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 Orientation effect on ground motion measurement
for Mexican subduction earthquakes
 
H.P. Hong ¹, A. Pozos-Estrada¹ and R. Gomez  ²

1. Department of Civil and Environmental Engineering, University of Western Ontario, Canada N6A 5B9

2. Institute of Engineering, National Autonomous University of Mexico, Mexico D.F.

Abstract: The existence of the principal directions of the ground motion based on Arias intensity is well-known. These
principal directions do not necessarily coincide with the orientations of recording sensors or with the orientations along
which the ground motion parameters such as the peak ground acceleration and the pseudo-spectral acceleration (PSA) are
maximum. This is evidenced by the fact that the maximum PSA at different natural vibration periods for horizontal excitations
do not correspond to the same orientation. A recent analysis carried out for California earthquake records suggests that an
orientation-dependent ground motion measurement for horizontal excitations can be developed. The main objective of this
study is to investigate and provide seismic ground motion measurements in the horizontal plane, including bidirectional
horizontal ground motions, for Mexican interplate and inslab earthquake records. Extensive statistical analyses of PSA are
conducted for the assessment. The analysis results suggest that similar to the case of California records, the average behavior
of the ratio of the PSA to the maximum resulting PSA can be approximated by a quarter of an ellipse in one quadrant; and that
the ratio can be considered to be independent of the value of the maximum resulting PSA, earthquake magnitude, earthquake
distance and the focal depth. Sets of response ratios and attenuation relationships that can be used to represent a bidirectional
horizontal ground motion measurement for Mexican interplate and inslab earthquakes were also developed.

Keywords: orthogonal horizontal excitations; bidirectional ground motion measure; attenuation relationship; pseudo-
spectral acceleration (PSA); response ratio; Mexican earthquake