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Antonio Emolo with Vincenzo Convertito and Aldo Zollo

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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

- 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

- Seismogenetic zone
- Seismicity recurrence characteristics
- Earthquakes effects
- Hazard evaluation

Antonio Emolo

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

- 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

After Zollo et al., 1999

Antonio Emolo

- number of simulated rupture processes: 150
- investigated area: 60×60 km2
- number of receivers: 64
- spacing between adjacent receivers: 5 km

Antonio Emolo

Antonio Emolo

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

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

Antonio Emolo

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

Antonio Emolo

Antonio Emolo

Antonio Emolo

characteristic earthquake model

Antonio Emolo

exponential magnitude distribution

Antonio Emolo

Antonio Emolo

- 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

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

that’s all

Thank you very much for your kindly attention

Antonio Emolo

ZS9 – Meletti and Valensise, 2004

- Each zone has uniform earthquake potential
- The configuration could be
point

line

area

volume

Antonio Emolo

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

Antonio Emolo

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

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

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

Antonio Emolo

Antonio Emolo

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

Antonio Emolo

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

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

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

Antonio Emolo