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Using Ambient Vibration Techniques for Site Characterization and Seismic Microzonation

Monday, March 4th to Sunday, March 10th 2019
L'Aquila, Italy

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

Regione Abruzzo  INGV  IRD  UP  CNRS  UGA  USMB  EPOS  SERA 

Over the last decades, 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 usually adopted in microzoning activities within highly populated regions.

Within the EU-SESAME, EU-SISMOVALP, EU-NERIES, EU-EPOS and EU-SERA projects, detailed research have been accomplished to assess both the reliability and robustness of ambient vibration analysis techniques for extracting soil dynamic properties (site characterization). Within this context hardware and open-source software developments have been carried out to ease the acquisition, processing and interpretation of ambient vibration 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 starting assumptions, the interpretation and the inversion of analysis results need a (self-)critical review.

The main purpose of this training course is thus to achieve the necessary understanding of the problems related to the acquisition and use of these techniques based on ambient vibration analysis. The final goal of such techniques is the quantitative assessments of shear-wave velocity structure.

The course is divided in two parts:

This course is targeted to students, engineers and researchers. Little or no experience with ambient vibrations and/or Geopsy software is required to attend the first six days. The second part of the course (Saturday afternoon and Sunday) will gather several experts from broad scientific horizons. All participants of the first part are also invited to attend.

Contributions

This training course is:

organised by ISTerre (Grenoble, France), INGV (L'Aquila, Italy), Institute of Earth and Environmental Science (Potsdam, Germany)
presented by Cécile Cornou, Giuseppe Di Giulio, Bertrand Guillier, Matthias Ohrnberger and Marc Wathelet

The open-source software development of Geopsy package is (was) supported by NERIES (EU-Project, 2006-2010), SESAME (EU-Project, 2001-2004) , Sismovalp (Interreg IIIB, Alpine Space, 2004-2006), EPOS-IP (EU-Project), SERA (EU-project), and IRD

Course outline

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

Monday 4th March
09:00-09:30 Reception and welcome  
 
  • Technical issues and program overview
09:30-10:30 Physical background of ambient vibrations 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.
  • INTERPACIFIC results.
  • Current scientific or practical questions to be addressed.
11:15-11:30 Coffee break
11:30-12:30 Introduction to Geopsy software package Exercise
 
  • Geopsy package philosophy.
  • Introduction to general features (figures handling, on-line command tools, data management, etc ...).
12:30-14:00 Lunch break
14:00-16:00 Single-station measurement, H/V Exercises
 
  • Computation and interpretation of horizontal to vertical spectral ratio technique (H/V) - (Rayleigh wave ellipticity versus diffuse wave field).
  • Effect of experimental conditions
  • 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 5th March
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 theoretical array response function.
  • gpfksimulator for showing possible problems/bias
  • Background of a widely used method, the high resolution f-k method after Capon (1969).
10:45-11:00 Coffee break
10:45-12:30 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 6th March
8:30-9:45 L'Aquila region from a seismic risk perspective Lecture
 
  • Geological structures, historical seismicity, building vulnerability
  • Available data sets for L'Aquila region and recent 2016-2017 seismicity in central italy (very briefly)
9:45-10:00 Coffee break
10:00-13:00 Field work Exercises
 
  • Setting up a small-aperture 2D array
12:30-14:00 Lunch break
14:00-16:00 Spatial autocorrelation method (SPAC) Lecture
 
  • Background of the spatial autocorrelation technique (SPAC) introduced by Aki (1957).
  • MSPAC / ESAC / Two stations SPAC / Long-term Cross-Correlation
16:00-16:15 Coffee break
16:15-18:30 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.
19:00-... Workshop Dinner
Thursday 7th March
09:00-10:45 Processing field data Exercises
 
  • Analysis of the signals recorded on the field: H/V / Ellipticity / f-k, high-resolution f-k, SPAC
10:45-11:00 Coffee break
11:00-12:30 Processing field data (continued) Exercises
 
  • Analysis of the signals recorded on the field: H/V / Ellipticity / f-k, high-resolution f-k, SPAC
12:30-14:00 Lunch break
14:00-16:00 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.
  • Combining Rayleigh dispersion curves with other observable: elliptiicty peak, ellipticity curves and Love dispersion curves
16:00-16:15 Coffee break
16:15-18:00 Dispersion curve inversion Exercises
 
  • Introduction to dinver software
  • Inversion of a 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.
Friday 8th March
9:00-12:30 Continuing analysis and Inversion on Field data Exercises
 
  • Inversion of dispersion curves found in previous exercises.
  • Handling shear-wave profiles: extraction of useful engineering parameters (e.g. Vs30).
12:30-14:00 Lunch break
14:00-16:00 Continuing analysis and Inversion on Field data Exercises
 
  • Handling shear-wave profiles: extraction of useful engineering parameters (e.g. Vs30, SH response).
16:00-16:15 Coffee break
16:00-17:30 Discussion of results from data sets Modarated discussion
 
  • Comparison of the individual results obtained during the inversion.
  • General discussion of experience gained during this complete test.
Saturday 9th March
09:00-12:30 Course summary. Discussion
 
  • Summary of the various steps involved for the task of ambient vibration array 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
14:00-18:00 Advanced techniques for better site caracterizations Workshop
 
  • H/V inversion (diffuse wavefield, Rayleigh ellipticiy)
  • Detailed program under preparation
Sunday 10th March
09:00-12:00 Advanced techniques for better site caracterizations Workshop
 
  • Three-component array methods (Rayleigh, Love, ellipticity)
  • Detailed program under preparation
12:30-14:00 Lunch break
14:00-18:00 Advanced techniques for better site caracterizations Workshop
 
  • Inversion (joint inversion, bayesien approaches, uncertainties)
  • Detailed program under preparation

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 14th 2019. If the number of applicants is larger than 20, the organizers reserve their rights to select the participants who will be informed by January 16th.

The course will take place at L'Aquila, Italy (Via Michele Jacobucci 4, Sala Ipogea, Consiglio Regionale dell'Abruzzo, Abruzzo). The registration fee is fixed to 700 euros per participant. The fees can be paid by bank transfer. The fees include all expenses related to tuition, training, support material, field experiment, workshop dinner, lunches and coffee breaks during the course. They do not include accommodation.

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) during the online registration.

The attendance to the advanced workshop is free of charge. If you want to register only to the advanced workshop you have to register on SERA workshop website

A list of suggested accommodations will be available soon.

Contacts

Cécile Cornou cecile dot cornou at univ-grenoble-alpes dot fr
Giuseppe Di Giulio giuseppe dot digiulio at ingv dot it
Matthias Ohrnberger matthias dot ohrnberger at geo dot uni-potsdam dot de
Bertrand Guillier Bertrand dot Guillier at ird dot fr
Marc Wathelet marc dot wathelet at univ-grenoble-alpes dot fr

Archives

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