Site-specific response spectra from the combination of microzonation with probabilistic seismic hazard assessment—An example for the Cologne (Germany) area

Seismic noise was measured at some 20 sites in the Cologne area (Germany) aligned nearly perpendicular to a graben structure. The H/V spectral noise ratio for each site was used to derive realistic S-wave velocity profiles down to the bedrock by means of a genetic algorithm inversion. Numerical simulations were performed for different combinations of source and propagation path parameters: focal depth, epicentral distance, attenuation and fault mechanism. Synthetic seismograms were produced and converted to Fourier and response spectra. Finally, the site-specific values from response spectral ratios, with their uncertainties, were used to modify attenuation functions entering the logic-tree algorithm of the probabilistic seismic hazard assessment (PSHA). The site-specific response spectra show the significance of taking into account the local S-wave velocity structure in PSHA.     

Characteristics of strong ground motion data recorded in the Gubbio sedimentary basin (Central Italy)

Various authors, analysing the set of accelerograms recorded at Gubbio Piana (GBP) (central Italy), have demonstrated that strong amplification occurs at this accelerometric station, which is installed within an alluvial basin. In particular, Ambraseys et al. [(2005a), Bull Earthq Eng 3:1–53; (2005b), Bull Earth Eng 3:55–73] observed that the strong motion peaks at GBP greatly exceed the median values predicted by the attenuation relationships they derived for Europe. In this work, we analyse and discuss some characteristics of the ground motion recorded at the GBP station. We show that the ground motion parameters, such as peak-ground acceleration and peak-ground velocity, are strongly influenced by the presence of locally induced surface waves that produce both a lengthening of the significant shaking duration and an increase in the peak values with respect to a nearby bedrock site. The basin-induced surface waves are observed in the three components of motion and their effects on the peak values are particularly evident in the vertical component. In the frequency domain, the energy of the surface waves is mostly restricted to the frequency band 0.4–0.8 Hz for both the horizontal and vertical components. The horizontal and vertical Fourier amplitudes are also very similar, and this indicates that the H/V spectral ratio technique is not applicable to describing the site response due to the propagation of seismic wave in a complex 2D/3D geological structure. Finally, a preliminary polarization analysis shows that the directions of polarization, as well as the degree of elliptical polarization, exhibit a strong variability with time, that may be related to a complex propagation of Love and Rayleigh waves within the basin.     

Evaluation of site effects in the Aterno river valley (Central Italy) from aftershocks of the 2009 L��Aquila earthquake

A temporary network of 33 seismic stations was deployed in the area struck by the 6th April 2009, Mw 6.1 (Scognamiglio et?al. in Seism Res Lett 6/81, 2010), L??Aquila earthquake (central Italy), with the aim to investigate the site amplification within the Aterno river Valley. The seismograms of 18 earthquakes recorded by 14 of the 33 stations were used to evaluate the average horizontal to vertical spectral ratio (HVSR) for each site and the standard horizontal spectral ratio (SSR) between a site and a reference station. The obtained results have been compared to the geological and geophysical information in order to explain the resonance frequencies and the amplification levels with respect to surface geology of the valley. The results indicate that there is no uniform pattern of amplification, because of the complex geologic setting, as the thickness and degree of cementation of the deposits is highly variable.     

Introduction to the special issue of the Consortium of Organizations for Strong Motion Observation Systems (COSMOS) international guidelines for applying noninvasive geophysical techniques to characterize seismic site conditions

Journal of Seismology -     

A review of near-surface QS estimation methods using active and passive sources

Journal of Seismology - Seismic attenuation and the associated quality factor (Q) have long been studied in various sub-disciplines of seismology, ranging from observational and engineering...     

A review of multiple natural hazards and risks in Germany

Although Germany is not among the most hazard-prone regions of the world, it does experience various natural hazards that have caused considerable economic and human losses in the past. Moreover, risk due to natural hazards is expected to increase in several regions of Germany if efficient risk management is not able to accommodate global changes. The most important natural hazards, in terms of past human and economic damage they caused, are storms, floods, extreme temperatures and earthquakes. They all show a pronounced spatial and temporal variability. In the present article, a review of these natural hazards, associated risks and their management in Germany is provided. This review reveals that event and risk analyses, as well as risk management, predominantly focus on one single hazard, generally not considering the cascading and conjoint effects in a full multi-hazard and risks approach. However, risk management would need integrated multi-risk analyses to identify, understand, quantify and compare different natural hazards and their impacts, as well as their interactions.     

Structural monitoring and earthquake early warning systems for the AHEPA hospital in Thessaloniki

This study aims at presenting the analyses of monitoring data that have been used in the context of structural monitoring and Earthquake Early Warning (EEW) for a hospital building in Thessaloniki. Permanent and temporary instrumentation arrays, implemented under the responsibility of Aristotle University of Thessaloniki (SDGEE-AUTH) in close cooperation with German Centre for Geosciences (GFZ) are presented. The ambient noise data recorded at the temporarily installed networks are used for the dynamic characterization of the building based on both vibrational and waveform approaches. Moreover, long-term ambient noise recordings from the permanent array installed within the hospital are used for the investigation of the daily and seasonal wandering of the building resonance frequencies related to environmental effects. The modal identification results are used in a comprehensive framework for the computation of the up-to-date fragility curves representing the actual structural state considering aging effects of the construction materials, possible pre-existing damages and changes in the geometry and mass distribution. The building-specific fragility functions are integrated into two independent EEW systems and rapid damage assessment approaches, namely the PRESTo software and an onsite EEW algorithm on the instruments of the permanent array, to provide the expected level of damage after strong ground shaking at the monitored building. The implemented monitoring networks and the developed operational tools can be used in the context of seismic risk mitigation and preparedness for structural safety assessment under earthquake loading.     

Site characterization by seismic noise in Istanbul,Turkey

Single station seismic noise measurements were carried out at 192 sites in the western part of Istanbul, Turkey. This extensive survey allowed the fundamental resonance frequency of the sedimentary cover to be mapped, and identify areas prone to site amplification. The results are in good agreement with the geological distribution of sedimentary units, indicating a progressive decrease of the fundamental resonance frequencies from the northeastern part, where the bedrock outcrops, towards the southwestern side, where a thickness of some hundreds meters for the sedimentary cover is estimated. The particular distribution of fundamental resonance frequencies indicates that local amplification of the ground motion might play a significative role in explaining the anomalous damage distribution after the 17 August 1999 Kocaeli Earthquake.     

Determination of dispersive phase velocities by complex seismic trace analysis of surface waves (CASW)

A method for deriving experimental dispersion curves of surface waves from active source recordings is presented. The method is based on the complex seismic trace analysis of surface waves (CASW) and is applicable when only two receivers are available.