For those interested in studying the earth modes, teleseismic events, volcanic slugs and other “VLP” events, properly insulating your broadband against thermal fluctuations is easy. Let’s take the Nanometrics Trillium Compact as an example. This beer can-sized broadband unit has little mass and no thermal insulation. When installed in the nude it reads like a thermometer at the long periods. Solve this cheaply by pouring a small cylinder of concrete around the Compact to give it mass. Then cut some Styrofoam for insulation. The gains are HUGE. See below for a before and after screen shot from PQLX for one of Panama’s many Compacts. Notice how the long-period signal drops to follow the Nominal Low Noise Model (lower grey line) after a make-shift thermal insulator was applied!
P.S. GO BOREHOLE for maximum thermal stability