随着地震断裂带气体观测技术的快速发展, 为了对地震进行精确的预报, 减少因地震给人民群众生命和财产带来的损失, 根据甲烷气体的释放与地震前上地壳岩石的微裂隙有直接关系的这一微观变化, 设计并研制中红外痕量甲烷气体检测仪。 仪器采用激发波长为7.65 μm的量子级联激光器(QCL), 结合双光路长度为76 m的多次反射herriott长光程气体吸收池, 可以在4 s的采样时间内实现40 nmol·mol-1气体检测灵敏度。 同时, 采用半导体激光器频率调制直接光谱吸收技术, 降低了该仪器噪声的主要来源1/f噪声, 使气体检测下限达到5 nmol·mol-1 (40 s采用时间)。 在野外实验中, 利用可控震源车作为模拟地震源, 将6个痕量甲烷检测仪以100 m为距离等间隔放置, 对距震源中心不同距离下的地表面甲烷气体浓度进行动态测量。 实验表明, 该仪器可以监测地震前地下痕量甲烷气体的释放, 为地震前兆预警提供新的途径。

With the rapid development of gas observation technology in seismic fracture zone, in order to accurately predict the earthquake, and reduce the people’s lives and property losses caused by earthquake, a mid-infrared methane sensor was designed and developed, which is based on the microscopic relation between methane release and earthquake fissures on the crustal rocks. This instrument utilizes quantum cascaded laser (QCL) operating at 7.65 μm, combined with MIR multipass herriott cell with 76 m absorption path length to obtain low detection sensitivity down to 40 nmol·mol-1 level in 4s acquisition time. Meanwhile, to decrease the primary noise source (1/f noise), semiconductor laser frequency modulation of direct absorption technology was utilized to obtain gas detection limitation as low as 5 nmol·mol-1 (40 s acquiring time). In field experiments, controllable vibrator was used as vibration source, a number of trace methane detectors were placed with 100 m distance interval to carry out the dynamic measurement of methane concentration on the ground surface at different distances from the vibration source. Experimental results show that the instrument can monitor the release of underground methane before the earthquake and provide a novel measure as a pre-alarming for earthquake.