Crustal structure in the northern Fossa Magna region, central Japan, modeled from refraction/wide-angle reflection data

Abstract

The northern Fossa Magna (NFM) is a back-arc rift basin filled with thick Tertiary sediments, which show strong NW-SE shortening deformation. In the NFM, there exist two major active fault systems, the Itoigawa-Shizuoka Tectonic Line active fault system (ISTL) and the Western Nagano Basin active fault system (WNB), both of which have great potentials to cause destructive earthquakes. By reanalyzing five sets of refraction/wideangle reflection data, we successfully obtained detailed and consistent models of the crustal structure in the NFM region. It was a very effective modeling procedure to incorporate vicinal seismic reflection data and geologic information. The geometries of the active faults in the NFM region were revealed. The ISTL is east dipping, and the WNB is northwest dipping. The Tertiary sedimentary layer (<4.0 km/sec) west and adjacent to the ISTL extends to a depth of 4-5 km. The basement rocks below the Central Uplift Belt (CUB) form a wedge structure, which suggests the westward movement of the CUB basement rocks.

Two electrical conductors beneath Kusatsu-Shirane volcano, Japan, imaged by audiomagnetotellurics, and their implications for the hydrothermal system

“…1), where the volcanic front bends towards the south. It is a stratovolcano that is located at the eastern edge of the elevated Tertiary basement, called the Central Uplift Zone (Takeda et al, 2004), with an approximately north-south strike. Its volcanic activities have been recorded since 1805 and are characterized by phreatic eruptions (Uto et al, 1983).…”

The earth matter effects in neutrino oscillation experiments from Tokai to Kamioka and Korea

“…The distance from J-PARC along the baseline is shown by tick marks every 50 km. The shaded region is called Fossa Magna [22], where the North American plate and the Eurasian plate meet. Lower:…”

“…According to Ref. [22], the density of such sediment layer is 2.5g/cm 3 . On the other hand, the sediment layer near Kamioka, L > 230 km along the baseline, is mainly composed of granite whose density is about 2.8g/cm 3 .…”

“…In the upper figure, the scale along the baseline shows the distance from J-PARC by tick marks every 50 km. The shaded region is called Fossa Magna [22], which is the border between the two continental plates, North American Plate and Eurasian Plate. In this region, the sediment layer is estimated as 6 times deeper than that in the surrounding region.…”

“…[24]. In Fossa Magna, the sediment layer is as deep as 6 km [22], which is mainly composed of limestone and sandstone with others [24]. According to Ref.…”