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Underestimated uncertainty and bias in measured speed of light 1875-1960

Time-dependent seismic hazard maps for the New Madrid seismic zone and Charleston, South Carolina areas James Hebden Seth Stein Department of Earth and Planetary Sciences Northwestern University. Underestimated uncertainty and bias in measured speed of light 1875-1960.

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Underestimated uncertainty and bias in measured speed of light 1875-1960

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  1. Time-dependent seismic hazard maps for the New Madrid seismic zoneand Charleston, South Carolina areasJames Hebden Seth SteinDepartment of Earth and Planetary SciencesNorthwestern University

  2. Underestimated uncertainty and biasin measured speed of light 1875-1960 Uncertainties are hard to assess and generally underestimated

  3. IS NEW MADRID IS AS HAZARDOUS AS CALIFORNIA? Frankel et al., 1996 U.S. Geological Survey How robust is this model result?

  4. HIGH MODELED HAZARD RESULTS FROM ASSUMPTIONS • Redefined from maximum acceleration predicted at • 10% probability in 50 yr • to 2% in 50 yr • (1/ 500 yr to 1/2500 yr) • Large magnitude of 1811-12 and thus future large earthquakes • High ground motion in large events • - Time-independent recurrence of large events Arbitrary choice on policy/economic grounds Uncertainty in interpreting intensity data Lack of data Don’t understand how to best model recurrence

  5. New Madrid hazard higher than California results largely from redefining hazard as largest shaking expected every 2500 yr: Not so for 500 yr 500 yr 2500 yr Searer & Freeman, 2002 500 yr 2500 yr

  6. PREDICTED HAZARD DEPENDS ON ASSUMED MAXIMUM MAGNITUDE OF LARGEST EVENTS AND ASSUMED GROUND MOTION MODEL Newman et al., 2001

  7. EFFECTS OF ASSUMED GROUND MOTION MODEL Effect as large as one magnitude unit Frankel model, developed for maps, predicts significantly greater shaking for M >7 Frankel M 7 similar to other models’ M 8 Frankel & Toro models averaged in 1996 maps; Atkinson & Boore not used Newman et al., 2001

  8. ASSUMED HAZARD DEPENDS ON EARTHQUAKE PROBABILITY ASSUMPTION Constant since last event: time independent Small after last event, then grows: time dependent Time dependent lower until ~2/3 mean recurrence Results depend on model & parameters

  9. RELATIVE PREDICTED HAZARD DEPENDS ON POSITION IN EARTHQUAKE CYCLE Time dependent lower until ~2/3 mean recurrence Charleston & New Madrid "early" in their cycles so time dependent predicts lower hazard

  10. CHARLESTON 2% in 50 yr (1/2500 yr)

  11. NEW MADRID 2% in 50 yr (1/2500 yr)

  12. Time dependent model for eastern US predicts lower New Madrid & Charleston hazard Effect larger than lowering Mmax and thus ground motion model Mw 7.7 (NMSZ) Mw 7.3 (Charleston)

  13. Holocene Punctuated Slip 12k 9k 7k 6k 4k 3k 1k Today ? Slip Cluster Slip Cluster Slip Cluster ? Quiescent Quiescent Quiescent Portageville Cycle Reelfoot Cycle New Madrid Cycle NEW MADRID HAZARD WOULD BE EVEN LOWER IF RECENT EARTHQUAKE CLUSTER IS ENDING GPS sites show little or no interseismic motion Present seismicity may be 1811-12 aftershocks Stein & Newman, 1994 Earthquake history inferred from Mississippi river channels Holbrook et al., 2006

  14. Predicted seismic hazard depends on whether large earthquake recurrence modeled as time independent or time dependent Time dependent model predicts lower New Madrid & Charleston hazardsMagnitude of effect depends on model type & parametersEffect can be larger than Mmax or ground motion modelSignificant contribution to uncertainty SUMMARY

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