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OPCM 3274/2003

Seismic classification of the territory and technical rules for construction in seismic zones

In forceStrutturale & SismicaLegge/DecretoCogente● In review

Summary

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Civil-protection ordinance that reclassified the entire Italian territory into four seismic zones of decreasing hazard, ending the existence of 'non-seismic' areas, and set the first technical criteria for building in seismic zones (later replaced by the NTC). Published in Official Gazette no. 105 of 8 May 2003.

Scope of application

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It concerns the whole national territory for classification purposes, and works in seismic zones. Today seismic design is governed by NTC 2018 and the controls by D.P.R. 380/2001; the operational zone lists are adopted and updated by the Regions.

In depth

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The 2003 turning point: all of Italy is a seismic zone

Until 2003 large parts of the territory were not classified as seismic and were built without anti-seismic criteria. After the 2002 San Giuliano di Puglia earthquake, OPCM 3274/2003 reclassified the whole country: there are no longer 'non-seismic' areas, but four zones of decreasing hazard.

The four seismic zones
Zone 1
Zone 2
Zone 3
Zone 4
← highest hazardlowest hazard →

From the zone to the site: how design works today

The seismic zone remains the administrative frame, but structural design no longer starts from the zone: NTC 2018 (D.M. 17/01/2018) compute the seismic action site by site, from the coordinates and the base hazard, adjusted for the subsoil category and the reference period of the works. The zone tells you 'where we are in the national picture'; the NTC tell you 'how much seismic action to apply here'.

Who classifies and who controls

Operational classification is the responsibility of the Regions, which adopt and update the lists of municipalities by zone on the basis of the state criteria. As for controls, D.P.R. 380/2001 (the Consolidated Building Act, Part II) governs authorisations, filings and supervision of construction in seismic zones, with obligations graduated by zone and type of works.

Framing works in a seismic zone
  1. 01
    Municipality zoneFind the municipality's seismic zone from the regional list.
  2. 02
    Site parameters (NTC)Determine the site hazard and seismic parameters according to NTC 2018.
  3. 03
    Obligations and controlsCheck the obligations of D.P.R. 380/2001 for the zone (authorisation/filing, controls).
  4. 04
    Design and verificationDesign and verify the structure for the limit states required by the NTC.

Why it matters, beyond the building site

Classification also governs policies and incentives: mapping seismic risk is the precondition for measures such as the Sismabonus and for planning prevention. It is the level at which Italy chose, after 2003, to treat its whole territory as exposed — to differing degrees — to the action of earthquakes.

Key points

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  • Since 2003 the whole of Italy is classified as seismic: four zones of decreasing hazard, no more 'non-seismic' areas.
  • The zone is the administrative frame; design follows NTC 2018 with seismic action computed site by site.
  • The ag ranges per zone were defined by OPCM 3519/2006 (reference hazard map).
  • Operational classification is up to the Regions; controls follow D.P.R. 380/2001.
  • The 2003 technical annexes are superseded by the NTC; the zoning framework remains.

Frequently asked questions

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What did OPCM 3274/2003 change?

It reclassified the entire national territory into four seismic zones, removing the unclassified areas, and introduced the first technical criteria for building in seismic zones (later replaced by the NTC).

Is the seismic zone used to size the structure?

No: sizing follows NTC 2018 with the hazard parameters of the specific site. The zone has administrative and control value, it is not the design value.

How many zones are there and what do they mean?

Four: Zone 1 is the most hazardous, Zone 4 the least. The associated acceleration (ag) ranges were defined by OPCM 3519/2006.

Who decides which zone a municipality is in?

The Regions, which adopt and update the lists of municipalities by zone on the basis of the state criteria.

What is the relationship with the Sismabonus?

The incentives for seismic-upgrading works are graduated by seismic zone (in particular zones 1, 2 and 3): the classification is the basis of the measure.

Glossary

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Zona sismica
Area into which the territory is divided according to seismic hazard, with an administrative and control function.
Pericolosità sismica
Probability that, at a given site and over a given period, an earthquake of a given intensity occurs; it is the basis of classification.
ag
Peak ground acceleration: the maximum horizontal acceleration expected on rigid ground, referred to a probability of exceedance; the parameter used to quantify hazard.
Categoria di sottosuolo
Classification of the ground (A–E) that modifies the seismic action at the site in the NTC.
Sismabonus
Tax deduction for works reducing seismic risk, graduated by zone and by risk class.