Earthquake precursor monitoring is the foundation of earthquake prediction and geothermal monitoring is one of the basic methods of earthquake precursor monitoring. High temperature well contains more information and therefore its monitoring is more important. However, electric sensors are hard to meet the monitoring requirements of high sensitivity and long lifetime. For a better observation of the earthquake precursor, a high sensitive fiber Bragg grating (FBG) temperature sensor is designed to monitoring a well at 87. 5±1°C. The performance of the FBG sensor demonstrates that it's quite possible that applying FBG to high-sensitivity temperature-monitoring fields, such as geothermal monitoring. As far as we known, it is the first time that trying a high sensitive FBG temperature sensor in a practical application, let alone in the field of geothermal monitoring.
Earthquake precursor monitoring is the foundation of earthquake prediction and geothermal monitoring is one of the basic methods of earthquake precursor monitoring. Geothermal monitoring also reflects the Stress-strain, and therefore being a good complement to Stress-strain observation. High temperature well contains more information and therefore its monitoring is more important. However, electric sensor is hard to meet the monitoring requirements (high sensitivity and long lifetime). As a new generation sensing element, fiber Bragg grating has lots of advantages, such as immunity to electromagnetic interference and ease in signal transmission, which are very appealing to the field of geothermal monitoring. And temperature monitoring based on FBG is one of its hottest applications (Lee, 2003). FBG is sensitive to both temperature and strain by shifting its resonance Bragg wavelength. Its intrinsic temperature sensitivity is about 10 pm/ °C. For achieving a higher sensitivity, people first try to improve its sensitivity by attaching it to a large CTE (coefficient of thermal expansion) material (Cruz 1996, Mizunami 2001).
