Abstract
Abstract. Earthquake site response is an essential part of seismic hazard assessment, especially in densely populated areas. The shallow geology of the Netherlands consists of a very heterogeneous soft sediment cover, which has a strong effect on the amplitude of ground shaking. Even though the Netherlands is a low- to moderate-seismicity area, the seismic risk cannot be neglected, in particular, because shallow induced earthquakes occur. The aim of this study is to establish a nationwide site-response zonation by combining 3D lithostratigraphic models and earthquake and ambient vibration recordings. As a first step, we constrain the parameters (velocity contrast and shear-wave velocity) that are indicative of ground motion amplification in the Groningen area. For this, we compare ambient vibration and earthquake recordings using the horizontal-to-vertical spectral ratio (HVSR) method, borehole empirical transfer functions (ETFs), and amplification factors (AFs). This enables us to define an empirical relationship between the amplification measured from earthquakes by using the ETF and AF and the amplification estimated from ambient vibrations by using the HVSR. With this, we show that the HVSR can be used as a first proxy for site response. Subsequently, HVSR curves throughout the Netherlands are estimated. The HVSR amplitude characteristics largely coincide with the in situ lithostratigraphic sequences and the presence of a strong velocity contrast in the near surface. Next, sediment profiles representing the Dutch shallow subsurface are categorised into five classes, where each class represents a level of expected amplification. The mean amplification for each class, and its variability, is quantified using 66 sites with measured earthquake amplification (ETF and AF) and 115 sites with HVSR curves. The site-response (amplification) zonation map for the Netherlands is designed by transforming geological 3D grid cell models into the five classes, and an AF is assigned to most of the classes. This site-response assessment, presented on a nationwide scale, is important for a first identification of regions with increased seismic hazard potential, for example at locations with mining or geothermal energy activities.
Highlights
Site-response estimation is a key parameter for seismic hazard assessment and risk mitigation, since local lithostratigraphic conditions can strongly influence the level of ground motion amplification during an earthquake (e.g. Bard, 1998; Bonnefoy-Claudet et al, 2006b, 2009; Borcherdt, 1970; Bradley, 2012)
Rather than using ground motion prediction equations with generic site amplification factors conditioned on Vs30, we propose a novel approach for the development of a nationwide zonation of amplification factors
Since the ambient noise sources in the frequency band of interest (1–10 Hz) partly have an anthropogenic origin, one should be careful about contamination by local strong noise because it may seriously affect the amplitude of the horizontal-to-vertical spectral ratio (HVSR) as shown in Guillier et al (2007) and Molnar et al (2018)
Summary
Site-response estimation is a key parameter for seismic hazard assessment and risk mitigation, since local lithostratigraphic conditions can strongly influence the level of ground motion amplification during an earthquake (e.g. Bard, 1998; Bonnefoy-Claudet et al, 2006b, 2009; Borcherdt, 1970; Bradley, 2012). Site-response estimation is a key parameter for seismic hazard assessment and risk mitigation, since local lithostratigraphic conditions can strongly influence the level of ground motion amplification during an earthquake Bard, 1998; Bonnefoy-Claudet et al, 2006b, 2009; Borcherdt, 1970; Bradley, 2012). J. van Ginkel et al.: Development of a seismic site-response zonation map for the Netherlands face. This can be retrieved from in situ investigations; this is a costly procedure. Because of the time and costs involved, there is a lack of site-response investigations covering large areas, while the availability of detailed and uniform ground motion amplification maps is fundamental for preliminary estimates of damage on buildings Because of the time and costs involved, there is a lack of site-response investigations covering large areas, while the availability of detailed and uniform ground motion amplification maps is fundamental for preliminary estimates of damage on buildings (e.g. Falcone et al, 2021; Gallipoli et al, 2020; Bonnefoy-Claudet et al, 2009; Weatherill et al, 2020)
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