Hydrogeochemical temporal variations related to changes of seismic activity at Tenerife, Canary Islands

This work presents the results of a hydrogeochemical study conducted in two galleries on the island of Tenerife: Fuente del Valle and San Fernando, during a 2-year period with weekly sampling (July 2016 to July 2018). Groundwater temperature, pH, and electrical conductivity exhibited stable values throughout the study period, while significant temporal variations were observed in the total alkalinity, SO 4 2− /Cl − ratio (in meq·L −1 ), and isotopic composition (δ 18 O and δD). δ 13 C TDIC values showed an endogenous signature for both galleries, while δ 18 O and δD values indicated a meteoric origin with interaction with endogenous gases, mainly CO 2 . Changes in isotopic ratios coincided with variations observed in alkalinity and SO 4 2− /Cl − ratio. On October 2, 2016, a seismic swarm of long-period events was recorded on Tenerife followed by a general increase of the seismic activity in and around the island. A correlation was observed between some hydrogeochemical parameters in the groundwaters of the galleries related to observed changes of the seismic activity.