Journal of Geosciences and Geomatics, 2017, Vol. 5, No. 4, 167-172 Available online at http://pubs.sciepub.com/jgg/5/4/1 ©Science and Education Publishing DOI:10.12691/jgg-5-4-1 Empirical Study of the Frequency and Severity of Earthquakes in Taiwan Obi E. O. * , Abong A. A, Ogbeche J. U Department of Physics, Cross River University of Technology, Calabar, Nigeria *Corresponding author: emmanuelobi57@gmail.com Abstract The rate at which earthquake occurs in Taiwan was investigated for the period of fifty years (1961 – 2010). The result shows that the study area is characterized predominantly by minor, light and moderate earthquakes with the percentage of strong and major extremely low. The result also revealed that for each magnitude range, the number of shallow focus earthquakes is more than the intermediate focus earthquakes. No deep focus earthquake was observed. The shallow earthquake events with magnitude 4.0-4.9 (light) were the most frequent, followed by 5.0-5.9 (moderate), 3.0-3.9 (minor), 6.0-6.9 (strong) and the least frequent were with magnitude 7.0-7.9 (major). While for intermediate earthquakes, events with magnitude 4.0-4.9 were the most frequent, followed by 3.0-3.9, 5.0-5.9, 6.0-6.9 and the least frequent with magnitude 7.0-7.9 . It was also discovered that about three (3) shallow earthquakes occur monthly and about two (2) intermediate earthquakes occur yearly in Taiwan on the average. Furthermore the b-values were calculated for shallow and intermediate focus earthquakes to be 0.80 and 0.74 respectively. The b- values were calculated using the Gutenberg-Richter Relation. The low b- value indicates localized high stresses which are favourable for future rupture. Keywords: earthquake, magnitude, b value, rupture, Gutenberg-Richter Cite This Article: Obi E. O., Abong A. A, and Ogbeche J. U, “Empirical Study of the Frequency and Severity of Earthquakes in Taiwan.” Journal of Geosciences and Geomatics, vol. 5, no. 4 (2017): 167-172. doi: 10.12691/jgg-5-4-1. 1. Introduction Studies have shown that earthquakes are very complex phenomena which are caused by different processes taking place in the earth. Most earthquakes are too small to be noticed by people, only sensitive scientific instruments such as the seismograph can record their passage. Every year hundreds of earthquakes occur which are strong enough to change the face of the land and are capable of causing injuries, deaths and damage to property if there occur in a populated area [2]. Many studies have been carried out to develop reliable estimates on the pattern of seismicity in various regions in the world [5,6,9,10,12,14,15,20,21]. Seismological pattern of any area enables Seismologist to predict when (though not exact time) and where the next main shock will occur. The history of earthquake activity in the Taiwan can be dated back to the seventeenth century. Before 1897, the historical records of earthquakes in Taiwan primarily came from government documents. The earthquakes in Taiwan generally have a complex structural background. Most of the disastrous earthquakes in the history have occurred in the west seismic zone, a densely populated zone in Taiwan [7]. As Taiwan gradually evolves from a developing country to a developed country, one of its major challenges is how to cope with the rate at which earthquakes occur in the region. Earthquake being a natural event, cannot be prevented, but maximum efforts to reduce the damage associated with it have been put in place in the region [7]. Earthquake can be classified based on focal depth consisting basically of shallow, intermediate and deep- focus earthquakes. The focal depth refers to the depth at which an earthquake occurs. In seismology, Earthquakes occurring at a depth of less than 70km are classified as shallow-focus earthquake, while those with a focal depth between 70km and 300km are commonly termed mid- focus or intermediate-depth earthquakes, deep-focus earthquakes may occur at much greater depths in the mantle ranging from 300km up to 700km. Deep focus earthquakes typically occur at oceanic continental convergent boundaries along Wadati-Benioff zones (the zone of active seismicity). Earthquakes with shallow focal depths occur in all seismically active zones. The largest proportion (about 85%) of the annual release of seismic energy is liberated in shallow-focus earthquakes, the remainder is set free by earthquakes with intermediate focal depths (about 12%) and also by deep-focus earthquake (about 3%) [8]. In Taiwan, in the 20 th century, the largest earthquake on land was the chi-chi earthquake of 1999 [3]. 2. Earthquake Magnitude In 1935, C. F Richter attempted to grade the sizes of local earthquakes in Southern California on the basis of the amplitude of the ground vibrations they produced at a