Vibration Levels at Foundations of Houses in Groningen Due To
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Stieltjesweg 1 2628 CK Delft P.O. Box 155 2600 AD Delft The Netherlands TNO report www.tno.nl 2017 R10493-A T +31 88 866 20 00 Vibration levels at foundations of houses in F +31 88 866 06 30 Groningen due to induced earthquakes Date 30 June 2017 Author(s) ir. J.P. Pruiksma Á. Rózsás PhD Copy no 0100304947-A No. of copies Number of pages 115 (incl. appendices) Number of appendices Sponsor Nationaal Coördinator Groningen (NCG) Postbus 3006 9701 DA Groningen Project name Onderzoek Oorzaken Schades Project number 060.24911 All rights reserved. No part of this publication may be reproduced and/or published by print, photoprint, microfilm or any other means without the previous written consent of TNO. In case this report was drafted on instructions, the rights and obligations of contracting parties are subject to either the General Terms and Conditions for commissions to TNO, or the relevant agreement concluded between the contracting parties. Submitting the report for inspection to parties who have a direct interest is permitted. © 2017 TNO TNO report | 2017 R10493-A 2 / 71 Abstract This study investigates the vibrations on the foundation level of houses in the Groningen area. Its objective is to determine the earthquake-induced vibration levels and the associated uncertainties of past induced earthquakes. The study was initiated by the Nationaal Coördinator Groningen (NCG) and it is a component of a larger project lead by the Delft University of Technology (TU Delft). The main research question of that larger project is: What are the most probable causes of the reported damages of buildings in the Groningen region? This current study deals with one of such causes: induced earthquakes. Solely historical seismic events are considered and acceleration and velocity data are obtained from the TNO and KNMI sensors installed in the region. The historical seismic events are divided into two sets: (a) events with both TNO and KNMI data (five events in total since 2014-09-29); and (b) events with KNMI data only (nine events in total earlier than 2014-09-29). For each event in set (a) ground motion prediction equations (GMPE) are fitted to the TNO measurements using statistical techniques (referred to as T1.1 type GMPE in this study). Horizontal and vertical GMPEs are fitted to both velocity and acceleration as vibration intensity measures. For set (b) the most recent model available in the literature for the Groningen area is adapted for the purpose of this study (referred to as adapted V2 type GMPE in this study). For these events, only horizontal GMPEs are available. Both models (T1.1 and adapted V2) explicitly consider the uncertainty and variability of induced seismic events. This allows the calculation of exceedance probabilities of selected velocity and acceleration thresholds at any given location for historical seismic events. The main results in terms of GMPEs are collected in a Microsoft Excel workbook and provided to this report as a digital annex to facilitate the probabilistic damage assessment of buildings. Based on the completed analyses the following main conclusions and recommendations are drawn: • The TNO and KNMI measurements are in good agreement for both velocity and acceleration. The KNMI data are mostly within the 95% confidence band of T1.1 fitted to TNO measurements. • The T1.1 model is recommended to be used for (historical) seismic events for which TNO measurements are available, otherwise the adapted V2 model is advocated. • For the analysis of future seismic events the parameters of the T1.1 model can be determined using the same procedure as used for the five historical events in this study. TNO report | 2017 R10493-A 3 / 70 Contents Abstract .................................................................................................................... 2 Nomenclature ........................................................................................................... 4 1 Introduction .............................................................................................................. 6 1.1 Background ................................................................................................................ 6 1.2 Objective .................................................................................................................... 6 1.3 Approach ................................................................................................................... 6 1.4 Outline of the report ................................................................................................... 7 2 Data under study ..................................................................................................... 9 2.1 TNO database ........................................................................................................... 9 2.2 KNMI database ........................................................................................................ 16 3 Tools and methods ................................................................................................ 21 3.1 Earthquake engineering models .............................................................................. 21 3.2 Statistical tools ......................................................................................................... 29 4 Analysis of non-seismic events ........................................................................... 31 4.1 Overview .................................................................................................................. 31 4.2 Heartbeat data ......................................................................................................... 31 4.3 Statistical analysis of non-seismic events ............................................................... 33 5 Separate analysis of seismic events ................................................................... 41 5.1 Events with TNO and KNMI data ............................................................................. 41 5.2 Events with only KNMI data ..................................................................................... 59 5.3 Delivery of results .................................................................................................... 60 6 Discussion and recommendations ...................................................................... 64 7 Acknowledgments ................................................................................................. 67 8 References ............................................................................................................. 68 9 Signature ................................................................................................................ 70 Appendices A Digital annexes B Data – technical details C Tools and methods – technical details D Analysis of non-seismic events – technical details E Separate analysis of seismic events – technical details F Computer codes TNO report | 2017 R10493-A 4 / 70 Nomenclature Roman symbols AIC Akaike information criterion BIC Bayesian information criterion B Bayes factor F(.) cumulative distribution function f(.) density function IM intensity measure, i.e. velocity or acceleration in this report L(.) likelihood function l(.) log-likelihood function M earthquake magnitude R modified epicentre distance Repi epicentre distance SaX spectral acceleration from a seismic or non-seismic event in local X direction SaY spectral acceleration from a seismic or non-seismic event in local Y direction SaZ spectral acceleration from a seismic or non-seismic event in vertical (Z) direction Samax(X,Y) spectral accelerations from a seismic or non-seismic event in local X and local Y directions; max(SaXY , Sa ) SvX peak ground velocity from a seismic or non-seismic event in local X direction SvY peak ground velocity from a seismic or non-seismic event in local Y direction SvZ peak ground velocity from a seismic or non-seismic event in vertical (Z) direction Svmax(X,Y) maximum of peak ground velocities from a seismic or non-seismic event in local X and local Y directions; max(SvXY , Sv ) Greek symbols /θ inferred parameter(s) (.) univariate standard normal cumulative distribution function (.) univariate standard normal cumulative distribution function standard deviation error term (a random variable with standard normal distribution) median Other symbols ~ distributed as Acronyms/abbreviations AIC Akaike information criterion TNO report | 2017 R10493-A 5 / 70 BIC Bayesian information criterion GMP ground motion prediction GMPE ground motion prediction equation ID identification code KNMI Royal Netherlands Meteorological Institute LS least squares estimation mad median absolute deviation med median MLE maximum likelihood estimation NAM Nederlandse Aardolie Maatschappij NCG Nationaal Coördinator Groningen Sa peak ground acceleration Sv peak ground velocity std standard deviation TNO The Netherlands Organisation for Applied Scientific Research TNO report | 2017 R10493-A 6 / 70 1 Introduction 1.1 Background ln the north-eastern part of The Netherlands, induced earthquakes occur, as a result of the extraction of natural gas. These earthquakes cause ground-borne vibrations that transfer to the foundations of buildings causing the building itself to vibrate. These vibrations may result in damage to the building. Many building owners in the area have reported damage to buildings in varying degrees of severity. The Nationaal Coördinator Groningen (NCG) has asked Delft University of