Dacitic to rhyolitic glass shards from 80 widespread tephras erupted during the past 5 Mys from calderas in Kyushu, and SW, central, and NE Japan were analyzed. Laser ablation inductively coupled plasma mass spectrometry was used to determine 10 major and 33 trace elements and A few tephras from SW Japan were identified as adakite and alkali rhyolite and were regarded to have originated from slab melt and mantle melt, respectively. The Pb isotope ratios of the tephras are comparable to those of the intermediate lavas in the source areas but are different from the basalts in these areas. The crustal assimilants for the intermediate lavas were largely from crustal melts and are represented by the rhyolitic tephras. A large heat source is required for forming large volumes of felsic crustal melts and is usually supplied by the mantle via basalt. Hydrous arc basalt formed by cold slab subduction is voluminous, and its heat transfer with high water content may have melted crustal rocks leading to effective felsic magma production. Coincidence of basalt and felsic magma activities shown by this study suggests caldera-forming eruptions are ultimately the effect of a mantle-driven cause.

The 2011 Tohoku-oki earthquake and tsunami was the most destructive geohazard in Japanese history. However, little is known of the past recurrence of large earthquakes along the Japan Trench. Deep-sea turbidites are potential candidates for understanding the history of such earthquakes. Core samples were collected from three thick turbidite units on the Japan Trench floor near the epicenter of the 2011 event. The uppermost unit (Unit TT1) consists of amalgamated diatomaceous mud (30-60 cm thick) that deposited from turbidity currents triggered by shallow subsurface instability on the lower trench slope associated with strong ground motion during the 2011 Tohoku-oki earthquake. Older thick turbidite units (Units TT2 and TT3) also consist of several amalgamated subunits that contain thick sand layers in their lower parts. Sedimentological characteristics and tectonic and bathymetric settings of the Japan Trench floor indicate that these turbidites also originated from two older large earthquakes of potentially similar to the 2011 Tohoku-oki earthquake. A thin tephra layer between Units TT2 and TT3 constrains the age of these earthquakes. Geochemical analysis of volcanic glass shards within the tephra layer indicate that it is correlative to the Towada-a tephra (AD 915) from the Towada volcano in northeastern Japan. The stratigraphy of the Japan Trench turbidites resembles that of onshore tsunami deposits on the Sendai and Ishinomaki plains, indicating that the cored uppermost succession of the Japan Trench comprises a 1500-year-old record that includes the sedimentary fingerprint of the historical Jogan earthquake of AD 869.

Integrated Ocean Drilling Program Expedition 346 "Asian Monsoon" obtained sediment successions at seven sites in the Japan Sea (Sites U1422-U1427 and U1430) and at two closely located sites in the northern East China Sea (Sites U1428 and U1429). The Quaternary sediments of the Japan Sea are characterized by centimeter-to decimeter-scale dark-light alternations at all sites deeper than 500 m water depth. The sedimentary records from these sites allow an investigation of the regional environmental response to global climate change, including changes in the Asian Monsoon and eustatic sea level. However, the discontinuous occurrence of calcareous microfossils in the deep-sea sediments and their distinct isotope signature that deviates from standard marine δ 18 O records do not permit the development of a detailed stable isotope stratigraphy for Japan Sea sediments. Here, we present the tephrostratigraphy for the two southernmost sites drilled in the Japan Sea (Sites U1426 and U1427) and for one site drilled in the East China Sea (Site U1429) along with the benthic δ 18 O isotope stratigraphy for the shallower Site U1427 and the East China Sea Site U1429. Eighteen tephra layers can be correlated between sites using the majorelement composition and morphology of volcanic glass shards, and the compositions of grains and heavy minerals. Tephra correlations show that negative δ 18 O peaks in the Japan Sea correspond to positive glacial maxima peaks in the East China Sea. Using this integrated stratigraphic approach, we establish an orbital-scale age model at Site U1427 for the past 1.1 Myr. The correlation of tephra layers between the shallower Site U1427 (330 m below sea level: mbsl) and the deeper Site U1426 (903 mbsl) in the southern Japan Sea provides the opportunity for further age constraints. Our results show that alternations in sediment color at Sites U1426 and U1427 can be correlated for the past 1.1 Myr with minor exceptions. Thus, the stable isotope stratigraphy established at the shallower Site U1427 can be correlated to Site U1426, and in turn to all sites drilled during Expedition 346, based on correlations of dark-light layering.

Accurately evaluating the tempo and magnitude of prehistoric eruptions is essential for hazard assessments. Here we demonstrate the importance of integrating records from locations close to the volcano with those in distal regions to generate more comprehensive event stratigraphies. The annually laminated (varved) and intensely radiocarbon dated lacustrine sediments of Lake Suigetsu (SG06 core), Japan are used to place chronological constraints on the tempo of volcanism at two stratovolcanoes located favourably upwind of the lake along the SouthWest Japan Arc, Sambe and Daisen. Major and trace element glass compositions are used to assign visible ash (tephra) layers preserved in the SG06 sediment core to past explosive eruptions from these volcanoes. Integrating these stratigraphies confirm that the ~150 ka long lake sequence records nine visible ash layers from Daisen and five from Sambe. The SG06 record captures two periods of closely spaced eruptions at Daisen volcano. The first period begins at ~61.9 ka with three explosive eruptions over ~10 ka, with two events separated by as little as 1.5 ka. One layer (SG06-4281), dated at 59.6 ± 5.4 ka (95.4% probability), relates to the large magnitude, and widely dispersed Daisen Kurayoshi Pumice (DKP) eruption. The other period of frequent activity began at 29,837 ± 96 IntCal13 yrs BP (95.4% probability) with five widely dispersed ash fall events associated with explosive eruptions separated by approximately 6, 936, 5 and 438 years. The integrated proximal-distal event stratigraphy and the high-precision SG06 chronology provide unique insights into the timing and frequency of past explosive volcanism from Daisen and Sambe, which has implications for the prediction of future eruption scenarios.

The Pliocene to Pleistocene Series in each sedimentary basin or area of Japan has been investigated and described; however, their stratigraphic correlation is difficult because of complex geological structures. Regional stratigraphy has therefore been established using many intercalated tephra beds, i.e. by correlating tephra beds between distant areas. A standardized stratigraphic model of the Pliocene to Middle Pleistocene Series in Japan is put forward in this paper on the basis of tephrostratigraphy, magnetostratigraphy, and biostratigraphy. This stratigraphic model is important for studies of environmental changes and explosive volcanism in this period around the Japanese island‐arc.

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