Assessing Earthquake-induced Debris Flow Risk in the first UNESCO World Heritage in Malaysia

Abstract

The Mw 6.0 Ranau earthquake dated on 05th June 2015 was recorded as one of the strongest earthquakes in the history of Sabah, Malaysia. The earthquake induced many cascading geohazards and earth material in the vicinity of Mount Kinabalu, the first UNESCO World Heritage Site in Malaysia. The earthquake formed a temporary landslide dam that later breached and remobilized as debris flows. This paper provides a new insight into the cascading geohazards as a result of the 2015 Ranau earthquake in Sabah. We evaluated the surface changes of source area that contributes to the landslide damming formation using the remote sensing techniques and field validation. Two image classification methods were performed, including the Maximum Likelihood Classification (MLC), and Nearest Neighbor Classification (NNC). Both presented the supervised pixel- and object-based classifications respectively. This study delineated the source area of before- and after earthquake using the Geographic Information System (GIS), followed by the image classification, accuracy assessment, and surface changes. A series of field mapping was carried out to validate the local evidence. The findings determined three classes within the source area, namely; vegetation cover, bare earth, and stripped earth material (SEM). The surface changes resulted from the earthquake using the MLC was −1.62 km2 (vegetation cover), +0.23 km2 (bare earth), and +1.39 km2 (SEM), while using the NNC was −1.44 km2, +0.12 km2, and +1.32 km2 accordingly. The accuracy assessment of before and after earthquake for the MLC was 86% and 89%, whereas the NNC resulted in a 97% and 95% respectively. The NNC produced higher accuracy of 11% and 6% than the MLC. The increased SEM of 1.44 km2 has contributed to the accumulated earth material and resulted in the landslide damming formation. As a conclusion, this study explores the local risk of debris flow induced by the earthquake, by means of remote sensing technology with improved classification methods. A new insight of possible sediment-induced disaster was presented in the inaccessible and rugged topography, and rapid investigation of potential damming areas in a tectonically active region. This study provides an important clue to understand the local risk and substantially develop Disaster Risk Reduction (DRR) and resilience strategies in the vicinity of UNESCO World Heritage to support the achievement of global targets of the Sendai Framework for Disaster Risk Reduction 2015–2030.