The Frequency Distribution of Inter-Event Times of M e 3 Earthquakes in the Taipei Metropolitan Area: 1973 - 2010


M ≥ 3 earthquakes which occurred in the Taipei Metropolitan Area from 1973 through 2010 are used to study seismicity of the area. First, the epicentral distribution, depth distribution, and temporal sequences of earthquake magnitudes are described. The earthquakes can be divided into two groups: one for shallow events with focal depths ranging 0 - 40 km and the other with focal depths deeper than 60 km. Shallow earthquakes are mainly located in the depth range from 0 - 10 km 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°. Three statistical models, the gamma, power-law, and exponential functions, are applied to describe the single frequency distribution of inter-occurrence times between two consecutive events for both shallow and deep earthquakes. Numerical tests suggest that the most appropriate time interval for counting the frequency of events for statistical analysis is 10 days. Results show that among the three functions, the power-law function is the most appropriate for describing the data points. While the exponential function is the least appropriate to describe the observations, thus, the time series of earthquakes in consideration are not Poissonian. The gamma function is less and more appropriate to describe the observations than the power-law function and the exponential function, respectively. The scaling exponent of the power-law function decreases linearly with an increasingly lower-bound magnitude. The slope value of the regression equation is smaller for shallow earthquakes than for deep events. Meanwhile, the power-law function cannot work when the lower-bound magnitude is 4.2 for shallow earthquakes and 4.3 for deep events.

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