5:15 PM - 7:15 PM
[SVC36-P11] Relationship between the Noto Peninsula earthquake and geology (Oligocene-Miocene volcanic rocks)
Keywords:Noto Peninsula, Anamizu formation, volcanic rocks, andesite
The Noto Peninsula earthquake was caused by a reverse fault, and it is said that underground fluids were involved in the activity of the reverse fault, including the swarm of earthquakes that occurred around the Noto Peninsula (Amezawa et al., 2023, GRL 50; Nishimura et al., 2023 Sci. Rep 13; Yoshida et al., 2023 GRL 50). Since there is currently no volcanic activity in the Noto Peninsula, it cannot be said that the fluid originated from the subducting Pacific plate. On the other hand, Umeda et al. (2009 JGR 114), Umeda et al. (2024 GRL 51) and Kado et al. (2016 Geochemistry 50) analyzed hot spring water in the Noto Peninsula and pointed out the possibility that fossil seawater trapped underground and fluids showing high 3He/4He isotopes thought to be derived from the mantle may be welling up to the surface through the fault system. In other words, the origin of the fluids present in the Noto Peninsula has not been fully elucidated.
As a working hypothesis, we consider that "seawater penetrated into the mantle along normal faults when the Sea of Japan was formed." In mid-ocean ridges such as the Pacific Ocean, it is possible that seawater penetrated into the mantle along faults and caused hydrous melting of the low-pressure mantle (Tamura et al., 2022). Did something similar happen when the Sea of Japan was formed? Many normal faults were formed when the Sea of Japan was formed. Along these normal faults, a large amount of seawater must have reached the lower crust and perhaps the mantle. When the rising high-temperature mantle came into contact with seawater, the melting point of the mantle decreased, causing it to melt, and magma would have been generated. Especially at low pressures (< 1 GPa), hydrous melting of the mantle produces high-magnesium andesite (Tamura et al., 2022).
To verify this hypothesis, it is necessary to reexamine the geology and volcanic rocks (Anamizu Formation) of the Noto Peninsula that were formed during the formation of the Sea of Japan. Volcanic rocks from the Anamizu Formation will be sampled and petrography, whole-rock composition analysis, isotope analysis, etc. will be performed. High-magnesium andesite magma is formed when the mantle melts at high temperature and low pressure in a hydrous state. We will verify whether the parent magma of the volcanic rocks in Noto is high-magnesium andesite magma, and whether there was a reaction between the mantle and seawater.
As a working hypothesis, we consider that "seawater penetrated into the mantle along normal faults when the Sea of Japan was formed." In mid-ocean ridges such as the Pacific Ocean, it is possible that seawater penetrated into the mantle along faults and caused hydrous melting of the low-pressure mantle (Tamura et al., 2022). Did something similar happen when the Sea of Japan was formed? Many normal faults were formed when the Sea of Japan was formed. Along these normal faults, a large amount of seawater must have reached the lower crust and perhaps the mantle. When the rising high-temperature mantle came into contact with seawater, the melting point of the mantle decreased, causing it to melt, and magma would have been generated. Especially at low pressures (< 1 GPa), hydrous melting of the mantle produces high-magnesium andesite (Tamura et al., 2022).
To verify this hypothesis, it is necessary to reexamine the geology and volcanic rocks (Anamizu Formation) of the Noto Peninsula that were formed during the formation of the Sea of Japan. Volcanic rocks from the Anamizu Formation will be sampled and petrography, whole-rock composition analysis, isotope analysis, etc. will be performed. High-magnesium andesite magma is formed when the mantle melts at high temperature and low pressure in a hydrous state. We will verify whether the parent magma of the volcanic rocks in Noto is high-magnesium andesite magma, and whether there was a reaction between the mantle and seawater.