Understanding the physics of kappa (κ): Insights from a downhole array

At high frequencies, the acceleration spectral amplitude decreases rapidly; this has been modelled with the spectral decay factor κ. Its site component, κ0, is used widely today in ground motion prediction and simulation, and numerous approaches have been proposed to compute it. In this study, we estimate κ for the EUROSEISTEST valley, a geologically complex and seismically active region with a permanent strong motion array consisting of 14 surface and 6 downhole stations. Site conditions range from soft sediments to hard rock. First, we use the classical approach to separate local and regional attenuation and measure κ0. Second, we take advantage of the existing knowledge of the geological profile and material properties to examine the correlation of κ0 with different site characterization parameters. κ0 correlates well with Vs30, as expected, indicating a strong effect from the geological structure in the upper 30 m. But it correlates equally well with the resonant frequency and depth-to-bedrock of the stations, which indicates strong effects from the entire sedimentary column, down to 400 m. Third, we use our results to improve our physical understanding of κ0. We propose a conceptual model of κ0 with Vs, comprising two new notions. On the one hand, and contrary to existing correlations, we observe that κ0 stabilizes for high Vs values. This may indicate the existence of regional values for hard rock κ0. If so, we propose that borehole measurements (almost never used up to now for κ0) may be useful in determining these values. On the other hand, we find that material damping, as expressed through travel times, may not suffice to account for the total κ0 measured at the surface. We propose that, apart from material damping, additional site attenuation may be caused by scattering from small-scale variability in the profile. If this is so, then geotechnical damping measurements may not suffice to infer the overall crustal attenuation under a site; but starting with a regional value (possibly from a borehole) and adding damping, we might define a lower bound for site-specific κ0. More precise estimates would necessitate seismological site instrumentation

Microzonation Study of Duzce, Turkey

Duzce in Turkey was severely damaged during the November 12th, 1999 earthquake (Mw 7.2). The paper presents different surveys and studies performed after the earthquake, which resulted in the microzonation study of the city. At first we collected and analyzed all available geophysical and geological data. Then we performed a well focused geophysical and geotechnical campaign comprising a sufficient number of shallow and deep boreholes, seismic down-hole tests, array measurements of microtremors and ambient noise measurements. The synthesis of all these data resulted in the construction of the seismic geotechnical map and the geometry of the “seismic bedrock” of the city, adequate for site effect analysis. At a second stage we performed a thorough analysis of all available strong ground motion records and we carried out a detailed seismic hazard analysis, which provided the necessary input motion characteristics for the spatial analysis of the seismic ground response. Finally, we conducted a specific site effect analysis for the seismic scenario of the 1999 earthquake with a series of conventional 1D EQL analysis. The processing of the theoretical analysis results led to the estimation and the spatial distribution of the mean acceleration, velocity and displacement response spectra. As a result, Duzce was divided in seismic zones and for each one we proposed the corresponding mean design acceleration response spectra and all other characteristics of the expected ground response

Guidelines for harmonized hazard assessment for LP-HC events: STREST Reference Report 2

This report describes the main conclusions of the STREST project (and associated guidelines) to evaluate hazard of Low-Probability High-Consequences (LP-HC) events used to define stress tests for non-nuclear Critical Infrastructures (CIs). Several new approaches have been developed to assess these extreme hazard scenarios and to evaluate the associated uncertainties. This report presents a summary of the developments, results and products issued from Work Package 3 (WP3) of STREST. It is given as a set of “recommendations” for potential users responsible of the estimation of hazard for a particular non-nuclear CI in the European Union and other countries. The methods and guidelines are dedicated to two different target-users: project managers and hazard experts. It poses the main differences with a traditional Probabilistic Hazard Assessment analysis, the benefits and extra challenges, and the particular information requirements for the three selected infrastructure classes covered in STREST. In a simple and understandable manner, it summarizes the principal available tools, the main references and the application examples issued from the project in order to help the users in the realization of theirs studies.JRC.E.4-Safety and Security of Building

The web portal of the EUROSEISTEST strong ground motion database.

Οι καταγραφές της εδαφικής επιτάχυνσης του πολυδύναμου πεδίου δοκιμών EUROSEISTEST (Μυγδονία λεκάνη, Βόρεια Ελλάδα), που έχουν συλλεχθεί κατά τη διάρκεια των 20 χρόνων λειτουργίας του, ομογενοποιήθηκαν και οργανώθηκαν σε μια εύκολα προσβάσιμη, μέσω του διαδικτύου, βάση δεδομένων. Η δικτυακή πύλη του EUROSEISTEST και όλες οι λειτουργίες του διακομιστή της έχουν σχεδιαστεί με αποκλειστική χρήση ανοιχτού λογισμικού (MySQL v5.5; RubyOnRails, SAC, Gnuplot, διάφορα άλλα GNU εργαλεία). Το γραφικό περιβάλλον της δικτυακής πύλης παρέχει τα κατάλληλα εργαλεία για την εύκολη αναζήτηση δεδομένων από τους 26 σταθμούς του μόνιμου δικτύου του EUROSEISTEST και τους 200 περίπου σεισμούς που έχουν καταγραφεί μέχρι σήμερα. Παρέχεται επίσης δυνατότητα επισκόπησης των δεδομένων μέσω εικόνων με χρονοϊστορίες της επιτάχυνσης, ταχύτητας και μετάθεσης, φάσματα πλάτους Fourier, απόκρισης, καθώς και φασματογραφημμάτων. Ιδιαίτερη βαρύτητα έχει δοθεί στην υψηλή ποιότητα πληροφορίας των μετα-δεδομένων (σεισμών, σταθμών καταγραφής και εδαφικής δομής) που έχουν συμπεριληφθεί στη βάση. Όλα τα δεδομένα επιτάχυνσης του EUROSEISTEST και τα μεταδεδομένα που αφορούν τον γεωτεχνικό-γεωφυσικό χαρακτηρισμό και την απόκριση του εδάφους στις θέσεις των σταθμών καταγραφής είναι διαθέσιμα μέσω της σχετικής δικτυακής πύλης.Strong motion data that have been recorded during the 20-years of operation of the permanent network of EUROSEISTEST (Mygdonia basin, Northern Greece) have been homogenized and organized in an easily accessible, via the web, database. The EUROSEISTEST web portal and the application server running underneath are based solely on free and open source software (F/OSS; MySQL v5.5; RubyOnRails,SAC, Gnuplot and numerous GNU supporting utilities). Its interface allows the user to easily search strong motion data from approximately 200 events and 26 strong motion stations using event-related, record-related or station-related criteria. Further investigation of the data is possible in a graphical environment which includesplots of processed and unprocessed acceleration waveforms, velocity and displacement time histories, amplitude Fourier and response spectra and spectrograms. A great effort was directed toward the inclusion of accurate and most updated earthquake metadata, as well as a wealth of stations related information such as geotechnicaland geophysical site characterization measurements, subsoil structure and site effects. Acceleration data can be easily downloaded in either SAC or ASCII format, while all stations metadata are also available to download.

Understanding single-station ground motion variability and uncertainty (sigma) – Lessons learnt from EUROSEISTEST

Accelerometric data from the well-studied valley EUROSEISTEST are used to investigate ground motion uncertainty and variability. We define a simple local ground motion prediction equation (GMPE) and investigate changes in standard deviation (σ) and its components, the between-event variability (τ) and within-event variability (φ). Improving seismological metadata significantly reduces τ (30-50%), which in turn reduces the total σ. Improving site information reduces the systematic site-to-site variability, φS2S (20-30%), in turn reducing φ, and ultimately, σ. Our values of standard deviations are lower than global values from literature, and closer to path-specific than site-specific values. However, our data have insufficient azimuthal coverage for single-path analysis. Certain stations have higher ground-motion variability, possibly due to topography, basin edge or downgoing wave effects. Sensitivity checks show that 3 recordings per event is a sufficient data selection criterion, however, one of the dataset’s advantages is the large number of recordings per station (9-90) that yields good site term estimates. We examine uncertainty components binning our data with magnitude from 0.01 to 2 s; at smaller magnitudes, τ decreases and φSS increases, possibly due to κ and source-site trade-offs Finally, we investigate the alternative approach of computing φSS using existing GMPEs instead of creating an ad hoc local GMPE. This is important where data are insufficient to create one, or when site-specific PSHA is performed. We show that global GMPEs may still capture φSS, provided that: 1. the magnitude scaling errors are accommodated by the event terms; 2. there are no distance scaling errors (use of a regionally applicable model). Site terms (φS2S) computed by different global GMPEs (using different site-proxies) vary significantly, especially for hard-rock sites. This indicates that GMPEs may be poorly constrained where they are sometimes most needed, i.e. for hard rock

Geophysical prospecting in the Krousovitis dam (N. Greece) by seismic and resistivity methods

Abstract: The use of two geophysical methods in the investigation of the geological setting in the area of a dam foundation is presented in this study. The seismic method was used in order to map the structure of the upper layers near the riverbed. VES and resistivity tomographs were also carried out. The depth to the basement was estimated by interpreting the VES curves. Interpretation of the topographic images, along with the inferred models from the seismic data, revealed the thickness of the colluvial deposits

The phenomenon of rural depopulation in the Swedish landscape : Turning the trends

The objective of the study at hand is to explore the phenomenon of rural depopulation and more specifically to find out what are the methods that a region can apply in order to reverse it. Rural depopulation is a phenomenon that started taking place at the beginning of the century in Sweden. Lately the interest about urbanization and how to deal with it has increased tremendously, thus rural population decline was neglected. Some researchers though identified the problematic situation and the threats behind the phenomenon. The present paper focuses on Sweden, a country which is one of the most sparsely populated in Europe and where the phenomenon is also observed. Even though the overall population of the country keeps increasing, the number of inhabitants residing in certain peripheral municipalities decreases. The fact that Sweden experienced a significant influx of immigrants and asylum seekers during the last years doesn’t seem to have worked in an alleviating way for rural areas. As argued by previous researchers, this particular group could be a rejuvenating source for depopulated regions. Nevertheless the aforementioned group also seems to prefer relocating to the bigger centers due to better job opportunities. Starting from a research-based view the present paper will attempt to list the patterns advocating why people choose to move, and most importantly study the different initiatives that municipalities can follow in order to turn this trend that rural areas have to encounter

The phenomenon of rural depopulation in the Swedish landscape : Turning the trends

The objective of the study at hand is to explore the phenomenon of rural depopulation and more specifically to find out what are the methods that a region can apply in order to reverse it. Rural depopulation is a phenomenon that started taking place at the beginning of the century in Sweden. Lately the interest about urbanization and how to deal with it has increased tremendously, thus rural population decline was neglected. Some researchers though identified the problematic situation and the threats behind the phenomenon. The present paper focuses on Sweden, a country which is one of the most sparsely populated in Europe and where the phenomenon is also observed. Even though the overall population of the country keeps increasing, the number of inhabitants residing in certain peripheral municipalities decreases. The fact that Sweden experienced a significant influx of immigrants and asylum seekers during the last years doesn’t seem to have worked in an alleviating way for rural areas. As argued by previous researchers, this particular group could be a rejuvenating source for depopulated regions. Nevertheless the aforementioned group also seems to prefer relocating to the bigger centers due to better job opportunities. Starting from a research-based view the present paper will attempt to list the patterns advocating why people choose to move, and most importantly study the different initiatives that municipalities can follow in order to turn this trend that rural areas have to encounter