Title:
A DESCRIPTIVE STATISTICAL STUDY OF THE SEISMIC PROPERTIES IN TAIWAN

Authors:
Ko-Ming Ni, Taiwan

Abstract:

The purpose of this paper is to use descriptive statistics to study the properties of earthquakes in Taiwan from January 1995 to February 2021, i.e. 26.17 years or 314 months. The data used in the analysis are subtracted from the seismic archive of the Central Weather Bureau (CWB) of Taiwan. 11,965 earthquakes occurred during that 314 months, and among them, 3,454 are labeled with numbers, but the rest 8,511 are unlabeled local small-scaled ones. The statistical seismic properties evaluated in this paper include: yearly numbers, mean times per year, mean depth (km), maximum magnitude (M_L), 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. The properties of the total 11,965 earthquakes are scrutinized, but the labeled ones are used only for comparison. The data used are summarized in appendices A, B, and C.
The energy released by an earthquake is huge, in this study, the energy of earthquakes is “normalized” by the atomic bomb dropped at Hiroshima, Japan closed to the end of WWII with codename Little Boy, which release 6.3E+20 ergs.
There are 20 municipal areas in Taiwan. Yilan, Hualien, and Taitung are on the east coast where 77.3% of earthquakes occurred. Hualien has the highest frequency (5,399), the shortest period between two earthquakes (1.8 days), and the highest energy released (193.7 atomic bombs) place in Taiwan. 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 314 months (January 1995 to February 2021) the strongest magnitude (Richter magnitude scale, ML) is 7.3, which happened on September 21, 1999, and killed 2,415 people.
The regression equation of intensity with independent variables, such as magnitude, and depth of hypocenters is proposed in this paper, which shows that the intensity of Taiwan increases with increasing magnitude, and decreases with increasing depth. The coefficient of determination is 91.49%, which shows the dependent variable, intensity, is highly explained through the knowledge of the variability in the independent variables.