U.S. Department of the InteriorU.S. Geological Survey

Translating the 2009 Provisions into ASCE 7-10: Ground Motions Maps

Nicolas Luco

Research Structural EngineerNational Seismic Hazard Mapping Project (Golden, CO)

Project ‘07 Team (SDPRG) & ASCE 7 SSC

20 January 2010

Outline of Presentation

Description of ground motion maps in 2009 Provisions

Calculation of MCER ground motions from maps in 2009 Provisions

Maps of MCER ground motions (for Site Class B) in ASCE 7-10

Risk Coefficient maps for Chapter 21 (“Site-Specific …”) of 2009 Provisions & ASCE 7-10

USGS Web Application for ground motion values from 2009 Provisions & ASCE 7-10

Uniform-Hazard Ground Motion Maps

In 2009 Provisions … Spectral response accelerations that have an

exceedance probability of 2% in 50-years (a.k.a., a 2475-yr return period)

Denoted SSUH (for T=0.2s) & S1UH (for T=1s)

For Site Class B In the direction of maximum horizontal

response, so different than the USGS “geomean” hazard maps

In ASCE 7-10 … Not included

Risk Coefficient Maps

In 2009 Provisions … Derived using entire hazard curves (of

exceedance probability vs. ground motion) from which uniform-hazard values are read

= Risk-Targeted GM / Uniform-Hazard GM

Denoted CRS (for T=0.2s) & CR1 (for T=1s)

<0.85 near New Madrid Seismic Zone, Charleston, & coastal Oregon; >1.15 near Sacramento; 0.85-1.15 almost everywhere else

In ASCE 7-10 … Only included for use in site-specific ground

motion hazard analysis (Ch. 21), “Method 1”

Research Needs after ‘09 Provisions

Deterministic Ground Motion Maps

In 2009 Provisions … Considering characteristic earthquakes on all

know active faults …

SSD (not SDS!) = max( 84th-%ile Sa(0.2s) ; 1.5g ) S1D (not SD1!) = max( 84th-%ile Sa(1.0s) ; 0.6g )

For Site Class B In the direction of maximum horizontal

response, like uniform-hazard ground motions

In ASCE 7-10 … Not included

MCER Ground Motions (Site Class B)

In 2009 Provisions …

SS = lesser of SSUHCRS (Equation 11.4-1) & SSD (Equation 11.4-2)

S1 = lesser of S1UHCR1 (Equation 11.4-3) & S1D (Equation 11.4-4)

Called “Risk-Targeted Maximum Considered Earthquake (MCER) Ground Motions”

In direction of maximum horizontal response, like SSUH & S1UH and SSD & S1D

In ASCE 7-10 (& 2012 IBC) …

Maps of SS & S1 are provided …

ASCE 7-10 MCER Ground Motion Maps

Note: “Risk-Adjusted” terminology on MCER maps on 2009 Provisions CD has since been changed to “Risk-Targeted”, consistent with terminology in 2009 Provisions

Long-Period Transition Period (TL) Maps

In 2009 Provisions … Same as in ASCE 7-05, except map sizes are

smaller

In ASCE 7-10 … Same as in ASCE 7-05 (& in 2009 Provisions)

Peak Ground Acceleration (PGA) Maps

In 2009 Provisions … “MCE Geometric Mean PGA, %g, Site Class B” Lesser of probabilistic (2% in 50-year) & deter-

ministic PGA’s, like old MCE (not MCER) maps

For geometric mean spectral response acceleration across two horizontal comp-onents, also like old MCE (not MCER) maps

In ASCE 7-10 … Same as in 2009 Provisions, except labeled

“Maximum Considered Earthquake Geometric Mean (MCEG) PGA, %g, Site Class B”

http://earthquake.usgs.gov/designmaps

Site-Specific Ground Motions

Probabilistic (Risk-Targeted) GM = Uniform-Hazard (2% in 50-year) GM

x Mapped Risk Coefficient

Google “EERI NGA Seminar Presentations” for Videoor email nluco@usgs.gov for just PowerPoint

Summary (without TL & PGA Maps)

Deterministic MapsRisk Coefficient MapsUniform-Hazard Maps

MCER Maps

─ In 2009 Provisions─ In ASCE 7-10