Antonio Emolo with Vincenzo Convertito and Aldo Zollo

Prague, March 18, 2005Prague, March 18, 2005 Antonio EmoloAntonio Emolo 11

Seismic Hazard AssessmentSeismic Hazard Assessmentfor a Characteristic Earthquake Scenario:for a Characteristic Earthquake Scenario:Integrating Probabilistic and Deterministic Integrating Probabilistic and Deterministic

ApproachesApproaches

Antonio EmoloAntonio Emolowith Vincenzo Convertito and Aldo Zollo

Prague, March 18, 2005


Table of ContentsTable of Contents

• Brief review of Probabilistic Seismic Hazard Analysis Brief review of Probabilistic Seismic Hazard Analysis techniquetechnique

• Integration of Probabilistic and Deterministic Integration of Probabilistic and Deterministic approaches to seismic hazardapproaches to seismic hazard

• Application to the September 26, 1997, 9:40GMT, Application to the September 26, 1997, 9:40GMT, Colfiorito (Central Italy) earthquake, MColfiorito (Central Italy) earthquake, MWW=6.0=6.0


PSHA basic steps (Cornell, 1968)PSHA basic steps (Cornell, 1968)

• SeismogeneticSeismogenetic zone zone

• Seismicity recurrence characteristicsSeismicity recurrence characteristics

• Earthquakes effectsEarthquakes effects

• Hazard evaluationHazard evaluation


In our proposed approachIn our proposed approach

we aim atwe aim at

applying the classical PSHA technique to the applying the classical PSHA technique to the single fault casesingle fault case

by integratingby integrating

PSHA with a statistical - deterministic technique for predicting strong ground motion parameters associated with a characteristic earthquake occurring on a given causative fault


For doing this we needFor doing this we need

• the magnitude distributionthe magnitude distribution

• the seismicity rate for a single fault/magnitude the seismicity rate for a single fault/magnitude earthquakeearthquake

• a (deterministic) tool for evaluating earthquake a (deterministic) tool for evaluating earthquake effectseffects

• a statistical description of (deterministic) a statistical description of (deterministic) earthquake effectsearthquake effects


The Colfiorito earthquake: source The Colfiorito earthquake: source parametersparameters

fault length, Lfault length, L 12 km12 km

fault width, Wfault width, W 7.5 km7.5 km

bottom depth, zbottom depth, zmaxmax 8.0 km8.0 km

strike, strike, ΦΦ 152°152°

dip, dip, δδ 38°38°

slip, slip, λλ -118°-118°

seismic moment, Mseismic moment, M00 1.01.0×10×101818 Nm Nm

moment magnitude, moment magnitude, MMWW

6.06.0

rupture velocity, vrupture velocity, vRR 2.7 km/s2.7 km/s

After Zollo After Zollo et al.et al., 1999, 1999


The Colfiorito earthquake: simulation factsThe Colfiorito earthquake: simulation facts

• number of simulated rupture processes: 150number of simulated rupture processes: 150

• investigated area: 60investigated area: 60×60 km×60 km22

• number of receivers: 64number of receivers: 64

• spacing between adjacent receivers: 5 kmspacing between adjacent receivers: 5 km


The Colfiorito earthquake: simulation resultsThe Colfiorito earthquake: simulation results


The Colfiorito earthquake: simulation resultsThe Colfiorito earthquake: simulation results

Simulated PGAs vs. minimum distance from the surface fault projection are compared with the Sabetta and Pugliese (1987) attenuation curve for a magnitude 6.0 earthquake


from simulation studyboth characteristic

and exponential models

b-value = 0.8475

we do not need!average seismicity rates:

c=0.00204 yrs-1

exp=0.155 yrs-1

Coming back to the hazard integralComing back to the hazard integral

R M

aMR drdmrmArmApmfrfAAE ,),()()()( 00


Hazard mapsHazard maps

in terms of PGA values having a fixed frequency of in terms of PGA values having a fixed frequency of exceedance corresponding to three return periods:exceedance corresponding to three return periods:

TT11=1,000 yrs=1,000 yrs

TT22=5,000 yrs=5,000 yrs

TT33=10,000 yrs=10,000 yrs


Hazard maps – T=1,000 yrsHazard maps – T=1,000 yrs






Hazard curves for selected sitesHazard curves for selected sites

characteristic earthquake model


Hazard curves for selected sitesHazard curves for selected sites

exponential magnitude distribution


I nearly forgot: are PGAs log-normally I nearly forgot: are PGAs log-normally distributed?distributed?


In conclusionIn conclusion

• we account for time variable (return period, time of we account for time variable (return period, time of interest, …) in deterministic scenarios;interest, …) in deterministic scenarios;

• we account for source parameters (geometry, we account for source parameters (geometry, radiation pattern, directivity, …) in PSHA approach;radiation pattern, directivity, …) in PSHA approach;

• due to the waveforms availability, we can consider due to the waveforms availability, we can consider any ground motion parameter both in time and in any ground motion parameter both in time and in frequency domainsfrequency domains

• we can easily include site effects in the modeling if we can easily include site effects in the modeling if specific transfer function was availablespecific transfer function was available


Before ending…Before ending…

I would like to thankI would like to thank

the MAGMA center and all the peoplethe MAGMA center and all the people

who gave me the opportunity to spendwho gave me the opportunity to spend

a very useful period at the Charles Universitya very useful period at the Charles University


And finally,And finally,

that’s allthat’s all

Thank you very much for your kindly attentionThank you very much for your kindly attention


Seismogenetic zoneSeismogenetic zone

ZS9 – Meletti and Valensise, 2004ZS9 – Meletti and Valensise, 2004

• Each zone has Each zone has uniformuniform earthquake potentialearthquake potential

• The configuration could beThe configuration could be

pointpoint

lineline

areaarea

volumevolume


Seismicity recurrence characteristicsSeismicity recurrence characteristics

Recurrence relationship (e.g., Gutenberg and Richter, 1944)Recurrence relationship (e.g., Gutenberg and Richter, 1944)

MbaMNLog )(


Earthquakes effectsEarthquakes effects

The ground motion level at a given The ground motion level at a given site and for a selected range of site and for a selected range of magnitude is generally evaluated magnitude is generally evaluated through empirical attenuation through empirical attenuation relationships (e.g., Joyner and Boore, relationships (e.g., Joyner and Boore, 1981; Sabetta and Pugliese, 1986; 1981; Sabetta and Pugliese, 1986; …)…)


probability of exceedance of a threshold value A0

for given distance r and magnitude m

probability of occurrence of a given earthquake

having magnitude in the range (m, m+dm)

probability of occurrence of a given earthquake

at a distance in the range (r, r+dr)

seismic activity rate

(from catalogues)

Hazard evaluationHazard evaluation

It consists in the computation of the probability of It consists in the computation of the probability of exceedance of different levels of selected ground motion exceedance of different levels of selected ground motion parameter A thorough the evaluation of the hazard integralparameter A thorough the evaluation of the hazard integral

frequency of exceedance

of a given threshold A0

R M

aMRii drdmrmArmApmfrfAAE ,),()()()( 00

For a given time of interest t, the probability of exceedance can be computed as

tAAE ietAAP )(0

01);(






The characteristic earthquake modelThe characteristic earthquake model

is based on the hypothesis that individual fault tend to is based on the hypothesis that individual fault tend to generate similar size (i.e., “characteristic”) earthquakesgenerate similar size (i.e., “characteristic”) earthquakes

Characteristic earthquakes occur on a fault not at the Characteristic earthquakes occur on a fault not at the exclusion of all other magnitude events, but with a exclusion of all other magnitude events, but with a frequency distribution which differs from the exponential frequency distribution which differs from the exponential oneone

Several paleoseismic evidences in different tectonic Several paleoseismic evidences in different tectonic environments support the idea that geometry, environments support the idea that geometry, mechanism and average slip per event could be mechanism and average slip per event could be considered constant over a large time scaleconsidered constant over a large time scale


The magnitude distributionThe magnitude distribution


The seismicity rateThe seismicity rate

It can be evaluated both for the exponential model and for the characteristic earthquake model following the approach proposed by Youngs and Coppersmith (1985)


Earthquake effectsEarthquake effects

Seismic radiation emitted by an extended rupturing fault is computed by solving the representation integral in high frequency approximation (Aki and Richards, 1980)

d)Tt;(u)0,t;,r(G)t;r(u cFFcc

The HF Green function is computed in a flat-layered velocity medium

The slip function is approximated by a ramp

A k-squared final slip distribution on the fault is assumed (Herrero and Bernard, 1996)


Statistical description of earthquake effectsStatistical description of earthquake effectsIn the frame of a scenario simulation associated with a characteristic earthquake, some “low frequency” source characteristics can be considered constant over a large time scale in successive rupture episodes.

However the single rupture process does not repeat the same style of nucleation, propagation and stopping even if it keeps the mean characteristics.

With this in mind, we simulated a large number of rupture processes occurring on the same causative fault considering different positions of nucleation point and different final slip distributions.

Synthetic seismograms are computed for each considered rupture process and ground motion parameters of interest are then evaluated through a statistical analysis


Statistical description of earthquake effectsStatistical description of earthquake effects

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Antonio Emolo with Vincenzo Convertito and Aldo Zollo