“Strong” Ground motions in North America from the Bolivia Earthquake of June 9, 1994 (Mw=8.3)



The Bolivia earthquake was remarkable for being felt in North America, as far as 8680 km from the epicenter. This paper examines the characteristics of ground motions in North America from the perspective of strong motion seismology. Data on ground motions is mostly from high-gain stations, but we also have two strong motion accelerograms. The largest accelerations and highest frequencies are associated with the P and PcP phases, which also correlate with the felt reports in several instances. Felt locations are associated with a combination of favorable factors. Most are in a distance range where P-wave amplitudes tend to be relatively high, as observed in the empirical correction factors for body wave magnitude, and in regions with relatively high values of Q in the lithosphere. In addition, site effects, structural amplification, or both, seem to contribute to the selective detection of the earthquake in the regions where some people noticed it. Motions were far below design spectra for earthquake resistant design, and far below levels likely to be associated with damage.