| dc.description.abstract | The Milun fault is the northern extension part of the Longitudinal valley which is the suture between the Philippine Sea plate and the Eurasian plate on the Taiwan Island. The Milun fault relates to two destructive earthquakes on October 22nd, 1951, and February 6th, 2018, respectively. The 1951 ML 7.3 earthquake and the 2018 MW 6.4 earthquake both produced surface ruptures along the Milun fault, causing casualties and damage on buildings in the Hualien city. Although the Milun Fault is surely a hazardous fault, the subsurface configuration and history of this active fault remain little exposed. The purpose of this study is to uncover the fault at shallow depth, reason the activity and seismic history of the Milun Fault and estimate the recurrence interval. Three trenches and four boreholes were carried out at the Hualien Air-Force Base, where surface ruptures were reported during the 2018 earthquake. The main trench with two stages is 36 m in length, 4 m in width, and 7 m in depth. The Milun main fault revealed on the trench wall dips 80° to the east, and its branch faults dip 36°, 56°, and 70° to the east, respectively. Some clues are related to paleoseismic events, including the colluvial wedges, folded growth strata, and liquefaction. By compiling the results of restoration and stripping of strata in conjunction with the age constraints, five paleo-earthquake events associated with the Milun Fault are resolved: (1) the 2018 event (2) the 1951 event and the earlier ones occurred at (3) 790-144 cal yr BP (4) 2360-1301 cal yr BP (5) 3980-2306 cal yr BP. The intervals between each paleo-earthquake events indicate that the recurrence interval of the Milun fault might be irregular. Further investigation will be needed to evaluate the recurrence interval of the Milun fault. Based on the borehole data, the throw component of the Milun fault is 17.9-18.6 m. Combined with the dating result, the maximum uplift rate of the Milun fault is 2.9-3.4 mm/yr. | en_US |