PROCEEDINGS Jogja Earthquake in Reflection 2016 24–26 May 2016
ASSESSING HUMAN VULNERABILITY TO EARTHQUAKE HAZARD OF REGENCIES IN YOGYAKARTA: CASE STUDY IN M 6.3 YOGYAKARTA EARTHQUAKE, MAY 27TH, 2006 Sulastri*, Bambang Sunardi*, Andi Eka Sakya*, Masturyono*, Supriyanto Rohadi* *) Indonesian Agency for Meteorological, Climatological and Geophysics (BMKG)
[email protected] ABSTRACT Taking the M 6.3 Yogyakarta Earthquake as an example, the research objective was to identify the human vulnerability to earthquake hazard of each regency in Yogyakarta. In this paper, the evaluation of human vulnerability during the earthquake hazard was evaluated through human exposure and human sensitivity assessment. The human exposure is the ratio of the distance to the epicenter and the density of total population in affetced areas. The human sensitivity is the proportion of the ratio of population affected by earthquake hazard and its severity, that can be combination of the death and casualties caused by earthquake hazard and its seismic intensity. The result showed that Yogyakarta City,the most densed population, has the highest human exposure and the lowest human sensitivity, while the Bantul Regency has the highest human sensitivity, due to its location which was the nearest distance to the epicenter of Yogyakarta earthquake. The highest value of human sensitivity in Bantul Regency was caused by the highest ratio of total number of death and casualties to population was also highest, which correlated with the number of houses collapsed and damaged by the 2006 Yogyakarta earthquake. Keywords: Yogyakarta earthquake, earthquake hazard, human vulnerability, human exposure, human sensitivity
Introduction On Friday, May 26 th 2006 at 22:54 UTC or Sunday, May 27 th 2006 at 5:54 local time, Yogyakarta hit by a deadly earthquake, which can be called Yogyakarta earthquake. According to USGS, this earthquake had 6.3 magnitude, located on land fault, 7.96° South and 110.43° East, with a depth of 17.1 km (earthquake.USGS.gov). The Shake Map of Yogyakarta eartquake from USGS can be seen in Figure 1. Even its magnitude only 6.3, but it made 4,680 people dead and 19,897 people injured, only in Yogyakarta Special Province. It also made 117,182 houses heavy damaged, and 156, 568 houses light damaged also in Yogyakarta Special Province, with the worst damages were in Bantul regency (Haifani, 2008; Sunardi and Sulastri, 2015). It also damaged the public facilities, such as hospitals, railways, airport and disturbed water pipes, electricity, and
communication facility (Gatignon et al., 2010; Sunardi and Sulastri, 2015). Yogyakarta Special Province dealing directly with South Java subduction zone. Subduction zones are divided into megathrust / interplate and Benioff zone / intraslab. Megathrust zone located at a depth of less than 50 km and Benioff zone at a depth of more than 50 km (Sunardi, 2013; cited by Sunardi and Sulastri, 2015). Last year, a research about deaggregation hazard map of Yogyakarta has been done by Sunardi and Sulastri (2015). From its result, it is known that almost all area in Yogyakarta Special Province are influenced by earthquakes located in Opak fault, included the Yogyakarta earthquake. The number of houses damaged because of Yogyakarta earthquake can be linked with the geological condition. The geological condition of Yogyakarta from Quarternar y Age to the historical period cited from Mulyaningsih et al., (2006). The uplift of Southern Mountains in Early Pleistocene has formed the Yogyakarta Basin. The Merapi volcanic activity has been developing in this basin. A flat valley had been form due to the high in the south and the appearance of Merapi volcanic dome in the north. The valley is bounded by the Southern Mountains on the south and bounded by the West Progo Mountains on the west. The geological environment of lacustrine active volcano has grown in this valley. Volcanic activity of Merapi which form geological condition occured from 20,000 up to 310 years ago. In present time, lithology of the areas which are interpreted as a palaeo-valley is composed of black cla y deposits. This black clay is a contact between the basement rocks and Merapi volcanic deposits (Mulyaningsih et al., 2006). The most damaged areas of Yogyakarta earthquake are located in this valley. The research objective was to identify the human vulnerability to earthquake hazard of regencies in Yogyakarta.This study took a different perspective on the earthquake hazard, which focused on human living on the earthquake prone area. The researches about human related to earthquake hazard became popular since the last decade. Gupta et al., (2006) studied about earthquake risk to Himalayan population. The research purpose was to examine risk assessment of human settlements due to seismic-tectonic setting of a populated area in the Himalayas, so that mitigation measures may be taken
142
PROCEEDINGS Jogja Earthquake in Reflection 2016 24–26 May 2016 before the next earthquake takes its toll. They linked the percent of population with peak ground acceleration of earthquakes. They focused on spatial aspects of the global exposure dataset and mapping needs for earthquake risk assessment.
offshore, and R in industrialized world is about two to three times larger than in the developing world. They proposed R as measure of change in resistance of buildings to shaking because it does not depend directly on the magnitude of earthquakes but on intensity, regardless of the magnitude that generated it. R can be smaller than 1 if the number of people killed at high intensities can be larger than those injured, and R can reaching infinity if buildings are build such that they do not collapse, or zero fatalities, but numerous injured. Rosetto et al (2011) highlighted the psychological drivers of seismic adjustment behaviours on the part of individuals, which are gleaned primarily from psychological studies. The psychological drivers are identified as perceived risk, community orientation and social norms, perceived trust, sense of responsibility, and fatalism and control, which are called socio psychological factors.
Figure 1. Shake Map of Yogyakarta Earthquake (USGS). A complete perspective about the link between human and earthquake can be found in a book by Springer (2011), Human Casualties in Earthquakes, edited by Spence, So, and Scawthorn. Some articles of the book are stated bellow. Guha-Sapir and Vos (2011) stated that distribution of deaths and injuries caused by earthquakes varies greatly according to the region and the economic development of the community in which it occurs. Statistical analysis of earthquake impact data can be useful for evaluating impact patterns over space and time. The mitigation of deaths and injuries is of primary concern to all disaster prevention efforts. Zuccaro and Cacace (2011) approached the percentage of seismic casualties is directly proportional the population density in the affected area (exposure) by ratio of injured and ratio of deaths. Ratio of injured is ratio of number of injured to number of people in the area, while ratio of deaths is ratio of number of deaths to number of people in the area. The sum of the both ratios represents the total physical damage to the population. The possible factors influencing the casualties occurring after an earthquake or in the other words vulnerability factors influencing the number of casualties are many, which can be listed as structural and non-structural damage, vertical building structural typology, geometrical characteristics, and distribution of the population in different building typologies. Wyss and Trendafiloski (2011) made the ratio injured to fatalities (R) in the worldwide. They found that R in earthquakes beneath land is typically half of that for events
Dell’Aqua et al., (2013) developed a Global Exposure Database for the Global Earthquake Model (GED4GEM), which requires compilation of a multi-scale inventory of assets at risk, for example, buildings, populations, and economic exposure. Wood et al. (2014) compared population exposure to multiple Washington earthquake. They made comparison of twenty earthquake scenarios in terms of residential exposure by MMI class and made conclusions that bear on future population-exposure studies related to earthquake hazards. The latest research is done by Liu and Wang (2015). They made differentiation in human vulnerability to earthquake hazard between rural and urban areas in China using two China earthquakes. They quantitatively analyzed the differentiation in human vulnerability to earthquake hazard between rural and urban areas. In this paper, the human vulnerability is stated in human exposure and human sensitivity. The definition of human vulnerability in this paper followed Liu and Wang's (2015), but the results of the human exposure and human sensitivity will be described in maps. These results will have advantage for the state holders to reconsider the earthquake management strategies, and also for disaster management agency (Badan Penanggulangan Bencana Daerah / BPBD Yogyakarta) to develop contingency plans to prevent the deaths caused by earthquake hazards. Data and Method This research took Yogyakarta Special Province as study area. This Province has five regencies, those are Yogyakarta City, Bantul Regency, Sleman Regency, Gunung Kidul Regency, and Kulon Progo Regency. It is located on the middle south of Java Island, from 110º05' to 110º 50' East and from 7º 33' to 8º 15' South. Its total area is 3185.81 km2 or about 0.17% of Indonesian area. The thread of earthquake in Yogyakarta are come from South
PROCEEDINGS Jogja Earthquake in Reflection 2016 24–26 May 2016 Java Subduction Zone, and also local faults such as Opak fault. Yogyakarta earthquake in 2006 was the worst earthquake since 2000, because it caused lot of damages and losses in human lives, properties, way of living, and also in public facilities. Data of the detail characteristics of Yogyakarta Earthquake including epicenter, and intensity are obtained from USGS. Other characteristics of Yogyakarta Earthquake are gathered from the previous researches and media reports, such as from World Bank. Distances to the epicenter were determined from the epicenter to the middle points of each regency. The statistics and description data of the characteristics of affected area including total area, total population, sex ratio, and population density were collected from Statistical Center Agency (Badan Pusat Statistik/ BPS) Yogyakarta Province. Number of deaths and number of injured by Yogyakarta earthquake are gathered from Media Center Gempa DIY, which can be found in Haifani (2008). The data of houses collapsed and damaged was from Social Ministry website. The definition of vulnerability in this paper followed the description by Liu and Wang (2015). Vulnerability is usually defined as the degree of loss resulting from a potentially damaging phenomenon. A consensus of vulnerability is that it is viewed as an internal side of risk, or the intrinsic characteristic of an individual or a system. Vulnerability covers three related concepts called factors of vulnerability: the level of exposure, the sensitivity of an individual or system, and the resilience to recover from an event. This paper focused on analyzing and assessing the human vulnerability during the earthquake hazard, and not the social and psychological factors. The human vulnerability can be stated in human exposure and human sensitivity function as bellow: Human vulnerability = {Human exposure (Ei), Human Sensitivity (Si)}
(1) Exposure can be defined as unsafe conditions of an individual or system. In this research the human exposure to earthquake hazard denotes external factor and also the severity of the impact of earthquake hazard on human. The human exposure to earthquake hazard is assessed based on two indicators, that are the distance to epicenter and the density of total population. It is assumed that the human exposure also refers to the number of people affected by the earthquake hazard, so a highly populated area will suffer more death and casualties than a less populated area. In the other words, the human exposure is the ratio of the distance to the epicenter and the density of total population occupied in the affected areas, which can be stated as: Ei=Ii/Di
(2)
Where Ei is the human exposure score of the i affected area; Ii is the density of total population occupied in the i affected areas (number of persons per sq km); Di is the distance to the epicenter of the i affected area.
Sensitivity is defined as the degree of a natural or social system to be susceptible to sustaining damage from earthquake hazard. Human sensitivity is considered to be largely determined by the human conditions, including physical aspects (such as gender, age) and also socioeconomic aspects (such as income and education). In this paper, the human sensitivity to earthquake hazard is assessed based on two indicators: the ratio of total affected population in earthquakes hazards (including death, injured and missing) and the severity of earthquake hazard (liedu/ the seismic intensity). In the other words, the human sensitivity is the proportion of the ration of population affected by earthquake hazard and the severity of earthquake hazard, that is Si =Ri/Li
(3)
Where Si is the human sensitivity score of the i affected area; Ri is the ratio of the affected population density and the total population density occupied in the i affected areas; Li is the liedu (the seismic intensity) of the i affected areas. The formulas of human exposure and human sensitivity above will be applied to the five regencies in Yogyakarta Special Province, and the results can be seen as maps of human exposure and human sensitivity of regencies in Yogyakarta.
Results and Discussions Human exposure to earthquake hazard stated the probability of population to be victims of earthquake hazard. Human exposure to earthquake hazard is proportional to the population density of the affected area and opposite to the distance of Yogyakarta earthquake epicenter. The greater the population density, the greater its human exposure. It can be concluded that urban area will have the bigger human exposure than rural area. From Figure 2 below, it can be noted that Yogyakarta City got the biggest human exposure to Yogyakarta earthquake hazard, than in the second place is Bantul Regency, and then following by Sleman, Gunung Kidul and Kulon Progo Regencies. According to BPS data, the population density of Yogyakarta City is 7 – 27 times than other regencies. Bantul and Sleman had almost the same population density, but Bantul was in number two, because its distance to epicenter was nearer than Sleman which came at third place. The lowest human exposure was Gunung Kidul, due to its lowest population density, even its distance to epicenter was nearer than Kulon Progo. The discussion came to the human sensitivity to earthquake hazard. The human sensitivity is proportional to ratio of the total number of affected to the population and opposite to the intensity of earthquake or liedu. From Figure 3, it can be noted that Bantul Regency got the highest human
PROCEEDINGS Jogja Earthquake in Reflection 2016 24–26 May 2016 sensitivity due to its most suffering to Yogyakarta earthquake. The number of deaths because Yogyakarta earthquake in Bantul Regency was 17 – 188 times than other regencies, and the total number of victims (total number of deaths and injured) was 4 – 30 times than others. The reason why Bantul Regency got the highest human sensitivity can be linked with the total number of houses damaged by Yogyakarta earthquake. From Figure 4, it was cleared that Bantul Regency got the most destructive effects of Yogyakarta earthquake. The number of houses damaged by Yogyakarta earthquake in Bantul Regency was more than 80%, while in other districts were less than 30%. Most of Bantul Regency is rural area, with residents who live mostly poor people, so they can not affort to make the earthquake resistant buildings. It can be concluded that Bantul Regency with most of rural area, was exposed higher human sensitivity, which was linked with the more houses collapsed and damaged, and related with poverties. The results above will be compared with the previous researches. First, it will be compared with World Bank data, then with Guha-Sapir and Vos (2011), Wyss and Trendafiloski (2011), Zuccaro and Cacace (2011), and Liu and Wang (2015). According to World Bank, the total damage and loss because of Yogyakarta earthquake is around US $ 3.134. The big amount of damage and loss because of Yogyakarta earthquake was caused by these things: the earthquake strucked Java island, one of the most crowded population in the world; the epicenter was located in shallow crustal, made the spread of structural damage; the failure of human in constructing earthquake resistant building; lot of household based industry, made economic loss due to house collapsed or damaged was so much great. The ownership percentage of damaged and collapsed facilities can be seen in Figure 5. The damaged were centered on the private houses and productive asset. This will have a seriously impact to small and medium business, because the damaged area were the center of hand-made crafts business.
Figure 2. Human Exposure to Yogyakarta earthquake hazard of Regencies in Yogyakarta.
Figure 3. Human Sensitivity to Yogyakarta earthquake hazard of Regencies in Yogyakarta.
PROCEEDINGS Jogja Earthquake in Reflection 2016 24–26 May 2016 difference in the value of R in the above described by Wyss and Trendafiloski as follows. The numbers of fatalities and injured in a single earthquake is composed of contributions by numerous to thousands of settlements. Some are located close to the epicenter and experience high intensities. Those far away register only low intensities, and some environments are urban, others rural. R-values differ, depending on the composition of settlements affected.
Figure 4. Total number of houses damaged by Yogyakarta earthquake.
Figure 5. Percentage of the ownerships of the damaged and collapsed facilities due to Yogyakarta earthquake. Guha-Sapir and Vos stated that at ten most fatal earthquakes of the last 39 years, low- and middle income countries (including Indonesia). Earthquake risk increases with population growth and urbanization, as well as with poverty. Low quality building construction and inadequate spatial planning put people in danger, and we often find that earthquake damage is particularly destructive in countries with developing economies. Poor people are most vulnerable, being forced to settle on steep hillsides, floodprone alluvial land, low elevation coastal zones and valleys at risk of landslides, or to develop their livelihoods around terraced agriculture. It matched with World Bank data, that Yogyakarta earthquake made the poverty in affected area became worst. Almost all the damaged houses used low quality building material and without strong pillars. The poor are the least able to build safe houses and many of their homes were damaged. Wyss and Trendafiloski introducing R, ratio of injured and fatalities. In the Yogyakarta earthquake, minimum R value got by Yogyakarta City (less than 2) and the maximum R value got by Kulon Progo Regency (more than 100). The
Zuccaro and Cacace evaluate the variation of the exposure during the day, also in a year time. The variation in occupancy over a year is generally seasonal and mainly relates, in Italy, to tourist flows. They also made a seismic casualty model, which is based on the evaluation of four fundamental parameters in addition to the total population on the site: Mean of inhabitants by building type (vulnerability class); Occupancy rate by hour of the day and week; Touristic index by town and period of the year; and Casualty percentage by building type and damage level. This study is limited only the exposure of a single earthquake and the exposure over a year frequency also can be made for Yogyakarta, because it is known as favorite tourism city now. Liu and Wang made the differentiation in human vulnerability, between rural and urban areas. They stated that in their study areas, the average percentage of houses collapsed in the rural areas is 80 % in Wenchuan Earthquake and 79 % in Ya’an Earthquake. In this study, more than 80% houses collapsed and damaged in Bantul Regency. The percentage of deaths in the rural areas is 58.77 % in Wenchuan Earthquake and 91.08 % in Ya’an Earthquake. The percentage of deaths in Yogyakarta earthquake is only about 0.5% in Bantul Regency, and less than 0.05% in other Regencies, which made the human sensitivity values were very small if compared to that in Wenchuan and Ya’an earthquakes. Another important result of Liu and Wang’s is that the high percentage of houses collapsed and death in the rural areas, particularly the high human sensitivity and vulnerability of the rural areas made these rural affected areas be more vulnerable to earthquake hazards than other urban affected areas. The last result was in accordance with Yogyakarta earthquake condition, that the high percentage of house collapsed and death in Bantul Regency which is dominated with rural areas and filled by the poor, so it made rural affected areas be more vulnerable to earthquake hazards than other urban affected areas. Actually, between five regencies in Yogyakarta, only Yogyakarta City than can be said as urban area, and other four regencies are rural areas. The highest damages and victims are located in Bantul Regency can be explained from epicenter location and also from geological condition (see the Introduction).
PROCEEDINGS Jogja Earthquake in Reflection 2016 24–26 May 2016 Conclusions This paper concerned about human vulnerability in terms of human exposure and human vulnerability. If Yogyakarta City can be said as an urban area, and Bantul Regency can be said as rural area, then we could make a conclusion. Combining the human exposure and human sensitivity results, urban areas have high human exposure and low human sensitivity, while rural areas have high human sensitivity and low human exposure. The high human exposure is not always followed by high human sensitivity, as seen in Yogyakarta City and Bantul Regency. The large proportion of affected population in the rural areas represents the high human vulnerability to earthquake hazards than other urban areas. It reveals that the human vulnerability is highest in the rural area due to the highly sensitivity to earthquake hazards. The research about human vulnerability in this paper still need an advanced research. The measurement unit was regency, so the more detailed researches (for example: district or even village level) were needed to get a better and more accurate results.
References Dell’Acqua F, Gamba P, Jaiswal K (2013) Spatial aspects of building and population exposure data. Nat Hazards (68):1291–1309. Gatignon A, Wassenhove L N, Charles A (2010) The Yogyakarta earthquake: Humanitarian relief. Int. J. Production Economics (126): 102-110. Guha-Sapir D, Vos F (2011) Earthquakes, an Epidemiological Perspective on Patterns and Trends. In R Spence, E So, C Scawthorn, Human Casualties in Earthquakes Progress in Modeling and Mitigation (pp. 13-24), Springer. Gupta I, Sinvhal A, Shankar R (2006) Himalayan population at earthquake risk. Disaster Prevention and Management Vol. 15 (4):608-620. Haifani, A M (2008) Manajemen Resiko Bencana Gempa Bumi (Studi Kasus Gempabumi Yogyakarta 27 Mei 2006). Seminar Nasional IV SDM Teknologi Nuklir, (pp. 285-294). Yogyakarta, 25 - 26 Agustus 2008. http://earthquake.usgs.gov/earthquakes/shakemap/global/sh ake/neb6_06/download/pga.jpg, accessed on April 15th 2016. http://siteresources.worldbank.org/INTINDONESIA/Resou rces/226271-1150196584718/ExeSumBhs.pdf, accessed on April 16th, 2016. http://www.kemsos.go.id, accessed on April 16th, 2016 Liu J, Wang S (2015) Analysis of the differentiation in human vulnerability to earthquake hazard between rural and urban areas: case studies in 5.12 Wenchuan Earthquake (2008) and 4.20 Ya’an Earthquake (2013), China. J Hous and the Built Environ (30): 87–107. Mulyaningsih S, Sampurno, Zaim Y, Puradimaja D J, Bronto S, Siregar D A (2006) Perkembangan Geologi pada Kuarter Awal sampai Masa Sejarah di Dataran
Yogyakarta. Jurnal Geologi Indonesia Vol. 1 (2): 103113.Rosetto T, Joffe H, Solberg C (2011) A Different View in Human Vulnerability to Earthquakes: Lesson from Risk Perception Studies. In R Spence, E So, C Scawthorn, Human Casualties in Earthquakes Progress in Modeling and Mitigation (pp. 290-304), Springer. Sunardi B (2013) Peta Deagregasi Hazard Gempa Wilayah Jawa dan Rekomendasi Ground Motion di Empat Daerah, Tesis, Universitas Islam Indonesia, Yogyakarta. Sunardi B, Sulastri (2015) Deagregasi Bahaya Gempabumi Untuk Daerah Istimewa Yogyakarta. Simposium Nasional Sains Geoinformasi 2015 (pp. 187-195). Yogyakarta; 25 - 26 November 2015: PUSPICS Fakultas Geografi Universitas Gadjah Mada. Wood N, Ratliff J, Schelling J, Weaver C (2014) Comparing population exposure to multiple Washington earthquake. Applied Geography (52):191203. Wyss M, Trendafiloski G (2011) Trends in the Casualty Ratio of Injured to Fatalities in Earthquakes. In R Spence, E So, C Scawthorn, Human Casualties in Earthquakes Progress in Modeling and Mitigation (pp. 267-274), Springer. Zuccaro G, Cacace F (2011) Seismic Casualty Evaluation: The Italian Model, an Application to the L'Aquilla 2009 Event. In R Spence, E So, & C Scawthorn, Human Casualties in Earthquakes Progress in Modelling and Mitigation (pp. 171-184), Springer.
