Project

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Source and site-effect studies for probabilistic seismic hazard assessment in Switzerland

Applicant Mai Paul Martin
Number 126690
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.10.2009 - 31.10.2010
Approved amount 102'775.00
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All Disciplines (2)

Discipline
Geophysics
Other disciplines of Earth Sciences

Keywords (8)

probabilistic sieismic hazard; earthquake scaling; site-effects; micro-zonation; probabilistic seismic hazard; site effects; source effects; site amplification factors

Lay Summary (English)

Lead
Lay summary
This project investigates earthquake source characterization and site-effect assessment, as part of the large-scale study "New approaches to probabilistic seismic hazard assessment in Switzerland". The work is subdivided into two subjects (one PhD student for each subject).Subject 1: Earthquake source studies: Here we study earthquake scaling relations, and the impact of those relations on estimating near-fault ground motions. We compiled a dataset of earthquake sequences in Switzerland, ranging from 8 to 51 similar events with magnitudes 0 ? ML ? 4.1, augmented by data from induced earthquakes in the Basel region in 2006/2007. The data are analyzed for moment-magnitude (Mw) scaling with local magnitude ML, showing a deviation from theoretical expectations due to source- and/or path-effects. This ML-Mw-scaling may affect seismic hazard computation, requiring a re-calibration of earthquake magnitudes in the seismic catalogs. The work also addresses stress-drop and radiated-energy scaling. Using our high-quality dataset, we may be able to shed light onto this PSHA-relevant earthquake scaling. Finally, we plan to derive estimates of maximum ground-motions, based on the stress-drop and radiated-energy scaling which will be linked to dynamic rupture models. Using dynamic models for ground-motion simulations we can examine in more detail the spectral characteristic of the recorded and calculated seismic data.Subject 2: Site effect assessment: In this sub-project, we deploy a new method to analyze amplitude characteristics of three-component frequency-wavenumber transformation. The method has been tested extensively with ambient noise synthetics, and has been validated with field recordings. The new approach allows retrieving the ellipticity functions of Rayleigh-wave modes from the three-component noise wave-field, as well as the fundamental and higher modes of Love and Rayleigh-wave dispersion curves. This information allows for inverting for S-wave velocity profiles. This method will also be useful to optimize seismic array configuration. Initial measurements have been successfully performed in, requiring partial software coding to improve specific signal-processing programs. During 2009/2010, all measurements will be analyzed with the improved software, and the resulting "optimum" array configuration will be tested in a field experiment. These data are then integrated into the existing soil-class database at the Swiss Seismological Service. For each of these soil classes generic amplification functions will be developed that help to compute a site-specific seismic hazard for a large part of the area of Switzerland.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
112284 New approaches to probabilistic seismic hazard assessment in Switzerland 01.06.2006 Project funding
118019 Physics-based near-source ground motion prediction for structural engineering and geotechnical applications 01.10.2007 Project funding

Abstract

In 2006, the Swiss National Science Foundation partially funded the proposal “New approaches to probabilistic seismic hazard assessment in Switzerland” (SNF 200021-112284/1) to support the work of two PhD researchers. The objectives of this larger-scale proposal were combined into five research topics for improving probabilistic seismic hazard assessment (PSHA) in Switzerland. The work of the two PhD researchers addresses selected problems, related to source characterization (PhD Falko Bethmann) and site-effect assessment (PhD Valerio Poggi). This continuation proposal is submitted for finalizing the scientific research, partially guided by the experience of the PEGASOS project, partially by the experience of the SED 2004 hazard assessment, and partially derived from current important topics in seismological research.The research in Project 1 (PhD-candidate Falko Bethmann) comprises Tasks A, B, and C, addressing scaling relations between small and large earthquakes (Tasks A and B) and the potential impact of such scaling relations on estimating maximum near-fault ground motions (Task C). For this purpose, F. Bethmann has compiled a unique dataset of six earthquake sequences in Switzerland, ranging from 8 to 51 similar events with magnitudes 0 ? ML ? 4.1, augmented by the rich data from the induced earthquakes in the Basel region in 2006/2007. In Task A (completed), these data are analyzed for the scaling of moment magnitude Mw with local magnitude ML, illustrating a significant deviation from theoretical expectations that can be interpreted in terms of not-accounted for source and path-effects. However, this ML-Mw-scaling may directly affect seismic hazard computations since it may require a re-calibration of earthquake magnitudes in the seismic catalogs. Task B expands on the findings of Task A, addressing stress-drop and radiated-energy scaling. Many past studies have dealt with the potential scaling of apparent stress, but no conclusive answers have been found, partly due to limited data quality and processing. Using our unique high-quality dataset, Task B is able to shed light onto this PSHA-relevant earthquake scaling. In Task C of Project 1 we plan to derive estimates of maximum ground-motions, based on the fracture-energy scaling (from Task B) which will be linked to a suite of (existing) dynamic rupture models. The chosen set of dynamic models is used for ground-motion simulations which we calibrate against the general (spectral) characteristic of the data.Project 2 (PhD-candidate Valerio Poggi) covers Tasks A, B and C. In Task A, Valerio Poggi developed a new method to analyze amplitude characteristics of three components frequency-wave-number transformations using an improved minimum-variance algorithm. The method has been tested extensively with ambient noise synthetics, and has been validated with field-measurement recordings. The new approach allows retrieving the ellipticity functions of the different Rayleigh-wave modes from the three-component noise wave-field, as well as the fundamental and higher modes of Love and Rayleigh-wave dispersion curves. This information is then combined to invert for S-wave velocity profiles to better resolve subsurface structures. Task B combines passive ambient vibration data with active-source techniques by higher-frequency surface-wave excitation. This method will be useful to refine velocity models and to optimize the seismic array configuration. Initial test measurements have been performed in 2007/2008; the re-written signal-processing programs include a new weighted-window averaging procedure for a reliable discrimination between active-source and ambient-noise signals within the same recording. During 2009 and 2010, all test measurements will be analyzed with our improved software, and the resulting “optimum” configuration for combining active and passive methods will be tested in a field experiment. Task C integrates the results from our measurements (Task A and B) with the existing database at the Swiss Seismological Service (acquired in other projects) for deriving the characteristics of general soil classes in Switzerland. For each of these classes generic amplification functions will be developed. These functions will help to compute a site-specific seismic hazard for a large part of the area of Switzerland
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