Seismic-induced landslide hazard analysis of the recreational area of the Makiling Botanic Gardens, Los Baños, Laguna, Philippines

Abstract

The Makiling Botanic Gardens (MBG) is an educational and eco-tourism site located within the vicinity of Mount Makiling, a dormant volcano susceptible to landslides, and located less than 20 km away from at least two tectonic faults. The study assessed the seismic-induced landslide hazards in the recreational area of MBG mainly based on three parameters: factor of safety (FS), yield acceleration (ay), and slope displacement (Dn). Dynamic Cone Penetration Test (DCPT) served as the primary method for obtaining the shear strength of the soil within the area. Meanwhile, other relevant parameters, including material unit weight and internal angle of friction, were determined through laboratory testing, correlations, and available data and models. Moreover, the Peak Ground Acceleration (PGA) and Spectral Acceleration (SA) values were obtained through an interpretation of a probabilistic seismic hazard analysis (PSHA) study of the Philippines. Using the ArcGIS software, an FS map, yield acceleration map, and slope displacement map were generated. Results showed that the slopes within the area exhibit static stability. However, in the event of an earthquake, it is expected that the amplified PGA will exceed the expected yield acceleration values of the slopes in some parts of the recreational area, which could result in dynamic instability and slope displacements as high as 130 mm. Thus, the recreational area of MBG possesses some susceptibility towards a seismic-induced landslide.