ABSTRACT

The short- and long-period seismograms at both St. Louis and Florissant appear to indicate an opposite sense of the first P motion for the Montana earthquake of August 18, 1959. The P motions are impulsive and seem to arrive simultaneously on both the short- and long-period seismograms.

In order to avoid any doubt about the relation between trace and ground displacements, seismograms of the earthquake of August 26, 1959, are reproduced. The first P motion is impulsive, and shows the same sense on both the short- and long-period seismograms.

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