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

1. Evaluating and Communicating Seismic Risk in Low Probability - High Consequence Earthquake Regions Terry E. TullisBrown University Chair, National Earthquake Prediction Evaluation Council

2. Central US an Excellent Example • Annual probability of damaging earthquakes is small • However, the consequences to society of such events is large • In such situations it is even more difficult than in more seismically active areas to assign accurate probabilities of earthquake occurrence • Nevertheless, the seismological community must do the best we can • Given the uncertainties, disagreements about realistic levels of seismic hazard are bound to arise • 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

3. Nearby Seismicity Red – events, 1972-2004 Green – events before 1972

4. Current Situation in Central US • Attention is currently focused on the bicentennial of the large 1811-1813 earthquakes that occurred in the New Madrid region • Some well-publicized questioning of the official probabilities of earthquake occurrence in this region has occurred • For 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”

5. National Earthquake Prediction Evaluation Council (NEPEC) • Purpose is to provide advice and recommendations to the Director of the U.S. Geological Survey (USGS) on earthquake predictions and related scientific research • The Director of the USGS has the delegated responsibility under the Stafford Act (P.L. 93-288) to issue timely warnings of potential geologic disasters • Our website is http://earthquake.usgs.gov/aboutus/nepec/ • We have 8-12 members • Fewer than half can be federal employees • The Chair cannot be a USGS employee

6. Independent Expert Panel on New Madrid Seismic Zone Earthquake Hazard • We were lucky to convince a group of outstanding of scientists with a variety of relevant expertise to serve • The panel members were chosen to have no vested interests in the outcome of their review • They received input in writing and in face-to-face meetings with a variety of scientists, some having previously expressed strong opinions • The 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 • The report is available at http://earthquake.usgs.gov/aboutus/nepec/reports/NEPEC_NMSZ_expert_panel_report.pdf

7. Independent Expert Panel on New Madrid Seismic Zone Earthquake Hazard • The panel found: • There are considerable uncertainties about the underlying origins, nature, and history of earthquakes in the region • Nevertheless, the seismic zone is at significant risk for damaging earthquakes • These must be accounted for in planning and development

8. Independent Expert Panel on New Madrid Seismic Zone Earthquake Hazard • The 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: • Employ a scientifically sound, carefully implemented, open, and consensus-based process that incorporates a range of scientific data, views and interpretations • They represent the best means available to refine hazard estimates

9. Independent Expert Panel on New Madrid Seismic Zone Earthquake Hazard • The report acknowledges that • Uncertainties 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) • Nevertheless, the panel recommended that the 2008 national maps should continue to be used until their 2014 update

10. Independent Expert Panel on New Madrid Seismic Zone Earthquake Hazard Exploring sensitivity of peak ground acceleration to various assumptions Case 0 – 2008 Maps Case 1 – Lower Max. Mags. by 0.5 Case 2 – Lower Sigma in GMPEs Case 3 – New GMPEs Case 4 – Lengthen Recurrence Intervals (~500 -> ~1000 yrs) Case 5 – All of 1-4 (GMPE = Ground Motion Prediction Equations) Percent chance of exceedance in 50 years:

11. Independent Expert Panel on New Madrid Seismic Zone Earthquake Hazard • NEPEC 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 • Significant seismic hazard in the NMSZ and broader central US region is evident

12. Time-Dependent Earthquake Probabilities • In addition to dealing with long-term, time-independent earthquake probabilities, the subject of time-dependent earthquake probabilities is important • NEPEC is currently working to establish connections between • Those in the seismological research community who have the expertise to evaluate seismic hazard • The 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

13. Time-Dependent Earthquake Probabilities • Consider the Pacific Northwest • The 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 • However, the probability of occurrence of such an earthquake on any given day is extremely low • If 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 • Namely, there would be a significant time-dependent probability gain, even though the probability would still be low

14. Time-Dependent Earthquake Probabilities • Scientists can make imperfect estimates of these probabilities and their temporal changes • A NEPEC Subcommittee on Potential Earthquake Forewarning Scenarios in the Pacific Northwest has been formed • It 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 • Will provide the basis for creating appropriate prepared statements that could be transmitted when one of these event occurs

15. Time-Dependent Earthquake Probabilities • We 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 • Once 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 • The purpose will be • To convey to these officials what types of science-based information may be available, and from what authoritative sources • To learn from them so that such information is of a type, in a form, and delivered at a time that makes it useful • Work together to prepare appropriate prepared statements that could be transmitted when one of these event occurs

16. Conclusion • NEPEC is mandated to keep abreast of progress in understanding the predictability of earthquakes, and by extension to make this understanding useful to society • Only 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