INDONESIAN JOURNAL on GEOSCIENCE Landslide Potential
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Indonesian Journal on Geoscience Vol. 8 No. 3 December 2021: 313-328 INDONESIAN JOURNAL ON GEOSCIENCE Geological Agency Ministry of Energy and Mineral Resources Journal homepage: hp://ijog.geologi.esdm.go.id ISSN 2355-9314, e-ISSN 2355-9306 Landslide Potential Investigation for Disaster Risk Reduction in Central Bengkulu Regency, Bengkulu Province, Indonesia Arif Ismul Hadi, Refrizon, M. Farid, Budi Harlianto, and Julia Inti Sari Deprtment of Physics, Faculty of Mathematics and Natural Sciences, University of Bengkulu, Bengkulu 38371, Indonesia Corresponding author: [email protected] Manuscript received: November 23, 2020; revised: January 2, 2021; approved: Februari 18, 2021; available online: August 10, 2021 Abstract – Bengkulu Province is the converging path region between the Indo-Australian − Eurasian tectonic plates in the ocean and the Sumatran f ault crossing on the mainland. The condition implies that the sliding force of the slab is easy to trigger fractures and to cause the material to be relatively less elastic, resulting in high seismic intensity. This study aims to identify areas with the potential for landslides and its mapping, and to analyze the factors that cause landslides in Central Bengkulu Regency, Bengkulu Province, Indonesia. This study was conducted using rock physical parameters of ground shear strain (GSS) which were correlated with parameters of slope, slope height, Vs30 value, fault distance to measurement point, rock conditions, rainfall, and PGA value. Furthermore, these parameters were overlaid thoroughly by the statistical method of the Analytical Hierarchy Process (AHP). Data acquisition is divided into two stages, namely the secondary data collection stage and the field survey stage. Secondary data collection was carried out to support the creation of landslide potential maps, analysis, and field survey data input. Secondary data is the value of Vs30, the distance of the fault to the measurement point, rainfall, and the PGA value. Field survey data are in the form of GSS values, slope, slope height, and rock conditions. The results of this study are identified areas that have the category of high, medium, and low landslide potential. Based on the calculated parameters, the GSS parameter is the most dominant which affects the landslide potential in the studied area. Keywords: rock physical parameters of GSS, Vs30, rainfall, PGA, statistical method of AHP © IJOG - 2021. How to cite this article: Hadi, A.I., Refrizon, Farid, M., Harlianto, B., and Sari, J.I., 2021. Landslide Potential Investigation for Disas- ter Risk Reduction in Central Bengkulu Regency, Bengkulu Province, Indonesia. Indonesian Journal on Geoscience, 8 (3), p.313-328. DOI: 10.17014/ijog.8.3.313-328 Introduction can have implications for the movement of the slab glide force to easily trigger fractures that cause the Background material to be relatively less elastic, resulting in a Bengkulu Province is the converging path high seismic intensity compared to other areas on region between theIJOG Indo-Australian - Eurasian the island of Sumatra (Murjaya, 2011, Megawati tectonic Plates in the ocean and the Sumatran Fault et al., 2005, and Irsyam et al., 2017). crossing the mainland. The results of study on The compression force of the Indo-Australian seismicity in Sumatra Island show that the highest tectonic Plate and the Eurasian Plate has caused cumulative tectonic energy and strain rate values the Sumatran Fault System on the mainland to occur around the Bengkulu Province area. This be divided into nineteen main segments (Bock Indexed by: SCOPUS 313 Indonesian Journal on Geoscience, Vol. 8 No. 3 December 2021: 313-328 et al., 2003; Gafoer et al., 2012; Sieh and Na- 7 in the Musi Segment Fault is 165 years which is tawidjaya, 2000). Each segment has a different the highest among the Sumatran Fault segments slip rate (Natawidjaya and Triyoso, 2007). One in the Bengkulu region. Based on these condi- of the Sumatran Fault Systems cutting through tions, Central Bengkulu Regency is vulnerable Bengkulu Province is the Musi segment, which is to earthquakes both at sea and on mainland. The located in Kepahiang Regency, bordering Central average rainfall in Central Bengkulu Regency is Bengkulu Regency. also quite high, i.e. 2,673 mm/year (Anonymous, Earthquake and high rainfall are the main fac- 2020a). This can happen because Central Beng- tors that trigger landslides. The results of the study kulu is one of intertropical convergence zones by Zhang et al. (2014) relating to the character- (ITCZ) which has high rainfalls throughout the ization of earthquakes caused by the movement year (Sudradjat, 2007). of faults show that the earthquake in Wenchuan, Conditions with high seismicity in the sea and China on May 12, 2008 with a magnitude of 7.9 close to the Sumatra Fault of the Musi Segment on and a depth of 19 km caused 322 shallow land- land, high rainfall, and steep slopes make Central slides around a road that is traversed by four faults Bengkulu Regency are very vulnerable and have and partially located on the hanging wall of the the potential for landslides, especially in hilly Yingxiu-Beichuan Fault. The magnitude of the areas. Based on these conditions, it is very inter- earthquake and the volume of landslides from the esting to investigate the potential for landslides earthquake that occurred in Chuya on September in this area, because landslide prone points can be 27, 2003 with Ms = 7.5 and a depth of 18 km have identified through mapping of potential landslides an empirical relationship that the magnitude of the for disaster risk reduction. earthquake can increase the volume of the result- This study aims to identify the areas with poten- ing landslide. This earthquake caused massive tial for landslides, to map the areas with potential landslides and about three hundred houses were for landslides, and to analyze the factors causing destroyed (Nepop and Agatova, 2008). Another landslides in Central Bengkulu Regency, Bengkulu example of landslides caused by earthquakes due Province, Indonesia. This study was conducted to movement of faults is the earthquake in Papua using rock physical parameters of ground shear New Guinea or 560 km northwest of the capital strain (GSS) as a parameter of ground deformation Port Moresby on February 26, 2018 with a mag- level related to landslide potential. To strengthen nitude of 7.6 SR and a hypocentre depth of 17 the parameters of the GSS value, it is necessary km. This earthquake occurred due to deformation to use other factors that can contribute to land- activity in the New Guinea Highland (NGH) Fold slides, namely the influence of geomorphological and Thrust Belt which is an upward fault zone in parameters in the form of slope and slope height, the middle lane of the Papua New Guinea Moun- geological parameters in the form of Vs30, geologi- tains (Daryono, 2018). cal structure (fault distance to measurement point), Central Bengkulu is one of the regencies in rock conditions, and external parameters such as Bengkulu Province, Indonesia, which is geo- rainfall and peak ground acceleration (PGA). Fur- graphically located close to the source of earth- thermore, all of these parameters are overlaid by quakes both at sea and on mainland, namely the the statistical method of the Analytical Hierarchy Musi Segment SumatraIJOG System. Regions that are Process (AHP). AHP statistical method is used close to the source of this earthquake are regions in this study because this method is a method of that have a potential to trigger landslides greater decision making to determine the best alternative than other regions when an earthquake occurs from a number of alternatives based on certain (Hadi and Brotopuspito, 2015). According to criteria (Kusumadewi et al., 2006). This method Natawidjaya and Triyoso (2007), the frequency of describes a complex multifactors or multicriterion repeated large earthquakes with a magnitude of ≥ problem into a hierarchy. Hierarchy represents a 314 Landslide Potential Investigation for Disaster Risk Reduction in Central Bengkulu Regency, Bengkulu Province, Indonesia (A.I. Hadi et al.) complex problem in a multi-level structure con- will greatly affect the occurrence of landslides. sisting of objectives, followed by criteria, subcri- Stratigraphically, Central Bengkulu consists of teria, etc. to the last level of alternatives (Russo Tertiary and Quaternary sequences. The Tertiary and Camanho, 2015). Based on the hierarchy of stratigraphic unit consists of Bintunan Formation a complex problem, it can be broken down into (QTb), Simpangaur Formation (Tmps), Lemau groups which are then arranged into a hierarchical Formation (Tml), Bal Formation (Tmba), Hulu- form, so that a problem will be more structured simpang Formation (Tomh), Seblat Formation and systematic (Saaty et al., 1991). AHP is also a (Toms), and Diorit (Tmdi). structured quantitative decision-making process The rock units of Hulu Simpang Formation that can be documented and replicated, can be ap- (Tomh) are the oldest rock unit in the studied plied as decision support for situations involving area from the Late Oligocene to Middle Miocene. multicriteria, can be applied as decision support This formation was deposited in an intermediate for situations involving subjective assessments, environment between shallow land and marine. etc. (Steiguer et al., 2003). This formation interfingering with the Seblat Formation (Toms) is overlain by the Bal Forma- Geological and Stratigraphical Settings tion (Tmba) and Lemau