A study of residuals for strong ground motions in Adapazari basin, NW Turkey, by ground motion prediction equations (GMPEs)

Abstract

The city of Adapazarı -located in the Marmara Region of northwest Turkey -is situated on a deep sedimentary basin and was the city most heavily damaged by the strong ground motion of the 17 August 1999 Kocaeli earthquake (moment magnitude M w = 7.4). This study determines site amplifications of the attenuation relationships for shallow earthquakes in the Adapazarı basin by using the previous ground motion prediction equations (GMPEs) and the traditional spectral ratio method. The site amplifications are determined empirically by averaging the residuals between the observed and predicted peak ground acceleration (PGA) and spectral acceleration (SA) values for various periods. Residuals are significantly correlated with the known characteristics of geological units. A new attenuation model has also been developed for 5% damped spectral acceleration to determine the dependence of strong ground motions on frequency.Site amplification was evaluated at ten stations located in the Adapazarı basin. The PGA site amplification values varied between 1.130 and 3.120 in all stations except two; these exceptions resulted in de-amplifications. Calculated de-amplification values of these stations indicate a consistency for rock medium. The site amplification values of some stations indicate an increase while moving away from the surface rupture and approaching the contact between the alluvial deposits and bedrock. One station, located on the discontinuity between the two different media, has the highest site amplification value (3.12) in the study area. This high value might be a result of the focusing of the seismic waves due to the discontinuities located on both sides of the narrow basin.The traditional spectral ratio method was also used to determine amplification in the Adapazarı basin. One station on bedrock was chosen as a reference station. When the results of this method are evaluated, the amplifications at high periods are attributed to the thick sedimentary deposits in the basin and the apparent de-amplifications at low periods are partly due to the reference site response.When the spectral ratios or spectral residuals of the stations located on alluvial deposits or soft soils are considered, it is observed that these stations have high spectral ratio or residual values, especially at high periods. The source of these high period E. Ulutaş et al.

Geodetic observations of postseismic creep in the decade after the 1999 Izmit earthquake, Turkey: Implications for a shallow slip deficit

“…The superficial geology consists of alluvial and fluvial sediments deposited by the Sakarya River, which flows though the center of the basin [Yigitbas et al, 2004;Ulutaş et al, 2011]. The thickness of the alluvium in the midsection of the basin is estimated to be more than 200 m according to groundwater wells drilled by the State Hydraulic Works [1983;Ulutaş et al, 2011] and possibly up to 2 km thick determined from a seismic refraction survey across the basin [Karahan et al, 2001]. Figure 6a with velocities within 15 km perpendicular distance projected onto the line in grey circles.…”

“…After detailed analysis of the regional geology, fault pattern, morphology, and stress and strain pattern in the region, Neugebauer [] suggested a pull‐apart mechanism for the basin formation. The superficial geology consists of alluvial and fluvial sediments deposited by the Sakarya River, which flows though the center of the basin [ Yigitbas et al , ; Ulutaş et al , ]. The thickness of the alluvium in the midsection of the basin is estimated to be more than 200 m according to groundwater wells drilled by the State Hydraulic Works [; Ulutaş et al , ] and possibly up to 2 km thick determined from a seismic refraction survey across the basin [ Karahan et al , ].…”

Engineering geologic assessment of the slope movements and liquefaction failures of the 23 October 2011 Van earthquake (<i>M</i><sub>w</sub>= 7.2)

“…Soft soils increase the ground shaking, and other factors such as liquefaction, ground failure, and structural deficiencies may also lead to heavy damage (Ulutaş et al, 2011). One of the earthquake hazard assessments related to ground shaking is typically done by means of an earthquake ground motion attenuation relationship, which provides the estimation of ground motion for an earthquake of a given magnitude at a different distance through a curve fitted to observed data (Ulutaş andÖzer, 2010).…”

“…One of the earthquake hazard assessments related to ground shaking is typically done by means of an earthquake ground motion attenuation relationship, which provides the estimation of ground motion for an earthquake of a given magnitude at a different distance through a curve fitted to observed data (Ulutaş andÖzer, 2010). Although the hazard assessment is not a simple function of magnitude and distance alone, it is used because the most common information available immediately following a damaging earthquake is its magnitude and epicenter As a result of the increased number of stations and the database of strong ground motion after the 1999İzmit (Gölcük) (M w = 7.4) and Düzce (M w = 7.2) earthquakes, new specific attenuation relationships have been developed for peak ground accelerations (PGAs) and spectral accelerations (SAs) in Turkey (Gülkan and Kalkan, 2002;Özbey et al, 2004;Ulusay et al, 2004;Akyol and Karagöz 2009;Ulutaş andÖzer, 2010;Ulutaş et al, 2011). Most of the data employed in these relationships were from the Kocaeli and Düzce earthquakes of 1999.…”

A way of estimating the characteristic slip displacement

“…This study, focus on the estimate of the characteristic slip displacement, D c , of rate-and state-dependent law. D c is denoted by L and named the slip-weakening distance by Bizzarri (2011), Ulutaş (2008Ulutaş ( , 2013Ulutaş ( , 2015, and Ulutaş et al (2006Ulutaş et al ( , 2011. One of the weak points is that, as shown below, the law cannot be defined when the velocity is zero.…”