Agreement between DPC – INGV 2007-09 Project S4 – Italian Strong Motion Data Base Coordinators:...

Agreement between DPC – INGV 2007-09 Project S4 – Italian Strong Motion Data Base

Coordinators: F. Pacor (INGV Milan) R. Paolucci (Politecnico di Milano)

Seismic response of the Gubbio basin during the 26 September 1997 (Mw 6),

Umbria-Marche (Central Italy) Earthquake

M. Stupazzini, M. Pilz, L. Luzi, F. Pacor, R. Paolucci, S. Parolai, S. Pucci, and C. Smerzini

Progetto S4 – Wien, EGU, 20th April 2009

The Italian Project S4 (Agreement DPC-INGV 2007-2009)The Italian Project S4 (Agreement DPC-INGV 2007-2009)Italian Strong Motion Database, coordinated by R. Paolucci e F. Pacor Italian Strong Motion Database, coordinated by R. Paolucci e F. Pacor

The main objective of this Project is to make available through the Internet an updated and improved release of the Italian accelometric database (ITACA), originally developed within project S6, in the framework of the 2004-2006 DPC-INGV agreement.

Task Topic

1 ITACA update

2 Geological-geotechnical catalogue of ITACA sites

3 Site characterization by surface waves methods

4 Identification of anomalous sites and records

5 Site classification

One of the objectives of Task 4 concerns the numerical modelling of some of representative case studies, using up-to-date tools for 2D-3D seismic wave propagation and soil-structure interaction analyses (Stupazzini et al., 2009). Such numerical modelling will contribute to understand the physical reasons of the anomalies and the period range in which they mostly affect earthquake ground motion.


The Italian Project S4 (Agreement DPC-INGV 2007-2009)The Italian Project S4 (Agreement DPC-INGV 2007-2009)Italian Strong Motion Database, coordinated by R. Paolucci e F. Pacor Italian Strong Motion Database, coordinated by R. Paolucci e F. Pacor

http://itaca.mi.ingv.it/ItacaNet/http://itaca.mi.ingv.it/ItacaNet/


Umbria Fault System and historical seismicity. Focal mechanisms and magnitudes are for the 1997-98 Colfiorito sequence, for the Norcia earthquake and for the Gubbio earthquake (from Mirabella et al., 2004). The Colfiorito event of 26th September 1997 (26.09.1997, h9:40, MW6.0) is shown with a red star.

Seismic response of the Gubbio plain to the main shock of Seismic response of the Gubbio plain to the main shock of the 1997 Umbria-Marche sequence (Mw6)the 1997 Umbria-Marche sequence (Mw6)


Anomalous sites and records: Gubbio, Umbria-Marche 1997

1Complete record of the horizontal component

On the vertical component, identification of the onset of surface waves

2

Surface waves

Onset of surface waves

Response spectrum

Complete record

Surface waves removed


3D Numerical Model by Spectral Elements 3D Numerical Model by Spectral Elements

Layer # H (m) VP [m/s] VS [m/s] ρ [kg/m3] QS

B1 1000 3500 1800 2200 80

B2 1686 4000 2200 2400 100

B3 1000 4800 2666 2600 150

B4 3000 5500 3055 2800 250

B5 - 6300 3500 2900 300

Deep crustal model

3D Numerical model:

Model size (approximately):

62 km X 86 km X 11km

Spectral Degree = 4 (Order 5)

fmax = 2 [Hz]

# of elements = 152 263

# of nodes = 10 010 205

Tmax = 120 [s]

Element size: min = 100 [m]

max = 900 [m]

t = 5.0e-4 [s]


Investigations after Gubbio, Umbria-Marche 1997


3D Numerical Model by Spectral Elements 3D Numerical Model by Spectral Elements

Alluvial Basin (homogenous)

)s/m(z)z(VP 301000

)s/m(z)z(VS 30250


HYPOCENTERM0

[N m]L x W[km]

Strike[deg]

Dip[deg]

Rake[deg]

Depth of upper points [km]

Vr[km/s]

rise time τ [s]

43.0255°N, 12.8917°E5700 m depth

8.1.1017 12.5 x 7.5 144 42 270 0.7 2.6 1

Seismic source: 26.09.1997 h9.40 MSeismic source: 26.09.1997 h9.40 MWW6 6

Model M7 of Hernandez et al., 2004; available at the web-site http://www.seismo.ethz.ch/scrmod/Eventpages/s1997COLFI2hern

slip pattern source time function

2

221500 /

terf.)t(M


Movie of the Velocity Fault Normal comp. Movie of the Velocity Fault Normal comp.


PGDs and PGVs: comparison with GMPEs PGDs and PGVs: comparison with GMPEs

GBPGBP

GBBGBB

GBPGBP

GBBGBB

Alluvial Alluvial Bedrock Bedrock C

auzzi &

Faccio

li C

auzzi &

Faccio

li (2008)(2008)

Akkar &

Bo

mm

er A

kkar & B

om

mer

(2007)(2007)


Velocity time histories: comparison with Velocity time histories: comparison with earthquake recordings earthquake recordings

GBPGBP GBBGBB


5%-damping acceleration response spectra5%-damping acceleration response spectra

1 2 3T (s)

0.01

0.1

1

Sa

(m/s

2 )

1 2 3T (s)

3D num . sim ulationrecorded

Boore & A tkinson (2008)Cauzzi & Faccio li (2008)B indi et a l. (2009)

station G BP station G BB

Distinctive features of ground motion recorded at GBP with remarkable Distinctive features of ground motion recorded at GBP with remarkable ground motion amplification at long periods (T >ground motion amplification at long periods (T >~~0.6 s). This anomalous 0.6 s). This anomalous behaviour, not observed at GBB, is well reproduced by the 3D numerical behaviour, not observed at GBB, is well reproduced by the 3D numerical simulations. simulations.


Spectral ratios at GBP over GBB Spectral ratios at GBP over GBB

Simple numerical approaches based on 1D wave propagation turn out to be Simple numerical approaches based on 1D wave propagation turn out to be inadequate to reproduce the large amplification factors at long periods (T>~1 inadequate to reproduce the large amplification factors at long periods (T>~1 s), while a good agreement is found between the 3D numerical simulations s), while a good agreement is found between the 3D numerical simulations and the observations. and the observations.

0.1 1Frequency (H z)

1

10

Spe

ctra

l Ra

tio

1D analytica l (Vs=250+30z0.5)3D num erica l s im (G BP/G BB)26.09.1997 h9.40 (G BP/G BB)


Conclusions Conclusions

- Thanks to the quality of the geophysical and geotechnical data available it is - Thanks to the quality of the geophysical and geotechnical data available it is possible to constrain a 3D model of the Gubbio alluvial basinpossible to constrain a 3D model of the Gubbio alluvial basin

-Even if the 3D model here presented should be considered as a preliminary Even if the 3D model here presented should be considered as a preliminary attempt, the agreement between the records of the sequence of the 1997 attempt, the agreement between the records of the sequence of the 1997 Umbria-Marche earthquake and the 3D numerical simulation seems to Umbria-Marche earthquake and the 3D numerical simulation seems to capture important features like the maximum amplification, the duration and capture important features like the maximum amplification, the duration and the frequency content of the signals.the frequency content of the signals.

- - distinctive features observed at GBP with remarkable ground motion distinctive features observed at GBP with remarkable ground motion amplification at long period cannot be predicted by simple numerical amplification at long period cannot be predicted by simple numerical approaches based on 1D wave propagation in layered media, while 3D approaches based on 1D wave propagation in layered media, while 3D numerical simulations turn out to be capable of reproducing the large numerical simulations turn out to be capable of reproducing the large amplification levels at long periods (T>~1 s). This clearly points out the need amplification levels at long periods (T>~1 s). This clearly points out the need of advanced numerical analyses of wave propagation to reproduce such of advanced numerical analyses of wave propagation to reproduce such effects with a sufficient degree of reliabilityeffects with a sufficient degree of reliability

Agreement between DPC – INGV 2007-09 Project S4 – Italian Strong Motion Data Base Coordinators:...

Documents

Transcript of Agreement between DPC – INGV 2007-09 Project S4 – Italian Strong Motion Data Base Coordinators:...