These files describe the strainmeter recording at CI.ISA of the
1960 M9.5 Chile event.
According to Hiroo Kanamori:
I believe that this is produced from isa60.asc which I got from somewhere (very probably Guy Masters) many years ago.

Very probably this is the one Prof. Stewart Smith digitized from the original paper record.

It was hand-digitized at 1 min interval.  There are 26,668 points  (Approximately 444 hours (18.5 days).

I think this was used by BPS(1961), in which they say they used 16,000 points.

The spectrum they obtained is shown in Fig. 1 of their paper.  Luis and I did more or less the same in our 2019 paper.

BPS's spectrum was computed with autocorrelation with some fairly strong smoothing, but I believe that it is correct.

In those days, Caltech did not have a computer and they had to use Sandia's IBM704!

In any case, this is an historical data. I had the original "long" paper record which Dr. Stewart Smith gave to me.  I recently 
officially transferred it to Caltech Archive.
---
References: Benioff, H., F. Press, and S. Smith (1961), Excitation of the free oscillations of the Earth by earthquakes, 
J. Geophys. Res., 66(2), 605–619, doi:10.1029/JZ066i002p00605.

Hiroo Kanamori, Luis Rivera, Lingling Ye, Thorne Lay, Satoko Murotani, Kenshiro Tsumura, New constraints on the 1922 Atacama, Chile, 
earthquake from Historical seismograms, Geophysical Journal International, Volume 219, Issue 1, October 2019, Pages 645–661, 
https://doi.org/10.1093/gji/ggz302