Estimating Motions at a Site
Attenuation Relationships for Stable Continental Regions - Central and Eastern North America


Toro, Abrahamson, and Schneider

This relationship is used to calculate peak ground acceleration and horizontal spectral accelerations and is valid for moment magnitudes 5 to 8 and distances 1 to 500 km (with emphasis on the range 1 to 100 km). The distance rjb is defined as the closest horizontal distance from the site to a point on the earth's surface that lies directly above the rupture. Separate coefficients are provided for the midcontinent region group and gulf crustal region due to differences in geologic characteristics. These relationships are for rock sites; soil modification factors can be found in EPRI, 1993 and Silva, et al. 1996.
Spectral accelertation is given as a function of moment magnitude,
surface distance between the site and the fault:

lnPHA or Sa = C1 + C2(M-6) + C3(M-6)2 + C4lnRM - (C5-c4)max[ln(RM/100),0] - C6RM

where RM = [rjb2 + C72]1/2

Links to coefficient tables can be found in Appendix A.


Other Relationships for Central and Eastern North America