Central Geological Survey, MOEA

About: Central Geological Survey, MOEA is a government organization based out in Taipei, Taiwan. It is known for research contribution in the topics: Landslide & Fault (geology). The organization has 68 authors who have published 81 publications receiving 2037 citations. The organization is also known as: Jīngjì Bù Zhōngyāng Dìzhí Diàochá Suǒ.

Coseismic hydrological changes associated with dislocation of the September 21, 1999 Chichi earthquake, Taiwan

Abstract: [1] Being situated in the immediate vicinity of the 1999 Chichi earthquake epicenter, 178 automatic-recording monitoring wells of the Choshui fan-delta provided a very valuable data set for testing whether the coseismic water-level changes in confined aquifers can be explained as a poroelastic response of well-aquifer systems to coseismic volumetric strain. This study demonstrates that the polarities of the observed coseismic water-level and river discharge changes are in good agreement with those of the static volumetric strain calculated by a dislocation model, using the well-constrained rupture model of the seismogenic Chelungpu fault. The puzzling “bull-eye” patterns formed by the equipotential lines of the coseismic water-level changes in the confined aquifers in the middle parts of the fan-delta represent pressure enhancement due to their being situated at the pinch-out ends of conglomeratic layers.

Estimation of methane flux offshore SW Taiwan and the influence of tectonics on gas hydrate accumulation

Abstract: Widely distributed bottom simulating reflectors (BSRs) imply the potential existence of gas hydrates offshore southwestern Taiwan. To compare the distribution of methane concentrations along passive and active margins in the region, bottom waters and cored sediments were collected during four cruises from 2005 to 2006. The results reveal that sites with high methane concentrations are predominantly distributed in the active margin and site GS5 is the only site that contains very high methane concentrations in the passive margin of studied area. Anomalously high methane fluxes still can be obtained from the calculation of diffusive methane flux, although there might be some gas leakage during or after sampling procedures. The profiles of methane and sulfate concentration reveal very shallow depths of the sulfate–methane interface (SMI) at some sites. There is evidence that sulfate reduction is mainly driven by the process of anaerobic methane oxidation. Thus, sulfate fluxes can be used as a proxy for methane fluxes through the use of diffusion equations; and the results show that the fluxes are very high in offshore southwestern Taiwan. The depths of the SMI are different at sites GH6 and C; however, both methane profiles reveal parallel methane gradients below the SMI. This might be because of methane migration to surface sediments from the same reservoir with the same diffusion rates. Although BSRs are widely distributed both in the active margin and in the passive margin, most sites with high methane concentrations have been found in the active margin. Therefore, the specific tectonic settings in offshore SW Taiwan might strongly control the stability of gas hydrates, and thus affect the methane concentrations and fluxes of the sediments and sea waters. Furthermore, the carbon isotopic composition of methane shows that a biogenic gas source is dominant at shallower depth; however, some thermogenic gases might be introduced through the fracture/fault zones from deeper source in the active region of studied area.