1 Input accelerograms and expected accelerations for some dam sites in 2 southern

A. Rebez1, D. Sandron1, M. Santulin1, L. Peruzza1, A. Tamaro1, M. Eusebio2, M. Mucciarelli1, D. Slejko1

27 Novembre 2014 III Torre del Palazzo della Regione Emilia Romagna The study

① A probabilistic seismic hazard analysis (PSHA) has been developed for selected sites located in (southern Italy) with the specific aim of accurately assessing the largest expected ground acceleration. ② The selected sites host hydroelectric dams that have to be seismically assessed, as requested by the Italian authority, and response spectra and accelerometric time histories are required as input parameters. ③ The study has been developed for CESI S.p.A., that performs the dam seismic assessment under request of A2A S.p.A, owner of the plants. ④ The seismic hazard analysis was designed to provide a broad spectrum of input ground motions suitable for the verification, of the structural behaviour of the dams, through a mathematical model (FEM). Code

① According to the recent Italian technical dams code DM 2014 (Ministero delle Infrastrutture, 2014), for dams located in seismic areas with conventional hazard characterised by PGA greater than 0.15 g, a specific hazard study is mandatory; dam assessment must be performed using seismic input giving worst structural effects. ② Moreover, for dams located in areas with medium/high seismicity a dynamic analysis approaches (response spectrum and/or time history analyses) are suggested, with seismic action represented by acceleration time-series, i.e., a set of accelerograms (typically 3 to 7 in order to consider the effects on average) representative of the expected seismic event. In the present study, 2 alternative source models have been considered; ① one is based on composite sources adopted by DISS. ② Sources can collect more than one individual fault as segmentation is usually not clearly known. ③ Around these sources, large "background" areas have been considered, where the seismicity external to the sources was collected. ④ 9 composite sources have been considered: ITCS015 Crati Valley; ITCS019 Crotone-Rossano; ITCS068 Curinga – Squillace; ITCS069 Southern Calabria; ITCS053 Serre; ITCS082 ; ITCS080 Nicotera-Roccella Ionica; ITCS055 Bagnara-; The zonation developed by OGS specifically for the present study consists of 7 sources located around the sites of the dams:

Rossano: extensional EW structures. The M6.2, 1836 event is associated with this source; Crati W: NS structures on the western side of the Crati Valley, dipping to E, normal fault kinematics. All the major events that occurred along the Crati valley (M6.7, 1184; M6.0, 1767; M5.8, 1835; M6.2, 1854) are associated with this source; Laghi-Rizzuto: en-enchelon NW-SE segments with right stepover and dipping to the SW; the kinematics is mainly left transcurrent. The June 1638 (M6.9) event and the earthquake of 1832 (M6.6) are associated with this source. Catanzaro: NW-SE regional structures in right stepover, consistent with transpressive kinematics. The area includes the 1638 main shock (M7.0) and the 1626 (M6.0) earthquake. Serre: : Armo-Scilla: Instrumental catalogue: • Mw according to MPS04 The catalogue • threshold Mw=3. • N = 6960.

Historical catalogue: CPTI11 with 341 events. ① The CPTI11 catalogue has been the preferred choice in case of duplicity. ② The elimination of the dependent events has been done according to the Gardner and Knopoff (1974) approach. ③ The final declustered catalogue for the studied area consists of 2306 events. The catalogue

The temporal distribution of the earthquakes in the catalogue: ① earthquakes with M>6 are listed since very ancient times. ② earthquakes with M>7 have been reported since 1600; ③ the information on earthquakes with 4

For a comparison with MPS04, we used two GMPE of that study (AMB e S&P). The C&F has been added [global validity]

NB. The C&F has a lower magnitude limitation (5), not good in the near field (<15 km) [In the present work we extented the GMPE out of its range of definition]. Hazard curves The results, here presented as an example of the work done, refer to one of the sites hosting an operating dam. 100 PGA Rock Seismic hazard has been estimated in terms of PGA and spectral

acceleration (SA) for a 475-year return period, standard

s r

a reference for seismic design, and for 101- and 1950-year return

e y

-1

0 10

5

c

x br. 01 periods, respectively corresponding to the limit state of damage

E

b br. 02

o r P br. 03 (SLD) and the limit state of collapse (SLC) in the Italian building br. 04 br. 05 br. 06 code NTC08. The calculations have been repeated for three soil mean 10-2 +1std types: a) rock (VS30>800 m/s); b) stiff soil (360

0.1 1 m/s) and c) soft soil (180

1 1.6 3 Rock 1950 yr Rock 475 yr 2.8 Rock 101 yr mean+/-1sd 1.4 mean+/-1sd 2.6 mean 0.8 mean+/-1sd mean 2.4 br. 01 mean br. 01 1.2 2.2 br. 02

br. 01 br. 02 br. 03

) )

) 2

g g

g br. 02 br. 03 br. 04

( ( (

1

. .

. 0.6 br. 03 br. 04 1.8

c c

c br. 05

c c

c br. 04 br. 05

a a

a 1.6 br. 06

l l

l 0.8

a a

a br. 05 br. 06

r r

r 1.4

t t t

c c

c br. 06

e e

e 0.4 1.2

p p

p 0.6

S S S 1 0.4 0.8 0.2 0.6 0.2 0.4 0.2 0 0 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 Period (s) Period (s) Period (s) …comparison with MPS04 1.8 1.8 Rock Rock 1.6 101 yr 1.6 101 yr MPS04 101 yr NTC08 101 yr 1.4 475 yr 1.4 475 yr

MPS04 475 yr NTC08 475 yr )

1.2 1950 yr ) 1.2 1950 yr

g

g

(

(

.

MPS04 1950 yr . NTC08 1950 yr

c

c c

1 c 1

a

a

l

l

a

a

r

r t

0.8 t 0.8

c

c

e

e

p

p S 0.6 S 0.6

0.4 0.4

0.2 0.2

0 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 Period (s) Period (s) …comparison among the sites 1.8 Stiff 1950 yr The UHRSs for each site and for the three return periods 1.6 dam 01 dam 02 [101, 475, and 1950] have been compared with those 1.4 dam 03 dam 04

) 1.2 dam 05

obtained by the MPS04 map [rock], and with the reference g

(

. dam 06 c

c 1

spectra of the Italian building code NTC08 a

l

a r

t 0.8

c

e p

The UHRSs obtained for the six sites under study are S 0.6

compared, regarding only the 1950-year return period and 0.4

stiff soil. Given the vicinity of the six sites, the UHRSs are 0.2

quite similar with the maximum peak at 0.1 s. 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 Period (s) ① Recorded accelerograms can be downloaded Recorded accelerograms from national and international databases, and they should be representative of the seismicity of the site. ② Typically, the selection of the records is done according with the magnitude (M) and the epicentral distance (D), similar to those of the design earthquake for the study site, and considering site conditions of the recording station similar to those observed in the study site. The identification of the design earthquake derives often by the deaggregation of the PSHA results for the return period of interest. ③ In this work, 5 recordings have been selected, (three and seven respectively are the minimum and the maximum number of complete accelerograms requested by NTC08), amounting to 15 accelerograms for each site: 2 for the horizontal components and one for the vertical one for each event. … comp. among spectra

① Horizontal (top panel) and vertical (bottom panel) response spectra of all the selected accelerograms (horizontal and vertical components) have been calculated together with the average value (black line) and its standard deviation (grey dotted line). ② 1950-year return period UHRS (red line). ③ reference spectra of the Italian building code NTC08 (blue line) “match” to the TARGET spectrum

In the case that the real accelerogram does not fully satisfy the selection criteria, it can be scaled through the addition of wavelets. To adapt the real accelerogram to a specific target response spectrum, the software SeismoMatch. In the present study, we have selected as target spectrum: 1) the spectrum of the Italian building code NTC08 (blue line), 2) the average horizontal UHRS obtained in this work (red line). Synthetic time histories The use of real accelerograms and their matching to a specific target spectrum is recommended by the Italian legislation for obtaining a set of recordings to be used in the dynamic non-linear analysis of the structures.

However, if the access to real accelerograms presents, for any reason, difficulties, it is allowed to generate synthetic accelerograms to be matched to a specific target response spectrum.

[despite a sufficient number of real accelerograms have been collected for each site] an additional set of synthetic accelerograms have been calculated using the SeismoArtif v2.1 software, that:

① first generates a synthetic accelerogram, whose characteristics of duration, amplitude, envelope and phase distribution are determined according with the magnitude (M) and the (JB) distance of the seismic event to be

simulated. The soil type (based on VS30) and the tectonic regime (intra-plate, inter-plate; active extensional tectonic regimes) of the site under study are also taken into account. ② In a second step, an iterative procedure modifies the distribution of the amplitudes in the frequency domain to obtain the spectrum convergence to the desired response.

The result is an accelerogram that fulfills all the legislation requirements. Conclusions

New PSHA UHRS SLD (101 year RT) Rock SLC (1950 year RT) Stiff Soft

Deaggregation SLD 5 Real time histories (3c) SLC Real Time histories UHRS matched to: NTC08

Synthetic time histories UHRS matched to: Mean spectrum of real TH Conclusions

① The present study is an example of integration between disciplines traditionally associated with both the research and industrial worlds, with a direct practical application. ② In fact, the experience gained by a research group is here focused on the definition of a specific and more reliable seismic hazard of industrial sites in terms on spectral analysis and time-histories, that can be directly applied in the structural assessment of strategic structure under consideration. ③ This study can also be seen as a specific example of the application of seismology to increase the safety level of a territory.