To honor the Albuquerque Seismic Laboratory's (ASL) 50th Anniversary, IRIS produced a helicorder plot that displays a continuous record of the digital seismic data recorded by seismometers at ASL. These instruments have produced digital seismic data for over 40 years, beginning with station ALQ from 1972-1974 as part of the High Gain Long Period Seismic network and station ANMO for the Seismic Research Observatory Network before joining the Global Seismographic Network (GSN) in 1989. The United States Geological Survey (USGS) partners with IRIS and University of California-San Diego in the operation of the GSN, and ASL currently operates more than two-thirds of these stations.
The instruments at ASL reside in well-insulated quiet boreholes and vaults, producing extremely high-quality data while recording local, regional, and teleseismic earthquakes. The 40-year helicorder plot has been decimated, equalized in gain, bandpass filtered from 50-250 seconds, and cleaned of instrument calibration pulses. The seismograms are printed at monthly intervals, and the approximate timing of prominent earthquakes is highlighted along the margin. In addition to showing the spectacular quality and continuity of the data recorded at ASL, this unique presentation is a powerful teaching tool to stimulate discussion of the history of great earthquakes over almost a half century. The relative amplitude of large, globally significant earthquakes is striking in relation to more numerous but significantly smaller regional events.