Ground motion simulations and site effect estimation for Istanbul, Turkey Mathilde Bøttger Sørensen 1, Nelson Pulido 2, Sylvette Bonnefoy-Claudet 3, Kuvvet Atakan 1 1 Department of Earth Science, University of Bergen, Norway, 2 Earthquake Disaster Mitigation Research Center EDM, NIED, Kobe, Japan, 3 LGIT, 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 parameters Total seismic momentM 0 = 2.0·10 20 Nm Asperity areaS a /S = 0.22 Average stress drop5 MPa Asperity stress drop10 MPa Rise timeRandom, average 3.0 s Rupture velocityRandom between 2.8 – 3.2 km/s f max 10 Hz Q100 · f 1.5

Velocity model

PGV results

PGA results

Istanbul Earthquake Rapid Response and Early Warning System Kandilli Observatory and Earthquake Research Institute Bogazici 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 Institute Bogazici 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 example Avcilar district

Geology of Istanbul Map from Istanbul Metropolitan Municipality web pages,

Geology of Istanbul Map from Istanbul Metropolitan Municipality web pages,

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, SSR all events

Event locations

Results, SSR events 2 + 4

SSR results comparison

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