Late Cenozoic Igneous Activity and Crustal Structure in the NE Japan Arc: Background of Inland Earthquake Activity

Abstract

GNSS data analyses reveal that recent large inland earthquakes in the Northeast (NE) Japan occurred in strain concentration zones. Seismic low-velocity anomalies, indicative of mechanically weak materials (weak zones) , are estimated below the strain concentration zones at depths corresponding to the lower crust. Such crustal structures with weak zones have been formed as an accumulation of tectonic movements and igneous activities since early Miocene. Volcanic activity in the NE Japan during the Late Cenozoic Era can be subdivided into three prominent stages: continental margin volcanism stage, back-arc basin opening stage, and island-arc volcanism stage. The crustal structure of the NE Japan arc is characterized by many rift structures and large transcurrent faults formed during the back-arc basin opening stage, and by many large caldera volcanoes formed during the island-arc volcanism stage. The relationships among

Quaternary caldera-forming eruptions at the Sanzugawa caldera, NE Japan, revealed by zircon U-Pb geochronology

“…The Mukaimachi caldera, west of the Akakura caldera, is thought to have been formed after the Akakura caldera formation (Otake, 2007). Finally, the Hanayama caldera to the east of the Onikobe caldera is hypothesized to have been formed during the late Miocene (Tsuchiya et al, 1997;Yoshida et al, 2020).…”

“…An outcrop sample (INNAI), composed of rhyolite fine tuff, was obtained in the Innai caldera. Yoshida et al (2020) assumed the caldera-forming volcanic activity of the Innai caldera occurred at 5.0-3.5 Ma.…”

“…The Tohoku region, NE Japan, is an archetypal island arc, where the Pacific Plate has been subducting beneath the Eurasian Plate at a rate of 8-9 cm/yr with a relatively shallow dip angle of about 30 °since at least 2 Ma (Acocella et al, 2008;Yoshida et al, 2014). The resulting volcanism and tectonism have been well documented in the Tohoku region (e.g., Acocella et al, 2008;Yoshida et al, 2014, Yoshida et al, 2020. In essence, in this island arc tectonic setting, numerous (>80) calderas were formed under NE-SW compression during late Miocene-Pliocene, and subsequently a larger volume of andesite (mainly stratovolcanoes) was erupted under E-W compression during the Quaternary (Acocella et al, 2008) (Figure 1).…”

Heat flow data and thermal structure in northeastern Japan

“…On the other hand, there are cases where calderas are assumed to have been active for more than 600,000 years after their formation (Takehara et al 2017), and hydrothermal reservoirs and low-velocity bodies have been observed beneath calderas formed in the Late Miocene (Sato et al 2002). It has also been pointed out that magma reservoirs with lifetimes longer than several million years may exist if conditions like continuous fluid supply from deep underground are met (Yoshida et al 2020). However, the distribution of calderas in Northeastern Japan (Yoshida et al 2013) shows no evidence of calderas extending over the central Kitakami Mountains and the Sendai Plain.…”

Heat Flow Data And Thermal Structure In North East Japan

“…On the other hand, there are cases where calderas are assumed to have been active for more than 600,000 years after their formation (Takehara et al, 2017), and hydrothermal reservoirs and low-velocity bodies have been observed beneath calderas formed in the Late Miocene (Sato et al, 2002). It has also been pointed out that magma reservoirs with lifetimes longer than several million years may exist if conditions like continuous uid supply from deep underground are met (Yoshida et al 2020). Therefore, it becomes important to compare the subsurface and temperature structures in high heat ow regions.…”