On the single-plot page, you can click on the plot to bring up information about that region of the plot. The main part of this information page is a list of time spans of the channel data during which the plot feature was produced. For people with access to BSL computers, You can cut and paste an entry from this time span list into the qdata command line to extract data for that period.
The PSD plots presented here are produced using programs developed by Dan McNamara and Ray Buland (BSSA 94:4 2004) at USGS, Golden. We have extended that code to allow processing of most of the real-time data collected by the NCEDC: broadband, strong motion and bore-hole seismic data, strain and electro-magnetic data. You will also want to see the PSD plots for other stations and networks at the IRIS DMC using their QUACK system.
There is a large amount of information condensed into each of these plots. It
takes some effort to learn how to interpret many of the features you will see
here. See McNamara's discussion
of some of these features for a useful introduction.