Analytical Hierarchical Process (AHP) has determined the weights of various components and sub-indicators within the components of earthquake vulnerability. For data analysis and processing, the use of a Geographical Information System (GIS) is beneficial and plays a vital role in this stage (Alam & Haque, 2018). Similarly, Statistical Package for Social Sciences (SPSS) is also used as a supportive data analysis tool in this study. The collected data is processed in the following order sequentially. Initially, earthquake vulnerability scores and socio-economic data of Quetta city were stored in the SPSS software. Then, the ArcGIS environment is used for geo-processing the geological and structural earthquake vulnerability of Quetta city. In the next step, databases were combined with the study area map using ArcGIS. The systematic earthquake vulnerability score was joined and reclassified with the study area map of Quetta city using ArcGIS. Finally, WLC is used to prepare the composite earthquake vulnerability map of the study area based on the reclassified score using ArcGIS.
5.1. Systematic Vulnerability
The Geometric mean is used to identify the distances from the center of each Zone in the Arc-GIS environment to measure the systematic vulnerability of the study area. The four main indicators used for systematic vulnerability are open spaces, emergency centers, hospitals, and fire services. Results of Fig. 3 show that 4 out of 13 Zones (Hazar-Gungi, Quetta East, Quetta North, and Samungli) are found in high earthquake vulnerable Zones in terms of systematic vulnerability due to long distances among Zones and facilities available within the city. Similarly, 4 Zones of Quetta city (Satellite Town, Saryab, Hazara Town, and Quetta Cantt) fall in the medium systematic earthquake vulnerable Zones. Among the 13 Zones of the study area, only five Zones have low systematic earthquake vulnerability. These Zones have close spatial inks with four major facilities. Indicator-wise assessment is carried out on a scale of 0–1 of systematic earthquake vulnerability of Quetta city shown in Fig. 5.3. Based on the results of Fig. 8, most of the Zones in Quetta city are systemically have medium to high vulnerability due to their long spatial links from health care centers (0.29), fire services (0.28), open spaces (0.25), and emergency centers (0.18) respectively. In a destruction-type event like an earthquake hospital is the primary and significant facility for emergency response in an affected community. Only ten Government hospitals are available in Quetta city. However, most of these hospitals are spatially located in the middle and core areas of the city, while 4 Zones are outside of these hospitals’ Service Areas. The earthquake can also damage and destroy the gas lines, power stations of electricity, or other causative fire sources outside or inside of a building, which can cause the threat of fire hazards in the community after an earthquake disaster (Alam & Haque, 2021). But there are only 4 fire service stations located in the middle part of the city area of 1.16 million population. These four service stations are located only in two Zones (Centrum of Quetta and Jinnah Town). Some Zones have more than 10 Km long distances from the fire services, and thus it becomes difficult to provide efficient and timely rescue and fire services to these Zones during earthquake emergencies. Disaster emergency centers located within communities play a vital role in timely emergency response. In Quetta city, PDMA Balochistan had designed four emergency centers located only in two Zones (Centrum of Quetta city and Jinnah Town). Again these crucial services were not uniformly distributed in each Zone for earthquake emergency response. Most of the Zones have more than 8 Km long distances from emergency centers. All the four emergency centers are located in the middle part of Quetta city, which makes the remote Hazar Gunji, Samugli, Quetta East, and Quetta North Zones systematically high vulnerable.
5.2. Structural Earthquake Vulnerability
The indicators of structural earthquake vulnerability relate to the built-up environment factors such as bridges, buildings, roads, etc. indicators related to structural earthquake vulnerability have a potential influence on earthquake damage and the vulnerability of a community prone to earthquake hazards (Alam & Haque, 2021). In this research study, the nine most significant structural indicators are carried out to assess the structural earthquake vulnerability of Quetta city. Results of the structural earthquake vulnerability of Quetta city show that; five Zones among the thirteen are highly vulnerable in terms of structural earthquake vulnerability. These include (Hazraganji, Quetta East, Saryab, Pashtoon Abad, and Kharotabad). Similarly, Samungli, Quetta North, Centrum of Quetta, and Haazar Town have medium structural earthquake vulnerability. Only four Zones have low structural earthquake vulnerability as shown in Fig. 4.
Further the results of the analysis show that; about (40.53%) of buildings in the study area are made with poor quality infrastructure and most of these buildings are located in the eastern and northern parts of the city. Almost 40% and 13% of the buildings within Zones of Quetta city are built with flexible roofs and irregular shapes respectively. Road width is one of the influential indicators of structural earthquake vulnerability. The road and streets with more width have low vulnerability during emergency response, fire rescue, and evacuation process. Among the Zones, four Zones have less than 10 feet of road width, which makes the Zones vulnerable during earthquake response and emergencies.
Building story is also considered for structural earthquake vulnerability. Building with more stories has a high level of vulnerability. In each zone of the study area, the building exists with more than two stories, but the high-rise buildings with 6 stories and basements are observed in the centrum of Quetta city, Satellite Town, and Jinnah Town.
Building density per acre is also considered one of the important indicators of earthquake vulnerability. Zones with more than 15 households per acre are considered highly vulnerable in terms of structural earthquake vulnerability. Results of the analysis show that four Zones (Centrum of the city, Hazargunji, Hazara Town, and Samungli) are declared highly vulnerable Zones of the study area in terms of building density per acre.
Building age is also one of the important indicators in earthquake risk identification. Buildings with less than 10 years of age have a low level of vulnerability, between 10–20 years of age have a medium level of vulnerability, and buildings with more than 20 years of age are considered highly vulnerable. Three Zones (Centrum of Quetta, Quetta Cantt, and Quetta East) among the thirteen Zones have been found highly vulnerable in terms of building age.
Quetta city is one of the oldest cities in Balochistan, a large portion of the building were made before the designing of building codes. About 17% of the buildings in the study area have a very high chance of pounding during a quake. Three Zones (Saryab, Hazargungi, and Pashtoon Abad) are highly vulnerable in terms of the possibility of the pounding of buildings.
Identification of overhanging buildings in urban areas is one of the important aspects of earthquake risk quantification. Overhangs are the components of physical structures such as balconies, cantilevers, etc. these elements are hanging outside with less support and have a high chance of falling during an earthquake disaster. Centrum of Quetta, Hazargunji, and Hazar Town are highly vulnerable Zones in terms of heavy overhanging.
The map of the structural earthquake vulnerability is presented in Fig. 4. It is important to know which indicator has most influenced the structural earthquake vulnerability of Quetta city to prioritize urban planning and management implications. Indicator-wise assessment is carried out on a scale of 0–1 of structural earthquake vulnerability of Quetta city shown in Fig. 9. Results of the analysis of the overall structural earthquake vulnerability found that high pounding possibility (0.17), road width (0.14), the possibility of overhanging (0.13), building with poor condition (0.12), building with irregular shapes (0.11), and building with Flexible roofs (0.09), respectively are the significant contributing factors of structural earthquake vulnerability in Quetta city.
5.3. Socio-Economic Vulnerability
To identify the complete and comprehensive vulnerability condition of Quetta city, it is also important to know the socio-economic conditions of people living in various zones of the study area. In recent years, experts have not paid proper attention to socio-economic indicators therefore this study also focused on the socio-economic parameters for socio-economic earthquake vulnerability. In this research study, eight important indicators like the children’s population, population above 60 years of age, women’s population, dependent population, illiteracy rate, family members, family, income, and population density are considered for socio-economic earthquake vulnerability.
The identification of human vulnerable groups for effective disaster response is so important. Based on literature and past studies four special groups i.e. children, aged, women, and disabled people in a community are more vulnerable during the evacuation to any natural hazard like an earthquake, tsunami, and flood (Ainuddin et al., 2015b). Results of the analysis show that about 15% and 6% of the total population of Quetta city are children and aged population respectively. The higher ratios of children and aged people are mainly found in Saryab, Pashtoon Abad, Kharot Abad, Quetta East, and Quetta North. In these five Zones, the ratio of child population less than 10 years of age is more than 15% and the ratio of aged people more than 60 years of age is more than 6%, which makes the Zones highly vulnerable to earthquake hazards.
The overall ratio of the female to the male population in Quetta city is about 48:52. But these ratios vary from Zone to Zone. Zones with more than 45% women population are considered highly vulnerable. The ratio of women population of more than 45% has been found in the three Zones i.e. (Samungli, Hazara Town, and Quetta North). The literacy rate of Quetta city is about 59%. This is somewhat high in the context of Balochistan. This percentage varies from Zone to Zone across the study area. Zones with a more than 60% illiteracy rate are considered highly vulnerable Zones. Four Zones (Saryab, Quetta East, Pashtoon Abad, and Kharot Abad) of Quetta city are found highly vulnerable Zones in terms of an illiteracy rate of more than 60%.
Income is also one of the important indicators of socio-economic vulnerability. The average household income varies from Zone to Zone of Quetta city due to the long distances of Zones from proximity to central business markets, employment opportunities, industry, etc. In this study, income is categorized into three categories. The per capita income which is $1.25 per person per day is taken as a threshold level to assess the poverty level in the study area. Households with less than the given benchmark are considered highly vulnerable. Four Zones of the study area (Saryab, Kharot Abad, Pashtoon Abad, and Quetta east) are the most vulnerable in terms of economic conditions. The city of Quetta is the most highly populated in the province. The total population of the city is about 1.16 million. Three Zones (Centrum of Quetta, Quetta east, Pashtoon Abad, and Salim town) are the most vulnerable Zones due to the congested population.
Family size is also one of the influential social parameters in earthquake vulnerability. Households with large family sizes are more vulnerable in a disaster situation. Households with an average of more than 10 family members are considered highly vulnerable as shown in. In the study area, three Zones (Quetta east, Pashtoon Abad, and Kharot Abad) are highly vulnerable in terms of greater family size. Generally, children populations below 15 years of age and above 60 years of age are considered economically vulnerable and dependent populations. (Alam et al., 2019c). Results of the analysis show that about 31% of the population of Quetta city is economically dependent and the values of dependency vary from Zone to Zone of the study area. Six out of thirteen Zones (Quetta north, Quetta east, Hazargunji, Saryab, Pashtoon Abad, and Kharot Abad) are highly vulnerable Zones in terms of income dependency. Considering all the analysis and indicators of the aforementioned socio-economic vulnerability component, the result confirms that 6 out of 13 Zones of Quetta city are highly vulnerable to earthquake hazards in terms of socio-economic vulnerability as shown in Fig. 5.6. Whereas three out of thirteen Zones have a medium level of vulnerability and only 4 Zones (Quetta Cantt, Centrum of Quetta, Jinnah Town, and Satellite Town) are the low vulnerable Zones in terms of socio-economic vulnerability. The indicators-wise assessment of the Zones of Quetta city for socio-economic vulnerability is shown in Fig. 10. The study area is mainly vulnerable due to the high percentage of children population (0.21), elderly population (0.20), a high percentage of women (0.13), low family income (0.12), population density (0.10), dependent population, and illiteracy rate with (0.07), and family size with (0.06) are the aforementioned parameters which makes the city highly socio-economically vulnerable.
5.4. Geological Earthquake Hazard and Vulnerability Assessment
Geological vulnerability is based on three main components; fault lines, soil type, and PGA. Based on the results of geological dimensions; four out of thirteen Zones (Hazargunji, Samungli, Hazara Town, and Quetta North) are highly vulnerable, and four Zones (Quetta East, Kharot Abad, Salim Town, and Jinnah Town) as medium vulnerable, and five Zones (Satellite Town, Pashtoon Abad, Saryab, Centrum of the city, and Quetta Cantt) as low vulnerable in term of geological vulnerability in Quetta city as shown in Fig. 6. Similarly, Fig. 11 shows the influence of each geological dimension on a scale of 0–1 earthquake hazards. The highest influence of soil type (0.43) is observed, followed by Peak Ground Acceleration (0.34). Whereas, fault lines (0.22) have the least influence among the three geological dimensions used in the analysis. The soil of the study area is classified into three categories hard, swift, and soft. The energy quickly passes with a low level of amplitude through hard soil and thus causes minimum destruction to the buildings on the surface. But soft soil increases the amplitude and slows down the energy of the motion of a quack, which is the main cause of earthquake destruction to the infrastructure. The PGA value of Quetta city varies from 0.311 to 0.481 g. This range is declared a severe perceived shaking range by USGS, Instrumental Intensity Scale (Bendito et al., 2014). The highest PGA values are observed in the northern and western parts of Quetta city, which will cause huge destruction in the future. The fault lines are also considered one of the important dimensions of geological earthquake vulnerability. The two fault lines observed in the study area pass through different Zones. The closest Zones with fault lines are considered highly vulnerable.
5.5. Composite/Overall Earthquake Vulnerability
Results of the composite earthquake vulnerability are based on 24 important indicators jointly taken from four components (socio-economic, structural, geological, and systematic) of earthquake vulnerability. The combined result of the composite earthquake vulnerability shows that 7 out of thirteen Zones of Quetta city are highly vulnerable to all four components of vulnerability as shown in Fig. 7. Four Zones have a medium level of vulnerability and only two Zones are considered low earthquake vulnerable Zones in the study area. To identify the influence of each indicator on the overall earthquake vulnerability of Quetta city, indicator wise assessment is carried out on a scale of 0–1 as shown in Fig. 12. The policymakers, development agencies, and urban planners may prioritize the earthquake mitigation and disaster risk reduction strategies in Quetta city based on the aforementioned earthquake vulnerability indicators. Based on the results of Fig. 12, it is found that the soil type (0.43), PGA (0.34), distance to Hospitals (0.24), distance to fire service stations (0.22), Fault lines (0.22), open spaces (0.21), aged population (0.21), children population (0.20), and the possibility of overhanging (0.17) respectively are the significant and topmost influential indicators that make the Quetta city highly vulnerable to earthquake hazard. Whereas building with irregular shapes (0.11) and population density (0.10) have a medium-level influence on earthquake vulnerability in the study area. Similarly, illiteracy rate (0.07), dependent population (0.07), building stories (0.07), building with flexible roofs (0.07), family size (0.06), and building density (0.06) have to somewhat low influence on overall earthquake vulnerability in the study area as shown in Fig. 12.