Identification and possible recurrence of an oversized tsunami on the Pacific coast of northern Japan

Geological evidence of severe tsunami inundation has been discovered in northern Japan. In the dune fields of Shimokita, in northernmost Tohoku, we have found two distinctive sand layers that are tsunami deposits. The run-up height of >20 m and inland inundation of at least 1.4 km are notably larger than any known historical case in Japan. The tsunami-genic earthquake that resulted in these deposits is thought to have taken place in the Kuril Forearc-Trench system nearly 700 years ago. The recurrence interval of major tsunamis originating in the Kuril subduction zone is about 400 years. Given that the most recent unusually large earthquake took place in AD 1611 (corresponding to the Keicho earthquake tsunami), the findings presented here increase the potential and hazard for an outsized tsunami striking the Pacific coast of northern Japan.     

Age and paleoclimatic implication of middle to upper Miocene plant-bearing strata in the southern Kanazawa area,Ishikawa Prefecture,Central Japan,based on refined Neogene palynostratigraphy in the Hokuriku district

13–8 Ma (middle to late Miocene) is a key period for understanding how the unique vegetation was established in Japan. Palynostratigraphy is useful for estimating the ages of plant-bearing strata deposited in shallow-marine and non-marine environments, but has low temporal resolution for this key period in Japan. We compiled Neogene and early Quaternary palynological records for the Hokuriku district of Central Japan to clarify palynostratigraphic events that may improve the temporal resolution. Our results showed that palynoassemblages changed considerably during 10–6.4 Ma in the Hokuriku district, following a relatively stable period during 13–10 Ma. We found that evergreen Quercus abundance increased at 11.5–10 Ma. We used these palynostratigraphic signatures, along with other biostratigraphic markers, to infer the ages of the Miocene plant-bearing Saikawa and Koderayama Formations in the southern Kanazawa area of Ishikawa Prefecture in the Hokuriku district. The ages of the Saikawa and Koderayama Formations were inferred as ~13 and 10–6.4 Ma, respectively. The palynoflora of the Koderayama Formation shows floristic similarity to that of present south China, implying that the unique flora of Japan established after the age of the Koderayama Formation.     

Contamination status of POPs and BFRs and relationship with parasitic infection in finless porpoises (Neophocaena phocaenoides) from Seto Inland Sea and Omura Bay, Japan

Contamination status of brominated flame retardants (BFRs) and persistent organic pollutants (POPs) in blubber of finless porpoises (Neophocaena phocaenoides) stranded along the coasts of Seto Inland Sea and Omura Bay in Japan were investigated. Levels of PCBs, DDTs and CHLs were significantly higher than those of HCHs, HCB, PBDEs and HBCDs. Concentrations of PBDEs and HBCDs, as well as organochlorine compounds in males increased with body length (p<0.05). Among 14 PBDE congeners analyzed, BDE-47 was the predominant, which is similar to those generally reported in biota. PBDEs, HBCDs and PCBs showed no obvious temporal trend in concentrations during the study period, suggesting continuous environmental release of these chemicals. On the other hand, levels of DDT, CHLs and HCHs have decreased. Concentrations of PCBs in liver trematode infected individuals were significantly higher than those in not infected individuals, implying there could be a relationship between contaminant levels and parasitic infection.     

Relationships between Kuroko volcanogenic massive sulfide (VMS) deposits, felsic volcanism, and island arc development in the northeast Honshu arc, Japan

The northeast (NE) Honshu arc was formed by three major volcano-tectonic events resulting from Late Cenozoic orogenic movement: continental margin volcanism (before 21?Ma), seafloor basaltic lava flows and subsequent bimodal volcanism accompanied by back-arc rifting (21 to 14?Ma), and felsic volcanism related to island arc uplift (12 to 2?Ma). Eight petrotectonic domains, parallel to the NE Honshu arc, were formed as a result of the eastward migration of volcanic activity with time. Major Kuroko volcanogenic massive sulfide (VMS) deposits are located within the eastern marginal rift zone (Kuroko rift) that formed in the final period of back-arc rifting (16 to 14?Ma). Volcanic activity in the NE Honshu arc is divided into six volcanic stages. The eruption volumes of volcanic rocks have gradually decreased from 4,600?km³ (per 1?my for a 200-km-long section along the arc) of basaltic lava flows in the back-arc spreading stage to 1,000?C2,000?km³ of bimodal hyaloclastites in the back-arc rift stage, and about 200?km³ of felsic pumice eruptions in the island arc stage. The Kuroko VMS deposits were formed at the time of abrupt decrease in the eruption volume and change in the mode of occurrence of the volcanic rocks during the final period of back-arc rifting. In the area of the Kuroko rift, felsic volcanism changed from aphyric or weakly plagioclase phyric (before 14?Ma), to quartz and plagioclase phyric with minor clinopyroxene (12 to 8?Ma), to hornblende phyric (after 8?Ma), and hornblende and biotite phyric (after 4?Ma). The Kuroko VMS deposits are closely related to the aphyric rhyolitic activity before 14?Ma. The rhyolite was generated at a relatively high temperature from a highly differentiated part of felsic magma seated at a relatively great depth and contains higher Nb, Ce, and Y contents than the post-Kuroko felsic volcanism. The Kuroko VMS deposits were formed within a specific tectonic setting, at a specific period, and associated with a particular volcanism of the arc evolution process. Therefore, detailed study of the evolutional process from rift opening to island arc tectonics is very important for the exploration of Kuroko-type VMS deposits.     

Coastal currents caused by superposition of coastal-trapped waves and near-inertial oscillations observed near the Noto Peninsula, Japan

Current observations were made from 14 July 2006 to 31 March 2007, using an acoustic Doppler current profiler mounted on the seafloor near the eastern coast of the Noto Peninsula, Japan, to investigate strong coastal currents induced by large-amplitude coastal-trapped waves (CTWs) and near-inertial fluctuations (NIFs). The CTWs were generated by the winter monsoon and the passage of a typhoon during the observation period. Two types of strong currents with velocities higher than 50 cm s^-1 were observed. One type, the strong current in winter (SCW), had the coast on the left to its direction of flow. This current was observed after a strengthening of the winter monsoon in January 2007. The other type, the strong current in fall (SCF), had the coast on the right to its direction of flow and was observed after the passage of a typhoon in September 2006. The SCW was inferred to be formed mainly by low-mode CTWs without NIFs. Compared to the SCW, the SCF had a more complicated vertical structure and time variations. The SCF was inferred to be generated by low-mode CTWs strengthened by NIFs. The contributions of NIFs to the strong coastal currents became important when the wind stress direction was rotating clockwise.     

New compact ocean bottom cabled seismometer system deployed in the Japan Sea

The Japanese islands are positioned near the subduction zones, and large earthquakes have repeatedly occurred in marine areas around Japan. However, the number of permanent earthquake observatories in the oceans is quite limited. It is important for understanding generation of large earthquakes to observe seismic activities on the seafloor just above these seismogenic zones. An ocean bottom cabled seismometer (OBCS) is the best solution because data can be collected in real-time. We have developed a new compact OBCS system. A developed system is controlled by a microprocessor, and signals from accelerometers are 24-bit digitized. Clock is delivered from the global positioning system receiver on a landing station using a simple dedicated line. Data collected at each cabled seismometer (CS) are transmitted using standard Internet Protocol to landing stations. The network configuration of the system adopts two dual methods. We installed the first practical OBCS system in the Japan Sea, where large earthquakes occurred in past. The first OBCS system has a total length of 25 km and 4 stations with 5 km interval. Installation was carried out in August 2010. The CSs and single armored optical submarine cable were buried 1 m below the seafloor to avoid a conflict with fishing activity. The data are stored on a landing station and sent to Earthquake Research Institute, University of Tokyo by using the Internet. After the installation, data are being collected continuously. According to burial of the CSs, seismic ambient noises are smaller than those observed on seafloor.     

Abiki oscillations in Sakitsu Bay,west Kyushu,Japan

Sakitsu and Yokaku bays in Amakusa in west Kyushu, Japan, experienced inundation damage in the February 2009 meteotsunami (Abiki) event. The oscillation characteristics of both bays are investigated by taking field measurements and conducting numerical experiments with regard to flood mitigation with the aim to reduce the flood impact during Abiki events. A continuous wavelet transform and bandpass filtering both of the pressure and water level indicated that a sequence of pressure disturbances, as small as 1.0 hPa, caused the large amplified oscillation within Sakitsu Bay. When a sequence of ocean long waves entered the bay, a surf beat evolved in the early stages. Subsequently, the sea level began to undergo large amplitude oscillations, and there was a secondary peak of oscillation with a period of around 24 min, as seen in both field measurements and numerical experiments. A surf beat with the period of 12 min formed in Yokaku Bay owing to the continuous incidence of ocean waves with period of 12 min, but its wave period was almost half of that of the natural period of the bay. This surf beat may have entered Sakitsu Bay with natural period of 11.8 min and caused large water-level fluctuations.     

X-ray Line and Recombination Emission in the Afterglow of Grb

We calculate the time-dependent line and recombination spectrum of nonequilibrium plasma heated by the strong radiation as the test model of X-ray line emission of GRB afterglows. Our calculation shows that the non-equilibrium effect of plasma is complex and important to the time evolution of the spectrum. The origin of these lines puzzles us, but is essential to understand the nature of GRBs and their circumstellar matter.     

Estimation of water requirement per unit carbon fixed byEucalyptus camaldulensis in semi-arid land of Western Australia

Afforestation in arid land is a promising method for carbon fixation, but the effective utilization of water is highly important and required. Thus, the evaluation of the amount of water per unit carbon fixed with the tree growth is required to minimize the amount of water supplied to the plants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water and nutrients from roots, and CO₂ as the carbon source from leaves with outflow of water vapor from leaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutritional elements are dissolved in water flow in trees. They do not flow out by these reactions, but are accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluate the water/carbon ratio.

Assuming that nutrient concentration is constant in sap, and the differences in the ratios of nutrient to carbon in living trees and dead (i.e. litter fall, etc.) are neglected, the ratio of the used water to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratio of nutrient to water in sap. However, some nutrients are translocated and concentrated within the tree and some may be discarded through litter fall. Thus it is important to examine which nutrient element is the most suitable as the tracer.

In this paper, the results of the above method applied toEucalyptus camaldulensis in semiarid land of Western Australia are shown. The value of water requirement per unit carbon fixation determined from potassium balance is between 421 kg-H₂O/kg-C for mature trees and 285 kg-H₂O/kg-C for young trees, while the values from calcium balance are much larger than these. The cause of the discrepancy between these values is discussed based on the measured element concentrations in sap and trees and the plant physiology. Finally, the actual average value through the life of a tree is suggested to fall between the two values.