综合多频率地质雷达天线探测活断层浅层结构——以玉树活动断裂为例

THE APPLICATION OF MULTI-FREQUENCY GPR ANTENNA FOR IMAGING THE SHALLOW SUBSURFACE FEATURES IN THE YUSHU ACTIVE FAULT

地质雷达技术具有操作性强、分辨率高、探测深度深、对地表环境无破坏和可重复探测等特点,在活断层探测中具有很大的优势。为验证综合多中心频率地质雷达天线探测活断层地下浅层结构效果,以民主村处发育的玉树活动断裂为研究对象,采用25 MHz、100 MHz、250 MHz和500 MHz中心频率的地质雷达天线对活断层浅层结构进行探测,并与探槽剖面进行效果对比。研究结果表明:低中心频率的地质雷达天线(25 MHz和100 MHz)可获取大范围内深度较深(约32 m)的活断层地下浅层结构的整体形态,从雷达图像上可识别出主断层分布范围、断层倾向及地下浅层结构等;而中高中心频率的地质雷达天线(250 MHz和500 MHz)则可获取局部范围内深度较浅(约3 m)的地下浅层结构,尤其是500 MHz天线。探测结果与地表构造地貌形态和探槽剖面地质构造一致,表明综合多中心频率地质雷达天线探测玉树活动断裂浅层结构的有效性和适用性,为活断层研究提供多尺度数据及方法支持。

Ground Penetrating Radar(GPR) has the characteristics of strong operability, high resolution, deep detection depth, no damage to the surface environment and repeatable detection, so it is widely-used in active fault detection. In order to assess the effects of GPR for imaging the shallow subsurface geometry in active fault, the 25 MHz, 100 MHz, 250 MHz and 500 MHz GPR frequency antenna were firstly conducted on the Minzhu site of the Yushu active fault zone for the fault detecting. Moreover, the multi-frequency GPR profiles were compared with the three trench section, which were excavated by the previous researches. The research results show that: the low GPR frequencies(25 MHz and 100 MHz) were applied to delineate an excellent general view of deformation zones at a much wider area and greater depth(up to 32 m). The distribution and the direction of the active fault and the horst structure can be deduced on the GPR profiles. The high GPR frequencies(250 MHz and 500 MHz) provided more detailed analysis of the shallow subsurface geometry within 3 m depth. The GPR results are consistent with the surface morphology and trench wall, and the result show that multi-frequency GPR antenna is valuable for imaging the shallow subsurface geometry of the Yushu acive fault, and also provide multi-scale data and method for active fault study.