Urban Habitat Constructions under Catastrophic EventsFINAL CONFERENCE. Naples, 16th- 18th September 2010Chair of the Action: Federico Mazzolani, IT, fmm@unina.itCOST Science Officer: Thierry Goger, tgoger@cost.esf.org

COST Action C26

MEASUREMENTS OF SHEAR WAVE VELOCITIES FOR SEISMIC AND VOLCANIC HAZARD ASSESSMENT IN URBAN AREASC. Nunziataa, G. De Niscoa, M.R. Costanzoa, F. Vaccarib, G.F. Panzab,c

aDipartimento di Scienze della Terra, Univ. Napoli Federico II, Italy bDipartimento di Geoscienze, Univ. Trieste, Italy.cThe Abdus Salam International Centre for Theoretical Physics, ESP-SAND Group, Trieste, Italy.

Detailed VS profiles with depth can be obtained in urban areas from the nonlinearinversion with hedgehog method (Panza et al., 2007 and references therein) of theRayleigh waves group velocity dispersion curves of the fundamental mode extracted withthe FTAN (Frequency Time Analysis) method (Levshin et al., 1989) from the recordedsignal of active and passive seismic experiments at a single station.

REFERENCESAGIP, 1987. Geologia e geofisica del sistema geotermico dei Campi Flegrei. Int. Report, 17 pp.Bernard, M. L. & Zamora, M. 2003. Mechanical properties of volcanic rocks and their relations to transport properties, in the CD of: P. Capuano, P. Gasparini, A. Zollo, J.Levshin, A.L.,Yanovskaya, T.B., Lander, A.V., Bukchin, B.G., Barmin, M.P., Ratnikova, L.I., and Its, E.N. 1989. Seismic Surface Waves in a Laterally Inhomogeneous Earth, ed. Keilis-Borok,V.I., Kluwer, Norwell, Mass.Natale, M., Nunziata, C., Panza, G. F. 2004. FTAN method for the detailed definition of Vs in urban areas. Proc. 13th World Conference on Earthquake Engineering, Vancouver, B.C.,Canada, August 1-6, CD-Rom, pp. 11.Nunziata, C. 2004. Seismic ground motion in Napoli for the 1980 Irpinia earthquake. Pageoph, 161, (5/6), 1239-1264.Nunziata, C., Natale, M. and Panza, G.F. 2004. Seismic characterization of neapolitan soils. Pageoph 161 (5/6), 1285-1300.Nunziata, C., De Nisco, G., Panza, G.F. 2009. S-waves profiles from noise cross correlation at small scale. Eng. Geol., 105, 161-170.Panza, G. F., Peccerillo, A., Aoudia, A., Farina, A. 2007. Geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex ofgeodynamic setting: The Thyrrenian Sea and surrounding. Earth-Science Reviews, 80, 1-46.Zamora, M., Sartoris, G., Chelini, W. 1994. Laboratory measurements of ultrasonic wave velocities in rocks from the C. F. volcanic system and their relation to other field data. J.Geophys. Res., 99: 13553–13561.

A weight drop of 30 kg is used as source and one or more low frequency 4.5-1 Hz vertical geophones are used as receivers for offsets less or greater than 50 m. An

average dispersion curve

of Rayleigh group

velocities with errors is

computed, from FTAN

analysis made on a few

(4-5 or more) signals,

which can be inverted to

determine VS profiles

versus depth.

The VS solutions and the chosen solution (red line) for the MERG-PORT path. Theoverlap of the fundamental mode Green function extracted with FTAN method (redline) on cross correlation of 1-Bit 0.3-0.8 Hz band-pass filtered signal is shown togetherwith the average dispersion curve of the fundamental mode, with error bars. Ultrasonicmeasurements on specimens from Campi Flegrei (Zamora et al., 1994) and Vesuvio(Trecase drilling) (Bernard & Zamora, 2003) are reported together with VS valuescomputed from VP sonic log measurements (AGIP, 1987).

CONCLUSIONSThe results obtained in Napoli metropolitan area, with thenon linear inversion of Rayleigh wave group velocitydispersion curve of the fundamental mode extracted withFTAN method from both active seismic surveys and noisecross correlation, show that the procedure is a powerfuland reliable instrument to get VS profiles versus depth inurban areas. The proposed methodology is low cost, asone (active experiments) or two (passive experiments)receivers are requested on ground surface and isparticularly suitable for urban areas as doesn’t requirespreadings. The depth of penetration is manly controlledby the distance and the soil velocities.

Location of the seismic stations employed in the cross correlation experiments at the urban area of Napoli

Example of noise analysis: (a) noise recordings with1 Hz vertical geophones 50 m apart (1 and 2receivers) at SMN courtyard and 1-bit normalizedsignals; (b) power spectra of noise recordings (onthe left) and 1-bit normalized signals (on the right);(c) cross correlation of signals shown in (a) andband-pass filtered; (d) Cross correlation of 1-Bit 10-15 Hz band-pass filtered signals (top) and itssymmetric (bottom).

At urban sites, the impossible use of

explosive sources or heavy masses blows,

limits the penetration depth to the

uppermost 20-30 m, depending upon the

rock velocities. Recently, cross correlations

of long time series of ambient seismic noise

(Nunziata et al., 2009 and references

therein), recorded at a pair of station, have

been demonstrated to recover surface

wave dispersion (Green function) over a

broad range of distances. The resulting

cross-correlations contain surface wave

signals coming from opposite directions

along the path linking the stations. The

cross-correlations are often asymmetrical

due to the inhomogeneous distribution of

ambient noise sources. To simplify data

analysis and enhance the signal to noise

ratio, we average the positive and negative

lags of the cross-correlation to form

‘symmetric signals’. Cross correlation and

symmetric cross correlations are computed

for one-bit normalized signals. Then FTAN

analysis is performed to extract the

fundamental mode of Rayleigh waves.

The VS solutions and the chosen solution (redline) for SMN-SLOR path compared with thestratigraphy of the deep drilling at Plebiscitosquare. Legend: R=man made ground materialand recent pyroclastic deposits;NYT=Neapolitan Yellow Tuff; WT=Whitish tuff;IC= Campanian Ignimbrite; AT= Ancient Tuffs;ST= Tuffs and sedimentary rocks; S=Sedimentary rocks.

300 500 700 900

VS (m/s)

200

100

0

De

pth

(m

)

R

NYT

WT

IC

AT

ST

S

Royal

Palace

The VS solutions and the chosensolution (red line) for the spreading atPartenope st. with geophone distance of180 m. The statigraphy is relative toVittoria square borehole. In the top, thephoto of the investigated area;symmetric cross correlation of 1-Bit 6-25Hz band-pass filtered signals and thefundamental mode Green functionextracted with FTAN method (red line);average dispersion curve of thefundamental mode, with error bars.

0 40 80 120 160

Depth (m)

0

600

1200

VS (

m/s

)

Vs measurements

Neapolitan Yellow Tuff DH-CH FTAN

Compact

Fractured

Vacuous

Altered

soil facies

(pozzolana)

VS velocities of Neapolitan Yellow Tuff, bothsoil and lithoid facies (modified afterNunziata et al., 2004).

Top: Dispersion curves of group velocity relative toreceivers with different offsets at Napoli. Bottom:Shear wave velocity models: the dashed lineindicates the searched part of the parameter's space,while the accepted models are represented by thesolid lines. The chosen solution has been selected asthe closest to the known stratigraphy (green line).

ACTIVE EXPERIMENTS

PASSIVE EXPERIMENTS

Vs MEASUREMENTS AT VESUVIAN AREA

Urban map of Napoli showing thequarter limits and the representativestratigraphic column for each of the sixgeological zones (bold underlinednumbers), together with drillings (blackdots), FTAN measurement sites (bluedots) and all available Vs measurements(modified after Nunziata et al., 2009).