Evaluation of tsunami impacts on shallow marine sediments: An example from the tsunami caused by the 2003 Tokachi-oki earthquake, northern Japan

A combined approach of field geology and numerical simulation was conducted for evaluating the tsunami impacts on the shelf sediments. The 2003 Tokachi-oki earthquake, M 8.0, that occurred on 25 September 2003 off southeastern Hokkaido, northern Japan, generated a locally destructive tsunami. Maximum run-up height of the tsunami waves reached 4 m above sea level. In order to estimate the tsunami impacts on shallow marine sediments, we compared pre- and post-tsunami marine sediments in water depths of 38–112 m in terms of grain size, sedimentary structure, and microfossil content. Decreases of fine fractions, especially finer than very fine sand, which led to coarsen the mean grain size, were detected in the inner shelf of the northern part of the study area. Foraminiferal assemblages also changed in the coarsened sediments. On the other hand, the other shelf sediments largely unchanged or slightly fined. We also simulated the tsunami wave velocity and direction, and grain size entrained by the modeled tsunami. The numerical simulation resulted in that the 2003 tsunami could transport very fine sand in water depths shallower than 45–95 m at the northern part of the study area. This is comparable with the actual grain-size changes after the tsunami had passed. However, some storms and tidal currents might also be possible to stir the surface sediments after the pre-tsunami survey, so we could not conclude that the grain-size changes had been caused only by the tsunami. Nevertheless, a combined approach of sampling and modeling was powerful for estimating the tsunami impacts under the sea.     

Paleoclimatic Change Inferred from Carbon Isotope Composition of Organic Matter in Sediments of Dabusu Lake, Jilin Province, China

Study on the organic compounds and stable isotope composition of a sediment section in Dabusu Lake revealed that the organic materials in the sediments came mainly from terrestrial plants brought into the lake by rtmoff.The δ^13 C of the organic materials had high values during warm-dry climatic stages and decreased in cold-wet stages.Analysis of data on carbonate content and ^14C age showed that the lake basin had experienced several wet-cold and warm-dry climatic cycles since 15000 a BP. Since 6700 a BP, the climate reached a relatively stable warm-dry stage,so that the lake water was gradually condensed and finally a saline lake was formed.     

Lithology, Biostratigraphy, and Magneto stratigraphy of Gas Hydrate-Bearing Sediments in the Eastern Nankai Trough

Abstract: Stratigraphic controls on the formation and distribution of gas hydrates were examined for sediments from a BH-1 well drilled in the landward slope of the Nankai Trough, approximately 60 km off Omaezaki, Japan. Three lithologic units were recognized in the 250 m-thick sequence of sediments: Unit 1 (0–70 mbsf) consists of calcareous silt and clay with thin volcanic ash layers, Unit 2 (70–150 mbsf) consists of calcareous silt and clay with volcanic ash and thin sand layers, and Unit 3 (150–250 mbsf) consists of weakly consolidated calcareous silt and clay with thick and frequent sand layers. Soupy structures and gas bubbles in the sediments indicate the presence of two hydrate zones between 40 and 130 mbsf and below 195 mbsf. Nannofossil biostratigraphy and magnetostratigraphy indicate that the sequence recovered at the BH-1 well is mostly continuous and represents sediments deposited from 0 to 1.5 Ma. Calculation of the sedimentation rate reveals a condensed section between 65 and 90 mbsf. The inferred distribution of gas hydrates in the BH-1 well appears to be strongly controlled by the stratigraphy and lithology of the sediments. Thick, gently inclined sand layers in Unit 3 provide a conduit for the migration of gases from deeper regions, and are considered responsible for the formation of the hydrate zone below 195 mbsf. At shallower levels, thin, gently inclined sand layers are also considered to allow for the migration of gases, leading to the formation of the upper hydrate zone between 40 and 130 mbsf. The overlying sub-horizontal silt and clay of the condensed section, truncating the underlying gently inclined sand and silt/clay layers, may provide an effective trap for gases supplied through the sand layers, further contributing to hydrate formation in the upper hydrate zone.     

Recent uplift and hydrothermal activity at Tangkuban Parahu volcano, west Java, Indonesia

Tangkuban Parahu is an active stratovolcano located 17 km north of the city of Bandung in the province west Java, Indonesia. All historical eruptive activity at this volcano has been confined to a complex of explosive summit craters. About a dozen eruptions-mostly phreatic events- and 15 other periods of unrest, indicated by earthquakes or increased thermal activity, have been noted since 1829. The last magmatic eruption occurred in 1910. In late 1983, several small phreatic explosions originated from one of the summit craters. More recently, increased hydrothermal and earthquake activity occurred from late 1985 through 1986. Tilt measurements, using a spirit-level technique, have been made every few months since February 1981 in the summit region and along the south and east flanks of the volcano. Measurements made in the summit region indicated uplift since the start of these measurements through at least 1986. From 1981 to 1983, the average tilt rate at the edges of the summit craters was 40–50 microradians per year. After the 1983 phreatic activity, the tilt rate decreased by about a factor of five. Trilateration surveys across the summit craters and on the east flank of the volcano were conducted in 1983 and 1986. Most line length changes measured during this three-year period did not exceed the expected uncertainty of the technique (4 ppm). The lack of measurable horizontal strain across the summit craters seems to contradict the several years of tilt measurements. Using a point source of dilation in an elastic half-space to model tilt measurements, the pressure center at Tangkuban Parahu is located about 1.5 km beneath the southern part of the summit craters. This is beneath the epicentral area of an earthquake swarm that occurred in late 1983. The average rate in the volume of uplift from 1981 to 1983 was 3 million m³ per year; from 1983 to 1986 it averaged about 0.4 million m³ per year. Possible causes for this uplift are increased pressure within a very shallow magma body or heating and expansion of a confined aquifier.     

Dibenzofurans a greater global pollutant than dioxins ? : Evidence from analyses of open ocean killer whale

Three specimens of killer whales (Orcinus orca), an open ocean carnivore, were analysed for extremely toxic polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) to understand their long-range distribution patterns. Several PCDF congeners, including the highly toxic 2,3,7,8-tetra- and 2,3,4,7,8-penta-CDFs were identified in the blubber of those specimens. The PCDF isomeric pattern in killer whale is more complex than the reported patterns in humans and birds, indicating the weaker metabolic potency of killer whales for these toxic compounds. High levels of PCBs (about 400 mg kg⁻¹) have also been detected in those specimens. The 2,3,7,8-substituted PCDF congeners identified in commercial PCBs were also found in killer whale, indicating PCBs as the possible source. Isomer-specific and trace level determinations of PCDD in killer whale, revealed no detectable quantities. The detection of comparatively high levels ( > 300 ng kg⁻¹) of PCDFs and undetection of PCDDs in open ocean killer whales suggest that PCDFs are more ubiquitous than PCDDs.     

Principal stress directions from a natural occurrence of stress-induced clinoenstatite

Lamellae of clinoenstatite are common in enstatite grains in the high-grade ultramafic hornfelses around the Mount Stuart Batholith in the Central Cascades of Washington. Laboratory deformation experiments on enstatite have shown that shear stress on (100) planes parallel to [001] drastically promotes the formation of clinoenstatite. Petrofabric studies of a sample of the hornfels reveal a strong preferred orientation of clinoenstatite-bearing enstatite grains that is unrelated to the fabric of the complete set of enstatite grains. This preferred orientation is well explained by supposing that the clinoenstatite was produced by shearing due to N-S compression. Local and regional geological features are also consistent with N-S compression. These results suggest that there is considerable potential for the application of stress-induced clinoenstatite as a geopiezometer in rocks.Now with: Department of Geology, University of Wyoming, Laramie, WY 80271, USA     

Geochemical variation with time in the Cenezoic volcanic rocks of southwest Hokkaido, Japan

Abundances of major and trace elements were determined for the Tertiary volcanic rocks from SW Hokkaido. The Late Miocene to Pliocene volcanic rocks of this region show geochemical features similar to those of the Quaternary rocks, that is, K/Si, Th/Si and LREE/HREE ratios increasing across the arc, east to west, from the Pacific to the Japan Sea side. In contrast, the Early Miocene volcanic rocks, which are geographically restricted to the Japan Sea coast, are distinct from all later volcanics and show “within-plate” characteristics — in particular, high concentrations of HFS elements. The Quaternary basalts have low Hf/Yb ratios and Hf contents, whereas the Early Miocene basalts are high in Hf/Yb and Hf, similar to Hawaiian alkali basalts. The compositional variation with time may result from the progressive depletion of incompatible HFS elements in the mantle source. Th/Yb ratios increase from Early Miocene to Quaternary, possibly reflecting increase in the LIL element contribution to the mantle source during that time.     

Comparison of sinking particles in the upper 200 m between subarctic station K2 and subtropical station S1 based on drifting sediment trap experiments

Drifting sediment trap experiments were conducted during various seasons to elucidate the characteristics of particles sinking through the upper 200 m of the water column in the western Pacific at subarctic station K2 and subtropical station S1. The sinking particle flux increased when primary productivity was high at each station, during June–July at K2 and during February at S1. Biogenic opal (Opal) and CaCO₃ were the major components of the fluxes at K2 and S1, respectively. Contrary to the expectation of a high flux at the eutrophic station K2 and low flux at the oligotrophic station S1, the annual average organic carbon fluxes at 100 m were comparable at both stations: 62.7 mg C m^?2 day^?1 at K2 and 56.1 mg C m^?2 day^?1 at S1. The similarity of the fluxes was perhaps a reflection of the unexpectedly high primary production at S1. At K2, the organic carbon export ratio (organic carbon flux/primary productivity) was significantly and negatively correlated with primary production and tended to decrease with depth. The magnitude of the rate of attenuation of the organic carbon flux with depth was larger at S1 than at K2. This rate of attenuation tended to decrease and increase with primary production at K2 and S1, respectively. The explanation for these patterns may be that the flux of labile organic carbon at relatively shallow depths decreased with increasing primary production at K2, and zooplankton grazing pressure increased with increasing primary productivity at S1.     

Recent uplift and hydrothermal activity at Tangkuban Parahu volcano,west Java,Indonesia

Tangkuban Parahu is an active stratovolcano located 17 km north of the city of Bandung in the province west Java, Indonesia. All historical eruptive activity at this volcano has been confined to a complex of explosive summit craters. About a dozen eruptions-mostly phreatic events- and 15 other periods of unrest, indicated by earthquakes or increased thermal activity, have been noted since 1829. The last magmatic eruption occurred in 1910. In late 1983, several small phreatic explosions originated from one of the summit craters. More recently, increased hydrothermal and earthquake activity occurred from late 1985 through 1986. Tilt measurements, using a spirit-level technique, have been made every few months since February 1981 in the summit region and along the south and east flanks of the volcano. Measurements made in the summit region indicated uplift since the start of these measurements through at least 1986. From 1981 to 1983, the average tilt rate at the edges of the summit craters was 40–50 microradians per year. After the 1983 phreatic activity, the tilt rate decreased by about a factor of five. Trilateration surveys across the summit craters and on the east flank of the volcano were conducted in 1983 and 1986. Most line length changes measured during this three-year period did not exceed the expected uncertainty of the technique (4 ppm). The lack of measurable horizontal strain across the summit craters seems to contradict the several years of tilt measurements. Using a point source of dilation in an elastic half-space to model tilt measurements, the pressure center at Tangkuban Parahu is located about 1.5 km beneath the southern part of the summit craters. This is beneath the epicentral area of an earthquake swarm that occurred in late 1983. The average rate in the volume of uplift from 1981 to 1983 was 3 million m³ per year; from 1983 to 1986 it averaged about 0.4 million m³ per year. Possible causes for this uplift are increased pressure within a very shallow magma body or heating and expansion of a confined aquifier.     

Organochlorine contamination in some odontoceti species from the North Pacific and Indian Ocean

Concentrations of persistent organochlorines were determined in the blubber and melon of 11 species of adult male odontocetis collected from the North Pacific, Indian Ocean and nearby seas. Mean concentrations of DDs (33 μg/g wet wt) were the highest followed by PCBs (32 μg/g wet wt), chlordane compounds (CHLs: 3.7 μg/g wet wt), HCHs (1.1 μg/g wet wt), and HCB (0.32 μg/g wet wt). Odontoceti species inhabiting temperate waters revealed maximum residual concentrations of these contaminants, and the elevated DDT and PCB residues detected seem to suggest that some of the present species might potentially be at high risk. Relatively high DDT concentrations were found in tropical water species, which could be attributed to the current usage of DDT in the tropics and the less movable nature of this compound via long-range atmospheric transport. The HCH levels in animals inhabiting cold and temperate waters were higher than those inhabiting tropical waters, a result that was perhaps reflective of atmospheric transport from the tropical source to the northern sinks. A similar pattern was also observed in PCBs, CHLs and HCB, probably indicating the ongoing discharge of these compounds from mid-latitudes as well as those originating in tropical regions.