| dc.description.abstract | The study area is the most populated region, where the Taipei Basin, Tatun volcanic zone, the active fault-Shanchiao fault, and two nuclear power plants (Chinshan and Kuosheng) all lie in, in northern Taiwan. Understanding the underground velocity structure and the seismicity in this area is essential. However, the local seismicity is relatively low, and the lack of medium and large earthquakes along the Shanchiao fault. By contrast, the activity of micro-earthquakes in the Tatun volcanic zone is notable. In order to improve the resolution and increase ray path coverage for better understanding the complex region, we used a dense micro-earthquake monitoring network with more than 40 stations. Including real-time broadband station and dozens of stations operated by the other five organizations (CWB, TVO, IES, NCREE, ITRI). During 2015/04/06~2017/12/31, 1493 events detected by this network were used to invert the P wave velocity (Vp) and P wave to S wave velocity ratio (Vp/Vs) structures in the study area. After the preliminary locating of events, we applied the double-difference tomography (tomoDD), which is a method to solve for the 3-D velocity structure and more precise earthquake relocation. At the same time, in order to confirm the credibility of the data, we use the Derivative Weight Sum (DWS) method and the checkerboard test method for the resolution analysis. Because the seismic distribution is extremely uneven, the high-resolution area is mostly within 15 km at the northern part of the Shanchiao fault and the Tatun volcanic zone. In terms of three-dimensional velocity construction results, it can be concluded that the high-level anomaly values of Vp and Vs at the surface may be caused by the distribution of igneous rocks. The Tatun Volcano areas exhibit low Vp, Vs and Vp/Vs anomaly values, and the judgment may be high fractured and crack density. At the hot vapor distribution area, the seismic distribution results show that the earthquake has a clustering effect in the geothermal area. The longitudinal section at a depth of 4 to 8 km can see a northeastern-southwestern dip. The relocated seismicity and underground velocity structure can provide more details about the seismogenic and tectonic relations between the Shanchiao fault and the Tatun Volcano area. | en_US |