Terry E. Tullis Brown University Chair, National Earthquake Prediction Evaluation Council

Evaluating and Communicating Seismic Risk in

Low Probability - High Consequence Earthquake Regions

Terry E. TullisBrown University

Chair, National Earthquake Prediction Evaluation Council

Central US an Excellent Example0Annual probability of damaging earthquakes is small0However, the consequences to society of such events is large 0 In such situations it is even more difficult than in more

seismically active areas to assign accurate probabilities of earthquake occurrence

0Nevertheless, the seismological community must do the best we can

0Given the uncertainties, disagreements about realistic levels of seismic hazard are bound to arise

0 In addition, given the economic consequences of the occurrence of damaging earthquakes as well as of preparing for them, various groups with economic interests are bound to have differing views

Nearby Seismicity

Red – events, 1972-2004 Green – events before 1972

Current Situation in Central US0Attention is currently focused on the

bicentennial of the large 1811-1813 earthquakes that occurred in the New Madrid region

0Some well-publicized questioning of the official probabilities of earthquake occurrence in this region has occurred

0For these reasons, in the Spring of 2011, the National Earthquake Prediction Evaluation Council, convened an “Independent Expert Panel on New Madrid Seismic Zone Earthquake Hazard”

National Earthquake Prediction Evaluation Council (NEPEC)

0Purpose is to provide advice and recommendations to the Director of the U.S. Geological Survey (USGS) on earthquake predictions and related scientific research

0The Director of the USGS has the delegated responsibility under the Stafford Act (P.L. 93-288) to issue timely warnings of potential geologic disasters

0Our website is http://earthquake.usgs.gov/aboutus/nepec/

0We have 8-12 members0Fewer than half can be federal employees0The Chair cannot be a USGS employee

http://earthquake.usgs.gov/aboutus/nepec/



Independent Expert Panel on New Madrid Seismic Zone Earthquake Hazard

0We were lucky to convince a group of outstanding of scientists with a variety of relevant expertise to serve

0The panel members were chosen to have no vested interests in the outcome of their review

0They received input in writing and in face-to-face meetings with a variety of scientists, some having previously expressed strong opinions

0The panel wrote a succinct 25-page report that contains their charge, their membership, their activities and procedures, an executive summary and their more-detailed assessment of the seismic hazard

0The report is available at http://earthquake.usgs.gov/aboutus/nepec/reports/NEPEC_NMSZ_expert_panel_report.pdf

http://earthquake.usgs.gov/aboutus/nepec/reports/NEPEC_NMSZ_expert_panel_report.pdf




0The panel found:0There are considerable uncertainties about the

underlying origins, nature, and history of earthquakes in the region

0Nevertheless, the seismic zone is at significant risk for damaging earthquakes

0These must be accounted for in planning and development


0The panel also examined the USGS national seismic hazard maps and the process by which they are produced and updated. They concluded that the hazard maps:0Employ a scientifically sound, carefully implemented, open,

and consensus-based process that incorporates a range of scientific data, views and interpretations

0They represent the best means available to refine hazard estimates


0The report acknowledges that 0Uncertainties in our knowledge are sufficiently broad that

the current USGS national hazards maps could somewhat overestimate the seismic hazard within the New Madrid Seismic Zone (NMSZ)

0Nevertheless, the panel recommended that the 2008 national maps should continue to be used until their 2014 update


Percent chance of exceedance in 50 years:

Exploring sensitivity of peak ground acceleration to various assumptions

Case 0 – 2008 MapsCase 1 – Lower Max. Mags. by 0.5Case 2 – Lower Sigma in GMPEsCase 3 – New GMPEsCase 4 – Lengthen Recurrence Intervals (~500 -> ~1000 yrs)Case 5 – All of 1-4(GMPE = Ground Motion Prediction Equations)


0NEPEC hopes the report of our expert panel will be helpful for long-term and emergency planners facing societally relevant decisions in the New Madrid area

0Significant seismic hazard in the NMSZ and broader central US region is evident

Time-Dependent Earthquake Probabilities

0In addition to dealing with long-term, time-independent earthquake probabilities, the subject of time-dependent earthquake probabilities is important

0NEPEC is currently working to establish connections between 0Those in the seismological research community who have

the expertise to evaluate seismic hazard0The community of emergency managers with the

responsibility to decide what actions to take if there appears to be an increased hazard for some period of time


0Consider the Pacific Northwest0The probability is high for the eventual occurrence of a

large damaging earthquake similar to the Tohoku earthquake that struck NE Japan on March 11, 2011

0However, the probability of occurrence of such an earthquake on any given day is extremely low

0If various geological events occurred, for example a moderate-sized earthquake that might be a foreshock, then the probability would be multiplied by a large amount

0Namely, there would be a significant time-dependent probability gain, even though the probability would still be low


0Scientists can make imperfect estimates of these probabilities and their temporal changes0A NEPEC Subcommittee on Potential Earthquake

Forewarning Scenarios in the Pacific Northwest has been formed

0It is now drafting a comprehensive list of geologic events that could be envisioned as potentially providing information that would substantially increase the probability gain for the subsequent occurrence of a large damaging earthquake

0Will provide the basis for creating appropriate prepared statements that could be transmitted when one of these event occurs


0We need to work with emergency planners and response personnel so we can learn how to provide them with timely information that is suitable for their needs

0Once the list of potential earthquake forewarning scenarios is created, we will schedule a meeting with officials at those agencies responsible for guiding preparation, response and communication to the public

0The purpose will be0To convey to these officials what types of science-based

information may be available, and from what authoritative sources

0To learn from them so that such information is of a type, in a form, and delivered at a time that makes it useful

0Work together to prepare appropriate prepared statements that could be transmitted when one of these event occurs

Conclusion

0NEPEC is mandated to keep abreast of progress in understanding the predictability of earthquakes, and by extension to make this understanding useful to society

0Only by working as part of a team that includes planners, engineers, and emergency managers can scientists be effective in communicating our understanding, including its uncertainties, in a societally relevant way

Terry E. Tullis Brown University Chair, National Earthquake Prediction Evaluation Council

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