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34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Towards a new generation of seismic hazard maps for the volcanic region of
Mt. Etna
R. Azzaro1, G. Barberi1, O. Cocina1,S. D'Amico1, R. Gee2, H. Langer1, S. Lombardo3, M.G. Ordaz-Schroeder4, B. Pace5, M. Pagani6, F. Panzera3, L. Peruzza2, A. Saraò 2, G. Tusa1, T. Tuvè1
1INGV Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Catania2OGS Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Sgonico Trieste3Dip. di Scienze Biologiche, Geologiche e Ambientali, Università di Catania4UNAM Universitad Nacional Autonome de México, Mexico City, Mexico5DiSPUTer, Università degli Studi “G. d’Annunzio” Chieti-Pescara, Chieti6GEM Foundation Pavia, Italy
Project INGV-DPC V3 2012-2015
Focus on the use of the OpenQuake-engine
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Outline
• Overview of INGV-DPC V3 Project
• Implementation of Etna PSHA model – OpenQuake-engine
– Adding new GMPE
– Topography modifications
– Model construction
• Results
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Project INGV-DPC V3 (2012-2015)
Work Package 1: Earthquake Rupture Forecast (ERF)– Occurrence probability (poisson and time-dependant) of earthquakes
using historical (Azzaro et al., 2012b; 2013) and geological approaches (Azzaro et al., 2014; Pace et al., 2015)
Work Package 2: Ground Motion Prediction Equation (GMPE) and site response– Attenuation relationships (PGA) for Etna region (Tusa and Langer, 2015)– Site amplification factors obtained by instrumental measurements
(Panzera and Lombardo, 2015)
Work Package 3: Probabilistic Seismic Hazard Maps (PSHA)– New functionalities in PSHA software: CRISIS (Ordaz et al., 2013)
OpenQuake-engine (Pagani et al., 2014)– Model construction (3 alternative branches)– Preliminary analysis of results
Task 1 - Seismic hazard assessment in the eastern flank of Mt. Etna, due to local volcano-tectonic earthquakes
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Project INGV-DPC V3 (2012-2015)
Work Package 1: Earthquake Rupture Forecast (ERF)– Occurrence probability (poisson and time-dependant) of earthquakes
using historical (Azzaro et al., 2012b; 2013) and geological approaches (Azzaro et al., 2014; Pace et al., 2015)
Work Package 2: Ground Motion Prediction Equation (GMPE) and site response– Attenuation relationships (PGA) for Etna region (Tusa and Langer, 2015)– Site amplification factors obtained by instrumental measurements
(Panzera and Lombardo, 2015)
Work Package 3: Probabilistic Seismic Hazard Maps (PSHA)– New functionalities in PSHA software: CRISIS (Ordaz et al., 2013)
OpenQuake-engine (Pagani et al., 2014)– Model construction (3 alternative branches)– Preliminary analysis of results
Task 1 - Seismic hazard assessment in the eastern flank of Mt. Etna, due to local volcano-tectonic earthquakes
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
The OpenQuake-engine: Main Features
Seismic hazard and risk calculation engineSoftware for the calculation of seismic hazard and risk; implemented in Python
Open and TransparentPublic repository: http://github.com/gem can see what the software is doing
Developed by the GEM Foundation Creating global models and tools for seismic hazard and risk assessment
Tested and Documented User manual, hazard science manual, testing procedures manual
Hazard Risk
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Implementing the Etna PSHA model: GMPE
Volcanic areas exhibit specific seismic propagation properties
Distance (km)
PG
A (
cm/s
2)
• New GMPE calibrated for Mt Etna: Tusa and Langer, 2015
• Instrumental Catalogue (2004-2014) INGV-OE
• 3.0 <ML <4.8
• Distances <100km
• PGA, PGV, SA
0,01
0,1
1
10
100
1000
0,1 1 10 100 1000
M=4 TL15-HypTL13-EpiITA10 for soil B
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Implementing the Etna PSHA model: GMPE
https://github.com/gem/oq-hazardlib/tree/master/openquake/hazardlib/gsim
• Added to OpenQuake repository (70+ GMPEs)
• Tested against expected values
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Implementing the Etna PSHA model: Topography
• Use Digital Elevation Model (DEM) to model topography
• Elevation increases sharply moving from the coast (sea level) to the Central Craters (3000+ meters), in just 20 km
• Earthquakes are shallow , mostly upper 5km, and some above sea level (Alparone et. al, 2015)
Topography is always neglected in PSHA computations, but relevant at Etna
Catania
Elevation 3000+m
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Implementing the Etna PSHA model: Topography
Changes In OpenQuake:
• Sites are now defined in terms of 3D location instead of 2D (i.e. can be above sea level)
• Source hypocenters and ruptures extent can now be above sea level
The inclusion of topography influences the source-to-site distances (not topographic site effects)
Sea level
Site (x, y, z)
Site (x, y, z=0)
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Influence of Topography: Sensitivity Test
• Synthetic example of the contribution of the DEM (All faults assigned occurrence rate= 0.01, M4.0)
• Decrease in GM due to increase in source-to-site distance, accounted for by the GMPE (version Rhypo)
PoE: 10% 50 years
GMPE: TL15 SA(0.2)Site class A
DEM PSHA Without DEM PSHA With DEM
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Influence of Topography: Sensitivity Test
• Synthetic example of the contribution of the DEM (All faults assigned occurrence rate= 0.01, M4.0)
• Decrease in GM due to increase in source-to-site distance, accounted for by the GMPE (version Rhypo)
PoE: 10% 50 years
GMPE: TL15 SA(0.2)Site class A
DEM PSHA Without DEM PSHA With DEM
DifferenceMaximum: ~20% decrease
Zafferana: ~10% decrease
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
The Source Model
BRANCH 1
• Background seismicity: Area sources as Branch 1 until M=4.5• Major seismicity: Fault geometry and characteristic earthquake
model based on two approaches:
BRANCH 2
• Background seismicity: distributed seismicity with variable depths, modeled until M=4.5
• Major seismicity: Fault geometry and characteristic earthquake model based on two approaches:
BRANCH 3
POISSON
TIME DEP.
POISSON
TIME DEP.
POISSON
Historical
(Mmax=5.2)
Geological
(Mmax=5.6)
• Area Sources modeled as G-R calibrated on instrumental (a,b-values) and historical data (Mmax=4.7); effectve depth estimated by strain release (Approach similar to MPS04)
Historical
(Mmax=5.2)
Geological
(Mmax=5.6)
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Implementing the Etna PSHA model: Sources
Area Sources(branch 1,2)
Faults(branch 2,3)
Gridded Seismicity(branch 3)
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Implementing the Etna PSHA model: Sources
floating ruptures
point sources with spatially variable properties
grid of point sources with occurrence rate uniformly distributed across source
fault surface = mesh of points defined by top and bottom edges; allows variation in dip and width
Area Sources(branch 1,2)
Faults(branch 2,3)
Gridded Seismicity(branch 3)
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
BRANCH 1
BRANCH 2 BPTBRANCH 2 Poisson BRANCH 3 Poisson BRANCH 3 BPT
Geological Approach
Historical Approach
GMPE: TL15 PGASite class AResults: T=5 years
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
BRANCH 1
BRANCH 2 BPTBRANCH 2 Poisson BRANCH 3 Poisson BRANCH 3 BPT
Geological Approach
Historical Approach
GMPE: TL15 PGASite class AResults: T=30 years
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
GMPE: TL15 PGASite class ALogic Tree
T=30 years
All 3 branches weighted equally:
Branch 1 (0.33)
Branch 2 (0.33)
Branch 3 (0.33)
Historical, poisson (0.25)Historical, BPT (0.25)Geological, poisson (0.25)Geological, BPT (0.25)Historical, poisson (0.25)Historical, BPT (0.25)Geological, poisson (0.25)Geological, BPT (0.25)
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
GMPE: TL15 PGASite class ALogic Tree
T=30 years
All 3 branches weighted equally:
Branch 1 (0.33)
Branch 2 (0.33)
Branch 3 (0.33)
Historical, poisson (0.25)Historical, BPT (0.25)Geological, poisson (0.25)Geological, BPT (0.25)Historical, poisson (0.25)Historical, BPT (0.25)Geological, poisson (0.25)Geological, BPT (0.25)
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
GMPE: TL15 PGASite class ALogic Tree Branch 3
T=5 years T=30 years
Models weighted equally
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015
Conclusions
• Performed PSHA in the Etna region due to local volcano-tectonic earthquakes
– V3 Project utilizes a large dataset of input parameters: geological data, instrumental seismicity, GMPE, (site response implemented in CRISIS)
• Developed new capabilities in PSHA software to account for topography and a new GMPE for volcanic regions
• PGA calculated from geological approach (~0.3g for T=30) is higher compared to historical approach (~0.1g for T=30). MPS04 results are in between.
• First example of seismic hazard maps for Mt Etna useful for seismic mitigation in short to mid-term exposure periods (5, 30 years)
34° Convegno , Gruppo Nazionale per la Geofisica della Terra Solida Trieste 17-19, 2015