Annie Kammerer

January 2013

Transferable Methods from 

Seismic Hazard
 Need for both best estimate and uncertainties

 Limited data and long return periods

 10-4 for seismic design & larger range for risk assessment

 High uncertainty in rates of rare events

 Complex and sometimes contradictory data sets 

require the use of expert judgment

 Data permissive of alternate interpretations

 Needs to separate and address natural (aleatory) 

variability from epistemic (model) uncertainty
• NUREG/CR-6372, “Recommendations for 

Probabilistic Seismic Hazard Analysis: Guidance on 

Uncertainty and Use of Experts” 

• Developed in the 1980s as a result of differing NRC 

and EPRI Seismic Hazard Assessment Studies - the 

method used to engage experts differed more than 

the technical input

• SSHAC provides a framework for incorporating 

experts into scientific assessments through 

structured processes and interactions
Original report 

provides framework. 

New report provides 

additional details. Both 

describe how to 

undertake studies that 

develop hazard 

NUREG/CR-6372 NUREG 2117 assessment models (1989) (2012) 
 Objective is to develop a model that 

represents the center, body and range of 

technically defensible interpretations of the 

available data

 Center-best estimate 

 Body-shape of the distribution

 Range-extreme values of the distribution

 Achieved through a process with well 

defined evaluation and integration phases
 Compilation of comprehensive databases

 made available to all participants

 Defined roles and responsibilities for participants

 Technical Integration (TI) Team: Evaluate data, methods and 

models and develop distribution capturing center, body and 

range of technically-defensible interpretations

 Participatory Peer Review Panel (PPRP): Continuous 

process and technical review

 Resource Experts (neutral experts a dataset or topic)

 Proponent Experts (support an interpretation or model)
 Structured sequence of steps, including 3 

formal workshops

 WS1: Data needs and critical issues

▪ Probe the datasets available, identify and other 

data, and identify and discuss the critical issues

 WS2: Proponent viewpoints and alternatives

▪ Proponents experts go through a process of 

discussion, challenge and defense

 WS3: Investigation of the preliminary model
Process and Technical Review

PPRP

Evaluation of Models to Form Composite Distribution

TI 

Team

Hazard sensitivity 

Preliminary database calculations

WORKSHOP 1: Hazard Sensitive 

Issues and Data Needs

Resource 

Experts

Additional data collection & analysis

WORKSHOP 2: Review of Database and 

Discussion of Alternative Models

Resource Experts

Proponent Experts

Final database Preliminary SSC and 

GMC models

WORKSHOP 3: Presentation of Models and 

Hazard Sensitivity Feedback

Final SSC and GMC models, then final hazard calculations,

Documentation of all technical bases

Database Compilation

Technical Staff 

& Contractors
Uncertainty

Aleatory

Natural variability

Not reducible

Addressed through integration 

over parameter distributions

Epistemic

Modeling or knowledge 

uncertainty

Reducible with more 

information

Addressed through use of a 

logic tree
Uncertainty

Aleatory

Integration over distribution of 

expected parameter values

Epistemic

logic tree of technically 

defensible interpretations
Uncertainty

 Aleatory Epistemic

Acceleration (g)

Annual Prob of Exceedance

Aleatory 

variability gives 

the curve its 

shape.

Epistemic 

uncertainty leads 

to uncertainty 

85% bands 

Median

15%
Branch weights reflect relative 

degree of belief in each model or 

value, based on the data and 

scientific basis
Seismic Source 

Characterization: 

SSC Model

Ground Motion 

Characterization: 

GMC Model

Base figure from 

Reiter (1990)

Earthquake 

Recurrence

Source 

Geometry

Tsunami Source Characterization

Wave Propagation and Runup
The Central and Eastern United States Seismic Source 

Characterization for Nuclear Facilities Project 

(CEUS SSC Project 2008-2011, NUREG 2115) 

(NGA-East Project 2010-2014)