Site effect analysis by H/V Spectral Ratio analysis

From H/V Spectral ratio analysis to bedrock depth ?

Estimating the sediment thickness and the geometry of the bedrock is a key component of many hydrogeological and seismic studies and can be of major importance to understand how earthquake waves are transferred or attenuated through the upper crust. Among other aims, the horizontal- to vertical (H/V) spectral ratio ambient noise is a non-invasive passive seismic method that has been used to estimate the depth of the bedrock below sedimentary layers. The H/V method (Nakamura, 1989) uses a single, broad-band three-component seismometer to record ambient vibrations produced by local surface sources such as traffic and other human activities or from far-distance sources such as oceanic waves and wind for lower noise levels. The seismic noise recorded are signals of low-amplitude motions of the ground. Periods from noise associated to wind and human activities are predominantly below 0.1 Hz, whereas noise generated by near-shore oceanic waves and current is at higher periods (SESAME, 2005). For the measurement of the ambient noise I use a 24-bit Cityshark II acquisition system (LEAS) connected to a 3-component LE-3D/5s Lennartz seismometers. The seismometer allows recording ambient noise measurements between 0.2 Hz and 50 Hz and adjustment of the sampling rate. The spectral analysis is performed by using the open source GEOPSY software (Wathelet, 2005) and is mainly used to compute a sit's resonance frequency. The resonance frequency can be interpreted using regression equations to estimate depth to the bedrock and eventually also sediment thickness.

Currently, I'm working on H/V data gathered in Brussels to improve the bedrock depth map below the city. This in collaboration with the Geological Survey of Belgium.

In the past, I collaborated with T. Lecocq to develop a new workflow that includes the automated H/V calculation of continuous seismic data of a stationary station installed near a microzonation site. Continuous analysis benefits from nightly measurements that allow controlling the variation in HVSR results obtained by mobile stations during the day. This research is still in progress but offers great possibilities to improve bedrock depth estimations.

Conference presentations on H/V spectral ratio analysis, geophysical prospection and surface wave analysis

1. Van Noten, K., Burlet, C. Delaby, S., Lecocq, T. Jaubert, J., Verheyden, S. and the Bruniquel Team. 2018. Electric and passive seismic geophysical survey in a protected cave environment: the Bruniquel cave (France). 6th International Geologica Belgica Meeting. 12-14 September 2018. KU Leuven, Belgium. Poster presentation
2. Van Noten, K., Devleeschouwer, X., Goffin, C., Meyvis, B., Lecocq, T. 2018. Bedrock morphology modelling using geologically-dependent empirical equations between resonance frequency and bedrock depth. Geophysical Research Abstracts 18, EGU2018-10539, session SM4.02, 8-13 april 2018, Vienna. Oral presentation.
3. Burlet, C., Van Noten, K., Delaby, S., Lecocq, T., Verheyden, S., Genty, D. and Jaubert, J. 2018. Passive geophysics inside underground cavities: examples of HVSR surveys in the caves of Han-sur-Lesse, Belgium and Bruniquel, France. Geophysical Research Abstracts 18, EGU2018-16600, session SM4.02, 8-13 april 2018, Vienna.
4. Burlet, C., Delaby, S., Lecocq, T., Van Noten, K. & Verheyden, S.2017. Prospection géophysique non-invasive dans la grotte de Bruniquel (Tarn-et-Garonne, France). Journées 2017 de Spéléologie Scientifique, Han-Sur-Lesse, 18-19 November 2017.
5. Lecocq, T., Van Noten, K., Verheyden, S., Burlet, C. & Delaby, S. 2016. Investigations Géophysiques dans la Grotte de Han (salle Cornet): "Préparation pour Bruniquel". Journées 2016 de Spéléologie Scientifique, Han-Sur-Lesse, 11-13 November 2016.
6. Van Noten, K. & Lecocq, T. 2016. Continuous H/V Spectral Ratio Analysis of Ambient Noise: a necessity to understand microzonation results obtained by mobile stations. Geophysical Research Abstracts 18, EGU2016-4609, session SM2.2/NH4.13, 17-22 April 2016, Vienna, Austria.
7. Van Noten, K., Lecocq, T., Meyer, L., Molron, J. & Camelbeeck, T. 2015. Continuous H/V Spectral Ratio Analysis of Ambient Noise Recorded by Stationary Seismic Stations to Improve Microzonation Results Obtained by Mobile Stations. American Geophysical Union, AGU2015-NS41B-1936, 14-18 December 2015, San Francisco, USA.
8. Van Noten, K., Lecocq, T., Molron, J., Camelbeeck, T. & Van Camp, M. 2015. Shear wave velocity estimation of cover sediments by seismic array measurements. Geophysical Research Abstracts 17, EGU2015-7445, session SM4.1, 12-17 April 2015, Vienna.
9. Watlet, A., Van Noten, K., Lecocq, T., Chamber, J., Meldrum, P., Francis, O., Van Camp M., Kaufmann, O. 2014. Hydrogeophysical tools for investigating groundwater storage in the subsurface of a karst system, Near Surface Geoscience, Athens, September 2014
10. Van Noten, K., Lecocq, T., Watlet, A., Camelbeeck, T., 2014. Modelling sediment thickness for site-effect characterisation using H/V spectral ratio analysis and electrical resistivity tomography. Geophysical Research Abstracts 16, EGU2014-13252, session SM2.3, 27 april - 2 May 2014.
11. Van Noten, K., Lecocq, T. & Camelbeeck, T. 2013. Using H/V Spectral Ratio Analysis to Map Sediment Thickness and to Explain Macroseismic Intensity Variation of a Low-Magnitude Seismic Swarm in Central Belgium. American Geophysical Union, AGU2013-S53B-2406, 9-13 December 2013, San Francisco, USA.
12. Van Noten, K., Lecocq, T, Verbeeck, K., Vanneste, K. & Camelbeeck, T. 2012. Modelling the palaeotopography of the Brabant Massif: a necessity to understand the site effects of the 2008-2011 seismic activity in the Brabant Walloon. 4th International Geologica Belgica Meeting, 11-14 September 2012, Brussels, Belgium