Normal fault evolution in the Penghu Basin, a Paleogene Rift Basin in Western Taiwan Strait: A test of fault growth models

Abstract

The growth of normal fault systems affects the development of rift basins. These systems could grow via either non-coherent or coherent models, where segments either develop independently or merge into one fault, respectively. Also, they could experience decreases in fault system lengths, called lateral tip retreat, during the later fault-activity stage. In this study, we investigate the fault growth model by studying the Penghu Basin, a Paleogene rift basin in the western Taiwan Strait, and test the current fault growth models. Our methods include seismic interpretation and fault growth analyses, such as the spatiotemporal distribution of cumulative throw and throw increment and expansion index. In the Penghu Basin, the boundary and transfer fault systems grew via the non-coherent model followed by lateral tip retreat, while other studied fault systems grew via the coherent model before their tips retreated. Furthermore, segments could separate from their parent fault systems prior to the lateral-tip-retreat stage. During the evolution of the fault system, the shifting of a cumulative throw maximum could be accompanied by a throw increment minimum, i.e., segmentation, moving toward the migrated cumulative throw maximum inside segments or by the retreated fault tip of the fault system. This implies a change in the distributions of stress drop and increase regions. Finally, our results indicate that the specific rift phase of basin evolution is highly correlated with the development of fault systems. We suggest that the lateral tip retreat of fault systems marks a change in the rift phase of a basin and implies the end of basin evolution.