Characteristics of the Quaternary volcanoes along the Circum-Pacific Mobile Belt (CPMB) are outlined. Although most of the regions in CPMB are subduction zones, the types, volume and numbers of the volcanic edifices, the mineral and chemical compositions of the volcanic rocks are various in time and space, influenced by the differences of thermal states beneath the crust, vertical changes of field stresses in the crust (or lithosphere) etc. A few pairs of mountains and basins in parallel to mobile belts range in the most of the regions in CPMB. The volcanoes in Japan, Philippine Islands and southern Andes stand on the tops of the mountains while the volcanoes in Kamchatka, New Zealand, Mexico and USA conterminous have erupted within the basins accompanied with normal faults. Many stratovolcanoes exist in Japan, Philippine and Andes while pairs of basaltic scoria cones and lava flows and small shield volcanoes prevail in Mexico and USA conterminous. Morphology, structure and history of stratovolcanoes are various, suggesting the differences of thermal states, structures and field stresses of the crust.
We have discovered a distal tephra with similar petrographic and chemical properties to the Aso-3 pyroclastic flow deposits of the Aso caldera origin at several localities of Honshu, Japan, and adjacent seas. It is concluded to be a fallout ash associated with the Aso-3 pyroclastic flow, The tephra, named Aso-3, is a cry tal vitric fine-grained ash, consisting of dacitic pumiceous and bubble-walled glass shards, and orthopyroxene and crynopyroxene as mafic phertocrysts. It is identified with the aid of combined petrographic and stratigraphic parameters : relatively high index of glass (n = 1.5131.519), low index of orthopyroxene (γ =1.7021.705) and dacitic glass composition (rich in alkali, K2O> Na2O, rich in TiO2, FeO* and CaO low abundance in light rare earth elements and characteristic low degree of angle in chondritenormalized pattern). This tephra was dated by several radiometric methods : 103±4.2 (FT), 110±3 (TL) and 123±6 (K-Ar) in ka. The stratigraphic position of this tephra is above the last interglacial culmination in Kyushu and Honshu, and below such widespread time-marker tephras as Toya, Ata, On-Pml, SK, etc. In addition, the tephra occurs in the marine isotope stage (MIS) 5d in the abyssal sediment in the northwest Pacific. The occurrence of this tephra in the Quaternary sequence in northern coastal areas of Miyazaki, south Kyushu, clearly indicates that the sea level was more than c. 70 m lower than the preceding high stand of sea level of the MIS 5e. At the coastal cliff of Kawaminami, the Aso-3 tephra occurs 21 m above the present sea level in the basal part of the valley-filling deposits (Tohriyamahama formation) which followed the prominent marine terrace, Sanzaibaru of the MIS 5e. Former shoreline of this stage was uplifted to the elevation of c. 90 m. This tephra was also recognized in the brackish to fresh water layer sandwiched between marine sediments, called Shibikawa formation in Oga Peninsula, northern Honshu. It clearly suggests significant lowering of sea level at the time of Aso-3 eruption as well.
Correlation and dating of widespread rhyolite tephras erupted from Taupo Volcanic Zone, North Island, New Zealand, provides remarkable opportunities for correlating marine and terrestrial records of Quaternary environmental changes. Tephrostratigraphy, magnetostratigraphy and biostratigraphy of emergent marine sediments in Wanganui Basin allows correlation of strata to the isotope record of deep sea cores, with a precision of better than one isotope stage. Radiometric ages for several tephras are consistent with the astronomically calibrated isotope stage chronology of Shackleton et al. (1990). Pollen assemblages and oxygen isotope analyses from marine cores indicate that terrestrial vegetation changes in New Zealand were closely linked with global climatic changes. Major glaciations in the South Island were also closely synchronous with glaciations in the Northern Hemisphere, as evidenced by the isotope and sediment records of DSDP Site 594. Stratigraphic relationships between loess and marine terraces near Wanganui, provide a framework for linking terrestrial and marine records over the past 500 ka. Plant phytoliths in the loess indicate two major periods of climatically induced deforestation during the last 150 ka, one from 20-50 ka and one from 130-150 ka.
Various types of crustal movements are distributed in the mobile belts of the Circum-Pacific zone, which occur mostly along the subduction plate boundaries (cf. Table 1), and partly along the collision, transform fault, and divergent plate boundaries. Types of Quaternary crustal movements are fairly well recognized through tectonic landforms ; hence, types of tectonic landforms are treated as visible figures of crustal movements. Large scale tectonic features are classified by the concept of plate tectonics as shown in Fig. 1, and types of them are designated by abbreviations in the same figure. Compressional and extensional stress regimes are important criteria of the classification, therefore, features of Uyeda's two end members (two typical types) of subduction are compared in Fig. 2, and the Jarrard's seven strain classes in the upper plate of subduction boundary, which are cited in Table 1, are shown in Table 2. Neutral stress regime of subduction (Sn, strain class 4 in Table 2) should be added in Fig. 1, but the judgement of “neutral” is not easy task in practice. Oblique subduction and oblique transform fault are common as seen in the plate boundaries of Fig. 4 ; two contrasting tectonic features seen in forearc and back-arc under oblique subduction are shown in Fig. 3. Quaternary crustal movements around the Pacific Ocean and Philippine Sea are reviewed briefly, and their types of movements are given by the abbreviations in Fig. 4.
This paper critically reviewed the recent trends of the active fault study in Japan from the geological and geomorphological view points, and presented the future prospects and directions to recover the vigor and hope of the study. The active fault study in Japan having a progressive history of more than one hundred years has steadily accumulated various kind of data on the fault activity. In the end of 1970's, the Research Group for Active Fault systematically compiled these data. They published the first nationwide inventory of active fault titled “Active Faults in Japan” in 1980. This was the epoch-making result for the active fault research in Japan. Since then, the trend of the study has forked into following three courses. 1) The detailed reconstruction and description of the fault behavior, 2) The understanding of the relationship between active faults and regional or plate tectonics, and 3) The interpretation of the active fault information to the other scientific fields such as geophysics and civil engineering. The first course of these was the main trend of the active fault study in 1980's. In this trend, the trench excavation survey appeared as a useful method to reconstruct the paleoseismicity and fault activity. More than 60 trench surveys during the last 15 years revealed following two important results on the fault behavior. One is that the almost all of onshore active faults in Japan have the recurrence interval longer than 1, 000 years. The other result is that the trenching could confirm the source faults of the huge historical earthquakes of which hypocenters were previously unknown. Although the active fault study based on the trench excavations obtained thus fruitful results, on the other hand, some signs suggesting the declining of the study have appeared. These were the shortage of young scientist who interested with the active fault, and the decreasing of presentation numbers in the meeting. The declining of the study might be caused by the loss of attractiveness for young scientist due to the over-depending on the trench survey. However, the earthquake is a geoglogical phenomenon as well as a physical phenomenon. The active fault is an indispensable element to recognize the essence of earthquake. Therefore the author proposes the following three major items that is necessary for our study to overcome the recently rising problems. 1) To distinguish the segment barriers from the major active fault systems in Japan ; The barrier in the segmented fault system has a potential to be a rupture nucleation. Recognition of the barrier is very important for improvement of continual observatory system for precursor. Therefore we need much information on the paleoseismicity and activity of each discrete fault constituting a fault system. It is necessary to invent the various methods for the finding of segmented structure as well as the improvement of trench method. 2) To establish the seismotectonic model ; Seismotectonic model implies a kind of model that explains the relation between the earthquake, the active fault and the regional or plate tectonics. Ishibashi (1988) constructed the excellent one to show the plate tectonic implication for the future probable earthquake, called Odawara earthquake, in the northwestern part of Sagami Bay. The author thinks that we should build this type of seismotectonic model not only in Sagami Bay but also in various parts of Japan. The complement of the seismotectonic model in many parts of Japan will refine the ability of future prediction of large earthquake caused by onshore active fault.
New Zealand straddles the boundary between the Australian and Pacific crustal plates. There are three main elements to the Quaternay tectonic setting of New Zealand. They are; (i) The Kermadec-Hikurangi, west-dipping, subduction zone that extends along the east coast of New Zealand as far south as the Chatham Rise. (ii) In the southwest of the South Island, oceanic crust of the Australian plate is being subducted, at a steep angle, beneath continental crust of the Pacific plate at the Puysegur Trench. (iii) Between the two opposite-dipping subduction zones there is a transform fault system that accommodates relative plate motion between the plates. As a result of the complex tectonic setting there is a wide variety teceonic features, and variety in styles of deformation within New Zealand. The country can be divided into regions of similar tectonic style and rate, and this approach proves useful in identifying the principal components of the tectonic framework and in broadly assessing earthquake hazard.
This paper aims to review the data of marine and coral terraces of the last interglacial maximum (isotope stage 5e) and Holocene ones on the western Pacific rim, especially from New Zealand and Huon Peninsula, Papua New Guinea. Informations on Taiwan, two islands of New Hebrides and Australia are also briefly mentioned based on published data. Main subjects discussed in this paper are : 1) methods of terrace identification as isotope stage 5e, 2) uplift rate and pattern since stage 5e and its significance, 3) the formation of terraces younger than stage 5e as a function of uplift rate, 4) the formation and subdivision of Holocene terraces with special reference to coseismic uplift, 5) relationship of uplift pattern and rate between the last interglacial terrace and Holocene one, 6) accumulated nature of deformation pattern through time. In New Zealand, stage 5e terrace is identified at many sites from tephrocronological method and fission track age of major tephras, racemization ratio, and U-series age, TL dates of loess, in addition to morpho-stratigraphic observation of terraces and terrace deposits, such as terrace continuity, presence of thick transgressive deposits burying preexisted valley, and relationship between marine terraces and glacial deposits. However, radiometric age data are still rather limited and age of some important key tephras is still problematical to establish the detailed terrace chronology with accuracy of 1 ×105 year time scale. Detailed deformation patterns have been established at several areas. Uplift rate is usually high at the area, close to subduction zones ; for example, 2.5 m/ka at northeastern coast of North Island. Accelarated uplift toward present is established at several areas, especially at Mahia Peninsula. Holocene terraces are well studied in the east and south coast of North Island and coseismic origin for several regressive terraces are now confirmed. Fifteen subregions are identified on the basis of number of Holocene terraces and radiocarbon dates of regressive coseismic terraces. Coral terraces of Huon Peninsula provide the key information for Quaternary sea level changes. However, age data for stage 5e is not fully sufficient and two peaks within stage 5e is indicated. The high uplift rate reaching 3.5 m/ka make possible to form many terraces, corresponding to each relative high sea level position with nearly 1 × 104 years interval. Repeated coseismic uplift during the last 50 ka is identified from profiles of late Pleistocene and Holocene terraces. Large eartrhquakes associated with meter-scale uplifts have been repeated at Huon Peninsula during the late Quaternary with recurrence interval of 1, 000-1, 300 years. Coseismic uplift is certainly important tectonic process in this tectonically active coast, although the location of seismogenetic faults responsible for coseismic uplift is not able to establish at this stage. In contrast to New Zealand coast, uplift has proceeded at the same rate since stage 5e. Very high Holocene uplift rate in eastern Taiwan, up to 10 m/ka indicates the rapid uplift on the collision zone. No comparable data are available from late Pleistocene terraces, however. Coral terraces at Santo and Malekula Islands, close to New Hebrides Trench, show the high uplift rate, which has been accelarated between ca. 40 ka and Holocene. However, U-series ages were not obtained from high terrace which is assumed to be stage 5e. On the north Malekula, terrace uplift pattern is concordant with the 1965 coseismic uplift pattern. Average recurrence interval of large earthquakes is estimated to be 340 years. This interval is discordant with four or five steps within the Holocene coral terrace, and requires further interpretation. Australian coast provides data from stable continent. Uplift rate is usually small, with the highest rate of 0.2 m/ka at Tasmania.
There are two widely used sea level curves for the last glacial cycle, one based on coral terraces at Huon Peninsula (HP) in Papua New Guinea, the other on oxygen isotope data from deep sea cores. Previous sea level estimates from HP are 20-40 m higher than isotopic sea levels for the interval 30-75 ka but new sea level data from HP support the isotopic sea levels. Computer simulations of coral terraces are more similar to observed HP terraces when the computer model is driven by the isotopic sea level curve than by the previous HP sea level curve. HP sea levels and benthic isotope records were used previously to calculate deep sea temperatures through the last glacial cycle the new HP results lead to a sharper indication that deep sea temperatures were up to 1.8°C cooler during the last glacial cycle than in the interglacials. The temperature estimates depend on the isotopic composition of Pleistocene ice sheets. However, if deep sea temperatures did not change, the HP sea levels require unrealistically low oxygen isotope values for the Pleistocene ice sheets. The model of cooler deep sea temperatures during glacial cycles is adopted here and was used to derive isotopic sea level changes using the V19-30 record over the last 330 ka. The isotopic sea levels before the last interglacial are consistent with the limited data available but need to be tested by high quality data from older coral terrace sequences.
The geomorphic development of the modern coral reefs in the middle Pacifc has been studied on the basis of multiple shallow boring and the age determination of cored samples. The study area covers Ryukyu Islands, Mariana Islands and South Cook Islands. The geomorphic development of the modern coral reefs can be divided into three stages in terms of Holocene sea-level changes. (1) Most coral reefs of these islands have grown upward, in particular in the reef front before 6, 000 to 5, 000 y BP associated with a rapidly rising sealevel. (2) The reef crest caught up a gently rising sea-level during the period from 6, 000 to 3, 500 y BP and the zonal distribution of the surface features such as reef crest, reef pavement and moat has been accomplished. (3) Emergence of the reef flat occurred around 4, 000 to 3, 000 y BP in many islands and the reef front jumped seaward at the emergence. After 3, 000 y BP, the emerged reef flat has been eroded partly or totally into the erosional reef flat associated with a newly stabilized sea-level and the horizontal extention of the reef flat has occurred both seaward and landward. The high stand of sea-level in the middle Holocene has been recognized in many islands in the middle Pacific. The age of the highest sea-level in the Holocene in these oceanic islands is around 4, 000 to 3, 500 y BP and this age is significantly younger than that (=6, 000 y BP) along the coast of the continental margin. This implies that a part of regional difference in the emergence during the late Holocene would be caused by the hydro-isostatic effect.
Comparing mutually the records of several deep-sea cores from the North Pacific, it is concluded that glacial ages had high accumulation rate of organic carbon and weak carbonate dissolution rate than interglacial ages. However, the increase of biological productivity in surface water generally causes the drop of the pH of the underlying water and leads to high carbonate dissolution. A key to solve this contradiction is probably carbonate particles in aeolian dust which were extensively supplied to the entire ocean during glacial ages. By dissolving the carbonate particles in water column, the alkalinity of the sea water increased. Hence the atmospheric CO2 was absorbed by the upwelling water with high alkalinity, as well as by the photosynthesis of marine plankton increased during glacial ages. The variation of atmospheric CO2 concentration is not related to the deep water circulation but to the conditions of the surface and middle layers in the ocean.
Coral reefs are related to all the factors of the predicted global changes for the next century : CO2 increase, global warming and sea-level rise. The analysis and modeling of postglacial reef responses to these changes with a time scale of 103 years provide ground truth information as to the possible responses of reefs to the future changes. The sea-level rise might bring about submergence of reefs. The threshold rate is 4 m/1, 000 years : if the sea-level rise over 40 cm occurs in the next century, reef surface will not keep up with the rising sea. Rise in sea surface temperature might cause bleaching of corals in the tropical region. On the other hand, the distribution area of reef corals was expanded at the hypsithermal time in the subtropical region such as Japan. Calcium carbonate deposition in coral reefs releases CO2 into the atmosphere. The postglacial CO2 increase did not match the time of reef calcium carbonate deposition. This might show the effect of photosynthetic CO2 fixation which occurs simultaneously in reefs. Postglacial records show that reef responses to global changes are not simple ones.
The present snowline in the Peruvian Andes (5-17°S), rises from as low as 4.7±0.1km on the eastern (windward) to more than 5.3 ± 0.1km on the western (leeward) side of the central Andes. The effect of temperature on snowline altitude is isolated from the effect of precipition by subtracting the altitude of the mean annual 0°C isotherm from the altitude of the snowline. This difference, defined as the normalized snowline altitude, increases with decreasing precipitation. The lowest late Pleistocene snowline rose from east to west and ranged in altitude from 3.2 to 4.9 (±0.1) km. Both the present and lowest late Pleistocene snowlines indicate that moisture at both times was derived principally from tropical easterly winds. An east-west precipitation gradient steeper than present is inferred for the eastern slopes of the centralAndes from the steeper late Pleistocene snowline gradient. Mean annual temperatures were 10±1.9°C cooler that today at 3.52 km, as calculated from a late Pleistocene snowline as much as 1.4±0.2 km lower than today. Mean annual precipitation was 25 to 50% less than today along the eastern side, and more than 75% less on the western side of the central Andes. These estimates of lower temperature and decreased precipitation are more extreme than previous estimates. They imply that the amount of glacial-age cooling elsewhere, such as in western North America, may also have been underestimated by previous researchers because they did not adequately consider the effect of reduced ice-age precipitation on snowline lowering.
Using the 1-km grid map of plant communities prepared by the Environment Agency of Japan, we recognized the five natural forest vegetation zones in Japan based on climatic data. 0. alpine : : Pinus pumila and alpine grass-land (boundary WI= 23) 1. subalpine : : Evergreen coniferous trees (boundary WI= 45) 2. cool-temperate : : Deciduous broad-leaved trees (boundary WI= 74) 3. semi-temperate : : Evergreen coniferous replaced by deciduous broad-leaved trees : (boundary WI= 117) 4. warm-temperate : : Evergreen broad-leaved trees : In Japan, which receives sufficient precipitation in summer, the thermal condition during the plant growing season is the overwhelming factor that sets the limits of plant distributions. Using the 1-km grid map of monthly air temperature prepared by the Meteorological Agency of Japan, we made a grid map of WI (warmth index of Kira's), defined as the annual sum of monthly mean temperature above 5°C excluding negative values. This value, an indicator of summer warmth, ranges from 0.8 at the top of Mt. Fuji (3, 776 m) to some 200 in the subtropical islands of southernmost Japan. WI is also an approximate indicator of annual potential evapotranspiration and net radiation, which are major factors of plant productivity. W e calculated the boundary values of WI for the natural forest zones using the grid map of plant communities and the newly prepared map of WI. At a boundary value, the two adjacent zones have the same grid numbers, that is, occupy the same area. The boundary values are given above. These values were used for estimation of potential vegetation for the grid cells whose natural vegetation had been lost by human land use, and for simulation of probable vegetation zones under different climates cooler or warmer than the present. Before doing this we analyzed statistical relationships between plant occurrence and local topography such as the solpe and its direction, and the Laplacian value of height which indicates degree of convergence or divergence of water movements on the hill slope. 18.6 % of the total area of Japan is covered by natural vegetation, the rest by human-induced secondary forests (25.9 %), artificial afforestations (27.9 %), cultivated fields and grassland (21.4 %), rural and urban areas including industrial areas (6.2 %) etc. For these human-influenced areas we estimated potential vegetation on the basis of the boundary values of WI. Areal occupation ratios of the potential vegetation zones of Japan under present and different climates. are as follow : Areal Occupation (%) of potential vegetation zones under different climates natural potential -7°C cooler -1.5°C cooler +2°C warmer (remaining) (present) (full glacial) (little ice age) (CO2-doubling) alpine 0.3 0.8 26.9 1.4 0.6 subalpine 4.6 4.6 34.2 14.0 1.2 cool-temperate 12.0 31.8 37.8 34.1 22.1 semi-temperate 0.7 45.3 0.9 46.8 38.4 warm-temperate 1.0 17.5 0.2 3.7 37.7 Judging from the Plates on separate pages and the table above, it seemed that the shift of vegetation, zones from the glacial time to the present skipped over the adjacent zone. The horizontal distance was short in the case of the shift in mountanous districts but long in flatter lowlands. In addition to this, human land use interrupted the horizontal shift of vegetation, especially in lowlands, for the last several thousand years. These historical situations influence strongly the distribution and composition of the vegetation of Japan.