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

On 12 November 1999, only three months after the 17 August 1999 Kocaeli earthquake (M(w) 7: 4), an earthquake of Mw 7: 1 occurred immediately to the east of the Kocaeli rupture in northwestern Turkey resulting in extensive structural damage in the city of Duzce and its surrounding area. It was reported to be a right-lateral strike slip event on the previously unbroken segment of the North Anatolian fault zone with a north-dipping fault plane. This paper presents stochastic finite-fault simulation of near-field ground motions from this earthquake at selected near-fault stations based on a dynamic corner frequency approach using the computer program EXSIM (Motazedian and Atkinson, 2005). The method requires region-specific source, path, and site characterizations as input model parameters. The source mechanism of the 1999 Duzce event and regional path effects are well constrained from previous studies of the earthquake. The local site effects at the selected stations are studied as a combination of the kappa operator and frequency-dependent soil amplification. The model parameters are validated against recordings and a stress-drop value of 100 bars is estimated for the 1999 Duzce earthquake. The validated model is then used to compute synthetic records around the fault. Distribution of peak ground-motion parameters is observed to be consistent with the building damage distribution in the near-fault region most affected by the seismic shaking. The attenuation of synthetic ground-motion parameters is compared with recent ground-motion prediction equations proposed for the region by Gulkan and Kalkan (2002), Ulusay et al. (2004), and Akkar and Bommer (2007), as well as two next generation attenuation models by Boore and Atkinson (2007) and Campbell and Bozorgnia (2007). Despite discrepancies at several stations, stochastic finite-fault modeling based on a dynamic corner frequency approach confirms to be a practical tool to reproduce the ground motions of large earthquakes

Stochastic strong ground motion simulations in sparsely-monitored regions: A validation and sensitivity study on the 13 March 1992 Erzincan (Turkey) earthquake

Stochastic simulations have recently become quite popular for estimating synthetic ground motion time histories. For seismically active regions that are not well-monitored or studied extensively, input parameters of the simulations should be carefully selected as the reliability of the simulation results directly depends on the accuracy of the input parameters. In the first part of this study, 13 March 1992 Erzincan (eastern Turkey) earthquake (Mw=6.6), which is recorded at only three strong ground motion stations, is simulated using the stochastic finite-fault method. The source and regional path parameters for this event are adopted from previously validated studies whereas the local site parameters are derived herein. In the second part of the paper, sensitivity of the simulation results with respect to small changes in selected input seismic parameters is investigated. The parameters for which sensitivities are computed include stress drop, crustal shear-wave quality factor and kappa operator. A change of 20% in stress drop value results in 14% change in PGA, whereas a 20% difference in the Q(0) value causes 17% change in PGA, and a 20% variation in kappa leads to 15% difference in PGA. Numerical experiments presented in this study prove that the ground motion simulations are prone to trade-off between the source, path and site filters. Hence, input models must be implemented carefully for reliable synthetic ground motions. (C) 2013 Published by Elsevier Ltd

A Methodology for Seismic Loss Estimation in Urban Regions Based on Ground-Motion Simulations

Seismic vulnerability assessment of residential buildings in regions of high seismicity is an interdisciplinary problem requiring major inputs from fields of seismology and earthquake engineering. The basic two components of loss estimation methods are information on regional seismicity and building stock. This study presents a realistic loss estimation methodology where the first component, input ground motions, is obtained from regional ground-motion simulations using the stochastic finite-fault technique. The second component, building vulnerability information, on the other hand, is taken into account using fragility analyses. Introducing the ground-motion intensity parameters obtained from simulations to the fragility curves, we obtain seismic loss distribution in a region. In this study, we demonstrate the loss estimation methodology with an application to three northwestern cities in Turkey (Duzce, Bolu, and Kaynasli) that experienced two major earthquakes (M(w) 7.4 and M(w) 7.1) in less than three months in 1999. We initially verify the methodology with comparisons of observed and estimated damage ratios for the 12 November 1999 (M(w) 7.1) Duzce earthquake. Later, we present the estimated damage ratios under scenario earthquakes in the region for a magnitude range of M(w) 5.5-7.5. M(w) 6.5 is predicted to be the threshold magnitude for the cities of Duzce and Kaynasli where more than 60% of the building stock experience moderate and heavy damage. Because Bolu is at a farther distance from the fault plane, less damage is estimated for M(w) 5.5-7.0 than those in the other centers. For M(w) 7.5, all three cities are predicted to experience substantial rates of heavy damage and collapse

Strong-Ground-Motion Simulation of the 6 April 2009 L'Aquila, Italy, Earthquake

On 6 April 2009, an earthquake of M-w 6.13 (Herrmann et al., 2011) occurred in central Italy, close to the town of L'Aquila. Although the earthquake is considered to be a moderate-size event, it caused extensive damage to the surrounding area. The earthquake is identified with significant directivity effects: high-amplitude, short-duration motions are observed at the stations that are oriented along the rupture direction, whereas low-amplitude, long-duration motions are observed at the stations oriented in the direction opposite to the rupture. The complex nature of the earthquake combined with its damage potential brings the need for studies that assess the seismological characteristics of the 2009 L'Aquila mainshock

Site characterisation in north-western Turkey based on SPAC and HVSR analysis of microtremor noise

The geology of the north-western Anatolia (Turkey) ranges from hard Mesozoic bedrock in mountainous areas to large sediment-filled, pull-apart basins formed by the North Anatolian Fault zone system. Duzce and Bolu city centres are located in major alluvial basins in the region, and both suffered from severe building damage during the 12 November 1999 Duzce earthquake (Mw = 7.2). In this study, a team consisting of geophysicists and civil engineers collected and interpreted passive array-based microtremor data in the cities of Bolu and Duzce, both of which are localities of urban development located on topographically flat, geologically young alluvial basins of Miocene age. Interpretation of the microtremor data under an assumption of dominant fundamental-mode Rayleigh-wave noise allowed derivation of the shear-wave velocity (Vs) profile. The depth of investigation was similar to 100m from spatially-averaged coherency (SPAC) data alone. High-frequency microtremor array data to 25 Hz allows resolution of a surface layer with Vs < 200 m/s and thickness 5m (Bolu) and 6m (Duzce). Subsequent inclusion of spectral ratios between horizontal and vertical components of microtremor data (HVSR) in the curve fitting process extends useful frequencies up to a decade lower than those for SPAC alone. This allows resolution of two interfaces of moderate Vs contrasts in soft Miocene and Eocene sediments, first, at a depth in the range 136-209 m, and second, at a depth in the range 2000 to 2200 m

8 March 2010 Elazig-Kovancilar (Turkey) Earthquake: Observations on Ground Motions and Building Damage

An earthquake of MW = 6.1 occurred in the Elazig region of eastern Turkey on 8 March 2010 at 02:32:34 UTC. The United States Geological Survey (USGS) reported the epicenter of the earthquake as 38.873°N-39.981°E with a focal depth of 12 km. Forty-two people lost their lives and 137 were injured during the event. The earthquake was reported to be on the left-lateral strike-slip east Anatolian fault (EAF), which is one of the two major active fault systems in Turkey. Teams from the Earthquake Engineering Research Center of the Middle East Technical University (EERC-METU) visited the earthquake area in the aftermath of the mainshock. Their reconnaissance observations were combined with interpretations of recorded ground motions for completeness. This article summarizes observations on building and ground damage in the area and provides a discussion of the recorded motions. No significant observations in terms of geotechnical engineering were made. The major tectonic structure in Turkey is the north Anatolian fault zone (NAFZ), with right-lateral faulting extending from Istanbul in the west to Karliova in the east. During the twentieth century this fault zone has produced several large earthquakes ( MS > 7) with surface rupturing with a westward migrating sequence as demonstrated in Figure 1 (Barka 1996; Utkucu et al. 2003). Around the Karliova region, NAFZ joins the southwest-trending east Anatolian fault zone (EAFZ). The EAFZ is predominantly left-lateral strike-slip in nature, but its faulting is less continuous and less localized than that of the NAFZ (Ambraseys 2009). The EAFZ has nucleated relatively small magnitude earthquakes in the twentieth century (Figure 1). Recent GPS data indicates that the slip rate in the EAFZ has an upper bound of 8±1 mm/year (Ambraseys 2009). The epicenter (by USGS) of the 8 March 2010 Elazig-Kovancilar earthquake is in the segmented fault region