Spectral probabilistic seismic hazard assessment for Italy · The Ambraseys et al. (1996) attenuation relation with σwas used. where the attenuation was modelled differently, as

Abstract. During the last decade the Italian "Gruppo Nazionale per la Difesa daiTerremoti" has undertaken a project for assessing seismic hazard on probabilisticbases in the national territory, to be used as scientific background for the revision ofthe current seismic zonation; the seismic hazard was expressed there in terms of peakground acceleration and macroseismic intensity. A more detailed analysis is nowperformed. Probabilistic spectral seismic hazard maps at different frequencies of engi-neering interest demonstrate that the soil condition is a first order factor influencingthe level of the expected shaking, with an average increase of about 0.2 g for the pre-diction related to a 475-year return period, when passing from rock to soft soil. Theattenuation model similarly conditions the results, but in a more magnitude-dependentfashion. Here, the two relationships selected account for the effects of strong rare sei-smicity and moderate frequent earthquakes differently: differences going from 20% to80% of the predicted spectral accelerations are, therefore, model-dependent. Theuniform hazard response spectra for some major Italian towns are then compared tothe elastic response spectra of the present Italian seismic zonation, indicating that twoimportant towns such as Rome and Naples are not adequately represented by the pre-sent code. The effective peak acceleration is considered, finally, a good synthetic para-meter for representing seismic hazard in most engineering applications.

1. Introduction

A global project for seismic hazard assessment on Italian territory was defined in the frameworkof the “Gruppo Nazionale per la Difesa dai Terremoti” (GNDT) for updating the national seismiczonation. The project consisted in three main objectives: compilation of an earthquake catalogueand a seismological data base, preparation of the seismogenic zone (SZ) map, and hazard asses-sment by probabilistic methodologies. The final results were obtained and officially presented in the

VOL. 40, N. 1, pp. 31-51; MARCH 1999BOLLETTINO DI GEOFISICA TEORICA ED APPLICATA

Corresponding author: A. Rebez; Osservatorio Geofisico Sperimentale, C.P. 2011 Trieste, Italy; tel. +39 0402140250; fax +39 040 2140266; e-mail: [email protected]

© 1999 Osservatorio Geofisico Sperimentale

Spectral probabilistic seismic hazard assessment for Italy

A. REBEZ (1), L. PERUZZA (2) and D. SLEJKO (1)

(1) Osservatorio Geofisico Sperimentale, Trieste, Italy(2) C.N.R. Gruppo Nazionale per la Difesa dei Terremoti at O.G.S., Trieste, Italy

(Received January 25, 1999; accepted March 26, 1999)

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Boll. Geof. Teor. Appl., 40, 31-51 REBEZ et al.

summer of 1996 to the Civil Protection Department, which financed the project. The results will beconsidered by the Ministry of Public Works for use in legislation. The hazard assessment was doneaccording to the Cornell (1968) approach by applying the Seisrisk III (Bender and Perkins, 1987)code; the details of the computation are exhaustively described in Slejko et al. (1998), and the finalmaps, in terms of peak ground acceleration (PGA) and macroseismic intensity, are reported there.

Even if PGA is the most widely used parameter in seismic hazard analysis for its easy and prac-tical meaning nevertheless, it is, a rough shaking indicator because it is generally associated with ashort impulse of very high frequency and, therefore, cannot be easily correlated to the damageobserved. For this reason the majority of building codes define the elastic response spectrum andadopt the design spectrum to represent seismic actions. Examples of analyses in terms of uniformhazard response spectrum, in Italy, are rare (see, for example, Peruzza et al., 1994, where the extre-me theory statistics is applied in northeastern Italy), and only recently have they been performed forthe entire country and neighbouring areas (e.g. Romeo and Pugliese, 1997; Peruzza et al., 1998a,1998b).

The aim of this paper is to present spectral seismic hazard maps, calculated for the Italian ter-ritory using the Cornell (1968) method, and uniform hazard response spectra for some major towns.The basic PGA map is presented in Fig. 1: it differs from the official one presented to the CivilProtection Department in 1996 (Slejko et al., 1998) as the attenuation relation has been substitutedwith a more recent version (Ambraseys et al., 1996) which takes into account different soil typesand is related to a spectral version as well. The maximum values of PGA in Fig. 1 are reached, star-ting from the south: in the Calabrian Arc (north of Reggio Calabria), in the southern Apennines nearPotenza and less extensively near Campobasso, and in the eastern Alps NE of Venice. In all theseareas the PGA values exceed 0.32 g (is a gravity acceleration). Some other areas in the northern andcentral Apennines, in the zones between Florence and Bologna and between Perugia and L'Aquila,for example, show PGA values that are higher than 0.28 g. The results are generally lower than theprevious ones (Slejko et al., 1998) as rocky conditions are mapped here, while the previous relation(Ambraseys, 1995) takes into accounts only average soil conditions: the volcanic areas now show ahigher PGA, as no peculiar modifications of the attenuation were considered in this more recent

Town zonation PGA_95 PGA_95 PGA_96 PGA_96 SA(0.2) SA(0.2) SA(1.0) SA(1.0)code mean mean+σ mean mean+σ mean mean+σ mean mean+σ

Milan n.c. 0.039 0.080 0.044 0.074 0.098 0.178 0.019 0.045Venice n.c. 0.050 0.099 0.049 0.087 0.112 0.213 0.032 0.064Trieste n.c. 0.057 0.112 0.052 0.097 0.112 0.231 0.024 0.058Florence 2 0.131 0.203 0.108 0.169 0.235 0.404 0.055 0.106Rome n.c. 0.113 0.168 0.092 0.149 0.192 0.353 0.043 0.092Naples 3 0.123 0.181 0.135 0.195 0.289 0.461 0.081 0.146Messina 1 0.227 0.365 0.189 0.313 0.398 0.715 0.204 0.281Catania 2 0.135 0.240 0.139 0.256 0.292 0.591 0.096 0.160

Table 1 - Acceleration values (in g) with a 475-year return period for some main Italian towns. The zonation code indi-cates the anti-seismic level to which the towns are subjected at present (1 to 3 for decreasing severity, n. c. means notclassified). PGA_95 refers to the Ambraseys (1995) attenuation relation, PGA_96 to the Ambraseys et al. (1996) atte-nuation relation. SA indicates spectral acceleration at different periods.

analysis. For example, the high spot in eastern Sicily (mount Etna area), near Catania, is largelycaused by the attenuation relation which does not hold in volcanic environments. Table 1 shows thePGA differences for a 475-year return period in the eight major Italian towns selected for this study.The differences are limited, considering the different soil conditions as well, less than 15% with theexception of Florence, where the increase is of 20%. Only for Naples and Catania are the presenthazard estimates higher than the previous ones and this is because of the influence of volcanic SZ's,

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Boll. Geof. Teor. Appl., 40, 31-51Spectral PSHA for Italy

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Fig. 1 - PGA with a 475-year return period for rock. The Ambraseys et al. (1996) attenuation relation with σ was used.

where the attenuation was modelled differently, as already pointed out.

2. Spectral seismic hazard maps for Italy

Maps showing the expected spectral acceleration at different periods can be properly used asthe basis for seismic zonation (e. g.; Basham et al., 1997). Spectral attenuation relations useful forItaly are available in literature (e. g.; Pugliese and Sabetta, 1989; Tento et al., 1992; Sabetta andPugliese, 1996). A new relation (Ambraseys et al., 1996) was recently defined for absolute spectralacceleration (SA) based on the European strong motion data bank (Ambraseys and Bommer, 1991)and calibrated on 422 triaxial records generated by 157 earthquakes in Europe and adjacent regionsin the magnitude Ms range 4.0 to 7.9. It takes into account four soil typologies: rock, stiff, soft, andvery soft soil.

It is universally accepted that the two shaking periods of 0.2 s and 1 s can give a good repre-sentation of the most important part of the ground motion. They are suitable for considering highand low frequency seismic shakings, respectively. The methodology used for defining the PGA sei-smic hazard map of Italy (Slejko et al., 1998 and Fig. 1) was applied, in terms of SA, consideringspectral attenuation relations (Ambraseys et al., 1996). The SA values reported in all the followingmaps were calculated taking into account the proper standard deviation (σ ) of the spectral atte-nuation relation which changes slightly (from 0.27 to 0.32 in the frequency range of 0.5 - 10 Hz)from one period to another; mean values are also reported in Table 1 for the selected towns, to showthe influence of the scattering in the model. This is rather remarkable as, for both the periods repre-sented, σ produces values almost double the mean ones. The largest differences are encounteredin Trieste, where the predicted values are, in any case, small.

In Fig. 2 the SA(0.2) map with a 475-year return period referred to rock is shown. This figureshows that the largest values (exceeding 0.7 g) are found in the Calabrian Arc, southern and cen-tral Apennines, and in the eastern Alps. When considering Italian territory, values larger than 0.6 gare expected along almost all the Apenninic chain, in the Gargano (east of Campobasso), in theeastern Alps and east of Genova. Fig. 3 shows the SA(1.0) map with a 475-year return period refer-red to rock. In this case the values of acceleration are remarkably lower than in the equivalent mapand the maxima are reached in Calabria and the southern Apennines, with values larger than 0.3 g.Values larger than 0.2 g are found extensively along the Calabrian Arc and in the southernApennines, as well as in a small portion of the central Apennines. Some of the seismic areas iden-tified in the previous SA(0.2) map are repeated here too; it is noteworthy that a few, such as in thenorthern Apennines between Florence and Bologna, and especially in the eastern Alps, do notappear in this latter map. Fig. 4 shows the SA(0.2) map with a 475-year return period referred tosoft soil. The general features are the equivalent as in the similar map for rock: the largest values,which in this case exceed 1.0 g, are found in small spots in Calabria, in the southern, central andnorthern Apennines, and widely in the eastern Alps. We can generally say that the 0.6 g isoline inthe map for rock (Fig. 2) refers to 0.8 g in the map for soft soil (Fig. 4), but in the latter the hazar-dous areas of the Gargano and along the Calabrian Arc are wider. The equivalent map for stiff soildoes not show remarkable differences as against the soft soil map: the same values are reached but

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the pertinent areas are slightly smaller.According to the Cornell (1968) approach, the hazard estimates are determined by three main

items: the seismogenic zonation, the earthquake catalogue, and the attenuation relation. There areno choices at present for the first two, as they were expressly designed by GNDT for the probabi-listic hazard map of Italy; on the contrary, an alternative spectral attenuation relation suitable forthe present investigation does exist. The Sabetta and Pugliese (1996) relation was calibrated on 95

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Fig. 2 - SA(0.2) with a 475-year return period for rock. The Ambraseys et al. (1996) attenuation relation with σ was used.

Italian strong motion data from 17 earthquakes in the magnitude range of 4.6 to 6.8; groundshakings are given in terms of pseudo-velocity (PSV) and its σ ranges from 0.19 to 0.32 for fre-quencies from 0.25 to 25 Hz. This Italian relation is considered here for evaluating the differencesproduced and, then, quantifying the consequent uncertainty range in the hazard results. As theSabetta and Pugliese (1996) attenuation relation gives the values of PSV expected at the site, thederivative of these values represents, then, the pseudo-acceleration (PSA) values. For earthquake-

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Fig. 3 - SA(1.0) with a 475-year return period for rock. The Ambraseys et al. (1996) attenuation relation with σ was used.

like excitations PSA and SA are almost identical over most of the usual frequency range (Hudson,1979). The results of PSA(0.2) for a 475-year return period on rock are reported in Fig. 5. Themaxima are located in Calabria and the southern Apennines with values which are larger than 1.0g. Values larger than 0.8 g relate to the Messina Straits, Calabria, some segments of the southern,central, and northern Apennines, and the eastern Alps. Roughly speaking we can say that for most

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Fig. 4 - SA(0.2) with a 475-year return period for soft soil. The Ambraseys et al. (1996) attenuation relation with σ wasused.

parts of the territory the 0.8 g isoline of this map (Fig. 5) corresponds to the 0.7 isoline of theSA(0.2) map (Fig. 2); but, for quantifying the difference caused by the use of the two different atte-nuation relations, the ratio between the PSA(0.2) values according to Sabetta and Pugliese (1996)and SA(0.2) according to Ambraseys et al. (1996) is mapped in Fig. 6. The results according toSabetta and Pugliese (1996) are always higher than those of Ambraseys et al. (1996): the most

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Fig. 5 - PSA(0.2) with a 475-year return period for rock. The Sabetta and Pugliese (1996) attenuation relation with σ wasused.

striking differences are encountered in Calabria (values larger by more than 40%) and, to a lesser

extent, in all of southern Italy. This is explained by the characteristics of the two relations: the

Sabetta and Pugliese (1996) relation predicts greater accelerations where the contribution of high

magnitudes is relevant. Fig. 7 highlights the different behaviour of the two relations, when σ are

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Fig. 6 - Ratio between PSA(0.2) computed with Sabetta and Pugliese (1996) and SA(0.2) with Ambraseys et al. (1996)attenuation relations for rock with σ. Cells where at least one of the two quantities is lower than 0.4 g are not map-ped.

considered and when they are not, for three magnitude values (4.0, 5.5, and 7.0) and for the twoperiods considered in the present work (i. e. 0.2 and 1.0 seconds). At 0.2 s (Figs. 7a and 7c) therelations are always rather similar and σ seems to reduce their differences slightly. At 1.0 s (Figs.7b and 7d) the Sabetta and Pugliese (1996) relation is definitely higher, especially in the near field(a less than 50 km distance). As a general comment, it can be said that differences among attenua-tion relations are always significant (see Abrahamson and Shedlock, 1997); those shown here,although notable, especially for 1.0 s, are not surprising if we consider that the relations were cali-

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Fig. 7 - Comparison between the Ambraseys et al. (1996) (solid lines show SA) and the Sabetta and Pugliese (1996)(dashed lines show PSA) spectral attenuation relations for rock: a) 0.2 s; b) 1.0 s; c) 0.2 s considering s; d) 1.0 s con-sidering σ. ML values were converted (Camassi and Stucchi, 1996) into Ms values when necessary in the Sabetta andPugliese (1996) relation.

brated on different data sets (the Italian one has only two earthquakes with a magnitude larger than6), and regressions were made for different parameters (SA and PSV). The hazard results depend,therefore, on these aspects of the attenuation considered here.

It is, then, interesting to analyze the differences encountered when considering the values at a1 s period. Fig. 8 shows PSA(1.0) computed according to the Sabetta and Pugliese (1996) relation.

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Fig. 8 - PSA(1.0) with a 475-year return period for rock. The Sabetta and Pugliese (1996) attenuation relation with σwas used.

Values larger than 0.4 g are found extensively in Calabria and the southern Apennines; values lar-

ger than 0.2 g cover most of the Apennines and eastern Alps. The results according to the Sabetta

and Pugliese (1996) relation are, again, definitely larger than those of the Ambraseys et al. (1996)

relation. This aspect clearly stands out in Fig. 9, where the ratio between PSA(1.0) and SA(1.0) is

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Fig. 9 - Ratio between PSA(1.0) computed with Sabetta and Pugliese (1996) and SA(1.0) with Ambraseys et al.(1996) attenuation relations for rock with σ. Cells where at least one of the two quantities is lower than 0.1 g are notmapped.

mapped. The general features of this map are similar to those of the PSA/SA ratio at 0.2 s (Fig. 6)but the values are now remarkably higher, since the Sabetta and Pugliese (1996) PSA(1.0) valuesin the southern Apennines and eastern Sicily are now from 60% to 90% larger than the Ambraseyset al. (1996) SA(1.0) ones.

3. Uniform hazard response spectra

The previous spectral maps give enough information on the regional seismic hazard but cer-tainly do not give the complete information which could be useful in urban planning. This kind ofinformation is given by the uniform hazard response spectra that are calculated here for rocky soilat 14 periods in the range of 0.1 - 2.0 s and refer to SA with a 475-year return period. Some appa-rently anomalous fluctuations in the shape of the spectra are related to the processing of the acce-lerograms performed by Ambraseys et al. (1996): the authors, in fact, computed raw regressioncoefficients, admitting some statistical fluctuation of the coefficients that can be caused by the spec-

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trum sampling too. This effect is particularly evident when σ is taken into account, as the differentvalues of σ for each frequency can modify the shape of the spectrum, independently from the cha-racteristics of the seismicity affecting the site (see Peruzza et al., 1998b).

The complete spectrum was computed for all the 8101 Italian municipalities. We show thosewhich refer to eight main Italian towns, from south to north: Catania, Messina, Naples, Rome,Florence, Milan, Venice, and Trieste (see their location in Fig. 1). The results, referred to rockysites, are shown in Fig. 10; rock conditions only partly represent the municipalities, but are chosenin this case for comparison. It can be seen that for all the towns the maximum values are reachedin the period range of 0.1 to 0.3 s, when the decay becomes rapid. The maximum values obtainedare remarkably different, varying from less than 0.2 g (Milan) to more than 0.7 g (Messina). Theresults for the eight towns can be roughly grouped into three categories: high (Messina with valuesexceeding 0.7 g), medium (Catania, Naples, Florence, and Rome with values between 0.4 g and0.55 g), and low accelerations (Trieste, Venice, and Milan with values lower than 0.3 g). In the samefigure the elastic response spectra for the three categories of the present Italian seismic code areshown. It can be noted that the computed spectra for most of the studied towns are significantlylower than those of the proper seismic categories, especially in the low frequency band. Exceptionsare in the spectrum of Naples, which exceeds the official 3rd category one where the town is pla-ced, and in that of Rome, because the town is not classified (see Table 1).

The spectra show limited differences in their shape due to the dominant seismicity; this is anobvious consequence of the Cornell (1968) methodology, used here in considering homogeneousseismicity over seismogenic area sources. In addition, the σ values modify the original shape of thespectrum, and, therefore, the effects of the source influences. Nevertheless, some towns presentquite a flat spectrum, in the range of 0.1-0.3 s (Messina, Naples, Venice) while other localities exhi-bit a clearly defined maximum at 0.15 s (Catania, Florence, Rome, Trieste). It is interesting to notehow similar the Naples and Catania spectra are, differing only in the high frequency domain(periods smaller than 0.3 s).

Spectra referring to two soil types (rock and soft soil) are presented for Trieste, and Catania;both cities have a great terrain variability, from hard limestone (Trieste) and lava banks (Catania)to soft Holocene clays and incohesive sea deposits. Fig. 11 shows that the soil type has a notableinfluence in determining the expected values, which are about 30% larger for soft soils, and also indefining the shape of the spectra, as the maximum values move to higher periods when taking softsoils into account.

4. The effective peak acceleration map

The complete uniform hazard response spectra, presented in the previous section, giveexhaustive information about seismic hazard at a site. On the other hand, comparing hazard fordifferent sites cannot be easily appreciated. It is quite interesting to compare seismic hazardgiven in a more complete way than PGA, at regional or national scale, on a single map. The ave-rage SA value in a frequency range of engineering interest, which is called effective peak acce-leration (EPA), can satisfy this need. Although EPA is a philosophically sound parameter for sei-

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smic hazard analysis, there is no standardised definition of this parameter at present (Uang andBertero, 1988). ATC-13 (1985) defines EPA as follows:

EPA = PSA'/2.5where PSA' is the 5% dumped mean PSA value in the period range of 0.1 to 0.5 seconds.EPA maps can, then, represent the characteristics of the dominant part of the response spec-

trum well and have been prepared according to the previously cited criteria (Ambraseys et al.(1996) attenuation relation for rock). Fig. 12 shows EPA with a 475-year return period for Italy.Many areas with values larger than 0.24 g can be identified, in southern Italy (Messina Straitsand Calabria), along the southern, central, and, less widely, the northern Apennines, as well as inthe eastern Alps: among these, one near Potenza and Calabria also exceeds 0.28 g. Comparingthis EPA map to the PGA one (Fig. 1), a general similarity can be noted but the EPA map empha-sises only some of the areas were PGA reaches the highest values.

For better pinpointing the seismic hazard with a short return period and, consequently, theregions frequently damaged by earthquakes, Fig. 13 shows EPA with a 100-year return period.Almost all the previously cited hazardous areas again appear with high values (larger than 0.12g). It is interesting to notice that the two high spots in Calabria do not correspond to the seismic

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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.1 1

spec

tral

acc

eler

atio

n (g

)

period (s)

soft

rock

soft

rock

CATANIA

TRIESTE

Fig. 11 - Uniform hazard response spectra with a 475-year return period on rock and soft soil for Trieste and Catania.The Ambraseys et al. (1996) attenuation relations with their σ’s were used.

area evidenced by Fig. 12.The differences between the two maps, in the higher EPA areas, are caused by the type of

seismicity experienced: in the southern Apennines strong earthquakes have occurred repeatedly,and have influenced the long return period hazard; in central and northern Italy high magnitudeevents are rare but medium magnitude quakes occur frequently, and they contribute to the shortreturn period hazard. In addition, the medium magnitude earthquakes show higher acceleration

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REGGIO CALABRIA

0.5 - 0.6

0.6 - 0.7

0.7 - 0.8

≥ 1.0

PGA (g)

0.20 - 0.24

0.24 - 0.28

0.28 - 0.32

≥ 0.32

EPA (g)

Fig. 12 - EPA with a 475-year return period for rock. The Ambraseys et al. (1996) attenuation relation with σ was used.

in the high frequency range, where EPA is defined.EPA with a 475-year return period for soft soil has been computed as well (Fig. 14): the atte-

nuation relation for this type of soil increases by about 0.08 g of the values computed on rock.In fact, the isolines of 0.24 g in Fig. 12 are very similar to the isolines of 0.32 g in Fig. 14.

In addition, EPA according to the Sabetta and Pugliese (1996) relation has been computedfor a general comparison (Fig. 15). The same seismic areas as in Fig. 12 are pointed out, and, as

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0.5 - 0.6

0.6 - 0.7

0.7 - 0.8

≥ 1.0

PGA (g)

0.08 - 0.12

0.12 - 0.16

0.16 - 0.20

≥ 0.20

EPA (g)

Fig. 13 - EPA with a 100-year return period for rock. The Ambraseys et al. (1996) attenuation relation with σ was used.

expected, the values are larger, especially in southern Italy.As a general comment on the EPA maps, it can be said that they show similar differences

between each other in the same way as the PGA maps (Slejko et al., 1998), such as: similar shapebut increasing value passing from rock to soft soil, and greater importance of the medium magni-tude frequent seismicity moving from the 475-year to the 100-year return period.

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REGGIO CALABRIA

0.5 - 0.6

0.6 - 0.7

0.7 - 0.8

≥ 1.0

PGA (g)

0.20 - 0.24

0.24 - 0.28

0.28 - 0.32

≥ 0.32

EPA (g)

Fig. 14 - EPA with a 475-year return period for soft soil. The Ambraseys et al. (1996) attenuation relation with σ wasused.

5. Conclusions

The PGA 475-year return period is the choice for the standard hazard map used for seismic

zonation. The information in this map, although relevant, is not exhaustive as representing the

hazard at specific sites. For this reason three further types of hazard representations were compu-

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EPA_Sr_475EPA_Sr_475

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REGGIO CALABRIA

0.5 - 0.6

0.6 - 0.7

0.7 - 0.8

≥ 1.0

PGA (g)

0.20 - 0.24

0.24 - 0.28

0.28 - 0.32

≥ 0.32

EPA (g)

Fig. 15 - EPA with a 475-year return period for rock. The Sabetta and Pugliese (1996) attenuation relation with σ wasused.

ted and presented. Namely: the spectral hazard maps referred to two periods, the uniform hazardresponse spectra for the main Italian towns, and the EPA maps. A more precise view of the Italianseismic hazard is given by considering them globally.

The PGA and the SA(0.2) maps are quite similar and point out many sectors of the southernand central Apennines, and the eastern Alps with almost the same accelerations. The SA(1.0) mapfocuses on Calabria and the southern Apennines as the areas with the highest hazard. The EPA mapagain enhances Calabria and the southern Apennines, giving the other areas of the PGA map sli-ghtly lower accelerations. As already mentioned, different aspects of hazard are displayed by themaps: the influence of very strong earthquakes (SA(1.0) map), the influence of local seismicity inaddition to strong seismicity (PGA and SA(0.2) map), as well as the average contribution of majorand local events with the exception of low frequency ones (EPA map).

In conclusion, it is the authors' opinion that the EPA maps offer more balanced information onthe varying contribution of the seismicity affecting a site, and, is, consequently, more suitable forzonation purposes. This knowledge can be improved by analysing the uniform hazard responsespectra, where the spectral shaking contents are detailed and the influence of the reference soil canbe taken into account.

Acknowledgements. This research was conducted in the framework of the activities of the “Gruppo Nazionale per laDifesa dai Terremoti”, contract n. 97.00537.PF54. Many thanks are due to Dieter Mayer-Rosa, for his very helpful reviewof the paper, and to Luis Decanini, for some information on the elastic response spectra of the italian seismic code.

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European Seismological Commission (ESC). Papers, ElAl, Tel Aviv, pp. 165 - 169.

Peruzza L., Rebez A and Slejko D.; 1998b: Probabilistic seismic hazard spectra for the Adriatic region. In: Bisch P.,Labbè P. and Pecker A. (eds), Proceedings of the Eleventh European Conference on Earthquake Engineering,Abstract volume and CD-ROM, pp. 48 and CD-ROM.

Peruzza L., Sirovich L. and Slejko D.; 1994: Spectral characteristics of the seismic hazard between the Alps and theDinarides. Soil Dynamics and Earthquake Engineering, 13, 213-217.

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Documents

Spectral probabilistic seismic hazard assessment for Italy · The Ambraseys et al. (1996) attenuation relation with σwas used. where the attenuation was modelled differently, as