[Pre-alarming apparatus for earthquake based on mid-infrared trace methane detection]

Area of Science:

• Geophysics and Seismology
• Environmental Science
• Optical Engineering

Context:

• Seismic activity is often preceded by changes in subsurface gas concentrations.
• Accurate earthquake prediction remains a significant challenge, necessitating novel monitoring techniques.
• Gas observation technology in seismic fracture zones is rapidly advancing.

Purpose:

• To develop a sensitive mid-infrared methane sensor for detecting underground methane release.
• To establish a correlation between methane emissions and crustal rock fissures preceding earthquakes.
• To provide a novel technological solution for earthquake pre-alarming.

Summary:

• A mid-infrared methane sensor was designed using a quantum cascaded laser (QCL) at 7.65 μm and a 76 m multipass Herriott cell, achieving a detection sensitivity of 40 nmol x mol(-1) in 4s.
• Semiconductor laser frequency modulation with direct absorption technology was employed to reduce 1/f noise, lowering the detection limit to 5 nmol x mol(-1) (40 s acquisition).
• Field experiments using a controllable vibrator demonstrated the instrument's ability to monitor underground methane release at varying distances, confirming its potential for earthquake prediction.

Impact:

• The developed methane sensor can monitor underground methane release prior to seismic events.
• This technology offers a new method for earthquake pre-alarming, potentially mitigating earthquake-related losses.
• The findings contribute to the advancement of gas observation technologies for seismic monitoring.