Seismic Microzonation (SM) is a key tool for planning strategies for risk mitigation; it represents the assessment of Local Seismic Hazard by identifying and mapping, at scale 1:10.000 or higher, zones with homogeneous seismic behavior within a given geographic area. SM studies are complementary to the Regional Seismic Hazard (RSH) studies, which calculate with probabilistic and deterministic methods ground motion parameters at a site under conditions of rigid and flat soil (NTC 08).

In the 2008, the Conference of Regions and Autonomous Provinces of Italy and the Civil Protection Department publish the "Indirizzi e criteri per la Microzonazione Sismica" (“Guidelines for Seismic Microzonation”, 2015).

The “Guidelines for Seismic Microzonation” is a national reference document for studies to estimate the seismic risk of a territory.They describe the principles and elements for basic studies and for applications in land and emergency planning. This document also describes operational tools for the implementation of Seismic Microzonation studies, including the schedule investigations and the production of thematic maps.

The seismic microzonation (SM) identifying zones with homogeneous seismic behavior. The identified microzones are classified basing on the expected local ground motion in case of earthquake, and are subdivided into:

• stable zones, where no substantial deviations are expected from the ground motion produced by a seismic event on rigid and flat soils;

• stable zones prone to local amplification, where ground motion is amplified because of local stratigraphic and morphological conditions;

• instability- prone zones, where permanent instabilities, slope instability, liquefaction, differential settlement, active and capable faults, are expected.

Italy has a long history of seismological history concerning also seismic hazard and risk assessment.

The importance of local effects emerged in the 1846, when the scientist Leopoldo Pilla in the “Istoria del tremuoto che ha devastato i paesi della costa toscana il 14 agosto 1846” claimed that “La esperienza ha dimostrato in Italia che i paesi sono flagellati dal tremuoto principalmente in ragione della natura e forma del suolo in cui sono situati […] si può ad essi assegnare l'ordine crescente che segue di esposizione al pericolo: paesi situati sopra monti di rocce sode; paesi in pianura; paesi giacenti sopra poggi di rocce friabili (The experience showed in Italy that villages are struck by earthquakes mainly because of the nature and shape of the soil on which they lay […] to them it can be assign the increasing order of exposure to danger: villages sited above mountains made of compact rocks; villages sited on plains; villages lying on hills of loose rocks)”. Despite the observations of Pilla, 50 years were spent before these matters were considered in Italy.

The purpose of Seismic Microzonation studies is to identify the local conditions that can significantly modify the characteristics of expected seismic motion or cause major permanent deformations on buildings, structures and infrastructures. The results of studies are useful to plan and to realize actions for seismic prevention and risk assessment.

Application areas of Seismic Microzonation are described in “Guidelines for Seismic Microzonation” and can be summarized below:

• territorial and urban planning: they integrate the knowledge of those components that give rise to seismic risk and provide decision-making criteria related to the prevention and mitigation of this risk both at area – wide and municipal scale (for further details see Chapter 1.7 of Guidelines for Seismic Microzonation);

• emergency planning: at both the municipal and provincial level, SM studies may help identify the strategic elements of an emergency plan and, in general, of civil protection resources (for further details see Chapter 1.8 of Guidelines for Seismic Microzonation);

• design of buildings or structures: (both existing and in project) SM studies highlight possible phenomena of motion amplification induced by local lithostratigraphic and morphological conditions, as well as instability and permanent deformations caused by earthquakes (for further details see Chapter 1.9 of Guidelines for Seismic Microzonation).