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Using Ambient Vibration Array Techniques for Site Characterization and Seismic Microzonation

Monday, February 17th to Sunday, February 23rd 2014
Grenoble, France

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

ujf  cnrs  ird  ifsttar  uds           ieu  isterre

Over the last decade, 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 EU-SESAME, EU-SISMOVALP and NERIES projects, detailed research have been accomplished to assess the reliability and robustness of ambient vibration analysis techniques for site characterization. Within this context open-source hardware and software developments have been carried out to ease the acquisition, processing and interpretation of ambient vibration wave field recordings. The main findings of these projects 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.

The main purpose of this course is thus to achieve the necessary understanding of the problems related to the acquisition and use of these techniques for quantitative assessments of shear-wave velocity structures. This course is targeted to students, engineers and researchers with a minimum background in signal processing for geophysical/seismological applications.

Contributions

This training course is:

organised by ISTerre (Grenoble, France), UP (Potsdam, Germany)
presented by Marc Wathelet (IRD-ISTerre), Cécile Cornou (IRD-ISTerre), Matthias Ohrnberger (UP Potsdam), Bertrand Guillier (IRD-ISTerre) and Philippe Guéguen (IFSTTAR-ISTerre).

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.

Monday
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.
10:30-11:15 Scientific issues regarding use of ambient noise for site characterization Lecture
 
  • Results from an international benchmark performed within the last ESG2006 Symposium.
10:45-11:00 Coffee break
11:30-12:30 Single station measurement, H/V Lecture
 
  • Computation and interpretation of horizontal to vertical spectral ratio technique (H/V)
  • Effects of experimental conditions.
12:30-14:00 Lunch break
14:00-15:15 Introduction to sesarray package Exercises
 
  • Sesarray software philosophy.
  • Introduction to general features (figures handling, on-line command tools, data management, etc ...) .
 
15:15-16:00 Single station measurement, H/V Exercises
 
  • Geopsy tools for H/V.
  • Field data examples.
16:00-16:15 Coffee break
16:15-18:00 Single station measurement, H/V (continued) Exercises
 
  • Geopsy tools for H/V.
  • Field data examples.
Tuesday
9:00-10:45 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).
10:45-11:00 Coffee break
11:00-12:30 Array geometry and f-k response Exercises
 
  • Computation of array response with warangps software: optimum usage and functionalities.
  • Building experience on how modifications in array layout affect the theoretical array performances.
12:30-14:00 Lunch break
14:00-16:00 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 synthetics.
16:00-16:15 Coffee break
16:15-18:00 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 synthetics.
Wednesday
9:00-10:45 Spatial autocorrelation method (SPAC) Lecture
 
  • Background of the spatial autocorrelation technique (SPAC) introduced by Aki (1957).
10:45-11:00 Coffee break
11:00-12:30 Spatial autocorrelation method (SPAC) Exercises
 
  • Application of the method to the synthetic data set, previously mentioned.
  • Comparison with FK estimates: advantages and limitations of each approach.
12:30-14:00 Lunch break
14:00-15:30 Active surface waves techniques (SASW, MASW) and passive linear array technique Lecture and exercises
 
  • The SASW, MASW and passive linear array techniques: theory, acquisition, processing and resolution limits.
  • Application of MASW to real data set.
15:30-16:15 Grenoble basin from a seismic risk perspective Lecture
 
  • Geological structures
  • Historical seismicity
  • Buidling vulnerability
16:15-16:30 Coffee break
16:30-18:00 Preparation of the field experiment Lecture
 
  • Presentation of the WARAN (wireless array network) equipment.
  • Presentation of the active seismic equipment.
Thursday
8:00-18:00 Field experiment Field
 
  • Field experiment in Grenoble downtown (noise array and MASW).
19:00-... Workshop Dinner
Friday
9:00-10:45 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.
10:45-11:00 Coffee break
11:00-12:30 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.
12:30-14:00 Lunch break
14:00-16:00 Dispersion curve inversion (continued) Exercises
 
  • Inversion of dispersion curves found in previous exercises.
16:00-16:15 Coffee break
16:15-17:15 Dispersion (autocorrelation) curve inversion Exercises
 
  • Influence of the frequency range and prior information.
  • Integrating to a single dispersion curve (autocorrelation curve) dispersion curves (autocorrelation curves) obtained through different processing.
  • Handling shear-wave profiles: extraction of usefull engineering parameters (e.g. Vs30).
Saturday
9:00-10:45 Processing field data. Exercises
 
  • Analysis of the signals recorded on the field with f-k, high-resolution f-k, SPAC and MASW techniques.
10:45-11:00 Coffee break
11:00-12:30 Processing field data. Exercises
 
  • Analysis of the signals recorded on the field with f-k, high-resolution f-k, SPAC and MASW techniques.
12:30-14:00 Lunch break
14:00-16:00 Processing field data. Exercises
 
  • Combining results of arrays dispersion/autocorrelation curves estimated by the different arrays.
  • Comparison with dispersion/autocorrelation curves obtained in previous measurements .
  • Decision on the usable frequency range for the inversion target.
16:00-16:15 Coffee break
16:15-18:00 ... Processing field data. Exercises
 
  • Inversion of dispersion/autocorrelation curve in order to derive velocity model.
  • Extraction of velocity models and Vs30.
Sunday
9:00-10:45 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.
10:45-11:00 Coffee break
11:00-12:30 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.
12:30-14:00 Lunch break
14:00-... 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 course aims at transfering and promoting scientific and technical achievements of current and past research projects. This course is targeted to students, engineers and scientists with a background in signal processing for geophysical/seismological applications. The official language is English.

Online registration is open until January 16th 2014. If the number of applicants is larger than 20, the organizers reserve their rights to select the participants who will be informed by January 17th.

The course will take place at ISTerre, Grenoble, France. The registration fee is fixed to 1500 EUROS per participant excluding accommodation. The fees include all expenses related to tuition, training, support material, field experiment, workshop diner, lunches and coffee breaks during the course. Profits will support further developments and improvements of Geopsy.org tools. For French applicants, this course is provided through CNRS formation entreprise, recognized as a training organization (N° 117 537 671 75).

Participants are requested to attend the course with their own laptop, if possible. In such a case they are requested to indicate their operating system (windows/linux/mac, etc.) during the online registration.

A list of suggested accommodations will be available soon.

Contacts

Cécile Cornou cecile dot cornou at ujf-grenoble dot fr
Marc Wathelet marc dot wathelet at ujf-grenoble dot fr
Matthias Ohrnberger mao at geo dot uni-potsdam dot de

Archives

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