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Margaris B.,ITSAK Institute of Engineering Seismology and Earthquake Engineering | Athanasopoulos G.,University of Patras | Mylonakis G.,University of Patras | Papaioannou C.,ITSAK Institute of Engineering Seismology and Earthquake Engineering | And 5 more authors.
Earthquake Spectra | Year: 2010

The Mw6.5 Achaia-Elia (Greece) earthquake on 8 June 2008 was a rightlateral strike-slip event on a nearly vertical faul. Moment tensor solutions coupled with geologic structure and aftershock distributions suggest a fault strike of approximately 210° on a previously unmapped fault. Rupture appears to have been concentrated over a 10-25 km depth range and did not break the surface. The northern rupture limit appears to correspond to a NW-striking normal fault near the Kato Achaia coastline. The mainshock was recorded by 27 accelerometers at distances from the surface projection of the fault ranging from approximately 15 to 350 km. The data demonstrate faster distance attenuation than predicted by contemporary Greek ground motion prediction equations (GMPEs). On the other hand, an NGA GMPE generally captures the distance attenuation but shows underprediction bias at short and long periods. Despite the presence of a range of site conditions at recording stations in the city of Patras, we find no obvious effect of sediment depth on response spectra. We show the possible presence of rupture directivity at the north end of this bilateral rupture, but no apparent effect at the southern end. We described several relatively well-documented incidents of nonground failure and ground failure associated with liquefaction/lateral spreading and landslides. © 2010, Earthquake Engineering Research Institute.

Pitilakis K.,Aristotle University of Thessaloniki | Raptakis D.,Aristotle University of Thessaloniki | Makra K.,ITSAK Institute of Engineering Seismology and Earthquake Engineering | Manakou M.,Aristotle University of Thessaloniki | Chavez-Garcia F.J.,National Autonomous University of Mexico
Geotechnical, Geological and Earthquake Engineering | Year: 2011

Euroseistest is currently the longest running instrumented test site in the world. It was originally defined as the 2D (N-S) cross section of the Mygdonian basin, N-E from Thessaloniki Greece, epicenter area of the M6.4 1978 earthquake. In this paper, we present the effort to extend the test site to a larger portion of the whole sedimentary structure, i.e., from 2D to a 3D structure. To this end we have compiled available geological and geotechnical information.We have analyzed microtremor and earthquake data. We present the results of the analysis of all available information and data. The synthesis of all data allowed us to propose reliable image of the geometry and the properties of the basin. We have also obtained a reliable estimate of the site response throughout the basin and we have discussed several aspects of site effects in complex geologic structures, including the increase of spectral amplification compared to 1D site amplification. © Springer Science+Business Media B.V. 2011.

Margaris B.,ITSAK Institute of Engineering Seismology and Earthquake Engineering | Skarlatoudis A.,Aristotle University of Thessaloniki | Savvaidis A.,ITSAK Institute of Engineering Seismology and Earthquake Engineering | Theodoulidis N.,ITSAK Institute of Engineering Seismology and Earthquake Engineering | And 2 more authors.
Geotechnical, Geological and Earthquake Engineering | Year: 2011

The destructive earthquakes that occurred over the last years in the broader Greek region urged the need for acquiring high quality strong ground motion recordings. This necessity led to the enhancement of accelerographic networks by deploying a significant number of new sensors all around Greece, improving their spatial coverage. Within the framework of this work, a new, more efficient, strong motion data processing technique is presented and the properties of the updated Greek strong motion database are presented. The resulted high quality dataset will be used in various applications of engineering seismology, soil dynamics and earthquake engineering with the main goal being the derivation of new ground motion prediction equations (GMPEs) for the broader Aegean area. Updated seismological and geotechnical information such as site classification of ITSAK accelerographic stations based on VS30, is adopted for the derivation of new GMPEs. © Springer Science+Business Media B.V. 2011.

Cadet H.,Geological Institute of Catalonia Balmes | Cadet H.,ITSAK Institute of Engineering Seismology and Earthquake Engineering | Macau A.,Geological Institute of Catalonia Balmes | Benjumea B.,Geological Institute of Catalonia Balmes | And 2 more authors.
Soil Dynamics and Earthquake Engineering | Year: 2011

As local site effects have a drastic influence on seismic hazard, it is a major issue to characterize them in vulnerable areas such as highly urbanized zones, like Barcelona city. The aim of this work is to improve the knowledge of geophysical characteristics of Barcelona in the perspective of a seismic microzonation that takes into account site effect. The first step was to gather the existing data from geological, geotechnical, geophysical, and seismological investigations, bringing us to keep the four zones proposed by previous work as a base of zonation. The second step was to characterize each zone by time-averaged shear-wave velocity and fundamental resonance frequency, with ambient noise techniques over 17 sites, providing new knowledge about the soil of Barcelona. The third step was to propose an amplification function between an average soil for each zone and a standard reference rock site, using empirically based propositions and to compare them to previous numerical approaches. © 2010 Elsevier Ltd.

Heloise C.,CNRS Institute of Earth Sciences | Heloise C.,Center Detudes Techniques Of Lequipement | Heloise C.,ITSAK Institute of Engineering Seismology and Earthquake Engineering | Bard P.-Y.,CNRS Institute of Earth Sciences | Rodriguez-Marek A.,Virginia Polytechnic Institute and State University
Bulletin of Earthquake Engineering | Year: 2012

When data is available, the estimation of site effects is usually performed using the "standard spectral ratio" (SSR) technique with respect to an outcropping, reference rock site. This study uses the Japanese KiK-net network, which has more than 600 pairs of surface-downhole stations allowing the computation of empirical borehole transfer functions, consisting of mean spectral ratios of surface over downhole recordings. The borehole transfer function deviates from the SSR in two respects: the reference is located at depth, and the downhole velocity varies from one site to another. These differences bias the estimation of the transfer function with reference to a standard outcrop rock site. The goal of this paper is to develop a simple and robust methodology to correct for such bias. The proposed correction procedure consists of two steps: a depth correction designed to account, in a simplified and physically acceptable way, for the existence at depth of destructive interferences and the absence of free-surface effects in the high-frequency range; and an impedance correction designed to normalize the shear wave velocity at depth. The depth correction involves a simple, frequency-dependent curve to be adapted for each site as a function of the first destructive interference frequency at depth. The impedance normalization combines the use of "generic" rock velocity profiles and a quarter-wavelength approach, resulting in a smooth frequency-dependent amplitude correction. The proposed methodology is applied on a large subset of KiK-net data in view of analysing the correlation between site amplification factors and site parameters in a companion paper. © 2011 Springer Science+Business Media B.V.

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