The MIU Project is under implementation at Shobasama site (14ha) owned by JNC. The Tono area, where the Shobasama site is located is bounded in the northwest by Mino-Hida Mountains, in the southeast by Mikawa Mountains, and occupies a boat-shaped topography with an axis extending northeast-southwest between the two Mountains as is shown in Fig.2.2. Kiso River cuts the northern mountains as a deep antecedent valley. The boundary between the southeast mountains and boat-shaped hills is clearly marked by a northeast-southwest running fault (Byobusan Fault) near Mt.Byobusan (794.1m in altitude). This fault can be identified by a steep cliff with talus deposits. This steep cliff has become obscured toward the southwest. In the central part of the boat-shaped hills flows Toki River from northeast to southwest. Terraces develop along Toki River and its tributaries with low lying alluvial land. There is a clear relationship between the geology and topography. The mountainous regions, hilly regions and hilltops correspond to Mesozoic basement rocks, Neogene/Quaternary sedimentary rocks and the Pliocene Seto Group (Toki Gravel), respectively.⁹⁾

The geology of the Tono area consists of sedimentary rocks of the Mino Belt (Triassic to Jurassic), granites and rhyolite (Cretaceous to Palaeogene), Miocene, Pliocene and later sedimentary rocks.

The sedimentary rocks of the Mino Belt are mostly sandstone, mudstone and chert with a strike of ENE-WSW and represent repeated sequence of Triassic to Late Jurassic strata¹⁰⁾.

Granites are mainly so-called Ryoke Granite and distributed in Mino-Mikawa Plateau. Toki Granite with 10km diameter is exposed in the Toki-Mizunami Basin and intrudes into sedimentary rocks of the Mino Belt discordantly. The Toki Granite is regarded as a part of Naegi-Agematsu Granite complex located to the east. In Toki Granite near Toki City, dikes of quartz porphyry are found with a strike of NNW¹¹⁾.

Nohi Rhyolite is distributed in Kamado district, Mizunami City in the north-eastern part of the study area and eastward. It is composed of monolithologic welded tuff, and is intruded by Toki Granite in Mizunami City¹²⁾.

Miocene sedimentary strata (Mizunami and Kani Groups) cover basement rocks in Toki-Mizunami and Kani basins. Mizunami Group is divided into Toki Lignite-bearing Formation, Hongo Formation, Akeyo Formation and Oidawara Formation. As a whole, there is a trend of upward fining and wider distribution indicating transgression. The thickness of the Mizunami Group in the south of Toki-Mizunami Basin is over 300m. The Pliocene Seto Group consists mainly of gravels (Toki Gravel) of chert and Nohi Rhyolite. A clay bed (Tokiguchi Formation) occurs in the lower horizon of Seto Group¹³⁾.

The area is divided into several tilted blocks by faults and tilting movements from Late Pliocene to Pleistocene. Geographically important fault include Byobusan Fault and Kasahara Fault occurring near Nakatsugawa-Tajimi (strike : NE-SW), Enasan Fault parallel to the above to the south, and Sanageyama Fault bordering east- side of Mt.Sanageyama. All of these faults form steep cliffs. Ako Fault and Hanadate Fault crosscut Byobusan Fault and Kasahara Fault nearly perpendicularly to the north¹⁴⁾. In Mizunami Basin are Tsukiyoshi Fault (strike : EW) and the Yamada Fault Zone (strike : NE-SW/WSW)¹³⁾.

The Shobasama site is located in the hilly country between the Kiso and Toki Rivers, where the Toki Granite is overlain by the Mizunami and Seto Groups. Geology in the vicinity of the Shobasama site is shown in Fig.2.3.