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Using Ambient Vibration Array Techniques for Site Characterization and Seismic Microzonation

Saturday, December 6th to Friday, December 12th 2008
Thessaloniki, Greece

All aspects of ambient vibrations analysis are reviewed during a seven-day course, read more ...

itsak ird up lgit

In recent years, the number of research papers dealing with ambient vibration analysis methods has increased considerably. Clearly, the interest in these methods originates from both the economical attractive cost benefit ratio and the straightforward data acquisition. Being a non-destructive passive technique, these methods also complement geotechnical and/or active geophysical methods within highly populated regions.

Within the SESAME project (''Site EffectS assessment using AMbient Excitation'', EU-Project EVG1-CT-2000-00026, 2001-2004), the Sismovalp project (Interreg IIIB, Alpine Space, 2004-2006) and the on-going NERIES project (EU-FP6, "Network Research Infrastructure for European Seismology", 2006-2010) detailed research has been accomplished to identify the capabilities and limitations of ambient vibration analysis techniques. Within this context a set of software tools has been developed to ease the processing and interpretation of ambient vibration wave field recordings.

The main findings of the SESAME project however show, that ambient vibration array analysis techniques have to be applied with care. It requires not only a careful measurement, but especially the interpretation and the inversion of analysis results need a (self-)critical review. From these conclusions it has been agreed among SESAME-partners, that it is highly necessary to distribute the software tools together with adequate training.

The main purpose of this course is to achieve the necessary understanding among the course participants for the problems related to these techniques. By doing so, we try to enable a correct usage of the software tools and to avoid misuse of these methods (''black-box usage''). The course fees are intended to support current and future improvements of the software package, distributed under an open source and free license.

Contributions

This training course is:

organised by LGIT (Grenoble, France), IGUP (Potsdam, Germany) and ITSAK (Thessaloniki, Greece)
presented by Marc Wathelet (LGIT), Cécile Cornou (LGIT), Matthias Ohrnberger (UP Potsdam), Bertrand Guillier (LGIT), Alexandros Savvaidis (ITSAK), Nikos Theodulidis (ITSAK)
supported by ITSAK, IRD

The software development (was) is supported by NERIES (EU-Project, 2006-2010), SESAME (EU-Project, 2001-2004) , Sismovalp (Interreg IIIB, Alpine Space, 2004-2006), IRD

Course outline

This is a program which may be subject to slight changes in the future.

Saturday
09:00-09:30 Reception and welcome  
 
  • Technical issues and program overview
09:30-10:30 Physical background of ambient vibrations and their use for site microzonation Lecture
 
  • State of the art about the nature of the ambient vibration wave field.
  • The linkage between subsurface structure and wave field propagation properties: relationships between site conditions, Rayleigh ellipticity, Airy phase of Love waves and SH transfer function.
  • Review of world-wide studies using ambient vibrations.
10:30-11:30 Scientific issues regarding use of ambient noise for site characterization Lecture
 
  • Results from an international benchmark performed within the last ESG2006 Symposium.
11:30-11:45 Coffee break
11:45-12:45 Single station measurement, H/V Lecture
 
  • Computation and interpretation of horizontal to vertical spectral ratio technique (H/V)
  • Effects of experimental conditions.
12:45-13:30 Introduction to sesarray package Exercises
 
  • Sesarray software philosophy.
  • Introduction to general features (figures handling, on-line command tools, data management, etc ...) .
 
13:30-15:00 Lunch break
15:00-15:30 Introduction to sesarray package (continued) Exercises
 
  • Sesarray software philosophy.
  • Introduction to general features (figures handling, on-line command tools, data management, etc ...) .
 
15:30-16:30 Single station measurement, H/V Exercises
 
  • Geopsy tools for H/V.
  • Field data exemples.
16:30-16:45 Coffee break
16:45-18:00 Single station measurement, H/V (continued) Exercises
 
  • Geopsy tools for H/V.
  • Field data exemples.
Sunday
9:00-11:00 Basic array processing concepts (conventional and high-resolution frequency wavenumber, f-k) Lecture
 
  • Overview array processing methods.
  • The intuitive shift-and-sum technique in time domain and its transposition into the frequency wavenumber (f-k) domain.
  • Discrete spatial sampling of the continuous seismic wave field (by small groups of seismic stations - arrays) : concepts of resolution and aliasing.
  • Resolution and aliasing of simple linear array layouts and generalisation to bi-dimensional array settings.
  • Relation between array geometry and resulting estimation capabilities: rules of thumb and the array response function.
  • Background of a widely used method, the high resolution f-k method after Capon (1969).
11:00-11:15 Coffee break
11:15-12:45 Array geometry and f-k response Exercices
 
  • Computation of array response with build_array software: optimum usage and functionalities.
  • Building experience on how modifications in array layout affect the theoretical array performances.
12:45-13:30 Conventional and high-resolution f-k processing Exercises
 
  • Application of the conventional and high-resolution f-k algorithms to estimate the dispersion curves from noise recorded in Volvi basin within SESAME project.
13:30-15:00 Lunch break
15:00-16:30 Conventional and high-resolution f-k processing (continued) Exercises
 
  • Application of the conventional and high-resolution f-k algorithms to estimate the dispersion curves from noise recorded in Volvi basin within SESAME project.
16:30-16:45 Coffee break
16.45-18.00 Conventional and high-resolution f-k processing (continued) Exercise
 
  • Application of the conventional and high-resolution f-k algorithms to estimate the dispersion curves from noise recorded in Volvi basin within SESAME project.
Monday
9:00-10:30 Spatial autocorrelation method (SPAC) Lecture
 
  • Background of the spatial autocorrelation technique (SPAC) introduced by Aki (1957).
10:30-10:45 Coffee break
10:45-13:30 Spatial autocorrelation method (SPAC) Exercise
 
  • Application of the method to the real data set, previously mentioned.
13:30-15:00 Lunch break
15:00-16:30 Active surface waves technique (MASW) Lecture and exercise
 
  • The MASW technique: theory, acquisition, processing and resolution limits.
  • Application of MASW to real data recorded in Volvi basin.
16:30-17:00 Coffee break
17:00-18:00 Active surface waves technique (MASW) Exercices and moderated discussion
 
  • Comparison of the methods used for array and MASW processing, advantages and limitations of each approach.
Tuesday
8:00-18:00 Field experiment Field
 
  • Introduction to seismic equipment.
  • Field experiment in Volvi basin (noise array and MASW).
21:00-... Workshop Diner
Wednesday
9:00-11:00 Dispersion curve inversion Lecture
 
  • Short introduction to the fundamentals of inversion theory.
  • Direct search methods based on a random sampling, and particularly the Neighbourhood algorithm.
  • Specific issues solved for the inversion dispersion curves: robustness of the forward computation, non-uniqueness of the final solution.
11:00-11:15 Coffee break
11:15-13:30 Dispersion curve inversion Exercises
 
  • Introduction to dinver software
  • Inversion of theoretical dispersion curve in order to identify critical issues.
  • Model parameterisation and parameter range (vP, vS), a natural way to introduce prior information and to reduce the non-uniqueness.
13:30-15:00 Lunch break
15:00-16:45 Dispersion curve inversion Exercises
 
  • Inversion of synthetic dispersion and autocorrelation curves.
  • Influence of the frequency range used for inversion.
  • Influence of prior information for reducing non-uniqueness.
16:45-17:00 Coffee break
17:00-18:00 ... Dispersion curve inversion Exercises
 
  • Integrating to a single dispersion curve (autocorrelation curve) dispersion curves (autocorrelation curves) obtained through different processing.
Thursday
9:00-11:00 Processing field data. Exercises
 
  • Analysis of the signals recorded on the field with f-k, high-resolution f-k, SPAC and MASW techniques.
11:00-11:15 Coffee break
11:15-13:30 Processing field data. Exercices
 
  • Analysis of the signals recorded on the field with f-k, high-resolution f-k, SPAC and MASW techniques.
  • Comparison with dispersion/autocorrelation curves obtained in previous measurements .
13:30-15:00 Lunch break
15:00-16:45 Processing field data Exercises
 
  • Combining results of arrays dispersion/autocorrelation curves estimated by the different arrays.
  • Decision on the usable frequency range for the inversion target.
  • Inversion of dispersion/autocorrelation curve in order to derive velocity model.
16:45-17:00 Coffee break
17:00-18:30 ... Processing field data Exercices
 
  • Inversion of dispersion/autocorrelation curve in order to derive velocity model.
Friday
9:00-11:00 Discussion of results from data sets Moderated discussion
 
  • Comparison of the individual results obtained during the inversion.
  • General discussion of experience gained during this complete test.
11:00-11:15 Coffee break
11:15-13:30 Course summary Discussion
 
  • Summary of the various steps involved for the task of ambient vibration array and MASW analysis and site characterisation by the inversion of one-dimensional earth models. Recall of the advantages and limitations of using ambient vibrations to site characterisation.
13:30-15:00 Lunch break
15:00-... Departure of Participants Open discussion

Suggested readings

All deliverables and reports of the SESAME project are available here (especially, D18.06, D19.06, D24.13 may be of interest).

Registration and Fees

This international training course is opened to any student/researcher/engineer from any country. To offer the best attention to each of the course attendees, the maximum number of participants is fixed to 15. A minimum of 8 registrations is required for the organisation of this session. The official language is english.

Online registration is open until October 20th 2008. If the number of applicants is greater than 15, the organisers reserve their rights to select the participants, who will be informed few days after the registering deadline. The main criteria for selection will be: PhD students, young researchers, researchers and engineers involved in on-going or future microzonation or site response projects.

The registration fee is fixed to 800 euros per participant for applicants from public institutions and to 1200 euros per participant for applicants from private companies.

The fees, dedicated to cover course related costs, include lectures, practical exercises, the workshop dinner, coffee breaks and the cost of field trip. One computer per participant will be made available during the exercises. Besides, the course will take place in an hotel downtown Thessaloniki.

Contacts

Cécile Cornou cecile dot cornou at obs dot ujf-grenoble dot fr
Alexandros Savvaidis alekos at itsak dot gr
Marc Wathelet marc dot wathelet at ujf-grenoble dot fr
Matthias Ohrnberger mao at geo dot uni-potsdam dot de
Bertrand Guillier bertrand dot guillier at obs dot ujf-grenoble dot fr

Archives

Here you can find the program of last editions and all photos taken during these courses: