[O-08] Poster presentations by senior high school students

[O08-P49] Spatial distribution of hot springs and tremors zone derived from the Philippine Sea Plate

*Yui Kobayashi¹ (1.Shizuokahigashi High School)

Keywords:slab-derived fluid, slab-derived hot spring, deep tremor

In the Southwest Japan Arc, seawater subducted beneath the continental plate along with the Philippine Sea Plate (PHS) hydrates olivine, which makes up the mantle wedge and sinks deeply as hydrous minerals. At deeper and hotter conditions, hydrous minerals decompose and release slab-derived fluids. This fluid is thought to be involved in the generation of hot springs and deep tremors (tremors). The current study examines the relationship between slab-derived hot springs and tremors and the spatial distribution of tremors zone, focusing on the fact that slab-derived fluids are involved in both. As a method, the number of tremor occurrences and the Li/Cl ratio of slab-derived hot springs were used to compare the overlap and correlation between tremors and hot springs while shifting their locations to the north, south, east, and west, respectively. The direction of PHS sinking was calculated and based on the hypocenter of the microearthquakes, the sinking PHS boundary was visualized and compared to the surface depth of the PHS (Figure 1) and comparisons were made between the tremors and the surface depth of the PHS and the temperature inside the PHS calculated by One-dimensional heat conduction in the sinking slab (Figure 2). The results show that slab-derived hot springs tend to gush south of the tremors hypocenter location and that the tremors onset zone is along an isothermal zone with a PHS temperature of about 400 °C. There is a gap in the tremor zone in Ise Bay and Kii Channel, but there is no mantle wedge on the upper plate side of Ise Bay where the PHS temperature is about 400 °C. The gap is due to the lack of a mantle wedge on the upper plate side of the Ise Bay. The gap in the Kii Channel is compensated by tremors in the northern part of Shikoku toward the subduction extension and is not a gap. These suggest that mantle wedge and slab surface temperatures on the upper plate side are important in the generation of tremors and slab-derived hot springs.