Hazard mapping related to structurally controlled landslides in Southern Leyte, Philippines

Paul Kenneth Luzon,Jam Galang,Jasmine May Sabado,Raquel Felix,Alfredo Mahar Francisco Lagmay,Kristina Montalbo,Carmille Marie Escape

doi:10.5194/nhess-16-875-2016

Paul Kenneth Luzon, Jam Galang + Show 5 more

Open Access

https://doi.org/10.5194/nhess-16-875-2016

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Abstract

Abstract. The 2006 Guinsaugon landslide in Saint Bernard, Southern Leyte, is one of the largest known landslides in the Philippines in recent history. It consists of a 15–20 million m3 rockslide-debris avalanche from an approximately 675 m high mountain weakened by continuous movement of the Philippine Fault. The catastrophic Guinsaugon landslide killed 1221 people and displaced 19 000 residents over its 4.5 km path. To investigate the present-day morphology of the scar and potential failure that may occur, analysis of a 5 m resolution InSAR-derived digital elevation model was conducted using Coltop3D and Matterocking software, leading to the generation of a landslide hazard map for the province of Southern Leyte in central Philippines. The dip and dip direction of discontinuity sets that contribute to gravitational failure in mountainous areas of the province were identified and measured using a lower Schmidt–Lambert color scheme. After measurement of the morpho-structural orientations, potential sites of failure were analyzed. Conefall was then utilized to compute the extent of rock mass runout. Results of the analysis show instability in the scarp area of the 2006 Guinsaugon landslide and in adjacent slopes because of the presence of steep discontinuities that range from 45 to 60°. Apart from the 2006 Guinsaugon landslide site, runout models simulated farther rock mass extent in its adjacent slopes, revealing a high potential for fatal landslides to happen in the municipality of Saint Bernard. Concerned agencies may use maps produced in the same manner as this study to identify possible sites where structurally controlled landslides can occur. In a country like the Philippines, where fractures and faults are common, this type of simulated hazard maps would be useful for disaster prevention and facilitate disaster risk reduction efforts for landslide-susceptible areas.

Highlights

IntroductionIdentified as a rockslide-debris avalanche (Lagmay et al, 2008), the fatal landslide happened on the slopes of Mt. Can-abag along a steep scarp defined by the Philippine Fault Zone or PFZ (Allen, 1962) (Fig. 1)
1.1 Guinsaugon landslideOne of the largest known mass wasting events in the Philippines happened in the province of Southern Leyte
The study area is part of the Southern Leyte segment of the sinistral PFZ, which has an average movement of 0.55 cm yr−1 (Cole et al, 1989) up to 3.5 cm yr−1 (Duquesnoy, 1997, as cited by Catane et al, 2006)

Summary

Introduction

Identified as a rockslide-debris avalanche (Lagmay et al, 2008), the fatal landslide happened on the slopes of Mt. Can-abag along a steep scarp defined by the Philippine Fault Zone or PFZ (Allen, 1962) (Fig. 1). The study area is part of the Southern Leyte segment of the sinistral PFZ, which has an average movement of 0.55 cm yr−1 (Cole et al, 1989) up to 3.5 cm yr−1 (Duquesnoy, 1997, as cited by Catane et al, 2006). This has led to formation of regional discontinuities and development of thick clay-rich gouge zones in the surface prominent in the en-

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