Development of improved short-period geophone: Implementation of low-frequency compensation

Short-period geophones are widely used instruments in dense seismic array investigations. However, inherent limitations in capturing low-frequency signals restrict their versatility. This study implements a low-frequency compensation algorithm via a state-variable filtering circuit to enhance the frequency response of a traditional short-period geophone. Through simulation experiments and vibration testing, we validated the performance of the proposed bandwidth-extension (BE) system. Additionally, time-frequency earthquake signal analysis compared outcomes between our BE seismometers, benchmark short-period seismometers, and high-fidelity broadband seismometers across three seismic events with epicentral distances up to 5,186 km. Results demonstrate the BE system successfully extends the natural frequency cutoff from 4.5 Hz to below 0.2 Hz while maintaining strong consistency with broadband counterparts. Moreover, negligible power demands (10 mW) facilitate embedding the BE circuit directly within acquisition hardware. Given these advantages, the BE method shows promise for upgrading future sensors of seismic networks to record low-frequency content with minimal costs.