Directivity in NGA Earthquake Ground Motions: Analysis Using Isochrone Theory (Abstract)
by Paul Spudich, USGS and Brian Chiou
Spudich, Paul, Brian Chiou (2007). Directivity in NGA Earthquake Ground Motions: Analysis Using Isochrone Theory (Abstract). SMIP07 Seminar on Utilization of Strong-Motion Data, p. 111 - 112.
We present correction factors that may be applied to the NGA models of Abrahamson and Silva, Boore and Atkinson, Campbell and Bozorgnia, and Chiou and Youngs to model the azimuthally varying distribution of the GMROTI50 component of ground motion (commonly called 'directivity') around earthquakes. Our correction factors are non-zero for M > 6.0 and rupture distance less than 70 km. They may be used for planar or nonplanar faults having any dip or slip rake. The correction factors are a product of an approximation, based on isochrone theory, of true directivity, a term simulating the earthquake's slip distribution, and a point-source approximation of the earthquake's radiation pattern.