Study of blind thrust faults underlying Tokyo and Osaka urban areas using a combination of high-resolution seismic reflection profiling and continuous coring

We acquired high-resolution seismic reflection profiles and continuously cored boreholes to evaluate active flexures produced by major blind thrust fault systems within two densely populated Neogene-Quaternary sedimentary basins in Japan: the Fukaya Fault System near Tokyo in the Kanto Basin and the Uemachi Fault System in the Osaka Basin. The high-resolution seismic reflection survey made clear the length, geometry and growth history of fault-related folds, or flexures formed above the two blind thrusts. Continuously cored boreholes linked with high-resolution seismic profiles enabled us to estimate the uplift rate as defined by shallow stratigraphic horizons and constrain the age of the most recent growth of the flexures during earthquakes on the Fukaya and Uemachi fault systems. Even with the high quality of the data we collected, it is still not possible to exactly constrain the age of the most recent blind thrust earthquake recorded by flexure of these fault-related folds. Data presented in this paper form the basis for future efforts aimed at mechanical and kinematic models for fault growth to evaluate the activity of blind thrusts underlying urban areas

Expedition 306 summary

The overall aim of the North Atlantic paleoceanography study of Integrated Ocean Drilling Program Expedition 306 is to place late Neogene–Quaternary climate proxies in the North Atlantic into a chronology based on a combination of geomagnetic paleointensity, stable isotope, and detrital layer stratigraphies, and in so doing generate integrated North Atlantic millennial-scale stratigraphies for the last few million years. To reach this aim, complete sedimentary sections were drilled by multiple advanced piston coring directly south of the central Atlantic “ice-rafted debris belt” and on the southern Gardar Drift. In addition to the North Atlantic paleoceanography study, a borehole observatory was successfully installed in a new ~180 m deep hole close to Ocean Drilling Program Site 642, consisting of a circulation obviation retrofit kit to seal the borehole from the overlying ocean, a thermistor string, and a data logger to document and monitor bottom water temperature variations through time

Tsunami run-up heights of the 2003 Tokachi-oki earthquake

Tsunami height survey was conducted immediately after the 2003 Tokachi-oki earthquake. Results of the survey show that the largest tsunami height was 4 m to the east of Cape Erimo, around Bansei-onsen, and locally at Mabiro. The results also show that the tsunami height distribution of the 2003 Tokachi-oki earthquake is clearly different from that of the 1952 Tokachi-oki earthquake, suggesting the different source areas of the 1952 and 2003 Tokachioki earthquakes. Numerical simulation of tsunami is carried out using the slip distribution estimated by Yamanaka and Kikuchi (2003). The overall pattern of the observed tsunami height distribution along the coast is explained by the computed ones although the observed tsunami heights are slightly smaller. Large later phase observed at the tide gauge in Urakawa is the edge wave propagating from Cape Erimo along the west coast of the Hidaka area.The 2003 Tokachi-oki earthquak

Identification of the Changbaishan ‘Millennium’ (B-Tm) eruption deposit in the Lake Suigetsu (SG06) sedimentary archive, Japan: Synchronisation of hemispheric-wide palaeoclimate archives

The B-Tm tephra, dispersed during the highly explosive Changbaishan ‘Millennium’ eruption (ca. 940–950 CE) and a key marker layer within the Greenland ice cores, has now been identified in the Lake Suigetsu (SG06) sedimentary sequence, central Japan. The major element geochemistry of the volcanic glasses within this tephra layer are compared to a new glass dataset from the distal type-locality (Tomakomai Port, Hokkaido) and other published ‘Millennium’ eruption/B-Tm deposits, to verify this correlation. The discovery of the B-Tm tephra in the Lake Suigetsu record provides, to date, the most southerly identification of this ash and, crucially, the first direct tie-point between this high-resolution, mid-latitude palaeoclimate archive and the Greenland ice cores. These findings present significant encouragement for on-going research into the tephrostratigraphy of East Asia, focusing on the identification of widely-dispersed tephra layers which can facilitate the synchronisation of disparate palaeoclimate archives and thus enable the assessment of spatio-temporal variations in past climatic change

A reference time scale for Site U1385 (Shackleton Site) on the SW Iberian Margin

We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using log(Ca/Ti) measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to 166.5 meters composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopes of benthic foraminifera were correlated to a stacked δ^18O reference signal (LR04) to produce an oxygen isotope stratigraphy and age model. Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulation of these cycles provides a powerful tool for developing an orbitally-tuned age model. We tuned the U1385 record by correlating peaks in L* to the local summer insolation maxima at 37^oN. The benthic δ^18O record of Site U1385, when placed on the tuned age model, generally agrees with other time scales within their respective chronologic uncertainties. The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflect relative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacial and interstadial climate states and decreases during glacial and stadial periods. Much of the variance in the log(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereas the residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti) variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can be used as a proxy for millennial-scale climate variability over the past 1.5 Ma. Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climates over the past 1.5 Ma, including glacial periods of the early Pleistocene (‘41-kyr world’) when boundary conditions differed significantly from those of the late Pleistocene (‘100-kyr world’). Suborbital variability was suppressed during interglacial stages and enhanced during glacial periods, especially when benthic δ^18O surpassed ~ 3.3-3.5‰. Each glacial inception was marked by appearance of strong millennial variability and each deglaciation was preceded by a terminal stadial event. Suborbital variability may be a symptomatic feature of glacial climate or, alternatively, may play a more active role in the inception and/or termination of glacial cycles.This research was supported by the Natural Environmental Research Council Grant NE/K005804/1 to DH and LS and NE/J017922/1 to DH.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.gloplacha.2015.07.00