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Abstract:
Through statistical study of the seismic archive of the Central Weather Bureau (CWB) of Taiwan to make people understand more the properties of earthquakes in each city and county in Taiwan is the purpose of this paper. From January 1995 to June 2018, there were 3,257 labelled as well as 10,898 total (labelled plus unlabeled) earthquakes recorded in the Central CWB of Taiwan. The statistical seismic properties evaluated in this paper include: yearly numbers, mean times per year, mean times per month, mean depth (km), maximum magnitude (ML), mean interval of time between two earthquakes, energy released ratio, and energy equivalent to the number of atomic bombs in each city and county. These properties are plotted as diagrams to facilitate reading.
Haulier, a county on the east coast of Taiwan, is the place that has the highest frequency of earthquakes, the shortest time interval between two earthquakes, and releases most energy. The energy released from total earthquakes in Haulier in the period of January 1995 to June 2018 is equivalent to 188.9 atomic bombs, which were dropped over Hiroshima, Japan. Most of the earthquakes in Taiwan's twenty municipal areas are categorized to be shallow (<70km), except Keelung, which has an average depth of hypocenters at 114.9 km (intermediate-depth). Maybe it is because the hypocenters of Keelung are in the submerged tectonic plate. In the past 282 months (January 1995 to June 2018) the strongest magnitude (Richter magnitude scale, ML) was 7.3, which happened on September 21, 1999. This study shows that if the unlabeled earthquakes (usually small in magnitude and impact locally) are neglected, the total energy will be uncounted up to 2.4E+22 ergs. Such an energy lost is equivalent to 37.72 atomic bombs. Therefore, to put all records in the CWB seismic archive in the analysis is strongly recommended to avoid obtaining inaccurate results.
The regression of intensity with independent variables, such as longitude, latitude, magnitude, and depth of hypocenters shows that the intensity of Taiwan decreases with increasing longitude, increases with increasing latitude, increases with increasing magnitude, and decreases with increasing depth. The coefficient of determination is more than 91%, which shows the independent variable, intensity, is highly explained through the knowledge of the variability in the independent variables. The depth of hypocenters, intensities, and magnitudes of all earthquakes are plotted with three-dimensional diagrams, and the results are consistent with the statistical analyses.
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