OGS - Near surface seismostratigraphic modelling of the ......35 Convegno Nazionale GNGTS –Lecce...

35° Convegno Nazionale GNGTS – Lecce 22-24 novembre 2016

Near surface seismostratigraphic modelling of the Bandita plain in Palermo town (Italy) from integrated analysis of HVSR and stratigraphic data R M A R TO R A N A 1 , M A G AT E 1 , P C A P I Z Z I 1 , F C AV ER A 1 , A D ’A L ES SA NDR O 21 D i p a r t i m e n t o d i S c i e n z e d e l l a Te r r a e d e l M a r e ( D i S Te M ) - U n i v e r s i t à d e g l i S t u d i d i P a l e r m o2 I s t i t u t o N a z i o n a l e d i G e o f i s i c a e V u l c a n o l o g i a , C e n t r o N a z i o n a l e Te r r e m o t i , R o m a

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R Martorana, M Agate, P Capizzi, F Cavera, A D’AlessandroNear surface seismostratigraphic modelling of the Bandita plain in Palermo town

(Italy) from integrated analysis of HVSR and stratigraphic data


The studied area

Palermo

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Geological outline

BANDITA

Mrse (calcarenites, sands and clays)

FYN (Numidian Fysch)

TRB (Trubi)

FUN (Fanusi dolostones)

Legend

AFL (continental and lithoral deposits)

Carta geologica della Piana di Palermoin scala 1:50.000

(Catalano et Alii, 2013 - Progetto Carg)

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Lithostratigraphic and HVSR data

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93 boreholes

50 microtremor measures




Body WavesHb, Vb

Surface Waves Hs, Vs Seismic NoiseHr, Vr

Body WavesHb, Vb

AmplificationAh, Av

Hr and Vr spectra of the horizontal and vertical motion observed on the surface;

Ah and Av amplification of the horizontal and vertical motion of the body waves;

Hb and Vb spectra of the horizontal and vertical motion at the bedrock;

HS and VS spectra of the horiz. and vertical motion of surface waves on the surface.

Quasi Transfer Spectrum

B-waves prevalence

Nakamura technique (1989):Horizontal to Vertical Spectral Ratio of microtremors

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Evaluation of the HVSRVisual selection of temporal windows;

Calculation of the FFT (Fast Fourier Transform) with tapering filter for each nth window on

each signal component to get the amplification spectra;

Smoothing on results using a moving average;

The ratio H/V of each single window is calculated by summing the horizontal components

(NS and EW) with a quadratic average:

For each nth window the distribution of log10(H/V) as a function of frequency is obtained. Finally geometric average of H/V and its standard deviation is calculated:




GRILLATM: Signal processing

Averaged spectra of three components

Average HVSR

H/V temporal variation

H/V azymuthal variation




H/V temporal variation

H/V azymuthal variation

Significant peak

GRILLATM: transient noise filtering

Averaged spectra of three components

Average HVSR




Filtering HVSR time windows by Cluster Analysis (D’Alessandro et al. 2016)

D'Alessandro A., Luzio D., Martorana R., Capizzi, P. 2016. Selection of time windows in the Horizontal to Vertical Noise Spectral Ratio by means ofcluster analysis. Bulletin of the Seismological Society of America, 106, 2, 560–574, doi: 10.1785/0120150017.

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HVSR 01

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Inversion of HVSR curves constrained by litho-stratigraphic data

HVSR 01 – Log 58

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HVSR 33

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Depth at the

bottom [m]

Thickness

[m]

Vs [m/s] Poisson ratio

1.50 1.50 180 0.43

6.50 5.00 280 0.42

8.50 2.00 650 0.33

12.50 4.00 450 0.37

14.50 2.00 490 0.38

65.50 51.00 450 0.35

inf. inf. 1080 0.28

Inversion of HVSR curves constrained by litho-stratigraphic data

HVSR 33 - Log 9

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Site effects: f0 peak frequency map

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Seismic bedrock - Depth of top

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Cell dimensions

3D Seismo-stratigraphic modeling

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Borehole Data Manager




Lithology database

Reorganization and classification of the main lithotypes

93 Lithology logsMax. depth of investigation = 30 m

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Seismic database

Physical parameters from 1D inverse model

I-data log50 inverse models

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Max. depth of investigation = 150 m




N

Top

Base

Lithology logs

N

S

Top

Base

N

W

Lithology logs and shear-wave velocity models

vs models

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3D plotting




S

Top

Base

N

W

E

25

0

-25

BaseW

Top

E

WBase

N

S

3D lithology model

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30 m

0 m

-30 m

30 m

0 m

-30 m




3D shear-waves velocity modelTop

Base

Top

Base

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0 m

-50 m

-100 m

-150 m

0 m

-50 m

-100 m

-150 m



35° Convegno Nazionale GNGTS – Lecce 22-24 novembre 2016 22

3D shear-waves velocity model

Near surface zone

30 m

0 m

-30 m30 m

0 m

-30 m

Top

Base




Geological and seismic sections

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surface deposits

calcarenites and sands

gray-blue clays

Numidian flysch

LEGEND

Line A-A’

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ENE WSW




surface deposits


gray-blue clays

Numidian flysch

LEGEND

Line A-A’

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ENE WSW




Line B-B’

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ENE WSWsurface deposits


gray-blue clays

Numidian flysch

LEGEND




Line B-B’

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ENE WSW

surface deposits


gray-blue clays

Numidian flysch

LEGEND




surface deposits


gray-blue clays

Numidian flysch

LEGEND

Line C-C’

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SSW NNE




Line C-C’

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SSW NNE

surface deposits


gray-blue clays

Numidian flysch

LEGEND




surface deposits


gray-blue clays

Numidian flysch

LEGEND

Line D-D’

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SSE NNW




Line D-D’

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SSE NNW

surface deposits


gray-blue clays

Numidian flysch

LEGEND




Robust HVSR inversion constrained by thickness of the near surface layers by lithological logs;

Lithological and seismic GIS referred databases; 3D lithological and seismic coherent models; 2D schematic geological sections aided by 3D models.

Joint correlation and interpretation allowed: a high detailed seismostratigraphic model of the studied area: Extended knowledge on stratigraphic trend over the depth of

investigation of direct surveys; Estimate of shear waves velocity range for each lithological complex. Accurate detection of the seismic bedrock.

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Conclusions

OGS - Near surface seismostratigraphic modelling of the ......35 Convegno Nazionale GNGTS –Lecce...

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