Database for design-compatible waveforms
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Date
2023-09-22
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Report
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Abstract
Abstract on selection of ground motions for microzonation.
We have analyzed and compared the stations metadata of three strong motion databases: KiK-net (Japan), ESM (Europe and Middle East), and NGA-West2 (USA). For each data-base, we propose a subset of stations suitable for the purposes of the project. These sub-sets of stations comprise 772 sites classified in terms of SIA261 (2020) soil categories (A-E), inspecting the provided VS profiles. For these sites, the metadata of the stations were checked. To increase the number of recordings from earthquakes with large magnitude and short source-site distance, we added 870 three-component recordings, 28 related to the Chi-chi earthquake sequence recorded by 11 Taiwanese seismic stations and 842 from 69 seismic stations in ESM classified by using geologic criteria. This further selection was made to enlarge the dataset of waveforms mostly related to soil class A. The resulting subset of waveforms comprise 51,144 three-component recordings, that we subdivided in terms of SIA261 (2020) soil categories (A-E), inspecting their distribution in terms of magnitude and Joyner-Boore distance. From this database, we extract 15,303 three-component recordings based on the relevant scenarios from the disaggregation of the seismic hazard for Switzer-land. This collection of recordings was then supplemented with synthetic strong-motion waveforms from the BB-SPEED set to fill gaps in the magnitude-distance distribution.
Once the disaggregation and the waveforms database are ready, we set a strategy for the selection of 11 waveforms, compatible with the elastic response spectrum defined in SIA261 for each seismic zone. Among the existing algorithms used to select compatible waveforms to a target, the most adaptable to our waveforms database is the one proposed by Baker and Lee (2018). The key steps of the algorithm are: the screening of the ground motion database for suitable motions, statistically simulating response spectra from a target distribution, finding scaled motions whose spectra match each statistically simulated re-sponse spectrum, and then performing an optimization to further improve the consistency of the selected motions with the target distribution (more details in Baker and Lee, 2018). For the selection of the 11 design-compatible waveforms, we further implement the Euro-code 8 (2022) criteria. Our selection in this report is made for microzonation purpose. We fit the target elastic response spectrum for a return period of 475 years, in the waveforms’ period range 0.02-2.0 s. The selection is initially attempted using unscaled waveforms, but if necessary, a scaling factor between 0.5-2 is then allowed.
For each seismic zone, we selected all possible combinations of 11 scaled waveforms. Among these, we choose the set of waveforms with the lowest RMSE if most of the wave-forms are nearby or better inside the disaggregation borders, otherwise we check for an-other set of waveforms. Finally, we provide recommendations for the use of the selected and scaled waveforms in microzonation studies in Switzerland.
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Swiss Seismological Service at ETH Zurich
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Subject
Microzonation; STRUCTURAL ANALYSIS (CIVIL ENGINEERING); seismic risk; Waveform
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02818 - Schweiz. Erdbebendienst (SED) / Swiss Seismological Service (SED)