| Summary: | 碩士 === 國立中央大學 === 地球物理研究所 === 94 === Abstract
In this study, Magnetotellurics (MT) was used to survey the southern Longitudinal Valley of east of Taiwan, where the famous Chi-Shang fault lies. This valley, about 10 km in width, with 2-3 cm/y of creep, absorbed nearly 1/3 convergent strain of the two plate between Philippine Sea Plates and the Eurasia plate.
The survey area is in the Taitung county. There are 23 MT soundings form a W-E profile of about 30 km in length. Initially, the observed MT data was made a series of data processing , including FFT, statistical analysis , and signal filter, etc., so as to decide and select the good quality data for inversion. Then 2D-NLCG inversion was applied to obtain the best fitting of the underground electrical structure profile for further analysis and explanation
The 2D electric image of the profile shows that the distributions of the resistivity anomalies are uneven. However, we can distinguish the low resistivity anomaly and the high resistivity anomaly by using the resistivities of lower than 50 ohm-m and higher than 500 ohm-m, respectively, in this area:
1. In the Central Mountain Range, the west of the profile, e.g., locations of Li-Dao, Wu-Lu and Shin-Wu, low resistivity anomalies display at the shallow part of depth of about 2 km, where are well correlated with the surface faults and hot springs; whereas to the high resistivity anomaly display at depth from 2 to 10 km, reflecting the hard rocks of the Central Range.
2. In the Longitudinal Valley, the central of the profile, at the shallow part (about 0.5 km) shows low resistivity anomaly, indicating alluvial or talus; moreover, as depth increase to more than 4 km, a large low resistivity anomaly displays, possibly reflecting the intrusion of the eastern oceanic crust.
3. In the Coast Range, the east of the profile, the low resistivity anomaly correlated well with the surface melange, which extend from the surface to the depth of 10 km by our MT results.
|
|---|
