Towards a new generation of seismic hazard maps for the ... · Project INGV-DPC V3 2012-2015 Focus on the use of the OpenQuake-engine. ... Ground Motion Prediction Equation (GMPE)

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


Outline

• Overview of INGV-DPC V3 Project

• Implementation of Etna PSHA model – OpenQuake-engine

– Adding new GMPE

– Topography modifications

– Model construction

• Results


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


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


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

http://github.com/gem


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


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

https://github.com/gem/oq-hazardlib/tree/master/openquake/hazardlib/gsim


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


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)


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


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


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)


Implementing the Etna PSHA model: Sources

Area Sources(branch 1,2)

Faults(branch 2,3)

Gridded Seismicity(branch 3)


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)


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


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


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)


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)


GMPE: TL15 PGASite class ALogic Tree Branch 3

T=5 years T=30 years

Models weighted equally


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)


Documents

Towards a new generation of seismic hazard maps for the ... · Project INGV-DPC V3 2012-2015 Focus on the use of the OpenQuake-engine. ... Ground Motion Prediction Equation (GMPE)