Long-term data recording of the Earth’s rock-and-roll events

The term Seismograph comes from two Ancient Greek words, seismos, literally meaning earthquake, and graphein, to write. Although seismographs are widely used to monitor naturally occurring earthquakes, they can be used to monitor any shaking of the earth, including movement caused by man’s activities. Seismography is extensively used in geological exploration, for example, monitoring and recording the effects of explosions and the timed passage of their shock waves through the earth’s crust.

On a less dramatic scale, seismographs can be used to monitor ground vibrations caused by trains, lorries and other vehicles. On a smaller scale still, even footsteps and sub-soil digging can be detected by seismological techniques (as immortalized in films and books about WW2).

The seismograph described here constantly records data from a sensor that responds to any displacement between it and a reference source. The associated electronics can be set to react even to minor earth shifts or vibrations. It is worth noting that the electronics could also be used with an existing seismograph assembly if its sensor system outputs a d.c. voltage in the range of 0V to +5V. It might also be possible to add this design’s sensor and electronics in their entirety to any pendulum-based seismograph.

At the heart of the logger is a PIC microcontroller. Analogue signals from the sensor are amplified, limited by a low-pass filter, and fed to an analogue-to-digital input of the PIC. The PIC samples the data at 25Hz, constantly outputting it as a serial stream suitable for input to a PC and storage to its hard drive at a rate selected by the user. The data can be downloaded to a PC as a complete block whenever desired, at intervals of hours, days, or even weeks. At the PC, specially written software allows the data recorded to be selectively displayed on screen. It is also in a format suited to further analysis by Microsoft Excel or similar spreadsheet and graphing display software.