Aleutian Region Research Articles

Sediment provenance within subduction complexes—An example from the Aleutian forearc

The ultimate composition of any sandstone is affected by a host of primary and secondary factors, including the lithologies present in source terranes, climate, depositional environment and diagenesis. In the case of a subduction complex, however, unequivocal identification of detrital provenance may be impossible because of the cumulative effects of tectonic and sedimentary transport. Long-distance sedimentary transport (> 1000 km) is common within trenches, and abyssal-plain turbidites can be tectonically transported for long distances as the underlying oceanic basement drifts towards a subduction front. Post-accretionary displacement can occur as a consequence of strike-slip faulting, and the total distance of tectonic dislocation may reach several thousand kilometers. The present-day Aleutian forearc region (North Pacific Ocean) illustrates many of the “problems” which typify subduction zones. Several petrologic suites can be identified, and there are significant variations in detrital modes in both time and space. The Aleutian region serves as a sobering modern analog for accreted rock units such as the Franciscan Complex of California, where intercalations of discrete sandstone suites have been noted. In the absence of paleomagnetic control, interpretations of sediment provenance within ancient subduction complexes probably should be restricted to the generic level.

Teleseismic p-wave transmission through slabs

abstract Theoretical ray paths through velocity models constructed from numerically calculated thermal models of slabs were computed. The results were in good agreement with observed travel times. First motion amplitudes of P waves at teleseismic distances were measured from long- and short-period WWSSN records of intermediate focus earthquakes in the Tonga, Kermadec, and Kurile regions and of nuclear explosions and shallow earthquakes in the Aleutian region. These amplitudes were corrected for source mechanism. The Aleutian data were sufficient to show that intermediate focus earthquakes in that region occur in the colder regions of the slab. At short periods, for regions other than the Aleutians, shadowing effects which could be associated with the slab were not very marked, less than a factor of 2 reduction for epicentral distances between 30° and 50°. No systematic effects due to plates were found in the long-period data. Some stations in the predicted shadow zone of a Tonga earthquake recorded low amplitude precursors which probably were greatly defocused waves which ran the full length of the slab. Simple diffraction is incapable of explaining the short-period results.

Crust-mantle system in the central Aleutian region—A hypothesis

Abstract Seismic data acquired during the 1964 VELA UNIFORM Aleutian experiment have been used to construct a model of the local crust-mantle system. The M discontinuity of the model has a synclinal structure whose axis coincides with the islands of the arc. Just south of the islands, the shoaling M is terminated by a northward dipping thrust fault, resulting in a wedge-shaped crustal block sandwiched between mantle components.

Short-term seismic activity in the central Aleutian region

abstract Epicenters of small-magnitude earthquakes, occurring in the central Aleution region during the 1964 Aleutian Experiment, were located by an S minus P method. Shallow earthquakes, occurring mainly just south of the islands, seem to delineate a shallow earthquake belt approximately 20 to 40 km wide. Deeper earthquakes occurred north of the shallow earthquake belt, and they seem to indicate a zone of faulting which dips toward the island arc from the oceanic side of the arc.

北太平洋海域の海水から分離した酵母に関する研究

A large number of samples, water for the study of microorganisms, were obtained on the occasions of the cruises of the “Ryofu Maru” and “Oshoro Maru” in the North Pacific extending to the Bering Sea, Aleutian region, east off the Japan Proper Island, south off the Japan Proper Island and East China Sea during the years 1959-60. A total of 801 samples which were taken from various depths down to about 3000meters were placed to this study. For isolation of marine yeasts the medium adopted was ZOBELL 2216-E, and the classification of yeasts was made according to the method of LODDER and VAN RIJ. In this paper are reported species of yeasts identified, their distribution with geographical areas and depths, and the results of experiments on their growth in relation to the salinity, pH value and temperature conditions. One hundred forty-four isolates comprised of species belonging to genera, Rhodotorula, Torulopsis, Cryptococcus, Saccharomyces, Sporoboromyces or Candida. Among them species belonging to Rhodotorula were most abundantly and widely distributed. The number of isolated was larger than elsewhere at the layers of 0m, 100-150m and 750m depths, while it was very small below 1000meters. There was no difference of growth between marine and terrestrial strain at low saline media (0-5%), but the marine species grew better than in terrestrial strains at high saline media (7-9%). The marine species did not grow better than in terrestrial strains at low pH value (pH 2), but no difference of growth between them at high pH value (pH 4-12). There was a tendency to inhibition of growth by high temperature (37°C.) in marine strains, compared with terrestrial strains.

On the Main Chemical Components dissolved in the Adjacent Waters to the Aleutian Islands in the North Pacific

Abstract The authors carried out the analyses of the main dissolved components of sea water on the samples collected from the Aleutian region in order to examine the local characteristics of the region under study. At the same time the samples collected from the Kuroshio region were analysed to check the systematic errors introduced. The results were expressed in terms of ratios to chlorinity. As a result, the following conclusions have been deduced. 1. The relative decrease in sulfate and sodium equivalents was recognized on the samples collected from the layer of temperature minimum. This seems to relate to freezing phenomena of sea water. 2. A tendency of sulfate increase in the surface samples was noticed. 3. Averaged values for the Aleutian region were in close agreement with those for the Kuroshio region, both having been obtained by the present authors. The values also coincided with those obtained by other workers, except for higher potassium values. These facts may indicate that although the water masses existing in the Aleutian region are, on the whole, a portion of the oceanic circulation of the Pacific, a slight deviation from the normal composition appears in the main components in some characteristic layers.

On the Distribution and Variation of Nutrient Salts in the Adjacent Water to the Aleutian Islands in the North Pacific

Abstract The author was engaged in the oceanographical observations carried out in a region adjacent to the Aleutian Islands in 1952 and obtained a number of data, on which the present discussions are based. As the results, slight differences in distributions of nitrate-nitrogen, phosphate-phosphorus and silicate-silicon were found between the northern and southern areas separated by the Aleutian Ridge, although distributions are almost the same in the two areas. Characteristic features in distributions of these nutrient salts are that the high concentrations were found even in the surface layer, increasing further with maximum gradients in depths within 100–300m. The ratios of N:P in the region under study are lower than the normal ratio given by Cooper; and deficiencies in dissolved oxygen were recognized in the subsurface layers. These facts seem to be related to the characteristics of the decomposition processes in the Aleutian region. On the basis of the rate of phosphate consumption in the upper layers, the net production rate has been computed by introducing some simplifying assumptions; and has obtained the value of 56 mg. C/m3/day. This value is considered to be reliable, since it coincides with that derived from Riley’s data and with that calculated from the data concerning the diurnal variations of dissolved oxygen.

母船式鮭鱒沖取漁場の表面海流と海況

From middle of May to early August in 1953, survey of surface current was carried out by Salmon Factory Ship with current meter at the west Aleutian and South eastern Kamchatka regions. Observation were made simultaneously at the layer of 25 and 500 meters. Direction and speeds of surface currents were estimated as relative values to those of 500m layer in conception of that no current is present in the layer of 500m. Table 1. shows the result of the observation, and figures 1-8 show water currents relative to distributions of water masses and transparency in every 10 days. As the results of the present research, some presumption given below may be drawn out. In the southern offing of Aleutian Is., the current which flows to south from Bering Sea goes into the water mass which runs northwards, and in this contact zone current moves westerly with velocity of 0.5-1.0 miles per hour. The current that flows to the W or NW with velocity of 2-4 mils per hour exists in the intermediate region of Aleutian Is. and Kamchatka Pen. With above results, we may conclude there are counter currents of Kuroshio in the region of Kamchatka and West Aleutian, and the counter currents flow towards west or northwest. It may be decided that the salmon migrate to Kamchatka from West Aleutian region depending on these currents.

A study of the energy content of the seismic waves P and pP*

abstract The energy observed in the seismic waves P and pP in a large number of earthquakes is compared, by means of two partly independent methods, with the theoretical energy calculated from a standard equation. The results are analyzed, depth of focus, distance from epicenter to observing station, geographical location of epicenter, and azimuth from station being used as variables. When compared with the theoretical ratio, the ratio of the energy in pP to the energy in P averaged over a distance range 60°-90° is observed to decrease with depth, by 0.5 on a logarithmic scale of energy between 100 and 600 km. depth of focus. The results for the two waves are compared separately with theoretical values, and the observed effect appears to be about equally due to an increase of P energy and a decrease of pP energy with depth. The theoretical formula is reëxamined to determine if permissible changes in the assumptions or numerical values can account for the results. No such changes are found; certain assumptions with respect to increased absorption of energy near the surface of the earth provide a partial qualitative explanation, but quantitatively they cannot be reconciled with data from other sources. The variation with distance between observed and calculated energies is not large enough to be treated quantitatively; slight changes in the slope of the accepted velocity vs. depth curve are tentatively suggested on the basis of it. The energy ratio pP/P compared to the theoretical ratio is significantly too large in shallow earthquakes occurring in the Aleutian region and can be attributed to pP rather than P. For shallow shocks in the New Hebrides region and very deep shocks of the Southwest Pacific there is some indication that the energy ratio is smaller than for comparable shocks elsewhere. Data on observed wave periods are given. The effect of differences between instruments is considered.