The Relationship between Powerful Geodynamic Impacts and an Increase in the Mercury Content of the Water of the Angara River Source (Baikal Rift Zone)

Abstract

Abstract—The results of Hg content determination in the water of the Angara River source are considered in relationship with the seismic processes proceeding at different levels of the lithosphere in the Baikal Rift Zone (BRZ), the geodynamic rejuvenation of the South Baikal rifting attractor structure (RAS), and the time distribution of M ≥ 7 earthquakes which occurred at a significant distance from the water sampling station. The correlation coefficients calculated between the pairs Hg content–earthquake numbers n and Hg–logarithm of summary seismic energy lgΣES are most often low, thus indicating the absence of a statistically meaningful relationship between the remote seismic process and the dynamics of mercury release. However, the correlation coefficients in the vicinity of the Angara River source are high, thus proving the relationship of the mercury release with the deformation of this territory. The statistical validity of the «deformation–mercury release» cause-and-effect relationship is verified by the fact that strong geodynamic impacts precede all meaningful Hg release maxima. In the period 1997–1998, the South Baikal RAS produced the highest impact, being in the phase of the maximum geodynamic activity. The combined impact of the RAS and the South Baikal earthquake of 1999 resulted in a series of the maximum mercury contents within 1999–2000. The subsequent gradual relaxation of the RAS activity led to a reduction in the average annual Hg content. Remote M ≥ 7 earthquakes and close strong earthquakes of the BRZ are responsible for the significant Hg release maxima. The predicted trend of the average annual Hg contents is their considerable increase in the fields of fluid discharge of faults under the powerful geodynamic impact of the RAS or strong earthquake. We assume that in the study lithosphere area, the powerful geodynamic impact caused an opening of fault zones leading to decompression with boiling and degassing of mercury and its rapid rise to the surface.