Seismic Microzonation is an essential tool for knowledge-based and site-specific seismic hazard analysis oriented to the mitigation of earthquake damage.
This research project is focused on the improvement of a few specific steps within the seismic microzonation process, which are critical at the current stage of implementation of Microzonation studies, as experienced in the last few years of application for both urban planning and for the reconstruction after destructive earthquakes in our Country.
More specifically, we propose the introduction of newly developed geophysical and GIS-based geostatistical tools to enhance the scientific quality and reliability of current seismic Microzonation studies.
Our research proposal is focused on three main objectives:
- Introducing innovative geophysical measurements and interpretation to enhance the quality of the parametric subsoil models used as input for Seismic Response analysis. The proposed geophysical techniques are targeted to specific hard-to-solve problems such as down-to-bedrock characterization and site-specific seismic attenuation estimation.
- Enhancing the imaging and reconstruction of active faults through a mix of low-budget and high resolution geophysical investigations.
- Defining a quantitative geostatistical approach to produce the final Microzonation maps and to extend unbiasedly the results of the local clusters (which are generally the subject of in-depth analysis at the third and most detailed level of microzonation) to the neighbouring areas.
From a more general point of view, the scientific motivation of this research is to bridge the gap between what is needed in theory for a thorough seismic hazard assessment and what is actually implemented in practice (as a trade-off between resolution, costs and time) by the introduction of newly designed GIS-based tools and affordable geophysical measurements which are cost-effective and innovative in design, layout and diagnostic capability.
Recent destructive earthquakes in Central Italy showed the limits of current land management policies related to seismic risk. Today, the reconstruction of the areas struck by these seismic events is a National priority and a detailed seismic Microzonation of grade-tree degree is one of the key input to the process.
Current practices and regulations for seismic microzonation need to be tuned to the specific geologic complexity of the geographical region of Central Italy, where the current standards of seismic Microzonation may not cover properly some theoretical requirements needed for realistic seismic hazard assessment.
The development of new, low budget but reliable methods to cover essential topic for subsoil seismic characterization, such as the assessment of shear-wave velocities down to the seismic bedrock, the on-site measurements of seismic attenuation and the location of buried faults meets a dual objective:
- To increase the quality of the grade-3 seismic Microzonation studies, in the sense of increasing the accuracy of the seismic models used in ground response simulation.
- To lower the budget for a complete subsoil characterization through cost-effective innovative geophysical measurements, allowing to widespread the number of clusters (specific sites) for detailed seismic hazard assessment within a certain area or territory.
In the case of complex geology, subsurface characterization is an optimization procedure, where the objective function to be minimized is the uncertainty related to the subsoil features, under the constraint of fixed resources and logistical limitations. In geologically complex areas, geophysical surveys should be performed extensively and down to the bedrock depth to build a seismic model which is representative of the physical reality: advanced software solutions for seismic modeling need to be based on a complete and thorough subsoil characterization to avoid serious pitfalls in seismic hazard evaluation.
A chain is only as strong as the weakest link, and today what should be theoretically needed for a complete seismic characterization is often out of reach in practice for lack of resource and investigation methods. These uncertainties strongly affect seismic amplification modeling as experienced in the site-effect seismic hazard evaluation of the areas in Central Italy struck by the seismic sequence of 2016-2017.
Another issue is to increase the quality of the seismic Microzonation map produced for grade-three seismic Microzonation an unambiguous procedure is needed to spatially interpolate the results obtained at specific points (clusters) which are scattered and sparsely located within the territory under examination. Although the newly designed geophysical investigation should increase the number of clusters to be obtained within a fixed budget, the problem of spatial interpolation of these data is currently not addressed in practice, because it is often the case that the preliminary seismic zonation obtained without detailed investigations in a grade-1 study is inconsistent with the new results obtained at the grade three level, so that the micro-zones need to be updated accordingly. We propose a new method encompassing geostatistics and GIS interface for unbiased interpolation of the results of single clusters, to come full circle providing advanced and unbiased tools to handle the entire microzonation workflow. In this frame, a robust geological model can greatly contribute to tune the interpolation techniques as well as to validate the interpolation results.
Although engineered on the basis of the post-earthquake reconstruction emergency, the result of this research project can be adopted in other areas of similar geology, to ease the application of seismic microzonation in time of seismic silence as a tool for long-term land planning and development. Hundreds of professionals and practitioners may benefit of these advances with a direct impact on the communities involved. For these reasons, the scientific dissemination of the results should be considered an integral part of this research project, to encourage the application of the newly developed, cost-effective geophysical investigation to support quantitative evaluation of seismic risk assessment for Microzonation studies.
The entire workflow described above finds an urgent and essential application to give improved scientific tools to the Microzonation studies, in particular for the seismic reconstruction of the province of Rieti (RI), where our research team supports the activities of the local office of Sapienza University (and specifically in the B.Sc. and M.Sc. Degree in Building and Environmental Engineering).