The Component of shaking of interest for an Intensity Measure (IM).
Current options in OpenSHA include:
Usually defined as the geometric average of the maximum of the two horizontal components (which may not occur at the same time).
Because Average Horizontal, above, is dependent on seismometer orientation, this was defined by Boore et al. (2006, Bull. Seism. Soc. Am. 96, 1502-1511) as an orientation-independent alternative. All the NGA Relationships use this measure. See also page 7 of Campbell and Bozorgnia's (2006) NGA Report.
A randomly chosen horizontal component.
The vertical component.
The largest value obtained from two perpendicular, horizontal components.