THE SOCIETY FOR EARTHQUAKE AND CIVIL
ENGINEERING DYNAMICS
AN ASSOCIATED SOCIETY OF THE INSTITUTION OF CIVIL ENGINEERS
EVENING LECTURE
AT THE
INSTITUTION OF CIVIL ENGINEERS
ONE GREAT GEORGE STREET, WESTMINSTER, LONDON SW1P 3AA
Thomas Telford Theatre
WEDNESDAY 26TH APRIL 2017, 6:30PM
The 2017 William B Joyner Memorial Lecture
Seismic Hazard Analysis: Capturing Uncertainty in the Post-Truth
Era
Speaker:
Dr William R Lettis
Lettis Consultants International
NON-MEMBERS OF THE SOCIETY ARE WELCOME TO ATTEND
Please note that there is no charge to attend.
Seats are allocated on a first come, first served basis.
Tea and biscuits will be served from 5.30pm - 6pm.
For further information please contact Shelly-Ann Russell, Associated Societies Executive, at the ICE on
Tel: +44 (0) 20 7665 2147, or Email: [email protected]
Visit the SECED website at http://www.seced.org.uk
Dr William R. Lettis
William R. Lettis was selected as the Joyner Lecturer for 2017. Dr. Lettis founded
William Lettis & Associates, Inc in 1990 and Lettis Consultants International, Inc. in
2011 to provide consultancy at the interface of earthquake science and earthquake
engineering. He will deliver his lecture in April 2017 at the SSA Annual Meeting in
Denver, CO and in March 2017 at the EERI Annual Meeting in Portland, OR. Dr.
Lettis has characterized seismic sources for probabilistic seismic hazard analyses
for high-risk facilities at over 100 locations within the United States and throughout
the world, in a range of seismic environments. His paleo seismic research on
active faults has resulted in over 100 publications and in guidance documents for the Nuclear
Regulatory Commission and the International Atomic Energy Agency. Dr. Lettis is a current member of
the National Seismic Hazard and Risk Assessment Steering Committee and the California Geological
Survey Mapping Committee. From 1996-2008, Dr. Lettis also served as co-chair for the American
Nuclear Society Working Group Committee 2.27 to develop evaluation criteria for assessing seismic
hazards for nuclear materials facilities. He has performed post-earthquake reconnaissance of
numerous earthquakes worldwide, including as co-leader of the EERI 2001 Bhuj Earthquake
Reconnaissance Team. Dr. Lettis’ current interest is in developing models to capture uncertainty in
earthquake behaviour and ground motion parameters for seismic hazard assessment, including
implementation of procedures from the Senior Seismic Hazard Analysis Committee (SSHAC).
https://www.seismosoc.org/awards/joyner/william-b-joyner-memorial-lectures/
SYNOPSIS
The earthquake engineering community and regulatory agencies are moving, at varying rates, toward
risk-informed engineering decisions and design. Risk-informed decision making, in turn, requires that
probabilistic seismic hazard analyses explicitly and transparently incorporate uncertainty in hazardsignificant seismic source and ground motion parameters. This uncertainty arises from limited data and
from the existence of multiple alternative models that purport to explain these data. When uncertainty
in the various inputs to the probabilistic analysis is high but is not properly captured, one may obtain
misleading results; one also deprives the decision maker of useful context. Proper quantification of
uncertainty also helps guide future research efforts.
The Earth science community, following traditional practice (e.g., the scientific method), often
publishes a “proponent” interpretation or model with little or no expression of uncertainty beyond the
limits of the immediate data that were considered in the research. This practice leaves it incumbent on
the PSHA analyst (often a consultant) to capture the proper range of uncertainty for a parameter based
on the body of published literature or, at times, based on the analyst’s own interpretations of available
data. This is an important, often critical, interface issue between the Earth science community and the
engineering community. Over time, some published interpretations or models become incorporated
into “common belief” and become accepted paradigms whose uncertainties are rarely challenged even
when more recent data or studies no longer support (if not outright reject) the original interpretation or
model.
Emerging best practice, originating in the nuclear industry, is to use a formal, structured process to
capture the “center, body and range” of uncertainty for inputs to a hazard model. This process
engages the Earth science community as resource experts (e.g., providers of data) and proponent
experts (e.g., providers of interpretations or model), and requires the PSHA analysts to consider
whether full parameter uncertainties are captured within the available data or whether uncertainties
ought to extend beyond the available data, expert interpretations, and current paradigms. An overall
goal of current PSHA practice ought to be the focus on capturing the full range of uncertainty, so that
the next generation of PSHA, which will be constructed with more and better information, will have
results that fall within today’s uncertainty limits. This presentation will address some of the issues and
questions that have evolved in the assessment of uncertainty and suggestions for a path forward in
improved communication of uncertainty between the Earth scientist and the PSHA practitioner.