Towards risk-targeted seismic hazard models for Europe

Area of Science:

• Earthquake Engineering
• Seismology
• Risk Assessment

Background:

• Seismic design codes often use uniform hazard maps, leading to non-homogeneous limit state (LS) exceedance probabilities and uneven seismic risk across regions.
• This disparity arises from capacity and demand models used to estimate failure probability, impacting both new and existing structures.

Purpose of the Study:

• To develop a seismic probability assessment formulation and a risk-targeted intensity measure for uniform seismic risk.
• To introduce a framework that accounts for structural over-capacity or under-capacity relative to code-based demand.
• To apply the framework to peak ground accelerations in Europe and derive risk-based modification factors for design codes.

Main Methods:

• Developed a seismic probability assessment using a linear model in log-log coordinates of hazard, assuming log-normal capacity and demand.
• Introduced a factor to adjust code hazard-based demand for structural capacity variations.
• Applied the framework to European peak ground accelerations and calculated risk-target levels and modification factors.

Main Results:

• The study determined risk-target levels for peak ground acceleration (PGA) in Europe for new and existing constructions.
• Derived risk-based intensity and mean return period modification factors for implementation in design standards.
• Identified significant areas in Europe where design PGA should be increased, especially for existing constructions.

Conclusions:

• The proposed framework enables risk-targeted seismic design, achieving uniform limit state exceedance probabilities across territories.
• Current seismic design practices in Europe may require increased design PGAs to meet uniform risk targets, particularly for existing buildings.
• The developed modification factors offer a practical method to enhance seismic safety and achieve uniform risk through updated standards.