Fingerprint Identification Using Noise in the Horizontal-to-Vertical Spectral Ratio: Retrieving the Impedance Contrast Structure for the Almaty Basin (Kazakhstan)

Detailed knowledge of the 3D basin structure underlying urban areas is of major importance for improving the assessment of seismic hazard and risk. However, mapping the major features of the shallow geological layers becomes expensive where large areas need to be covered. In this study, we propose an innovative tool, based mainly on single station noise recordings and the horizontal-to-vertical spectral ratio (H/V), to identify and locate the depth of major impedance contrasts. The method is based on an identification of so-called fingerprints of the major impedance discontinuities and their migration to depth by means of an analytical procedure. The method is applied to seismic noise recordings collected in the city of Almaty (Kazakhstan). The estimated impedance contrasts vs. depth profiles are interpolated in order to derive a three-dimensional (3D) model, which after calibration with some available boreholes data allows the major tectonic features in the subsurface to be identified

Ein Vergleich verschiedener seismologischer und geotechnischer Parameter zur Standortcharakterisierung

The geometry of the subsoil structure, the soil types involved and the variation in their properties with depth, lateral discontinuities and surface topography are causes of lateral variation in earthquake-induced ground motion, over relatively small scales, referred to as "site effects" The modification of ground motion can manifest itself through amplification at particular frequencies (the lowest one defining the fundamental resonance frequency), depending on the thickness and the velocity structure of the uppermost layers, and deamplification due to the competitive effect of the attenuation of the wavefield in shallow soft layers. Therefore, a detailed characterization of the properties of shallow geological structures in terms of the fundamental resonance frequency f0 , local shear wave (S-wave) velocity structure and a quality factor (Qs ) profile, which quantifies the effects of anelastic attenuation on the seismic wavelet, is necessary. Over the last decades, techniques based on the analysis of seismic noise, which is generated by natural and anthropogenic sources, have been found to have the potential to significantly contribute to site effect evaluation as they can provide sufficiently accurate estimates of the underlying Vs profile. Recently, modification of the same methods have proved to be able to provide realistic Qs versus depth estimations. A now generally adopted approach in seismic hazard assessment for mapping seismic site conditions is estimating the average shear wave velocity in the uppermost 30 m (Vs30 ) as a proxy of the site response. This approach was also applied to the quality factor within the uppermost 30 m (Qs30 ). In this thesis, data sets of seismic noise recorded in different regions of Europe and Central Asia by microarrays of seismic stations was used to calculate both Vs and Qs profiles. By applying innovative analysis techniques, it is shown that the values are consistent and that seismic noise analysis has the potential to provide a comprehensive (Vs and Qs ) description of the geological structure below a site.Die Geometrie des Untergrundes, die beteiligten Bodentypen und die Variation ihrer Eigenschaften mit der Tiefe, laterale Diskontinuitäten und Oberflächentopografie sind Ursachen für die laterale Variation der erdbebeninduzierten Bodenbewegung über relativ kleine Skalen, die als „Standorteffekte“ bezeichnet werden. Eine solche Veränderung der Bodenbewegung ist häufig gekennzeichnet durch eine Verstärkung der Erschütterung für bestimmte Frequenzen (die niedrigste definiert die Eigenschwingungsfrequenz des Untergrundes), abhängig von der Schichtmächtigkeit und Geschwindigkeitsstruktur der obersten Schichten bzw. auch durch eine Verringerung der Bodenbewegung aufgrund von gegenläufigen Effekten wie der Abschwächung des Wellenfeldes in oberflächennahen Sedimentschichten. Für eine genaue Berücksichtigung dieser Effekte in seismischen Gefährdungsanalysen sowie für geotechnische Untersuchungen ist eine genau Charakterisierung der Eigenschwingungsfrequenz (f0 ), der lokalen Scherwellen (S-Wellen) Geschwindigkeitsstruktur sowie des Qualitätsfaktors, welcher die Abschwächung des Wellenfeldes beschreibt, erforderlich. In den letzten Jahrzehnten wurde festgestellt, dass Methoden, die auf der Analyse von seismischem Rauschen basieren, welches durch natürliche und anthropogene Quellen erzeugt wird, das Potenzial haben, wesentlich zur Evaluierung der Standorteffekte beizutragen, da sie ausreichend genaue Abschätzungen des zugrunde liegenden Vs -Profils liefern. Neueste Entwicklungen konnten zeigen, dass ebenso verlässliche Aussagen auch hinsichtlich des Qualitätsfaktors und seiner Tiefenverteilung getroffen werden können. Ein inzwischen allgemein anerkannter Ansatz in der seismischen Gefährdungseinschätzung zur Kartierung seismischer Standortbedingungen ist die Abschätzung der durchschnittlichen Scherwellengeschwindigkeit in den obersten 30 m (Vs30 ) als „Proxy“ der Standortantwort. Dieser Ansatz wurde auch auf den Qualitätsfaktor innerhalb der obersten 30 m (Qs30 ) angewandt. In dieser Arbeit wurden Datensätze von seismischem Rauschen, die in verschiedenen Regionen Europas und Zentralasiens durch Mikroarrays seismischer Stationen aufgenommen wurden, zur Berechnung von Vs - und Qs -Profilen verwendet. Durch den Einsatz innovativer Analyseverfahren wird gezeigt, dass die Werte konsistent sind und dass die seismische Rauschanalyse das Potenzial hat, eine umfassende (Vs und Qs ) Beschreibung der geologischen Struktur an einem Standort zu liefern.EC/FP7/262330/Network of European Research Infrastructures for Earthquake Risk Assessment and Mitigation/NERAECHO/SUB/2014/695550/SeIsmic monitoring and vulnera BilitY framework for civiL protection/SIBY

A Comparison of Different Seismological and Geotechnical Parameters for Site Characterization

The geometry of the subsoil structure, the soil types involved and the variation in their properties with depth, lateral discontinuities and surface topography are causes of lateral variation in earthquake-induced ground motion, over relatively small scales, referred to as "site effects" The modification of ground motion can manifest itself through amplification at particular frequencies (the lowest one defining the fundamental resonance frequency), depending on the thickness and the velocity structure of the uppermost layers, and deamplification due to the competitive effect of the attenuation of the wavefield in shallow soft layers. Therefore, a detailed characterization of the properties of shallow geological structures in terms of the fundamental resonance frequency f0 , local shear wave (S-wave) velocity structure and a quality factor (Qs ) profile, which quantifies the effects of anelastic attenuation on the seismic wavelet, is necessary. Over the last decades, techniques based on the analysis of seismic noise, which is generated by natural and anthropogenic sources, have been found to have the potential to significantly contribute to site effect evaluation as they can provide sufficiently accurate estimates of the underlying Vs profile. Recently, modification of the same methods have proved to be able to provide realistic Qs versus depth estimations. A now generally adopted approach in seismic hazard assessment for mapping seismic site conditions is estimating the average shear wave velocity in the uppermost 30 m (Vs30 ) as a proxy of the site response. This approach was also applied to the quality factor within the uppermost 30 m (Qs30 ). In this thesis, data sets of seismic noise recorded in different regions of Europe and Central Asia by microarrays of seismic stations was used to calculate both Vs and Qs profiles. By applying innovative analysis techniques, it is shown that the values are consistent and that seismic noise analysis has the potential to provide a comprehensive (Vs and Qs ) description of the geological structure below a site

The Multi-Parameter Wireless Sensing System (MPwise): Its Description and Application to Earthquake Risk Mitigation

The Multi-Parameter Wireless Sensing (MPwise) system is an innovative instrumental design that allows different sensor types to be combined with relatively high-performance computing and communications components. These units, which incorporate off-the-shelf components, can undertake complex information integration and processing tasks at the individual unit or node level (when used in a network), allowing the establishment of networks that are linked by advanced, robust and rapid communications routing and network topologies. The system (and its predecessors) was originally designed for earthquake risk mitigation, including earthquake early warning (EEW), rapid response actions, structural health monitoring, and site-effect characterization. For EEW, MPwise units are capable of on-site, decentralized, independent analysis of the recorded ground motion and based on this, may issue an appropriate warning, either by the unit itself or transmitted throughout a network by dedicated alarming procedures. The multi-sensor capabilities of the system allow it to be instrumented with standard strong- and weak-motion sensors, broadband sensors, MEMS (namely accelerometers), cameras, temperature and humidity sensors, and GNSS receivers. In this work, the MPwise hardware, software and communications schema are described, as well as an overview of its possible applications. While focusing on earthquake risk mitigation actions, the aim in the future is to expand its capabilities towards a more multi-hazard and risk mitigation role. Overall, MPwise offers considerable flexibility and has great potential in contributing to natural hazard risk mitigation

Shear wave velocity versus quality factor: results from seismic noise recordings

The assessment of the shear wave velocity (vs) and shear wave quality factor (Qs) for the shallow structure below a site is necessary to characterize its site response. In the past, methods based on the analysis of seismic noise have been shown to be very efficient for providing a sufficiently accurate estimation of the vs versus depth at reasonable costs for engineering seismology purposes. In addition, a slight modification of the same method has proved to be able to provide realistic Qs versus depth estimates. In this study, data sets of seismic noise recorded by microarrays of seismic stations in different geological environments of Europe and Central Asia are used to calculate both vs and Qs versus depth profiles. Analogous to the generally adopted approach in seismic hazard assessment for mapping the average shear wave velocity in the uppermost 30 m (vs30) as a proxy of the site response, this approach was also applied to the quality factor within the uppermost 30 m (Qs30). A slightly inverse correlation between both parameters is found based on a methodological consistent determination for different sites. Consequently, a combined assessment of vs and Qs by seismic noise analysis has the potential to provide a more comprehensive description of the geological structure below a site.ISSN:0956-540XISSN:1365-246

The Multi-Parameter Wireless Sensing System (MPwise): Its Description and Application to Earthquake Risk Mitigation

The Multi-Parameter Wireless Sensing (MPwise) system is an innovative instrumental design that allows different sensor types to be combined with relatively high-performance computing and communications components. These units, which incorporate off-the-shelf components, can undertake complex information integration and processing tasks at the individual unit or node level (when used in a network), allowing the establishment of networks that are linked by advanced, robust and rapid communications routing and network topologies. The system (and its predecessors) was originally designed for earthquake risk mitigation, including earthquake early warning (EEW), rapid response actions, structural health monitoring, and site-effect characterization. For EEW, MPwise units are capable of on-site, decentralized, independent analysis of the recorded ground motion and based on this, may issue an appropriate warning, either by the unit itself or transmitted throughout a network by dedicated alarming procedures. The multi-sensor capabilities of the system allow it to be instrumented with standard strong- and weak-motion sensors, broadband sensors, MEMS (namely accelerometers), cameras, temperature and humidity sensors, and GNSS receivers. In this work, the MPwise hardware, software and communications schema are described, as well as an overview of its possible applications. While focusing on earthquake risk mitigation actions, the aim in the future is to expand its capabilities towards a more multi-hazard and risk mitigation role. Overall, MPwise offers considerable flexibility and has great potential in contributing to natural hazard risk mitigation

Spatio-temporal variability of seismic noise above a geothermal reservoir

We report on the application of seismic noise investigations, including H/V (horizontal to vertical) spectral ratio and array techniques, to a shallow gas-rich geothermal reservoir in Heybeli, southwestern Turkey. Fundamental resonant frequencies were determined to estimate the sediment thickness. Using small-scale seismic arrays, phase velocity dispersion curves were derived by correlating noise recordings according to the extended spatial autocorrelation method. Improved shear wave velocity profiles were estimated by combining Rayleigh wave dis- persion curves and horizontal to vertical spectral ratios in a joint inversion. We found that the velocities obtained for the reservoir site are higher than those for a location outside the reservoir. In addition to the fundamental res- onant peaks in the spectra, a clear 6-Hz-signal could be identified originating from the center of the geothermal field, repeatedly observed in 2010 and 2011. It had been claimed that low frequency (1–10 Hz) seismic signal anomalies were correlated with the occurrence of hydrocarbons. One of the physical mechanisms under consid- eration to explain these tremor-like signals above such reservoirs is resonant amplification due to the oscillation of bubbles. Based on the signal similarity with volcanic tremors, it is not a priori given that the liquid phase must be oil for resonance effects to occur. We therefore applied array techniques to identify potential noise originating from the Heybeli reservoir. In fact, the frequency–wavenumber (f–k) method clearly indicated a noise source coming from the main production well of the reservoir. In 2011, as part of our assessment, the operators of the spa facility stopped the extraction of thermal water for 2 h: the 6-Hz-signal disappeared after the pump had been stopped and reappeared after the pump began operating again. Thus, the 6-Hz-signal is likely of artificial origin. In addition, no natural noise source inside the reservoir could be identified

Assessing Earthquake Early Warning Using Sparse Networks in Developing Countries: Case Study of the Kyrgyz Republic

The first real-time digital strong-motion network in Central Asia has been installed in the Kyrgyz Republic since 2014. Although this network consists of only 19 strong-motion stations, they are located in near-optimal locations for earthquake early warning and rapid response purposes. In fact, it is expected that this network, which utilizes the GFZ-Sentry software, allowing decentralized event assessment calculations, not only will provide useful strong motion data useful for improving future seismic hazard and risk assessment, but will serve as the backbone for regional and on-site earthquake early warning operations. Based on the location of these stations, and travel-time estimates for P- and S-waves, we have determined potential lead times for several major urban areas in Kyrgyzstan (i.e., Bishkek, Osh, and Karakol) and Kazakhstan (Almaty), where we find the implementation of an efficient earthquake early warning system would provide lead times outside the blind zone ranging from several seconds up to several tens of seconds. This was confirmed by the simulation of the possible shaking (and intensity) that would arise considering a series of scenarios based on historical and expected events, and how they affect the major urban centers. Such lead times would allow the instigation of automatic mitigation procedures, while the system as a whole would support prompt and efficient actions to be undertaken over large areas