Drone-based mapping for surface ruptures of the 2018 Hualien, Taiwan, earthquake

The distributions and characteristics of coseismic surface ruptures are the key to understand fault behaviors. However, traditional field investigations could be time consuming while damaged buildings and infrastructures may be subject to repairs due to rescue missions and transportation recovery within a few days after the earthquake, leading to urgent needs for rapid, extensive surveys before surface breakages are modified. Therefore, we take advantage of UAS photogrammetry to collect aerial images and to map surface fractures for the M_w6.4 Hualien, eastern Taiwan, earthquake on February 6, 2018. The earthquake struck Hualien City and generated dense surface breakages over a distance of 8 km. Together with control surveys for ground control points by using RTK-GPS, UAS photogrammetry uses the SfM-MVS method to produce high-resolution orthoimages and digital surface models. We map surface ruptures based on the orthomosaic images. Our mapping results show that surface ruptures follow the trace of the Milun fault and northern Linding fault. Mapped surface ruptures are usually in en échelon arrays or distributed fractures rather than a through-going fault. Estimated sinistral offset based on orthoimages is more than 60 cm in Chihsingtan and decreases toward south. The fault behavior of the 2018 Hualien earthquake shows along-strike variations and is somewhat different from the October 1951 earthquake.