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Theses in progress

# Probabilistic fault displacement hazard: improved methodology and applications

Host laboratory: Seismic Risk Assessment Section (BERSSIN)

Beginning of the thesis: October 2018

Student name:  Fiia NURMINEN

Subject description

This Ph.D. project brings together the methods of earthquake geophysics and geology to estimate and model the risk of fault rupture and the amount and distribution of seismic fault displacements in active seismic zones.

The main objectives of this thesis are

• improve the methodological procedure for the probabilistic analysis of the risk of fault displacement
• create a free and intuitive software for fault displacement risk assessment,
• and apply this model to the selected areas.

Previous studies have focused their analysis mainly on the main fault and main fault kinematics (normal, stalled or reverse), and have also used different approaches to analyze the distribution of surface fractures, particularly with respect to off-fault fractures, or distributed surface fractures moving away from the main fault trace.

The goal of this thesis is to develop a unique methodology for the analysis of surface faults for all three types of earthquakes by using and further developing the data sets and approaches of the previous researchers.
The study begins by pooling the various datasets on fault parameters of historical surface faulting earthquakes.

The four key parameters required to build a model are

• the probability of a surface fracture on the main fault
• the distribution of dislocations along the main fault
• the probability of occurrence of a distributed surface fracture
• and the surface fracture distribution distributed as a function of distance from the main fault.

The first two parameters have been studied by previous research, thus this thesis focuses on the last two parameters.

Various statistical methods are tested in order to choose the most robust one for analyzing data that are incomplete and discontinuous in nature. The obtained parameters are used to build a mathematical modeling tool, which plots the spatial distribution of the expected dislocation, or the probability of exceeding a certain level of dislocation, on a map around the known trace of the fault. The parameters obtained are used to construct a mathematical modeling tool, which plots the spatial distribution of the expected dislocation, or the probability of exceeding a certain level of dislocation, on a map around the known trace of the fault.
Within the framework of this thesis, detailed characterization and probabilistic analysis maps of fault displacement risks are produced for three selected sites. This type of information is essential for land use management and construction engineering in the vicinity of active faults.

Involved IRSN laboratory

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