sigma 2 overview

Knowledge on faults is of primary interest when dealing with seismic hazard assessment, both deterministic and probabilistic, as it constitutes a key input for seismotectonic zoning characterization and fault modelling parameters. In the intraplate domain, low to moderate seismic activity level does not usually enable an accurate mapping of active structures. In addition, surface processes, such as erosion, are faster than tectonics and tend to erase expression of faulting (geometry of faults, kinematic or age of last movement). As a consequence, seismic hazard studies can suffer from large uncertainties associated to the lack of accurate fault characteristics. In addition, recent studies suggest that deformation processes in intraplate domains can result from surface processes interaction overlain on long-term slow tectonics processes. Understanding of tectonic deformation engine(s) in stable continental regions could also allow to better constrain input data for seismic hazard studies and contribute to improve their robustness.

WP1 proposes several actions related to the development or use of methods for the characterization of deformation processes and faults in Stable Continental Regions (SCRs).

Earthquake catalogs represent a key input ingredient for the localization of seismic activity and for the quantification of recurrence rates for seismic hazard assessment. Some important progresses have been made in recent years, often based on a long term work done in different countries. Extended seismicity time-histories have been elaborated to be used as the backbone for objective and reliable estimates of these quantities. This is done by merging datasets of different nature and accuracy, i.e. geological observations, historical reports and instrumental catalogues. Although this effort is aimed at gathering the most comprehensive information on past earthquakes, there are still some large uncertainties in the determination of the characteristics of old earthquakes, and in the determination of the focal depth of recent events.

The general objective of this work package is to improve our knowledge of past earthquakes, by developing innovative methods and improving existing datasets, with a particular focus on low-to-moderate seismicity areas.

The uncertainties affecting ground motion models remain the highest source of uncertainty in the results of seismic hazard studies.

Despite the progress already done, it is important to obtain a prediction of ground motion adapted to rock conditions (as an input for site response simulation), and adapted to various types of sites.

The main scope of WP3 is to improve the understanding and description of ground motion, in order to provide a more realistic assessment of seismic motion for seismic hazard assessment.
The work axes include:

• Improving empirical ground motion estimates for both generic and site-specific hazard assessment studies
• Improving the quantification and the physical understanding behind seismic wave attenuation
• Ground Motion in low seismicity regions
• Ground Motion modeling through simulations 

The objective of this work package is to reduce uncertainties on ground motion at surface level by a proper consideration of the site effect. It aims at taking into account the realistic non-linear soil behavior for strong motions as well as the evaluation of the reliability of site characterizations based on geotechnical measurements.

The work package uses different approaches:

• a numerical approach by calculation using physical models – (e.g. finite elements, spectral elements) or analytical resolution – to solve the wave propagation equations, implying many simplifications of the reality 
• an experimental approach by comparison of actual recordings, either between two surface sensors – one at the site of interest and the other on a nearby rock reference site (SSR), or between a deep sensor at substratum and one at the surface level.

WP5 is dedicated to developing and implementing new and more realistic approaches for PSHA computations.  The work program of this WP gathers together a suite of research actions related to testing and updating PSHA results against observations, and to developing new methods to increase the robustness of source and recurrence models.

Selected topics of research include:

• non-Poissonian recurrence models
• alternative formulations for the maximum magnitude
• non-ergodic GMPEs and associated implementation into PSHA software
• analytical propagation of epistemic uncertainties on GMPEs
• hazard disaggregation
• vector hazard
• PSHA testing and model evalutation based on observations (fragile geological features, e.g. precarious rocks, instrumental records and/or historical macroseismic observations)

This work package aims at producing data and results for engineering purposes and at bridging the gap between PSHA results and earthquake engineering practices.

The research actions in this Work Package will focus on:

• methodologies for the use of Conditional (Mean) Spectra in an industrial context
• new approaches for the selection of time-histories matching a specific response spectrum
• the implementation of advanced representation of ground-motion (power spectral density)
• a seismic risk assessment study performed in the (macroseismic) intensity domain based on waveform modeling and fragility curves calibrated against site intensities.