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Abstract:
To compare the statistical properties of labeled and total (labeled plus unlabeled) earthquakes in Taiwan is the purpose of this paper. From January 1995 to June 2017, there were 3,129 labeled as well as 9,871 total earthquakes recorded in the seismic archive of the Central Weather Bureau (CWB) of Taiwan. The statistical earthquakes properties evaluated in this paper include: yearly numbers, mean times per month, mean times per year, mean depth (km), mean magnitude (ML), maximum magnitude, time period between two earthquakes, energy released ratio, and energy equivalent to the number of atomic bombs. Hualien, a county in the east of Taiwan, is the place with the highest frequency of earthquakes, the shortest time between two earthquakes, and the strongest released energy. The energy released from total earthquakes in Hualien in the period of January 1995 to June 2017is equivalent to 185.1 atomic bombs which were dropped in Hiroshima at the end of World War II. 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 114.92km (intermediate-depth). Maybe it is because the hypocenters of Keelung are in the submerged tectonic plate. In the past 270months (January 1995 to June 2017) the strongest magnitude (Richter magnitude scale, ML) was 7.3.Although Taitung also recorded the same magnitude, its epicenter is off-island, and no major damage and injury has been filed. This study shows that if the unlabeled earthquakes (usually small in magnitude and impact locally) are neglected, the total energy will be uncounted up to2.2E+22 ergs. Such an energy lost is equivalent to 35.36 atomic bombs. The energy gap increases with the increasing of time. Other statistical properties such as earthquakes amount order, and the interval between two earthquakes will be inaccurate if the researchers disregard those unlabeled ones. Therefore, to put all records in the CWB seismic archive in the analysis is strongly recommended to avoid obtaining inaccurate results.
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