The Chemical Composition of Ground Water in Observational Water Vents in the Petropavlovsk Geodynamic Test Site: The Classification and Effects of Large Earthquakes

Abstract

⎯This paper considers the chemical composition and classification of ground water at seven flowing wells and four springs using materials from the 2014 hydrogeochemical sampling and from continuous observations conducted by the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences (KB GS RAS) in 1989-1999. We estimated the saturation of ground water discharges at individual vents with alumosilicate, carbonate, and sulfate secondary minerals, following the behavior of saturation over time. We have found that the ground water undergoes an increase in the saturation with secondary minerals during large earthquakes that produced shaking of intensity I = 5-6 on the MSK-64 scale. Such changes in the saturation of ground water with secondary minerals are less pronounced during the precursory periods before earthquake occurrence. We discuss desirable future developments of the observational system at wells and springs in order to look for new types of hydrogeochemical precursors to earthquakes.

Anomalies in groundwater composition caused by earthquakes: examples and modeling issues

“…The results of regime observations data processing at wells and sources show changes of interaction in «water -rock» system caused by the impact of earthquake of 5-6 point intensity (according to the MSK-64 scale) (post-seismic effect). Before the Kamchatka earthquake on March 2, 1992, a new type of hydrogeochemical precursor was discovered in the form of increase in saturation of anhydrite of groundwater from the M-1 well [1].…”

“…The results processing of observational data show the changes of interaction in the «water -rock» system caused by the 5-6points shakes (on the MSK-64 scale), especially evident in the case of the March 2, 1992 earthquake. Before this earthquake was discovered a new type of hydrogeochemical precursor in the form of increasing saturation of the groundwater from the M-1 well by anhydrite [1] (Fig. 6).…”

“…The Kamchatka branch of Geophysical Survey RAS (KB GS RAS) carries out long-term observations on chemical composition of groundwater in seven deep self-flowing wells and three sources in vicinity of the city Petropavlovsk-Kamchatsky, East Kamchatka (Fig. 1) for the purpose of searching of hydrogeochemical precursors of earthquakes [1,2,3].…”

“…In addition, the study of hydrogeochemical anomalies in water of observational wells and sources on the basis of fundamental laws on the formation of groundwater composition in the «water -rock» systems allows their meaningful explanation not only for purpose of seismic forecast, and also for an assessment of seismic impact on the formation of chemical composition of groundwater in seismically active regions. Some issues of modeling such recorded anomalies were previously discussed in [1,4,5,6]. Table 2.…”

“…According to the results of chemical analysis of water composition estimated the degree of groundwater saturation relative to secondary minerals with using the saturation index SI in [1]: SI=lg(Q/Kp), where Qquotient reactions or ratio the actual product of the reaction products activities to the actual product of the activity initial materials, Kpreaction constant. Positive SI values show that the water is saturated with secondary minerals and the value of SI increases as the water is being saturated with secondary minerals.…”