| dc.description.abstract | The offshore of northern Taiwan is subject to post-collisional collapse and under an extensional regime. Because of the change from a compressional environment to an extensional environment, a series of normal fault structures has been formed. The reverse faults in the Gongliao area of Taiwan, include the Longdong Fault, Wentzukeng Fault, Aodi Fault, and Fangjiao Fault. Those faults are distributed to the coastline and may extend to the offshore area. In order to understand the situation of the fault extension to the offshore area and the possibility of fault activity. We conducted Sparker reflection seismic surveys in the offshore area of Gongliao. The Sparker seismic system is suitable for shallow water surveys and can provide high-resolution shallow structures.
To understand the geological structures of our study area, sequence stratigraphy, seismic facies and faults identification are used to analyze our seismic profiles. According to the sequence stratigraphy, the transgressive surface, the last glacial maximum (LGM) unconformity, and last maximum flooding surface can be identified. In addition, the sand wave base surface, syn-rift unconformity and the acoustic basement are also defined. For next part, there are 5 seismic facies correlated to the different depositional environments.
We have identified 5 normal faults (i.e. Fa, Fb, Fc, Fd and Fe) in the prolongation of the onshore faults. All the identified faults cut through the basement and caused large offsets, forming half-graben basins. Some faults have caused offset of the strata near the seafloor. For the activity of these faults, the strata in the half-graben basin A formed by Fault a, is tilted, which was probably caused by the continuous growth of the fault. The strata in the half-graben basin B formed by Faults b and c, are inclined below the LGM unconformity, but the strata above the LGM unconformity are relatively flat. Otherwise, only the sediments in the upper part of the half-graben basin B show the characteristics of sequence stratigraphy, which means the sediments deposit controlling by sea level change. In summary, we infer that the faults b and c were active before the LGM and relatively stable recently. For faults d and e, because they were covered by thick sediment layers, indicated early structures and not active at all. | en_US |