Development of a seismic site-response zonation map for the Netherlands

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.

New Challenges for Seismic Risk Mitigation in Urban Areas

“…We show that peat content plays an important role in P-wave ground motion amplification. while S-wave amplification is largely controlled by the stiffness of the Holocene sediments (van Ginkel et al, 2019(van Ginkel et al, , 2021. These insights are relevant for the Groningen region and as a consequence, it is not recommended to use the standard practise for assigning a single-value fraction of horizontal ground motion in order to assess motion in the vertical direction as suggested by ; Newmark et al (1973); Loads (2017) is not recommended.…”

“…Although the maximum magnitude of the local earthquakes is relatively low, the ground motions form a risk since the existing buildings and infrastructures are not built to withstand earthquake shaking. The Groningen shallow subsurface consists of low-velocity, unconsolidated sediments with strong site amplification which has been studied in detail for motions in the horizontal direction (Bommer J. J. et al, 2017;Rodriguez-Marek et al, 2017;van Ginkel et al, 2019van Ginkel et al, , 2021. So far, it has been assumed that for these low-magnitude earthquakes, vertical ground motion is not of enough importance to incorporate into the ground motion model and in seismic design for buildings (Bommer J. et al, 2017).…”

Induced seismicity red-light thresholds for enhanced geothermal prospects in the Netherlands

“…3b and S2), we also consider a global slope-based proxy for V S30 (Heath et al, 2020). Site amplification could also be updated with more sophisticated models, as they become available (van Ginkel et al, 2022). We consider variances in all of these models via their reported standard errors.…”

Capturing spatial variability in the regional Ground Motion Model of Groningen, the Netherlands

“…Other parameters include the site fundamental period obtained from earthquake horizontal-to-vertical spectral ratios (e.g. Zhu et al, 2020 andvan Ginkel et al, 2022). In the GMM, V S profiles were used in the site response calculations.…”