Seismic Microzonation Studies (SMS) and Limit Condition in Emergency (LCE): an integration approach for a better seismic hazards mitigation and prevention in Albania

Located next to the most active fault in Albania, the main cities of the country have experienced a number of strong earthquakes in the past, sometimes exceeding a magnitude of 6. The last earthquakes that hit Albania on September 21st, 2019 of Mw 5.4 and November 26th, 2019 of Mw 6.2 severely damaged the cities of Durrës, Thumanë, Tirana, Vora, Shijak and the villages around. The main event of the 26th November caused the deaths of 51 persons and the damaging of hundreds of buildings. The degree of damages produced by these earthquakes has been, in some cases, significantly enhanced by the characteristics of the earthquake ground motion affected by the local subsurface soil structure of the cities. This paper highlights the indispensable significance of the engineering-geological and geophysical methods for a deeper understanding of the subsoil characteristics, for an effective Seismic Microzonation Study (hereafter SMS). The main goal of the SMS is to identify, on a local scale, the areas that manifest a homogeneous seismic behaviour during an earthquake event. According to the Italian guidelines, a municipality territory could be characterised in accordance to three types of areas: a) stable areas, b) stable areas susceptible to local seismic amplification and c) areas susceptible to instability (e.g. earthquake-induced landslides, soil liquefaction and surface fractures and faulting). The LCE - Limit Condition in Emergency, is the condition whereby, following a seismic event, the urban settlement as a whole suffers physical and functional damage resulting in the interruption of almost all its functions (including residence) and retains only the operational functions of some pre-allocated strategic buildings for emergency management, accessibility and connectivity within the territorial context. By spatially superimposing the elements of LCE to the microzones identified by the SMS, certain criteria and guidelines can be defined that are more targeted to the choices of ordinary planning of the territory: a) orienting the choices for the new settlements; b) defining the eligible interventions in a given area; c) establishing methods and priorities for intervention in urbanized areas. Realizing an integrated SMS-LCE approach study at municipality level before an earthquake occurs can help decision-makers to highlight priority intervention areas and to define the best practices for existing structures where higher overall seismic hazard values are expected. For this purpose, a combined approach of the SMS with the LCE was applied to the ancient cities of Durrës and Gjirokastër.