Which seismic zone is your site in?
Italy’s 2024 Budget Law requires companies to insure against earthquakes, floods and landslides, and the premium must be set in proportion to risk. Here is the first of the three inputs, the one an insurer cites first: the municipality’s seismic zone.
The scale runs from 1, the most severe, to 4, the least.
This municipality’s territory falls into different base zones: the source assigns it no single value, and neither do we. A specific site needs point-level classification, which this dataset does not contain.
Ground acceleration, by point
The seismic zone is administrative and applies to a whole municipality: Milan and Turin sit in the same one. What actually separates two sites is peak horizontal ground acceleration, which Italy’s building code defines point by point on a national lattice of 10,751 nodes. Paste the site’s coordinates: below you get the mesh of four nodes that contains it, how much each one weighs, and the value at the point, computed with the decree’s own formula.
Search for a municipality above first: the map then opens on its province, with every municipal boundary, so you can see where you are pointing instead of guessing.
Coordinates not recognised. Two decimal numbers separated by a comma or a space, for example 45.4642, 9.1900.
The grid has no node within twenty kilometres of this point, and we do not show values fetched from far away. The building-code grid does not cover Sardinia: all 377 of its municipalities are in zone 4, the only Italian region entirely in zone 4. Outside Sardinia, a point with no nearby nodes is almost always at sea.
Value at the point
The lattice has no complete mesh around this point, which happens just off the coast. We show the nearest nodes but not the weighted average, because the Annex A formula applies to the four vertices of one mesh, not to any four nodes.
Where it falls in the national range, at TR 475
The mesh and your point
How much each vertex weighs
The four vertices of the mesh containing the point
| node | distance | weight | TR 50 | TR 475 | TR 975 |
|---|
Values are in metres per second squared, as the source publishes them — it never states the units — with the conversion to g alongside. The national maximum at TR 475 is 2.78 m/s², that is 0.284 g; at TR 975 it reaches 4.03 m/s², or 0.411 g.
The three return periods are not arbitrary scenarios: for an ordinary building with a 50-year reference period they are the three checks the building code asks for. The link is the decree’s formula 3.2.0, TR = −VR / ln(1 − PVR), applied to the probabilities in table 3.2.I.
- TR 50 years — a 63-in-100 chance of being exceeded within 50 years. This is the damage limit state: after that shaking the building must remain usable.
- TR 475 years — 10 in 100 within 50 years. This is the life-safety limit state, the one that sizes the structure. It is the column to read first.
- TR 975 years — 5 in 100 within 50 years. This is the collapse limit state.
- How you get from the nodes to the point is set out in Annex A to the decree of 14 January 2008, which the 2018 building code refers back to: for a point that does not fall on a lattice node, the values may be computed as a weighted average of the values at the four vertices of the elementary mesh containing the point, using the inverses of the distances as weights. That is formula [3] of the decree, and it is the one applied here. Beware of an easy confusion: these are the four vertices of the mesh, not the four nearest nodes — often they are not the same.
- What is computed here is the baseline seismic hazard, referred to stiff ground with a horizontal surface (category A). The design seismic action additionally requires the subsoil category, the topography and the nominal life of the works: that remains a designer’s job.
- The grid coordinates use the ED50 datum, everyday maps use WGS84: the two differ by roughly a hundred metres, immaterial for an order of magnitude and material for a design calculation.
- The lattice has no nodes over Sardinia and the smaller islands because the decree sets a different rule for them: response spectra are defined from values of ag, FO and TC* that are uniform across the whole territory of each island, for every island except Sicily, Ischia, Procida and Capri. Those uniform values are not part of the lattice and are not in the file we publish.
Point at the site
The map shows the municipalities of the province around the one you searched for, which is the highlighted one. The small squares are the nodes of the official grid. Tap where the site is, then refine the coordinates in the field if needed.
Administrative boundaries from Istat, generalised version as of 1 January 2021: they are there to help you get your bearings, not to delimit property.
Point selected—
At this scale one pixel is worth between a few tens and a few hundred metres, and a fingertip covers several of them: use the map to get close, then correct the coordinates in the field, where the precision is the one you type.
The other two hazards are not here yet
The law names five events, which are three families: earthquake, flood and landslide. Only the seismic one is here, and not by editorial choice: for flood and landslide there is no national source that can be queried by point. The ISPRA API stops at the municipality, and the polygons must come from the seven river-basin district authorities, with different scales, classes and dates. Stitching them without carrying provenance would produce data less precise than its sources, and we would rather not publish it until it is.
What this figure is not
- It is the administrative figure, the one an insurer cites: it applies to the whole municipality and does not separate two sites kilometres apart. It is not site-level seismic hazard, which is a different quantity, measured as peak ground acceleration.
- It is not insurance advice: it does not say whether a policy is adequate, does not estimate a fair premium and recommends no contract.
- It is not a survey: it says nothing about the state of a building, its structural vulnerability or expected damage.
- It does not discharge the insurance obligation: only a policy does that.
Source
Civil Protection Department, seismic classification of Italian municipalities, stated update May 2025. The “value as published by the source” field carries the original string unaltered, regional sub-zones included.
The seismic classification on the Civil Protection website · Download the normalised dataset (JSON) · The administrative boundaries of municipalities, on Istat
An information tool, not legal advice and not a conformity assessment. The references are the ones cited entry by entry; the text that counts is the official one.
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