Acceleration Spectrum Intensity (ASI) Values for a National Grid of Points in Italy

Description

The Acceleration Spectrum Intensity (ASI; Von Thun et al., 1988) is an engineering parameter that measures the intensity of earthquake ground-motion over selected ranges of structural vibration periods. It is computed as the integral of the 5%-damped pseudo-acceleration response spectrum (PSA) over a specified period range (ΔT). Following the Indirizzi e criteri per la microzonazione sismica (Gruppo di Lavoro MS, 2008), the ASI parameter was evaluated considering three overlapping period ranges as reported in Table 1 (Ordinanza n.24. del Commissario straordinario per la ricostruzione. https://dev.sisma2016data.it/wp-content/uploads/2017/05/Ordinanza-24-del-12-maggio- 2017.pdf; Mori et al., 2020) and illustrated in Figure 1 .

\( \langle ASI_i \rangle = \frac{1}{\Delta T_i}\int_{\Delta T_i} PSA\,dt \)

Figure 1. Example of a 5%-damped elastic pseudo-acceleration response spectrum and the three period bands: (left) 0.1-0.5s; (centre) 0.4-0.8s; (right) 0.7-1.1s. The shaded areas within the period bands represent the corresponding ASI values.

The ASI values are evaluated on rock conditions (site class A and flat topography T1) from the Italian Building Code (NTC18) spectra (horizontal component), defined by three parameters (ag, F₀, and TC*) on a grid with a spacing of 0.05°, comprising a total of 10,751 grid nodes. To increase the spatial resolution of the ASI estimates, the Italian territory was discretized using a regular grid with a spacing of 500 m, resulting in more than 1.22 million grid points.

Subsequently, to evaluate site-specific ASI values accounting for site effects, the entire Italian territory was classified into NTC18 soil categories and topographic classes according:

• Soil categories (A-D) derived from 1:100,000-scale national lithological map provided by the Italian Institute for Environmental Protection and Research (ISPRA) simplified classification by grouping units characterized by similar lithological and geomorphological conditions.
• Topographic classes (T1-T4) derived from high-resolution digital terrain models (Mascandola at al., 2022)

Figure 2. Maps of Italy classified into NTC18 soil classes based on lithological information (left) and NTC18 topographic classes (right).

For each node of the grid, the PSA was computed using the ESM REXEL-target-spectrum Web-Service and according to the NTC18, adopting the following assumptions: use class II (section 2.4.2 of NTC18), nominal design life of 50 years (section 2.4.1 of NTC18), Life Safety Limit State (SLV, section 3.2.1 of NTC18).

In addition to these parameters, which define the reference spectrum on rock, the corresponding subsoil category and topographic class were assigned to each grid point in order to apply the appropriate stratigraphic and topographic amplification factors. The resulting response spectra were then used to assess seismic hazard through the ASI1, ASI2, and ASI3 parameters.

The continuous ASI values were classified into five hazard classes based on the thresholds values provided by the Italian national seismic zonation (OPCM 3519/2006) for different soil category and topographic category T1 (Table 2).

Figure 3. Map of Italy showing the distribution of ASI values for the ΔT1 (left), ΔT2 (centre), ΔT3 (right) period ranges, including local site and topographic effects.

Download

• the dataset with all the ASI values and the corresponding hazard classes (ASI_1_2_3_italy_2026.csv)
• a supporting file (README.txt) explaining the fields.

• ASI1-ASI2-ASI3 dataset
• md5 checksum: 554bc2ff4d405208d85c240ec71ec431