Geophysical Instruments

Hard copy printout from ES-2415F shows evidence of 3 different materials: a top layer of P-wave velocity of 1500 ft/s, a deeper layer with a p-wave velocity of 6580 ft/s (channels 22 to 11) and bedrock with an apparent P-wave velocity of nearly 10,870 ft/second (channels 11 through 1). Actual paper is the color of aluminum foil. A dot-matrix type print head hammers away the aluminum, exposing the black backing. This image shows only the first 140 milliseconds of a record 250 milliseconds in length.