Figure - available from: Journal of Seismology
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Frequency–amplitude curve (blue curve). Standard deviation is represented by the grey-shaded area. The red horizontal line indicates maximum amplitude A0 and interpolated f0 (f0int) and is computed after resampling the .hv curve generated by Geopsy. The standard deviation on f0 (err) is indicated by dashed grey lines. The frequency–amplitude curve is converted to a virtual borehole by using the frequency-depth power law relation R’ developed in this study, with the amplitude as bedrock depth uncertainty. Example = Kleine hut borehole at Uccle, Brussels (A201; true bedrock at 0-m altitude, HVSR model predicts bedrock at 10 m altitude). TAW (‘Tweede Algemene Waterpassing’) = reference altitude in Belgium. See Electronic Supplement S3 for virtual boreholes of all data. See Van Noten et al. (2020) for the HVSR to Virtual Borehole python code to generate this figure
Source publication
The empirical power law relation (PR) between resonance frequency (f0), obtained from H/V spectral ratio analysis of ambient noise, and sediment thickness (h), obtained from boreholes, is frequently used in microzonation studies to predict bedrock depth. In this study, we demonstrate (i) how to optimally construct a PR by including the error on the...
Citations
... While HVSR amplitude values can approximate the ratio of S-wave and P-wave amplification spectra [Herak, 2008], they tend to underestimate the actual level of site amplification and cannot be directly used to approximate the levels of S-wave amplifications [Zhu et al., 2020]. Arai and Tokimatsu [2004a] proposed a method to estimate the S-wave velocity profile at specific sites by inverting the HVSR amplitude spectrum and resonance frequencies of microtremors, which is now widely used as a simple approach to seismic three-component surveys [van Noten, 2022;Spica et al., 2017; van Ginkel et al., 2020]. ...
Macroseismic intensity data have been gathered continuously in Belgium since the start of the twentieth century. In this study, we review the applied survey practices used over the previous century: from small-scale ad-hoc improvised surveys to the mass distribution of collective questionnaire versions sent to local authorities. The variety of survey methodologies causes a high degree of heterogeneity within the resulting macroseismic data, increasing the uncertainty in macroseismic applications that rely on homogeneous data. We thoroughly re-evaluated the original source material and intensity scale conversions in order to create the Belgian Traditional Macroseismic (BTM) database, a comprehensive compilation of 20th-century macroseismic data in which all sources are properly referenced. The BTM database currently consists of 23,950 intensity data points (IDPs) on the European Macroseismic Scale for 80 felt earthquakes, ranging from 2.4 to 5.8 on the local magnitude (ML) scale. Each IDP is provided with a source type and each earthquake is attributed a data quality parameter that indicates the level of uncertainty associated with its IDP source quality. The publication of the BTM database facilitates the use of Belgian macroseismic data for a variety of seismological purposes and allows us to summarize the overall seismic impact on Belgium for the duration of a century. Like in many other parts of the world, traditional procedures have practically been discontinued in Belgium in favour of an online enquiry. However, the potential for high-quality data following a traditional survey methodology is still large and we strongly recommend its continuation.
The use of Nodal systems based on autonomous geophone-based instruments entered the field of Seismology only recently. These lightweight solutions revolutionized seismological fieldwork through lightweight and wholistic instruments that are faster to deploy and easier to handle. The IGU-16HR series of SmartSolo® is one example, but yet lacking a thorough lab-based performance analysis. Here, we fill the knowledge gap, by performing a series of lab and field-based tests that focus on the sensors performance. The investigated parameters are the instruments transfer function, self-noise and overall performance to classical seismometer-based instruments. In the real-world application we show examples of H/V measurements of ambient vibrations in urban environments and the performance ranges with teleseismic waveform recordings. Under lab conditions, the nodal systems perform equally well as standard seismometers (e.g., Lennartz 3D/5s), even in the frequency range down to 0.2Hz, way below their natural frequency. The restitution can be carried out correctly with manufacturer given transfer function. At least for the vertical component, the instruments self-noise reaches the lower boundary of the global minimum noise level, confirming the ability to properly record teleseismic phases down to 0.1 Hz. In ambient noise studies the instrument limits are already reached at 0.8 Hz, but still resolve the fundamental frequencies within the methods uncertainty ranges, based on classical instrument data. These versatile and easy-to-use nodal systems are useful and reliable for a wide range of seismological applications. In addition, their installation is faster and reduced prices open the doors towards Large N installations and research studies for groups that face limited financial budgets.
