No abstract

For a city to perform successfully, and its citizens to feel safe and comfortable, the health of basic urban components and the overall resilience of the urban system is crucial. As the importance of the resilient urban system has been recognized in the scientific literature, many studies have been done on this topic. Therefore, to find out the gaps in the existing literature and the opportunities for further research, a new systematic literature review has been performed in three stages. Different bibliographic techniques (co-occurrence and co-citation analysis) have been applied and, in the final stage of the analysis, an in-depth study of the content of the selected papers addressing open space in relation to urban seismic resilience has been carried out. The obtained results and trends have shown a lack of research on the potential of open space for enhancing urban seismic resilience, as well as a challenge for its quantitative assessment. The ability of the affected resilient system is to achieve at least a pre-disaster performance level in an acceptable time, which can be gained, among others, by using the restorative potential of open space. Based on the synthesis of these findings the authors' draft model of an urban system integrating the potential of open space is presented in terms of a complex network theory.

Abstract. Urban system is a complex mix of interdependent components and dynamic interactions between them that enable it to function effectively. Resilience of urban system indicates the ability of a system to resist, absorb, accommodate to and recover from the effects of a hazard in a timely and efficient manner. In the relevant literature, most studies consider individual components separately. On the other hand, the purpose of this paper is to assess the urban system as a whole, considering all relevant components and their interactions. The goal is a study of possibilities for holistic evaluation of urban system resilience to natural disasters. Findings from the preliminary study are presented: (i) the definition of urban system and categorization of its components, (ii) a set of attributes of individual components with impact on disaster resilience of the entire system and (iii) review of different methods and approaches for resilience assessment. Based on literature review and extensive preliminary studies a new conceptual framework for urban resilience assessment is proposed. In the presented paper, a conceptual model of urban system by abstraction of its components as nodes (buildings), patches -specific nodes with spatial properties (open space), links (infrastructures) and base layer (community) is created. In the suggested model, each component is defined by its own quantitative attributes, which have been identified to have an important impact on the urban system resilience to natural disasters. System is presented as a mathematical graph model. Natural disaster is considered an external factor that affects the existing system and leads to some system distortion. In further analyses, mathematical simulation of various natural disasters scenarios is going to be carried out, followed by comparison of the system functionality before and after the accident. Various properties of the system (accessibility, transition, complexity etc.) are going to be analysed with graph theory. The final result is going to be an identification of critical points and system bottlenecks as basis for further actions of risk mitigation.

A comprehensive assessment of a city’s vulnerability and resilience is a prerequisite for an effective response to a natural disaster, such as an earthquake. However, an appropriate method for assessing the seismic performance of a complex urban system is still being researched. To address this gap, the purpose of this paper is to introduce a method for seismic performance assessment of a city as a socio-physical system. Therefore, various studies of individual urban components and their interactions were combined into a holistic framework and presented in a case study of a small mid-European town. The seismic vulnerability of the building inventory was assumed or assessed based on the fragility curves adopted from the literature on similar European building stock. Seismic scenarios of different earthquake intensity (PGA of 0.15 g and 0.30 g) combined with conservative and risky approaches were applied. Considering the human perspective, urban performance was evaluated on the basis of accessibility to urban services that satisfy basic human needs (for survival and protection) via graph theory measures of global efficiency and the shortest path. The temporal aspect (before the earthquake, immediately after it, after evacuation, and after recovery) was also included to obtain a comprehensive resilience assessment. It turned out that a stronger earthquake (PGA of 0.30 g) would have far-reaching consequences for the urban performance of the investigated town, and the old city center would be particularly affected. Following the event, the system’s performance is less than half as effective compared to the initial level, indicating a sharp deterioration in the quality of life as reflected in the possibility of meeting basic human needs.

The seismic performance assessment of an urban system can help raise awareness and improve a community's preparedness for extreme earthquake events. Addressing this issue, the authors' first attempt at a quantitative evaluation of a city's performance in the event of an earthquake is presented in this paper. The assumed city model comprised of four main urban components (buildings, transportation infrastructure, social community, and open spaces) takes into consideration their relationships and interactions. A set of preliminary analyses on the test model were performed using the GIS tools and graph theory. The analysed model was generated based on the combination of real (city layout, buildings' heights and footprints, road network configuration and length) and fictitious data (earthquake scenarios, structural fragility of the investigated building stock, the use of a building, etc.). In the main part of the study, several scenarios of possible earthquake events with various degrees of intensity and with different locations of damaged buildings were considered, and the assessment of a city's performance in terms of connectivity and accessibility (the graph theory measure of global efficiency) was carried out. The impact of building debris on the roads as a result of the earthquake damage and/or the collapse of nearby buildings and their non-structural components was included in the analysis as well by applying the measure of a building's impact radius and assessing the road traffic disruptions. Furthermore, certain practical results in relation to the analysed urban system were taken under observation and are discussed in the paper (travel time, affected population when considering the day-/night-time scenarios, etc.). The proposed framework has proven to be a viable tool for identifying network weaknesses and quantifying the loss of the city network functionality.