New USGS Hazard Models & the NEHRP Design Maps Nicolas Luco - PDF document

9/2/2015 New USGS Hazard Models & the NEHRP Design Maps Nicolas Luco Research Structural Engineer, USGS (Golden, CO) BSSC PUC Design Mapping Issue Team (“IT ‐ 11”) (Bachman, Crouse, Harris, Hooper, Kircher, Caldwell) Map ‐ Related Changes 1) New MCE R , MCE G & Risk Coefficient maps for Guam, the Northern Mariana Islands, & American Samoa 2) Reference to underlying uniform ‐ hazard and deterministic ground motion maps & values on USGS website 3) Updated maximum ‐ response scale factors (Part 3) 4) Updated MCE R , MCE G & Risk Coefficients maps for the conterminous US 1) Guam & Tutuila in ASCE 7 ‐ 10 1

9/2/2015 1) USGS Hazard Model for Guam 1) USGS Hazard Model for Tutuila 1) Hazard Model  Design Maps 2

9/2/2015 1) MCE R Maps for 2015 Provisions 200.2 16° 16° 16° 16° 0 6 Northern Northern 60 70 0 8 90 Mariana Mariana 100 Islands Islands 125 . S S = 176%g . S 1 = 44%g 150 15° 15° 15° 15° 0 0 2 250.6 14° 14° 14° 14° 50 243.9 . S S = 287%g . S 1 = 72%g 40 125 200 30 100 72.3 90 25 150 Guam 80 Guam 70 288.6 13° 13° 13° 13° 0.2 Second Spectral Response Acceleration 1.0 Second Spectral Response Acceleration (5% of Critical Damping) (5% of Critical Damping) 1) MCE R Maps for 2015 Provisions 172° 171° 170° 169° 168° 172° 171° 170° 169° 168° 11° 11° 11° 11° Swains Swains Island Island 2 12° 12° 12° 12° 4 American American 5 Samoa Samoa 10 6 13° 13° 13° 13° 1 5 8 20 25 10 30 40 0 5 15 35 Olosega Olosega 15 14° 14° 14° 14° 40 Ofu Ofu 60 Tutuila Tutuila . S 1 = 15%g . S S = 40%g 20 50 Aunu'u Rose 60 Aunu'u Ta'u Rose 2 Ta'u 5 70 Atoll Atoll 30 80 90 1 0 0 40 125 1 5 50 15° 15° 15° 15° 0.2 Second Spectral Response Acceleration (5% of Critical Damping) 1.0 Second Spectral Response Acceleration (5% of Critical Damping) 1) 2015 Provisions Ch. 22 Commentary … In comparing the MCE R ground motion maps derived from these USGS hazard models to the geographically-constant values stipulated for Guam and American Samoa (Tutuila) in the 2010 and previous editions of ASCE/SEI 7 , it is important to bear in mind that the latter were not computed via seismic hazard modeling. According to the commentary of the 1997 Provisions , the geographically-constant values were merely conversions, via rough approximations, from values on the 1994 Provisions maps that had been in use for nearly 20 years. As such, they did not take into account the 1993 Guam earthquake that was the largest ever recorded in the region and caused considerable damage, the 2009 earthquake near American Samoa that caused a tsunami, nor the 2008 “Next Generation Attenuation (NGA)” and another 2006 empirical ground motion prediction equation that have now been used for both Guam/NMI and American Samoa. … 3

9/2/2015 Map ‐ Related Changes 1) New MCE R , MCE G & Risk Coefficient maps for Guam, the Northern Mariana Islands, & American Samoa 2) Reference to underlying uniform ‐ hazard and deterministic ground motion maps & values on USGS website 3) Updated maximum ‐ response scale factors (Part 3) 4) Updated MCE R , MCE G & Risk Coefficients maps for the conterminous US 2) Ground Motions in 2009 Provisions 2) 2015 Provisions Ch. 22 Commentary UNIFORM-HAZARD AND DETERMINISTIC GROUND MOTION MAPS As alluded to above, implicit in the MCE R ground motion, MCE G PGA, and risk coefficient maps provided are uniform-hazard (2%-in-50-years ground motion exceedance probability) and deterministic (84th percentile) ground motions. The 2009 Provisions provided maps of such uniform-hazard and deterministic ground motions, but ASCE/SEI 7-10 and the 2015 Provisions do not. Instead, uniform-hazard and deterministic ground motion maps consistent with this chapter are provided via a USGS website (http://earthquake.usgs.gov/hazards/designmaps/). Furthermore, values from these maps can be obtained via the ground motion software tool described above. … 4

9/2/2015 2) USGS Design Maps Web Tool 2) USGS Design Maps Web Tool Map ‐ Related Changes 1) New MCE R , MCE G & Risk Coefficient maps for Guam, the Northern Mariana Islands, & American Samoa 2) Reference to underlying uniform ‐ hazard and deterministic ground motion maps & values on USGS website 3) Updated maximum ‐ response scale factors (Part 3) 4) Updated MCE R , MCE G & Risk Coefficients maps for the conterminous US 5

9/2/2015 3) Max ‐ Direction Factors in ASCE 7 ‐ 10 21.2 RISK-TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCE R ) GROUND MOTION HAZARD ANALYSIS … If the spectral response accelerations predicted by the attenuation relations do not represent the maximum response in the horizontal plane, then the response spectral accelerations computed from the hazard analysis shall be scaled by factors to increase the motions to the maximum response. If the attenuation relations predict the geometric mean or similar metric of the two horizontal components, then the scale factors shall be: 1.1 for periods less than or equal to 0.2 sec; 1.3 for a period of 1.0 sec, and, 1.5 for periods greater than or equal to 5.0 sec, unless it can be shown that other scale factors more closely represent the maximum response, in the horizontal plane, to the geometric mean of the horizontal components. Scale factors between these periods shall be obtained by linear interpolation. … 3) Updated Factors from PEER Reference: Shahi & Baker, 2013. “NGA ‐ West2 Models for Ground ‐ Motion Directionality,” PEER Report 2013/10. SA RotD100 � SA RotD50 SA RotD100 � SA GMRotI50 3) Proposed ÷ ASCE 7 ‐ 10 Factors 1.5 Proposed  ASCE/SEI 7-10 1.4 Proposed  Shahi & Baker 1.3 1.2 Ratio 1.1 1 0.9 0.8 0 1 2 3 4 5 6 7 8 9 10 Period (s) Conclusion: Incorporate updated factors into maps next cycle, concurrently with improvements to long ‐ period ground motions. 6

9/2/2015 3) Max ‐ Direction Factors in ASCE 7 ‐ 10 21.2 RISK-TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCE R ) GROUND MOTION HAZARD ANALYSIS … If the spectral response accelerations predicted by the attenuation relations do not represent the maximum response in the horizontal plane, then the response spectral accelerations computed from the hazard analysis shall be scaled by factors to increase the motions to the maximum response. If the attenuation relations predict the geometric mean or similar metric of the two horizontal components, then the scale factors shall be: 1.1 for periods less than or equal to 0.2 sec; 1.3 for a period of 1.0 sec, and, 1.5 for periods greater than or equal to 5.0 sec, unless it can be shown that other scale factors more closely represent the maximum response, in the horizontal plane, to the geometric mean of the horizontal components. Scale factors between these periods shall be obtained by linear interpolation. … Map ‐ Related Changes 1) New MCE R , MCE G & Risk Coefficient maps for Guam, the Northern Mariana Islands, & American Samoa 2) Reference to underlying uniform ‐ hazard and deterministic ground motion maps & values on USGS website 3) Updated maximum ‐ response scale factors (Part 3) 4) Updated MCE R , MCE G & Risk Coefficients maps for the conterminous US 4) Reasons for Updated Design Maps 2) Fragility curve  = 0.8   = 0.6, for 1) 2014 USGS National Seismic Hazard Model (including NGA ‐ West2, consistency with the site ‐ specific UCERF3, CEUS ‐ SSC) ground motion chapter (Ch. 21) of ASCE 7 ‐ 10 1  = 0.8 0.9  = 0.6 P [ Collapse | SA = a ] 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -1 0 1 10 10 10 Spectral Acceleration (1.0 sec), a [ g ] 7