dc.description.abstract | Application of multi-site and multi-frequency impedance tensor decomposition to resolve the crustal structures of the MT data in central Taiwan and Kinmen area
Sung-Ching Chi
Abstract
The purpose of this study was to strip the shallow 3D resistivity anomalies by using the multi-site and multi-frenquency impedance tensor decomposition (MSMFITD) during the inversion of the MT 2D profile.
Computer simulations of the MSMFITD technique, after using the synthetic data coming from the MT 3D forward modeling, indicated that: 1) MT data sensitively responses to high conductors; 2) the MSMFITD is quite powerful to strip the MT data pertubated by the local 3D inhomogenities, and perfectly recovered the true 2D structures.
The application of the MSMFITD technique to the MT data collected from the central Taiwan and the Kinmen area obtained three important results:
1) Two resistivity anomalies were dectected around the hypocenter of the Chi-Chi earthquake, the high resistivity anomaly on the west and the low resistivity anomaly on the east. This resistivity pattern mostly indicates that deep-crustal fluids may participate in the rupture process of the Chi-Chi earthquake. A striking spatial correlation between the crustal conductor and occurrence of aftershocks beneath the Chelungpu fault suggests a postseismic pore pressure adjustment ongoing after the mainshock. Additionally, the hypocenter exhibits an electrical resistive zone, consistent very well with a predicted compact zone from a crustal deformation and transient fluid flow modeling.
2) There were two MT profiles in the central Taiwan, cc-1 and cc-2. The resistivity structure of the northen MT profile cc-1 indicated that the depth of the Moho, about 248 ohm-m of resistivity, is at about 35km to the west, uplifting to 30km between MT soundings ccm-4 to ccm-12, and then deepening to 50km to the eastern end of the profile. As to the southen profile cc-2, the depth of Moho, about 167 ohm-m of resistivity , is at about 31km to the west and then gradually deepen to about 43km to the east.
3) The Kinmen islet, which is quite different from the Taiwan island geologically, belongs to the continental crust in the stage of the backarc spreading. Based on the resistivity profiles, in Kinmen area the depth of Moho, 129~219 ohm-m of resistivity, is around 32km with little variation in NS direction, but a little bit deepen to the west. | en_US |