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Accurately imaging seismogenic structures is crucial for seismic hazard assessment. This is especially important around the deformation front (DF) region off SW Taiwan, where seismic potential is high but the fault structure and seismic activity are still poorly understood. Here, we present a comprehensive delineation of seismogenic structures along the onshore and offshore DF of SW Taiwan, utilizing hypocenter relocations and first-motion focal mechanism solutions from January 1991 to March 2019. Five distinctive seismogenic structures are delineated. Particularly, the energetic seismic activity initialled after the 2017 Mw5.3 Tainan earthquake and migrated northeastward along the western side of the DF. The offshore trace of the DF could serve as a boundary delimiting the seismic activity driven by the flexural stress of the subducted Eurasia Plate to the west of the DF. This observation could constrain the magnitude estimation of future earthquakes offshore SW Taiwan. Meanwhile, the areas with higher seismic moment release are located near the DF rather than known faults, indicating that the DF may dominate the seismic moment release. However, further study is warranted into the intricate relationship among seismic strain variation, the structure of DF, and seismic activity to further understand the seismic potential. Our first-motion focal mechanism solutions show that several earthquakes in SW Taiwan were characterized by P-axis orientations parallel to the strike of the Taiwan orogeny. Those events are preferably explained by the lateral compression induced by the ongoing collision between the Eurasia and Philippine Sea plates. Key Points: The deformation front has high seismic potential but seismogenic structure remains unclear. The deformation front confined seismic activity and released relatively large seismic moments. The role of the deformation front must be considered in seismic hazard assessment. [ABSTRACT FROM AUTHOR]

Engineering risk assessment is to estimate the structure's failure probability multiplied by its failure consequences. On the other hand, the analysis was sometimes performed on a more general basis, utilizing a few indicators to quantify relative risk levels for decision-making. On the basis of such a framework, this paper introduces a novel risk assessment on 18 active faults in Taiwan, considering the fault's location, earthquake size and return period from the literature. The result shows that the Chelungpu Fault in central Taiwan has the highest risk score among the 18 active faults, in contrast to the Hengchun Fault in southern Taiwan which has the lowest risk. Besides this, the 18 active faults in Taiwan were classified into four groups based on this risk assessment, and the classification could help the region's sustainable development against earthquake hazard. [ABSTRACT FROM AUTHOR]

The region around Taiwan is known for active seismicity, and a few studies have reported a high seismic hazard in this region, including a deterministic seismic hazard analysis (DSHA) study. Essentially, DSHA is to estimate earthquake ground motions considering the worst-case earthquake size and location, but without considering the seismic hazards from non-controlling sources. Understandably, when many non-controlling sources are present, the original DSHA framework could be insufficient. Therefore, using the extreme probability theory, this study introduces a new DSHA framework taking non-controlling seismic sources into account during DSHA calculations. The new method was applied to a seismic hazard assessment for Taiwan, showing that near the conjunctions of seismic source zones, the increase in seismic hazard could be substantial after considering a total of 19 non-controlling sources. More importantly, like other seismic hazard assessments for Taiwan, this study conveys the same alarming message that a high level of seismic hazard should be present around the region. [ABSTRACT FROM AUTHOR]

According to the Central Geological Survey Taiwan (CGST), the Meishan fault in Central Taiwan, which induced a catastrophic earthquake in 1906, is considered capable of triggering equivalent events with a return period of 162 years. Therefore, as the next event is expected around 2070, the Meishan fault poses a high level of earthquake risk in Central Taiwan, especially for those cities and townships very close to the fault. However, the best-estimate return period (162 years) and earthquake magnitude (7.1 M) reported by the CGST must be subject to some uncertainty, because such an event is very unlikely to recur every 162 years. Therefore, this study carried out a series of seismic hazard assessments for three major cities close to the Meishan fault, with the uncertainty of the best-estimate information being determined using the Rosenblueth algorithm. The results show that for Chaiyi city, which the Meishan fault passes through, the probability of the current design value (i.e., PGA = 0.33 g) being exceeded by the earthquake motion induced by the Meishan fault in the next 50 years would be as high as 55 %. Therefore, further studies should be carried out to obtain a better understanding of the Meishan fault, to develop a robust hazard mitigation plan for nearby cities. [ABSTRACT FROM AUTHOR]