Ground motion scaling in the Marmara region, Turkey

Abstract

SUMMARY Predictive relationships for the ground motion in the Marmara region (northwestern Turkey) are parametrized after regressing three‐component waveforms from regional earthquakes, in the frequency range: 0.4–15.0 Hz, and in the distance range: 10–200 km. The data set consists of 2400 three‐component recordings from 462 earthquakes, recorded at 53 stations. Moment magnitudes, Mw, range between 2.5 and 7.2. The largest event for which we have waveforms available (Mw 7.2) occurred in Duzce on 1999 November 12. The aftershocks of that earthquake, together with the aftershocks of the 1999 August 17 Izmit event (Mw= 7.4), are included in the dataset. Regressions are performed, independently, on Fourier velocity spectra and on peak ground velocities, for a large number of sampling frequencies. A simple model is used to relate the logarithm of the measured ground motion to excitation, site, and propagation terms. Results obtained for peak velocities are used to define a piecewise continuous geometrical spreading function, g(r), a frequency‐dependent Q(f), and a distance‐dependent duration function. The latter is used, through random vibration theory (RVT), in order to predict time‐domain characteristics (i.e. peak values) of the ground motion. The complete model obtained for the peak ground motion was used to match the results of the regressions on the Fourier amplitudes. Fourier velocity spectra for the combined horizontal motion are best fit by a hinged quadri‐linear geometrical spreading function for observations in the 10–200 km hypocentral distance ranges as a function of frequency: f < 1.0 Hz, r−1.2 for r≤ 30 km; r−0.7 for 30 < r≤ 60 km; r−1.4 for 60 < r≤ 100 km; r−0.1 for r > 100, f≥ 1.0 Hz, r−1.0 for r≤ 30 km; r−0.6 for 30 < r≤ 60 km; r−0.9 for 60 < r≤ 100 km; r−0.1 for r > 100 km. The frequency‐dependent crustal shear‐wave quality factor Q (f) coefficient Q(f) = 180 f0.45. The T (5–75 per cent) duration window provides good agreement between observed and predicted peak values. By modelling the behaviour of the small earthquakes at high frequency, we also quantified a regional parameter κ= 0.055 s. Spectral models with one single‐corner frequency (Brune), and with two‐corner frequencies (Atkinson and Silva) fit the observed high‐frequency excitation levels equally well, whereas the model by Atkinson and Silva fits the low‐frequency observations slightly better than Brune's. RVT is used to predict the absolute levels of ground shaking, following Boore's implementation of the stochastic ground motion model (Boore's SMSIM codes). Our regional empirical predictive relationships are compared to the ones adopted in several regions of the world, from California to Western United States.

Stochastic Strong Ground Motion Simulation of the 12 November 1999 Duzce (Turkey) Earthquake Using a Dynamic Corner Frequency Approach

“…The best-fit line to the kappa factor for the vertical components versus distance is obtained as 0:0474 0:00004R. We note that this kappa value is in good agreement with the values that have been proposed previously for soft soil sites in northwestern Turkey, which vary between 0.047 and 0.054 (Anderson et al, 2001;Durukal, 2002;Akinci et al, 2006;Ansal et al, 2009). Figure 4 compares the regional average site effects function H=Ve πfκ 0vertical computed in this study with those of generic rock and generic soil site conditions defined in Boore and Joyner (1997).…”

“…For the anelastic attenuation, we examine two models for the frequency-dependent quality factor proposed for the region by Akinci et al (2006) and Birgoren and Irikura, (2005). The Q models defined in these studies underestimate the spectral decay at high frequencies.…”

vS30, κ, regional attenuation and Mw from accelerograms: application to magnitude 3-5 French earthquakes

“…Recent studies of regional weak motions (e.g. Bay et al 2003; Akinci et al 2006; Malagnini et al 2007; Drouet et al 2008a; Edwards et al 2008; Atkinson & Morrison 2009) confirm that clear regional particularities exist in terms of attenuation and/or stress drop. There is then a need to analyse the regional variation of ground motion and the scaling of both geometrical spreading and stress drops with magnitude (e.g.…”

Predictions of high-frequency ground-motion in Taiwan based on weak motion data

“…Bay et al 2003;Akinci et al 2006;Malagnini et al 2007;Drouet et al 2008;Edwards et al 2008;Atkinson & Morrison 2009). Bay et al 2003;Akinci et al 2006;Malagnini et al 2007;Drouet et al 2008;Edwards et al 2008;Atkinson & Morrison 2009).…”

“…At present, several studies demonstrate that the ground motions are different for different seismic regions (Malagnini & Herrmann 2000, Malagnini et al 2000a,b, 2002, 2004aAkinci et al 2001Akinci et al , 2006Akinci et al , 2010Cotton et al 2008;Drouet et al 2008Drouet et al , 2010Edwards et al 2008;Atkinson & Morrison 2009), so that region-specific ground motion models should be developed. At present, several studies demonstrate that the ground motions are different for different seismic regions (Malagnini & Herrmann 2000, Malagnini et al 2000a,b, 2002, 2004aAkinci et al 2001Akinci et al , 2006Akinci et al , 2010Cotton et al 2008;Drouet et al 2008Drouet et al , 2010Edwards et al 2008;Atkinson & Morrison 2009), so that region-specific ground motion models should be developed.…”