Geomagnetic Basement Relief of the Northern Taiwan Area

Abstract

A detailed magnetic survey has been carried out in the northern Tai wan area in order to determine the topographic surface of the magnetic basement. This survey covers an area of about 900 km2, and totally the observation point is 269. After geomagnetic corrections of the observed data, the magnetic anomaly map was obtained. For the purpose of resolving the deeper (relative to the shallow effects) magnetic basement, a low-pass filter was applied to the magnetic anomaly to obtain a smoothed magnetic anomaly. Thirteen profiles were designed to cross and cover evenly the smoothed geomagnetic anomaly in the study area. These geomagnetic anomaly profiles were inverted to obtain the magnetic basement profiles by trial and error method. Compiling these 1-D magnetic basement profiles, we outlined the 2-D magnetic basement relief. The pattern of the relief of the geomagnetic basement shows that the depth is ranged from 2.6 to 6 km. There exists a basement high under the Tatun volcano area. Compiling with the topographic relief, we can find that they correlate to each other well, except for a contravention in the mountainous area surrounding the Taipei basin. This converse can be explained by supposing that tectonic forces lifted the mountainous area after the basement was formed. In order to verify the "truth" of the solution, we calculated the theo retical geomagnetic anomaly using the model we have inverted. Compar ing the result with the observed geomagnetic anomaly map, we can find that they. are quite similar to each other, with only a small variance.

Geomagnetic anomaly at Lunping before the 1999 Chi-Chi earthquake (M w = 7.6) in Taiwan

“…Taiwan is located in conductivity anomaly region (Chen et al 2001;Chen and Chen 1998;Hsu et al 1998;Hsu et al 2008;Yen et al 2009) in the western Pacific Ocean and lies atop a well-known seismically active region. A great earthquake of magnitude 7.3 (M L = 7.3, M w = 7.6) occurred on September 21, 1999, near the small town of Chi-Chi in Nantou County in central Taiwan (Shin 2000).…”

Preface to the Special Issue on "Geomagnetic Research for Taiwan: Present and Future"

“…A series of geomagnetic surveys in Taiwan were conducted on land and the adjacent seas. These surveys include the western plains by the China Petroleum Company (Hu 1981), eastern and southern seismic zones by Academia Sinica (Yu and Tsai 1981), marine geomagnetic anomaly compilation (Hsu et al 1998), the Tatun volcanic group in northern Taiwan (Chen et al 2001), and a general survey in the plain and lowland areas (Wang et al 2002).…”