Almenn verkefni 2019
Almenn verkefni 2019
Heiti verkefnis : | Einkenni jarðskjálftasvörunar hraunlaga undir vegum og brúm út frá mælingum á jarðóróa | |
Verkefnastjóri : | ||
Stutt lýsing á verkefninu: | ||
The geological condition known as "rock" is desirable as foundation for structures such as bridges, and also for roads, due to the low seismic wave amplification, known as "site effects", that expected on hard geological material. In Iceland, this site condition is rather prevalent due to the generally thin and easily removable topsoil exposing older bedrock or more recent volcanic lava-rock. However, recent site effect investigations in Iceland using earthquake ground motions and microseismic measurements on alternating layers of lava-rock and soft sediments have shown markedly different site effects than on firm older bedrock. Important examples are the stark differences in site effects between the western abutment of the old bridge over Þjórsá river and the eastern side on bedrock, the towns of Hveragerði and Selfoss that are built on top of lava fields under which softer sedimentary layers are located, and on lava layers on north side of Reykjanes. These unique Icelandic site conditions may therefore have important practical implications for seismic design of structures and roads. However, such conditions are not considered in the seismic design criteria specified in the current version of the Icelandic building code (i.e., Icelandic National Annexes to Eurocode 8). In this study therefore a comprehensive, reliable, and environmentally friendly framework based on recording and analysis of seismic ground motion data set will be developed to quantitatively determine the physical parameters of the near-surface soil structure, with special focus on those alternating lava-rock and sedimentary layers. Moreover, to develop site amplification factors for these profiles that will find direct practical applications in seismic microzonation, earthquake-resistant design of lifeline and service networks (e.g., roads, bridges, power transmission networks, pipelines, water and sewage systems) as well as urban planning. | ||
Tilgangur og markmið: | ||
The long-term objective of this project is to contribute to improved understanding of site-specific characteristics in different geological conditions across Iceland. In turn, it will lead to more reliable seismic design criteria for infrastructures and lifelines (e.g., roads and bridges) and increased life safety. The short-term purposes of this project will be achieved by addressing the following research questions: (1) How and to what extent, we can identify the underlying site conditions from seismic recordings. We address this issue by outlining a rigorous physical and statistical approach to identify and constrain the subsoil physical parameters and their associated uncertainties. The proposed method is expected to be applicable for two types of soil conditions common in Iceland: Regular sites: shear-wave velocity and density values increase with depth; Reverse sites: shear-wave velocity increases with depth, and then suddenly decreases due to an underlying layer of softer sediments. The latter is a common subsoil feature in geologically younger parts of Iceland due to the basaltic volcanism in the Holocene, or since the end of the last ice-age, where basaltic lava has flowed over a sedimentary cover. When a sedimentary layer lies beneath a competent surface lava-rock layer, it has a fundamental effect on the seismic wave amplification at the surface. In some cases, such lava-sediment structures can be repeated with depth, complicating the site effects even further. It is therefore of utmost importance that this method be able to detect and quantitatively estimate the physical properties of the sedimentary layer beneath a surface lava layer. (2) How and to what extent, we can mitigate seismic risk and improve aseismic design criteria, for key service infrastructures as well as roads and bridges. We aim to improve an innovative tool based on Bayesian statistics to evaluate the reliability of the predefined/available site-effect proxies for the different key subsoil structures in Iceland. The following distinct milestones are expected over the duration of this project:
| ||
