Interreg IIIB: SISMOVALP

WP6: Generic alpine ground motion

A 2D Simulation benchmark for the A 2D Simulation benchmark for the study of the seismic response of study of the seismic response of

alpine valleyalpine valley

Sismovalp Meeting, Martigny, Switzerland, October 2-4

Participants to the 2D Benchmark

# Partner Participants Model Data 2D Methods 3D Methods

1 UJF-LGIT (Grenoble)

Chaljub Grenoble Valley 2D Spectral Element 3D Spectral Element

2 POLIMI (Milano) Paolucci Val D’Adige (Trento)

P-SV: Spectral Element Method

3D Spectral Element

3 UDST-DST(Trieste)

Suhadolc, Vaccari, Panza, Costa

Val Resia and Gemona

SH + P-SV: Hybrid FD – Modal Summation

4 INOGS(Trieste/Udine)

Priolo, Laurenzano

Tagliamento River High Valley (Tolmezzo)

SH + P-SV: Chebyshev Spectral Element

3D Pseudo-Spectral Staggered Fourier

5 ETH (Zurich) Faeh, Alvarez-Rubio

Valais Valley P-SV: Direct Boundary Element

3D Direct Boundary Element 3D Finite Difference

6 UNITN (Trento) Kaser P-SV: ADER-DG (no attenuation)

SISMOVALP PROJECT – 3nd annual meeting, Milano 15-16 September 2005

Geometry of the valley

W = 4050 mH = 450 mShape ratio: H/(0.5*W)= 0.22

Model 0 (M0)  

Stratigraphic layout Units H (m)

VS

(m/s)

Vp (m/s)

VP/VS (kg/m3)

QS Qp

Recent Deposits Sandy Gravel 0-15 250 500 2.5 1600 20 40

Fine Deposits Silt & clay 15-30 350 700 2.5 1700 20 40

Fluvial & Lacustrine Deposits

Silt, clay and gravel

30-100 450 900 2.5 1800 30 50

Fluvial & Lacustrine Deposits

Silt, clay and gravel

100-350 600 1200 2.5 1900 30 50

Moraine = 350-450 800 1600 2 2000 50 100

Bedrock Limestone 450- 2800 5200 1.85 2500 200 400

Model 1 (M1)  

Stratigraphic layout Units H (m)

VS

(m/s)

Vp (m/s)

VP/VS (kg/m3)

QS Qp

Recent Deposits Sandy Gravel 0-15 250 500 2.5 1600 20 40

Fine Deposits Saturated Silt & clay

15-30 350 1650 2.5 1700 20 40

Fluvial & Lacustrine Deposits

Silt, clay and gravel

30-100 450 900 2.5 1800 30 50

Fluvial & Lacustrine Deposits

Silt, clay and gravel

100-350 600 1200 2.5 1900 30 50

Moraine = 350-450 800 1600 2 2000 50 100

Bedrock Limestone 450- 2800 5200 1.85 2500 200 400

Model 2 (M2)  

Stratigraphic layout Units H (m)

VS

(m/s)

Vp (m/s)

VP/VS (kg/m3)

QS Qp

Fluvial & Lacustrine Deposits

Silt, clay and gravel

0-450 260 + 30 z1/2

525 + 60 z1/2

2 1600 + 59.5 z1/3

20 + 1.64 z1/2

40 + 3.3 z1/2

BedrockBedrock Limestone 450- 2800 5200 1.85 2500 200 400

2D benchmark

Simul. #

Model Incidence Angle

UJF POLIMI UNITS OGS ETH UNITN Simul. #

P-SV P-SV P-SVSH

P-SVSH

P-SV P-SV

1 M0 0 1

2 M0 -30 2

3 M0 30 3

4 M1 0 4

5 M1 -30 5

6 M1 30 6

7 M2 0 7

8 M2 -30 8

9 M2 30 9

Synthetic seismograms

Synthetic seismogramsComputed at the two reference receivers for simulation 2

They represent the input motion, to some extent

Left side Right side

Response Spectrum Spectra Ratios (RSSR)Angle=0

LGIT POLIMI

INOGS ETH

UNITN

Response Spectrum Spectra Ratios (RSSR)Angle=30

LGIT POLIMI

INOGS ETH

UNITS UNITN

Response Spectrum Spectral Ratios (RSSR)

Different models and incidence angles

Response Spectrum Spectral Ratios (RSSR)

Different models and incidence angles

Different models and incidence angles

Response Spectrum Spectral Ratios (RSSR)

Variation (%) due to incidence angle

Response Spectrum Spectral Ratios (RSSR)

Comparison of the methods for simulations 1 and 2

Response Spectrum Spectral Ratios (RSSR)

Comparison of the methods for simulations 2 and 3

Response Spectrum Spectral Ratios (RSSR)

1D transfer function(Wavenumber Integration Method, Herrmann, 2004)

Angle=0

Angle=-30

Source time function

LGIT POLIMI

INOGS ETH

UNITS UNITN

2D transfer functions

No attenuation

LGIT POLIMI

INOGS ETH

UNITN

2D vs. 1D transfer functions

1 2 3

1 2 3

Simulation 1

Simulation 2

Simulation 3

2D transfer functions

1 2 3

1 2 3LGIT

POLIMI

INOGS

ETH

Aggravation Factor

No attenuationAggravation Factor = SA2D / SA1D

u1D = STF * TF1D

LGIT POLIMI

INOGS ETH

UNITN

Aggravation Factor

Aggravation Factor

2D Benchmark

Status

• All synthetics have been computed. • Results have been analysed;• Conclusions are presently under discussion;• A scientific report will be delivered within the final report;• A paper will be prepared.

2D Benchmark – Preliminary conclusions

Evaluated features

Importance

RSSR AF

Vs fine details Low Low

Incidence angle Medium High

Numerical method Low Medium(???)

Spectral frequency Low MediumIn this benchmark, both valley shape and 1D reference layering were held fixed.

The valley shape-ratio is mainly 1D.

WP6 – Priority features

Element Importance

Shape (1D, 2D, 3D) and depth High

Main impedance contrast

(e.g. bedrock/sediments)

High

Vs average profile Medium-high

Shallow Vs (30-50 m) Medium-high

Numerical method Medium(-low)

Details of the valley shape Medium-low

Detailed Vs profile Low

Spectral variability of the amplification ????

Priority list of elements which must be investigated in order to assess

the seismic response of an alpine valley:

WP6 – Priority features

Element Importance How to assess them?

Shape (1D, 2D, 3D) and depth High ?

Main impedance contrast

(e.g. bedrock/sediments)

High ?

Vs average profile Medium-high ?

Shallow Vs (30-50 m) Medium-high ?

Numerical method Medium(-low) ?

Details of the valley shape Medium-low ?

Detailed Vs profile Low ?

Spectral variability of the amplification ???? ?

Priority list of elements which must be investigated in order to assess

the seismic response of an alpine valley: