquakes (ML = local magnitude) that occurred in the Taipei Metropolitan Area (TMA) from 1973 - 2013 are selected to study the dominant seismicity period of this area. The epicentral distribution and temporal sequences of earthquake magnitudes are simply described. These earthquakes can be divided into two groups: one for events shallower than 40 km and one for events deeper than 60 km. Shallow earthquakes are located mainly in the 0 - 10 km depth range north of 25.1°N, and down to 35 km for those south of 25.1°N. Deep events are located in the subduction zone, with a dip angle of about 70°. The Morlet wavelet technique is applied to analyze the dominant periods of temporal variations in numbers of monthly earth- quakes in the shallow and deep ranges for three magnitude ranges, i.e., ML ≥ 3, 4, and 5. The results show that for shallow earthquakes the dominant periods are 15.4, 30.8, 66.1, and 132.2 months when ML ≥ 3 and 30.8 months when ML ≥ 4; while for deep earthquakes, the dominant periods are 16.5 and 141.7 months when ML ≥ 3 and 141.7 months when ML ≥ 4. The dominant period cannot be obtained for both shallow and deep ML ≥ 5 earthquakes.

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