Theory and application of magnetic and self-potential methods in the detection of the Heshituoluogai coal fire, China

• Magnetic and self-potential anomalies in Heshituoluogai coal fire were analyzed.
• Several data processing methods are used to make the result more straight forward.
• The interpretation of results is consistent with the results of ground survey.

Coal fires are a major problem throughout the world. They threaten the environment and the health of people living nearby and result in significant economic losses. Efficient and economical control of these fires requires that the extent of the subsurface coal fire be delineated. In this paper, we first present laboratory experiments, revealing that new preferential alignment of magnetic moments, newly formed magnetite and thermoremanent magnetization are the root causes of magnetic anomalies in coal fire area. The redox potential and Thomson potential, which are the basis of the self-potential anomalies, are proposed additionally for application. Then, the geological setting and an overview of the Fifth Fire Area (FFA) of the Heshituoluogai coal fire in Xinjiang are introduced in detail. Finally, the magnetic and self-potential methods are combined to delineate the extent of the fire. Several data processing methods such as diurnal fluctuation rectification, reduction to pole and upward continuation are used to process the data to make the interpretation of results more straight forward. The locations of subsurface fire regions delineated by the magnetic and self-potential methods are consistent with the results of ground surveys, indicating that these two methods can be used effectively as a tool for the detection of coal fires.