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Ground motion simulations and site effect estimation for
Istanbul, Turkey
Mathilde Bøttger Sørensen1, Nelson Pulido2, Sylvette Bonnefoy-Claudet3, Kuvvet Atakan1
1Department of Earth Science, University of Bergen, Norway, 2Earthquake Disaster Mitigation Research Center
EDM, NIED, Kobe, Japan, 3LGIT, Université Joseph Fourier, Grenoble, France.
Outline
Introduction
Ground motion simulations
- technique
- results
Site effect studies
- 4 methods
- results
Summary and further studies
Ground motion simulations
• Hybrid method for simulating ground motions due to finite-extent earthquake source in Marmara Sea
• Pulido and Kubo (2004): Deterministic at low frequencies, semi-stochastic at high frequencies
• Simulation on regular grid and on irregular grid of Istanbul Earthquake Rapid Response and Early Warning System stations
Ground motion simulation technique
• Low frequency: Deterministic wave propagation from an asperity model in a flat layered velocity structure (Discrete Wave Number Method, Bouchon 1981)
• High Frequency: Semi-Stochastic Simulation based on an asperity model. The model combines the stochastic methodology of Boore (1986) with the empirical Green’s function method of Irikura (1986), and a high frequency radiation pattern model (Pulido et. al 2002).
Source parametersTotal seismic moment M0 = 2.0·1020 Nm
Asperity area Sa/S = 0.22
Average stress drop 5 MPa
Asperity stress drop 10 MPa
Rise time Random, average 3.0 s
Rupture velocity Random between 2.8 – 3.2 km/s
fmax 10 Hz
Q 100 · f1.5
Istanbul Earthquake Rapid Response and Early Warning
System
Kandilli Observatory and Earthquake Research InstituteBogazici University, Istanbul
Rapid Response system
• 100 accelerometer stations• When triggered, station produces spectral
acceleration at a number of frequencies, 12 Hz filtered PGA and PGV
• Data sent pr SMS every 20 s• Main data center produces shake, damage
and casualty maps, which are available to the end-users within 5 min
Istanbul Earthquake Rapid Response and Early Warning
System
Kandilli Observatory and Earthquake Research InstituteBogazici University, Istanbul
Early Warning system
• 10 accelerometer stations close to the Marmara fault
• When several stations triggers an alarm is declared
• Alarm level is sent to critical facilities, which can then shut down before the earthquake strikes
Use of RR/EW simulation results
• Calibration of Rapid Response system parameters• Calibration of Early Warning system parameters • Realistic scenario input for producing shake,
damage and casualty maps• Comparison to recorded earthquakes
1D modeling site
Representative of alluvial site:
5 m Alluvium
8 m Bakirköy formation
80 m Güngören formation
Bedrock
1D modeling, sources
• Point forces with delta-like source time function at 4 and 8 m depth
• Distributed randomly in space, time, direction and amplitude
• Green’s functions are calculated using Hisada (1994)
Summary
• Agreement between recorded and modelled microtremor H/V results
• Peaks at 1Hz and 3-6 Hz for alluvial site
• Peak at 1 Hz for Bakirköy formation
• SSR indicates high amplification levels, up to a factor of 10