Seismic Array in the Taiwan Mountain Area
Since early 90's, the Institute of Earth Sciences (IES) has decided to closed the SMA network. Instead of the SMA network, a new digital dense strong motion network (Taiwan Strong Motion Instrumentation Program, TSMIP) was widely deployed in the Taiwan area by the Central Weather Bureau (CWB). In the beginning of 1992, the TSMIP includes more than 600 stations and increases to 700 stations in 2007. However, most of the TSMIP stations are placed on plain area, only limited stations are located at mountain area.
In the meantime, the IES decided to deploy their own Central Mountain strong motion array (CMA) which was the region that lack of seismic data. The Central Mountain ranges are the high mountainous region of Taiwan, with peaks up to 4000 m. This region covers an area of 2/3 of the entire Taiwan island. There are only a few roads, and access is difficult in general. Since 1993, the CMA has been installed station by station. Most of the stations are deployed on the yards of local police station, local primary schools and Forestry Bureau in the mountainous region. It took a lot of efforts to deploy and maintain the array during the past few years. Eleven stations of the CMA recorded the 1999 Chi-Chi earthquake. Even with these improvements, there are still too few to attain a high probability of recording strong motion information for earthquakes. Thus, if we want to extract the source parameters from the data, extensive sets of ground-motion recordings are desirable.
In 2003, the IES decided an action plan to hunt of new sites for increasing the density of strong-motion stations of the CMA. At the initial phase, we started to add the free-field seismic station of the CMA throughout the vicinity of Taipei area and to expand the CMA to central part of Taiwan year by year. During 2004-2005, 20 stations were installed around the mountain area of the Taipei basin. Subsequently, the IES has contracted by the CWB to execute a project entitled “Construction, Collection and Data Analysis of Free-field Strong Motion Network in Taiwan Mountain Area” since 2006. During that time, the CMA was renamed to MTN. The project plans a selection sites to install seismic stations for observing and accumulating the strong-motion data at the mountain areas of Taiwan. In accordance with the plans indicated of this project, the stations were deployed in the northern part of Taiwan in 2006 and 2007 and extended through northern parts of Taiwan into the central part of Taiwan in 2008 and 2009. With significant efforts, the housing and installation of 54 new seismic stations were completed in November 2009. Since then, the ground motion database for the Taiwan mountain area has improved greatly.
The seismic data from MTN and TSMIP will be integrated to study the path effects and site effects from different seismogenic zones to the metropolitan area and provide significant information to reduce seismic hazard.