Spatiotemporal distribution on swarm earthquakes and induced crustal deformation in Hualien, Taiwan

From 1980 to 2008, there are 5 times index swarm earthquakes occurred in Hualien, Taiwan. These events occurred at the north of active tectonic boundary in Taiwan where the last disaster events were the Hualien-Yuli-Taitung earthquake sequences in 1951. We index the large earthquake (more than ML≧5.0) which happens after these swarm earthquakes and affects continuous GPS time series variation patterns. The first event began on 09 April, 1986, and after six days the earthquake about ML= 6.5 occurred. The second and third events happened on 03 January and 04 November, 1995, and nearly two months later the same ML = 5.8 earthquakes occurred. The forth event after an ML = 5.7 happened on 14 July, 2000, and the swarm gathered up on the east of Taroko. After 3 weeks the swarm change to the Xiulin for about 3 days. On 10 September, 2000, the ML = 6.2 happened. The fifth event occurred from 1 January to 4 April in 2005 and distributed north of Hualien. Then, the next swarm earthquakes occurred in Hualien city from 5 April to 17 April. After that the third swarm earthquakes occurred in the northern and southern part in the same place before. On 30 April, 2005, the largest earthquake about ML=5.6 (Hualien earthquake) occurred in Hualien city and its aftershock occurred more than 1000 times. This event recorded by the continuous GPS from daily solution the HUAL, PEPU and YENL indicates an obvious variation, and the largest one is about 22.1 ± 0.5 mm at HUAL station. According to this research, the period of the index swarm and large earthquakes is about 4 ~5 years.