ALBERT

Description: The Changning MS6.0 earthquake and its moderate to strong aftershocks, which occurred in the axial area of Changning anticline, exhibit different features with the moderate to strong earthquakes that occurred in the southern syncline area nearby, although these two areas are only a dozen kilometers away. Whether this difference is only caused by different fault structures, or caused by local change is still a matter of debate. In order to answer this question, basing on the correction of small earthquake location and seismic velocity structure through double-difference tomography inversion, this paper determined the fine structure of the crustal stress field by using comprehensive focal mechanism solutions, and analyzed its mechanical consistency with the focal mechanism solutions of moderate to strong earthquakes. It is found that for the different subareas of Changning area, the maximum principal stress remains horizontal, and its azimuth remains almost East-West oriented although it has a small clockwise rotation from north to south; meanwhile, the stress regime exhibit a significant local change, which is thrust stress regime for the axial area of Changning anticline, against strike-slip stress regime for the southern syncline area. The stress fields in these two subareas highly accord with the focal mechanism solutions of moderate to strong earthquakes in the corresponding area, but poorly accord with, or even contradict that in the non-corresponding area, which indicates that the local stress change of stress field is the necessary mechanical basis for the complex seismicity behavior in Changning area. Additional rock mechanics analysis points out that lateral difference of Poisson's ratio of rock is probably the main cause of this local change of stress field. This paper also discusses the seismogenic fault structure of Changning MS6.0 earthquake sequence, and suggests the activation of the basement fault(s) in the depth range of 6 to 9 km in the axial area of Changning anticline driven by regional stress field is the potential cause of the occurrence of Changning MS6.0 earthquake sequence.

Description: For a long time， with the continuous expansion of the oil and gas genesis theory and the increasing global demand for clean energy， hydrogen， as an important link connecting the theory of inorganic and organic hydrocarbon generation， as well as a promising clean energy， has gradually attracted widespread academic attention. The genesis of hydrogen in natural gas is relatively complex and diverse. According to its reaction mechanism， it can be divided into two categories： inorganic and organic. Inorganic genesis is mainly earth degassing， water rock reaction and water radiation decomposition， while organic genesis is dominated by biological action and organic matter pyrolysis. At present， hydrogen isotope and geochemical characteristics of associated gases are mainly used to identify the origin of hydrogen. However， due to the complex and diverse sources of hydrogen and its active chemical properties， it is still unable to identify the origin of hydrogen systematically and accurately. Due to the extensive genesis of hydrogen， natural gas with different hydrogen concentrations has been found in different geological conditions around the world， and the hydrogen content varies greatly （0.1%-99%）. Hydrogen can participate in hydrocarbon generation in Fischer Tropsch synthesis as a reducing agent， and also can be used as a hydrogen source to improve the hydrocarbon yield during the thermal evolution of organic matter. Therefore， the existence of hydrogen may extend the lower limit of deep gas exploration and development. Based on the systematic summary of the genetic mechanism and distribution of hydrogen， this paper discusses the energy significance of hydrogen in natural gas， and provides a reference for the future research on hydrogen rich natural gas resources.