KEM-02 Evaluation, validation and improvement of the site amplification component of the SHRA Groningen

Local site-amplification in the Groningen areas is an important factor influencing the damage potential. Site-amplification is observed to be spatially highly variable, due to the complex geological setting especially of the shallow subsurface (e.g., loosely packed sands, peat and 'knipklei'). While the existing Groningen seismic hazard and risk model has implemented a detailed layer of local site amplification, in parts based on micro-zonation measurement, independently evaluating and validating this model, also against the most recent data observed with the densified seismic observation network, are important goals.

The objectives of this project are thus:
1) To evaluate the site-amplification model, its sensitivities and the quality and resolution of the data available to constrain it
2) To validate how well the Groningen seismic hazard and risk model performed again the most recent data, thus evaluating its forecasting skill
3) To propose measurements and improvements to the model that would reduce the uncertainty in prediction local ground motions

RESEARCH REQUEST FULL TEXT

The project results are reported in three reports.

WP1 REPORT RESEARCH QUESTION 1
WP2 REPORT RESEARCH QUESTION 2
FINAL REPORT

The KEM-02 project investigated by reviewing literature, seismic records of Groningen earthquakes and 2D modelling a series of issues for variations in soil response during earthquakes in Groningen, which in turn can causes damage or losses to the built environment. The issues addressed can be roughly summarized as (1) the modification effect (amplification) of topography of the area on ground motion in case of earthquakes, (2) the lateral spreading following liquefaction of the soil (saturated of water) in the case of earthquakes in Groningen and (3) how well are the soil characteristics and spatial variability in Groningen captured in the current risk assessment. The results generically indicate the possible effects of topography and soil heterogeneity, which were not (yet) included in current versions (c.q. vs 5 and 6) of the seismic hazard and risk assessment instruments in Groningen.

It was concluded that topographic effects may locally occur to some extend and which could be included in the risk instruments, as detailed topographic information is available. Lateral spreading effect is highly unlikely given liquefaction hazard and risk assessments study results available.

Soil heterogeneity is captured in the earthquake risk assessments to a 250 m scale, smaller 1-100 m scale variations are not included due to lack of detailed information and can only be captured in uncertainty ranges.

 

The project results has been reviewed by KEM scientific experts.

RESEARCH PROJECT EVALUATION

The results of this project provide additional information for understanding variations in ground motions at short distances and additional approaches for modeling site response and for further updating of the earthquake risk assessment in Groningen.

In January 2022 project results were presented. The presentation in a KEM-DeepNL colloquium can be found.