site effects modeling by hybrid technique: the case study of sofia, bulgaria
DESCRIPTION
SITE EFFECTS MODELING BY HYBRID TECHNIQUE: THE CASE STUDY OF SOFIA, BULGARIA. IVANKA PASKALEVA PETIA DINEVA CRISTINA LA MURA GIULIANO F. PANZA. BULGARIAN ACADEMY OF SCIENCE. CENTRAL LABORATORY FOR SEISMIC MECHANICS AND EARTHQUAKE ENGINEERING BULGARIAN ACADEMY OF SCIENCE. - PowerPoint PPT PresentationTRANSCRIPT
SITE EFFECTS MODELING BY SITE EFFECTS MODELING BY HYBRID TECHNIQUE: HYBRID TECHNIQUE:
THE CASE STUDY OF SOFIA, BULGARIATHE CASE STUDY OF SOFIA, BULGARIA
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
UNIVERSITA’ DEGLI STUDI DI TRIESTEDIPARTIMENTO DI SCIENZE DELLA TERRA
BULGARIAN ACADEMY OF SCIENCE CENTRAL LABORATORY FOR SEISMIC MECHANICS AND EARTHQUAKE ENGINEERING
BULGARIAN ACADEMY OF SCIENCE
IVANKA PASKALEVA
PETIA DINEVA
CRISTINA LA MURA
GIULIANO F. PANZA
Main Topics Main Topics
HYBRID TOOL: a brief introduction; the viscoelastic isomorphism of Bardet
model: advantages and implementation in the hybrid technique;
simulation study: effect of the Bardet model, application to Sofia, Bulgaria;
conclusions
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
Review….Hybrid ToolsReview….Hybrid ToolsSite Effect: difference in earthquake ground motion between two nearby sites!
Lateral heterogeneities may give rise to complex wave patterns, so high performance methods have to be developed for simulating seismic wave propagation in complex media.
27o CONVEGNO GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
In hybrid computational schemes the numerical method is applied in the laterally inhomogeneous part of the medium,whereasthe laterally homogeneous part is treated with analytical method.
Combination of MSM and BIEM is the hybrid technique
used in this work.
Review…..MSM - BIEM…Review…..MSM - BIEM…
• lateral inhomogeneity • surface topography
• water saturation in soils • seismic source properties
MSM is applied for numerical simulation from the sourceposition to the local region of interest, while the BIEM isused inside the local multilayered geological region.
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
It has the potential to investigate the combined effects of different physical phenomena, like
VISCOELASTIC ISOMORPHISM…VISCOELASTIC ISOMORPHISM…In order to describe the poroelastic properties of the layers, the viscoelastic isomorphism of Bardet is used.
A two phase solid - fluid system (saturated system) is used its main components are:
• dry rock (dry soil)
• solid grain
• fluid
n = Vp/V is the porosity V is the total volume of the solidVp is the pore volume
Kg g Kf f Kdry dry =(1 - n)g
bulk modulus and density
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
VISCOELASTIC ISOMORPHISM…VISCOELASTIC ISOMORPHISM…Elastic properties of the saturated system
sat = dry + nf = (1-n)g + n fdensity
shear modulus = dry = sat =
governing equation of motion in the frequency domain are
describing the wave propagation in fluid saturated soils Biot (1956)
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
VISCOELASTIC ISOMORPHISM…VISCOELASTIC ISOMORPHISM…
Q and R are the Biot’s elastic constants for saturated soils
….BIEM has a limited usage in dynamic poroelasticity dueto the multiphase nature of the model…… an equivalent viscoelastic model is proposed (Bardet 1992)
saturated soil is considered as a viscoelastic material
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
VISCOELASTIC ISOMORPHISM…VISCOELASTIC ISOMORPHISM…Bardet introduced the viscoelastic isomorphism by equating
Wave numbers in Biot’sporoelastic model
Wave numbers inviscoelastic model
from this operation an equivalence between the poroelastic material and the linear Kelvin - Voigt viscoelastic material
is established
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
so a two phase poroelastic dynamic behavior is approximated by the dynamic response of one-phase
viscoelastic material
SIMULATION STUDY…..SIMULATION STUDY…..FORMULATION OF THE PROBLEMLet us consider a finite local saturated geological region imbedded in a vertical inhomogeneous half space where a seismic source is buried
all soil layers in Ωo are isotropic, anelastic and homogeneous
the non-parallel layers in Ω are water saturated
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
SIMULATION STUDY…..SIMULATION STUDY…..The main aim is to obtain synthetic seismograms at sites along the free surface of the region Ω.
TWO SUB-PROBLEMS
• external sub-problem: wave propagation from seismic source to the boundary
• internal sub-problem: wave propagation in the finite local geological region Ω
The two problems are combined through the fulfillment of thecompatibility and equilibrium conditions at the boundary
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
SIMULATION STUDY…..SIMULATION STUDY…..
2 and 3 are water saturated, 1 is not saturated, points S’s are the sites where solutions are computed
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
SIMULATION STUDY…..SIMULATION STUDY…..EARTHQUAKE SCENARIO
two earthquake scenarios have been used, they do differ for the value of the magnitude M
strike angle 21o
dip angle 44o
rake angle 309o
source depth 12kmsrc/rec dist 20km
for both
Scenario a) M= 3.7 Scenario b) M= 6.5
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
SIMULATION STUDY…..SIMULATION STUDY…..EFFECT OF THE BARDET MODEL
peaks are shifted to lower frequencies
main peak decreases forsaturated soils
earthquake scenario a)
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
SIMULATION STUDY…..SIMULATION STUDY…..EFFECT OF THE BARDET MODEL
earthquake scenario a)
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
SIMULATION STUDY…..SIMULATION STUDY…..EFFECT OF THE BARDET MODEL
earthquake scenario a)
main peak decreases forsaturated soils
duration of the signal isreduced in saturated soils
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
one station calledREDUTA from theresidential district
it is located in;here there is the Geo Milev Park together with a
medical center, a library and
one of the mostprestigious schools
of Sofia.
CASE STUDY: SOFIACASE STUDY: SOFIA
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
CASE STUDY: SOFIACASE STUDY: SOFIA
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
another calledMLADOST4 for
the same reason as the former;
in this district the Business Park
Sofia has been
constructed and theairport is not so far
CASE STUDY: SOFIACASE STUDY: SOFIAThe parametric study of site effects in two different water
saturated geological profiles, corresponding to twodifferent zones of the city, is made in
terms of acceleration response spectral ratio, i.e.
RSR = RS from signals along the laterally varying section
RS from signals for the bedrock
the single - degree - of - freedom damped oscillator used for the computation of the response spectra is with
5% damping
the earthquake scenario is b), so M = 6.5
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
CASE STUDY: SOFIACASE STUDY: SOFIAREDUTA
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1
Period (sec)
RSR
Site S 1 S2 S4
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1
Period (sec)
RSR
Site S1 S2 S4
dry soil saturated soilhorizontal component
vertical component
0
9
18
27
0 0.2 0.4 0.6 0.8 1
Period (sec)
RSR
Site S1 S2 S4
0
9
18
27
0 0.2 0.4 0.6 0.8 1
Period (sec)
RSR
Site S1 S2 S4 27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
CASE STUDY: SOFIACASE STUDY: SOFIAMLADOST4
dry soil saturated soilhorizontal component
vertical component
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
CASE STUDY: SOFIACASE STUDY: SOFIAdifferent response for different sites: there are site effectsdue to the mixed influence of lateral inhomogeneity andsaturation of soil
there is a shift of the peaks toward the higher periods forsaturated soils the main peaks of saturated soils decreases with respectto dry soilsthe fluid acts as stiffener of the material: the pore pressureinduced by the seismic load resists the compression andstiffens the rockfluid acts as a viscous damping element: a diffusion processdominated by viscous effects
27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY
CONCLUSIONSCONCLUSIONS
The hybrid MSM - BIEM technique, combined with theviscoelastic isomorphism of Bardet, is applied for the
investigation of the site effects phenomena
due to several different physical properties like lateral inhomogeneity and water saturation in soil.
The hybrid technique allows to study simultaneouslythe combined effects, hence a better
estimation of the seismic risk is provided.
The simulation has been performed for the city of Sofia; Soil mechanical properties and geotechnical parameters are those more common in the central part of the city.
THANKS for the ATTENTION!!!27o CONVEGNO NAZIONALE GRUPPO NAZIONALE di GEOFISICA della TERRA SOLIDA October 8, 2008 TRIESTE - ITALY