5:15 PM - 7:15 PM
[STT41-P07] Development and Trial Operation of a Small Seismic Source
Keywords:Small Seismic Source, Portable Seismic Source, Precision Control, Seismic Wave Exploration
Background and Objectives
In the field of seismic observation, technology has been used to generate artificial seismic waves and analyze their propagation to explore subsurface structures. Earthquake and Volcano Research Center at Nagoya University has been developing a system capable of precisely controlled vibrations (ACROSS). ACROSS stands for "Accurately Controlled Routinely Operated Signal System."
The conventional ACROSS vibrators are large-scale devices with strong excitation forces (several tons), allowing for deep seismic exploration. However, these devices weigh several tons, require heavy machinery for installation and relocation, and involve extremely high operational costs.
By developing a more portable small-scale ACROSS device, several advantages can be achieved: It can be manually transported and installed, allowing for usage of various purpose that could not be applied using conventional ACROSS vibrators. Significantly reduced costs enable the simultaneous operation of multiple units, allowing for three-dimensional tomographic monitoring. Miniaturization makes it feasible for use in urban areas, enabling finer-scale observations.
Design and Fabrication
The small ACROSS device was designed to meet the following five requirements: Portability by manual transport (each component weighing 20 kg or less) Ensuring safety (sufficient weight design against centrifugal force) Easy assembly (simple on-site assembly) Operation with a 100V (single phase) power supply (easy power availability) Compatibility with existing control systems The device was designed to fit within dimensions of 50 cm × 50 cm × 33 cm, with an eccentric rotor to transmit vibrations to the ground. A 25mm small bearing was adopted for the axis to reduce costs while maintaining high precision.
Initially, iron was used for the material, but due to rust issues, stainless steel was introduced for parts requiring high precision. The device was expected to operate at a maximum of 30 Hz, but experimental results revealed that motor constraints limited its operation to 18 Hz.
Experiment and Evaluation
The device was tested at the Mikawa Observation site in Toyohashi city, Japan. Velocity-type seismometers were placed at 50 m, 100 m, and 200 m distances to confirm wave propagation. The vibrator was stabilized by securing it to the ground with anchor bolts.
Although the expected operation at 30 Hz was not achieved due to motor step-out, an experiment was conducted at 18 Hz for one hour, successfully detecting clear signals at the 200 m distance seismometer. The control system functioned as expected, confirming stable oscillation. The usage of mass with smaller eccentricity will enable the operation of higher frequency.
Conclusion and Future Prospects
Compared to conventional ACROSS devices, this system significantly reduces manufacturing costs. This enables easier implementation of three-dimensional tomographic monitoring using multiple seismic sources and expands observation capabilities. Additionally, the device can be easily repaired in a laboratory, enhancing operational flexibility.
Moreover, achieving stable oscillation at the expected frequency in actual experiments is a significant milestone. Future plans include increasing the operating frequency and conducting long-term experiments lasting several days to weeks to confirm the practical usability of the small ACROSS device in various locations.
In the field of seismic observation, technology has been used to generate artificial seismic waves and analyze their propagation to explore subsurface structures. Earthquake and Volcano Research Center at Nagoya University has been developing a system capable of precisely controlled vibrations (ACROSS). ACROSS stands for "Accurately Controlled Routinely Operated Signal System."
The conventional ACROSS vibrators are large-scale devices with strong excitation forces (several tons), allowing for deep seismic exploration. However, these devices weigh several tons, require heavy machinery for installation and relocation, and involve extremely high operational costs.
By developing a more portable small-scale ACROSS device, several advantages can be achieved: It can be manually transported and installed, allowing for usage of various purpose that could not be applied using conventional ACROSS vibrators. Significantly reduced costs enable the simultaneous operation of multiple units, allowing for three-dimensional tomographic monitoring. Miniaturization makes it feasible for use in urban areas, enabling finer-scale observations.
Design and Fabrication
The small ACROSS device was designed to meet the following five requirements: Portability by manual transport (each component weighing 20 kg or less) Ensuring safety (sufficient weight design against centrifugal force) Easy assembly (simple on-site assembly) Operation with a 100V (single phase) power supply (easy power availability) Compatibility with existing control systems The device was designed to fit within dimensions of 50 cm × 50 cm × 33 cm, with an eccentric rotor to transmit vibrations to the ground. A 25mm small bearing was adopted for the axis to reduce costs while maintaining high precision.
Initially, iron was used for the material, but due to rust issues, stainless steel was introduced for parts requiring high precision. The device was expected to operate at a maximum of 30 Hz, but experimental results revealed that motor constraints limited its operation to 18 Hz.
Experiment and Evaluation
The device was tested at the Mikawa Observation site in Toyohashi city, Japan. Velocity-type seismometers were placed at 50 m, 100 m, and 200 m distances to confirm wave propagation. The vibrator was stabilized by securing it to the ground with anchor bolts.
Although the expected operation at 30 Hz was not achieved due to motor step-out, an experiment was conducted at 18 Hz for one hour, successfully detecting clear signals at the 200 m distance seismometer. The control system functioned as expected, confirming stable oscillation. The usage of mass with smaller eccentricity will enable the operation of higher frequency.
Conclusion and Future Prospects
Compared to conventional ACROSS devices, this system significantly reduces manufacturing costs. This enables easier implementation of three-dimensional tomographic monitoring using multiple seismic sources and expands observation capabilities. Additionally, the device can be easily repaired in a laboratory, enhancing operational flexibility.
Moreover, achieving stable oscillation at the expected frequency in actual experiments is a significant milestone. Future plans include increasing the operating frequency and conducting long-term experiments lasting several days to weeks to confirm the practical usability of the small ACROSS device in various locations.