Date: 16:00-18:00, Friday, April 24, 2026
Speaker: Zahra Zandvakili
Title: Research on Geofluids Involved in Earthquake Processes: Lithium
Isotope Applications in Case Studies from Japan
Abstract: Geofluids play an important role in earthquake processes by
influencing stress conditions, fault behavior, and fluid–rock
interactions within the crust. In particular, geofluids can facilitate
fault movement and affect seismic activity by increasing pore pressure
and weakening fault zones. However, their origin and temporal
variations are still not fully understood. Lithium (Li) isotopes are
effective tracers that reflect fluid–rock interaction and
high-temperature processes in deep Earth environments. Therefore, this
study uses Li isotopes as sensitive tracers to investigate the origin
of geofluids and to identify geochemical anomalies related to seismic
activity. This study focuses on case studies from Japan, particularly
the 2018 Hokkaido Eastern Iburi earthquake (M6.7). Prior to this
earthquake, a clear decrease in groundwater Na/K ratios was observed
several months in advance approximately 20 km from the epicenter. To
investigate the cause of this anomaly and its possible link to the
migration of fluids that experienced high temperatures at depth, Li
and Sr isotope ratios were analyzed as indicators of deep fluid input.
The results show no significant changes in Li or Sr isotopic
compositions, suggesting that the anomaly was not caused by the
contribution of deep-derived fluids. Instead, the decrease in Na/K
ratios can be interpreted to reflect CO₂ influx into the aquifer,
possibly due to leakage from a nearby carbon capture and storage (CCS)
site. This interpretation was first proposed by Sano et al. (2020),
who reported changes in δ¹³C (¹³C/¹²C ratio relative to a standard)
and radiocarbon (¹⁴C), both useful tracers of CO₂ sources, in
geofluids prior to the earthquake. Similar decreases in Na/K ratios
and increases in CO₂ concentrations have been reported before other
earthquakes, suggesting that CO₂ input into groundwater may represent
a common pre-seismic signal. By combining Li isotope data with
hydrogeochemical observations, this study demonstrates the value of
isotope geochemistry in distinguishing fluid sources and constraining
the processes responsible for geochemical anomalies.