A silica long base tiltmeter with high stability and resolution

Area of Science:

• Geophysics and Earth Sciences
• Instrumental Geodesy
• Seismology

Background:

• Multiparameter field operations require tiltmeters with stringent noise and stability specifications.
• Achieving low noise levels (≤ 10⁻⁹ rad) and long-term stability (10⁻⁷–10⁻⁸ rad/yr) is critical for valuable geophysical data.
• Insensitivity to thermal disturbances and robust coupling to bedrock are essential for accurate tilt measurements.

Purpose of the Study:

• To design and evaluate a long-base tiltmeter meeting high-performance criteria for geophysical field operations.
• To assess the stability, noise level, and thermal response of novel silica-based tiltmeters.
• To demonstrate the capability of these instruments in observing Earth's free modes.

Main Methods:

• Development of a long-base tiltmeter utilizing silica sensors with a low thermal expansion coefficient.
• Implementation of a linear variable displacement transducer based on alternative voltage-powered coil coupling.
• Careful consideration of base line horizontality, thermal response assessment, and bedrock coupling.
• Installation and testing of two 100m silica water tube tiltmeters in a mine for a hydrology research project.

Main Results:

• The developed tiltmeters exhibit remarkable stability (6.5x10⁻⁹ rad/month) and a very low noise level (around 10⁻¹¹ rad).
• Observed toroidal and spheroidal free modes of the Earth following major Sumatra earthquakes.
• Demonstrated suitability for multiparameter measurement field operations and geophysical research.

Conclusions:

• The novel silica tiltmeters meet and exceed the demanding requirements for geophysical measurements.
• These instruments offer a significant advancement in achieving high-stability, low-noise tilt sensing.
• The successful observation of Earth's free modes validates the performance and utility of the developed tiltmeters.