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Seismic Hazard Assessment for a Characteristic Earthquake Scenario: Integrating Probabilistic and Deterministic Approaches. Antonio Emolo with Vincenzo Convertito and Aldo Zollo. Prague, March 18, 2005. Table of Contents. Brief review of Probabilistic Seismic Hazard Analysis technique

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

Antonio Emolo

with Vincenzo Convertito and Aldo Zollo

Prague, March 18, 2005

Antonio Emolo

table of contents
Table of Contents
  • Brief review of Probabilistic Seismic Hazard Analysis technique
  • Integration of Probabilistic and Deterministic approaches to seismic hazard
  • Application to the September 26, 1997, 9:40GMT, Colfiorito (Central Italy) earthquake, MW=6.0

Antonio Emolo

psha basic steps cornell 1968
PSHA basic steps (Cornell, 1968)
  • Seismogenetic zone
  • Seismicity recurrence characteristics
  • Earthquakes effects
  • Hazard evaluation

Antonio Emolo

in our proposed approach
In our proposed approach

we aim at

applying the classical PSHA technique to the single fault case

by integrating

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

Antonio Emolo

for doing this we need
For doing this we need
  • the magnitude distribution
  • the seismicity rate for a single fault/magnitude earthquake
  • a (deterministic) tool for evaluating earthquake effects
  • a statistical description of (deterministic) earthquake effects

Antonio Emolo

the colfiorito earthquake source parameters
The Colfiorito earthquake: source parameters

After Zollo et al., 1999

Antonio Emolo

the colfiorito earthquake simulation facts
The Colfiorito earthquake: simulation facts
  • number of simulated rupture processes: 150
  • investigated area: 60×60 km2
  • number of receivers: 64
  • spacing between adjacent receivers: 5 km

Antonio Emolo

the colfiorito earthquake simulation results1
The 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

Antonio Emolo

coming back to the hazard integral

average seismicity rates:

c=0.00204 yrs-1

exp=0.155 yrs-1

from simulation study

we do not need!

both characteristic

and exponential models

b-value = 0.8475

Coming back to the hazard integral

Antonio Emolo

hazard maps
Hazard maps

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

T1=1,000 yrs

T2=5,000 yrs

T3=10,000 yrs

Antonio Emolo

hazard curves for selected sites
Hazard curves for selected sites

characteristic earthquake model

Antonio Emolo

hazard curves for selected sites1
Hazard curves for selected sites

exponential magnitude distribution

Antonio Emolo

in conclusion
In conclusion
  • we account for time variable (return period, time of interest, …) in deterministic scenarios;
  • we account for source parameters (geometry, radiation pattern, directivity, …) in PSHA approach;
  • due to the waveforms availability, we can consider any ground motion parameter both in time and in frequency domains
  • we can easily include site effects in the modeling if specific transfer function was available

Antonio Emolo

before ending
Before ending…

I would like to thank

the MAGMA center and all the people

who gave me the opportunity to spend

a very useful period at the Charles University

Antonio Emolo

and finally
And finally,

that’s all

Thank you very much for your kindly attention

Antonio Emolo

seismogenetic zone

ZS9 – Meletti and Valensise, 2004

Seismogenetic zone
  • Each zone has uniform earthquake potential
  • The configuration could be





Antonio Emolo

seismicity recurrence characteristics
Seismicity recurrence characteristics

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

Antonio Emolo

earthquakes effects
Earthquakes effects

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

Antonio Emolo

hazard evaluation

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

frequency of exceedance

of a given threshold A0

seismic activity rate

(from catalogues)

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)

probability of exceedance of a threshold value A0

for given distance r and magnitude m

Hazard evaluation

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

Antonio Emolo

hazard evaluation1
Hazard evaluation

Antonio Emolo

hazard evaluation2
Hazard evaluation

Antonio Emolo

the characteristic earthquake model
The characteristic earthquake model

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

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

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

Antonio Emolo

the seismicity rate
The 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)

Antonio Emolo

earthquake effects
Earthquake effects

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

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)

Antonio Emolo

statistical description of earthquake effects
Statistical description of earthquake effects

In 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

Antonio Emolo