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

North Anatolian Fault Zone

Westward migration of earthquakes on the NAF

after Barka et. al. (2002)

Coulomb Failure Stress Change after the 1999 Izmit earthquake

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 evaluation from asperity model

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).

Tectonic Setting Marmara Sea Region

Okay et. al 2000

Scenario earthquake

Active tectonic map of the Marmara Sea (Okay et. al 2000)

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

Velocity model

PGV results

PGA results

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

PGV

PGA

Waveform exampleAvcilar district

Geology of Istanbul

Map from Istanbul Metropolitan Municipality web pages, www.ibb.gov.tr

Geology of Istanbul

Map from Istanbul Metropolitan Municipality web pages, www.ibb.gov.tr

Ataköy area, geology

Ataköy

From I.T.Ü. Gelistirme vakfi iktisadi isletmesi

Ataköy area, accessibility

3 approaches

• H/V spectral ratio

• Standard spectral ratio

• 1D modelling

H/V spectral ratio

Noise recording

Site A019

H/V results, Alluvium

H/V results, Bakirköy formation

Standard spectral ratio

Event locations

Results, SSRall events

Event locations

Results, SSRevents 2 + 4

SSR resultscomparison

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)

1D modeling, results

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

Future plans

• Ground motion simulations for different source parameters

• Use simulation results as input in RR and EW system

• Assign site amplification factor to RR and EW sites