10:45 AM - 12:15 PM
[SCG45-P20] Lithium isotopic indicator for the origin of deep-derived fluids involved in generating earthquake swarms and deep low-frequency earthquakes
Keywords:deep fluid, lithium isotope, earthquake swarm, deep low-frequency earthquake
Understanding deep-seated fluid helps us to understand the process of earthquake generation. Regions of low seismic wave velocity and low resistivity have been observed around the epicenter during earthquake swarms. It is believed that earthquakes are induced by deep fluids originating in the lower crust, mantle wedge, or slab, which move within the crust. Information on the temperature and chemical composition of deep-derived fluids provide clues to understanding the origin of water in the subsurface. However, the origin of these fluids remains unclear. Several studies have explored the migration of deep-derived fluids before and after earthquakes based on changes in the chemical composition of spring water. However, no systematic changes have been confirmed, and the relationship between earthquakes and these changes is unclear.
In this study, we compared the lithium isotope ratio (7Li/6Li) of spring water from an earthquake swarm zone (Nishio et al., 2010), deep low-frequency seismic zones (Umam et al., 2022, Shintani et al., 2022), and low seismic activity zone (This study). 7Li/6Li provides information about the origin of deep-derived fluids. Therefore, we could gain insights into the origin and temperature of the deep-derived fluids involved in earthquake occurrence based on the lithium isotope.
The 7Li/6Li of the springs in the deep low-frequency seismic zone was at the same lower limit as the value for the low seismic activity zone. The 7Li/6Li of the spring water in the swarm seismic zone was lower than that in the deep low-frequency seismic zone. These results imply that the upward velocity of deep-derived fluids is slower in the deep low-frequency seismic zone. On the other hand, the upward velocity of the deep-derived fluid is faster in the earthquake swarm zone.
In this study, we compared the lithium isotope ratio (7Li/6Li) of spring water from an earthquake swarm zone (Nishio et al., 2010), deep low-frequency seismic zones (Umam et al., 2022, Shintani et al., 2022), and low seismic activity zone (This study). 7Li/6Li provides information about the origin of deep-derived fluids. Therefore, we could gain insights into the origin and temperature of the deep-derived fluids involved in earthquake occurrence based on the lithium isotope.
The 7Li/6Li of the springs in the deep low-frequency seismic zone was at the same lower limit as the value for the low seismic activity zone. The 7Li/6Li of the spring water in the swarm seismic zone was lower than that in the deep low-frequency seismic zone. These results imply that the upward velocity of deep-derived fluids is slower in the deep low-frequency seismic zone. On the other hand, the upward velocity of the deep-derived fluid is faster in the earthquake swarm zone.