Distribution of the Surface Ruptures in the Kalaotoa Due to the 2021 M w 7.3 Flores Sea Earthquake, Indonesia

Abstract

A magnitude 7.3 earthquake occurred at precisely 11:20 on December 14, 2021, within the Flores Sea region of Indonesia, precipitating a consequential landslide event. This seismic incident induced the creation of an extensive rupture zone spanning approximately 8 kilometers along the Kalaotoa fault (KF) system, which exhibits an NNE-NW-SSE trend. The objective of this study was to concentrate specifically on the Kalaotoa Island vicinity, situated approximately 40 kilometers from the earthquake’s epicenter, encompassing meticulous orientation and comprehensive field surveys conducted during the reconnaissance phase. The results of the ground assessment have been combined with spatial analysis data to ascertain the configuration and dispersion of ruptures subsequent to the earthquake, thus delineating the affected region as a prospective area susceptible to seismic events and subsequent calamities. In the vicinity proximate to the northern epicenter, fractures resulting from the seismic activity were consolidated, exhibiting considerable devastation in the form of ground fissures, rock avalanches, landslides, and structural collapses, and were predominantly oriented in a roughly NE-SW direction. Notably significant are the southern beaches of Lato’do and the eastern extremity of the rupture zone in the Lembang Mate’ne area, where coastal transgression and extensive inundation during high tides have been observed due to subsidence of 1.2 meters since the 2021 Flores Sea earthquake. Horizontal displacement around Kalaotoa Port, north of the Karumpa-Kawawo area. Displacement distribution, slip sense, and crustal deformation after earthquake propagate unilaterally to the north, resulting in a movement of the northeast side of the fault concerning SE.