Correlation between seismic activities in the focal region of the Hyogo-ken Nanbu earthquake and in the surrounding regions were investigated. We found that seismic activity in the Tanba region had been well correlated with that of the Wakayama region, but the correlation has disappeared in 1990s. Activity to the west of Tanba region shows a tendency to be delayed to the activity in the Tanba region and this tendency is concordant with the f eature shown by Yoshida and Takayama (1992) that activity in the Mino region is advanced a few years against the activities in the Tanba and Wakayama regions. Such seismic correlations with time lags between surrounding areas of the Kinki triangle are considered to mean that tectonic stress in that district has a tendency to propagate or diffuse to the west at the velocity of 10 km/year. We present some evidence which decrease of the seismicity in the Tanba region in 1992-1993 period and increase in 1994 might be precursory changes for the Hyogoken Nanbu earthquake. Just after the Hyogo-ken Nanbu earthquake seismic activity in the Tanba region increased remarkably and an activity of small earthquakes was observed near the Yamasaki fault located to the west of the Hyogo-ken Nanbu earthquake. However, no unusual change of seismicity was seen in the Wakayama active region. Because a disastrous intraplate earthquake is likely to be followed by another large earthquake, and the most probable site of the succeeding large earthquake is the place where seismicity becomes active after the first earthquake (Yoshida and Ito, 1995), the Tanba region and its surrounding areas should be watched intensively in the following several to ten years.
In this paper the new methodology for quantitative estimation of uplift rates at inland region was discussed using fluvial terrace surfaces and deposit bases. Previous studies have revealed that river profiles regularly changed according to the cyclic fluctuation of climate and sealevel ; therefore, in the interglacial ages (the marine isotope stage 5e and the present) similar profiles with large concavity formed, and in the glacial ages (stage 6 and 2) linear profiles appeared on the contrary. In upper reaches of rivers, stage 5e valley bottoms were filled with the deposit accumulated in the subsequent glacial stages. Based on these observations, the value of relative height between the stage 5e burned valley bottom and the present river floor (BV value) is considered to indicate uplift during those stages (120-130 ky). Similarly, the value of relative height between the stage 6 terrace and the stage 2 terrace (TT value) can be used as an indicator of uplift during the period between those two stages. The BV values and TT values distributed along Japanese major rivers were reviewed on the basis of previous studies on terrace development and tephro-chronology. In middle reaches of most of rivers, the TT and BV values at the same sites are concordant to each other. The BV values remarkably decrease upstream in spite of no reduction of the TT values in the upper reaches or branches. This implies that present river profiles have not completely been in equilibrium and are now degrading in the upper streams and branches. As an indicator of long-term uplift rate, the TT values have the advantage of applicability to upper reaches and availability of field data in comparison to the BV value. However, it is impossible to apply these methods in the upper reaches or branches where fluvial terraces are not well developed. Up until now, the uplift rates in mountainous region were presumed from the outlined altitude of mountains or the amount of eroded material trapped in reservoirs, but have not been examined by direct data. The uplift rates obtained by using TT values and BV values are 0.10.8 mm/year in large number of sites, which are not located in very high mountainous area. Large uplift rates more than 1 mm/year were estimated from TT values at the Kurobe river basin, in the northern part of Chubu mountainous region.
Taking advantage of capability of SAR (Synthetic Aperture Radar) on board Japanese earth observation satellite, JERS-1, which can observe ground condition through clouds, an attempt is made to investigate of tropical rain forests in two sites in Central Amazonia, Brazil. The first site extends from 0.5 S to 5.5 S and from 59 W to 65 W and the second site is a smaller area of about 75 km×150km located to the south of the first site. Since the coverage of 1 scene of SAR image is approximately 75 km×80km, it is necessary to mosaic 90 scenes of SAR images for the first site and 2 scenes of SAR images for the second site respectively. A practical scheme of processing a large amount of SAR image data is developed. Through the analyses of the mosaic images following features are found. The tropical rain forest is well conserved in the first site while a fairly lage deforestation is found in the second site. The estimated deforested area from SAR images is at least 607.1 km2 on October 27 1992 and 661.5 km2 on June 4 1993 in Sena Madureira, while in Rondonia it is estimated that at least forest of 302.7 km2 was newly cut down between July 19 1992 and April 9 1993 and the deforested area is at least 4, 629.0 km2 on October 2 1993. It is also found that features of river system under the continuous coverage of tree layer can be detected. As the typical values of σ° (differential scattering coefficient, which is the average value of the scattering cross-section per unit area) following values are obtained. (1) Dense forest -10.88-5.96dB, (2) Forest in wet lands (or flooded land) -7.67-2.48 dB, (3) Deforestedarea -15.24-8.68 dB, (4) Shrubs/short trees in sterile soils called “campinarana” -17.87-8.16dB.
An immense quantity of the ancient literature exists on the great eruption of Asama in 1783. They were written on the northern flank of the volcano, Joshu, and also on the southern flank, Shinshu, including some diaries written in Kanazawa, Edo (present Tokyo), Nagoya and as far as Kyoto (300km SW). They have been compiled by Susumu Hagiwara exhaustively for forty years and published recently. We read them critically to reconstruct the sequence of the eruption. The first explosion was noticed on May 8, by the Gregorian Calendar. The volcano had been erupting at the summit crater intermittently since. On August 2, the tephrafall from a Plinian eruption column became so intense and continuous in Shinshu that the inhabitants prepared for flight. In the afternoon of August 4, the Agatsuma pyroclastic flow spread northward up to 8 km from the summit. Coincidentally, hot lahars, caused by slumping of steep slopes thickly covered with fallout pumice, had successively surged along the Yukawa river southward to Kutsukake (present Naka Karuizawa), where a house was overwhelmed and another flooded under floor. The climactic phase attained late at the night and maintained until the morning of August 5, during which the Oni Oshidashi lava overflowed from the northerm lowest rim of the summit crater. At 10 a.m. of August 5, a part of the northern flank suddenly collapsed, probably triggered by a strong earthquake. It gave rise to the generation of debris avalanche which destroyed Kambara village. At the same time, the flank failure resulted in an explosive decompression of the inner massive part of Oni Oshidashi lava flow to produce a Pelean nuee ardente. The debris avalanche turned into a hot lahar after it cascaded into the Agatsuma river. It caused a disastrous flood on the lower part of the river and reached Edo at 2 p.m. of the same day. A large-scale collapse occurred reportedly at 8 a.m. of August 1 at Kananuma village may not be a fact.
A continuous long core of peaty sediments bored from the Naka-Ikemi Moor Central Japan (lat. 35°39' N., long. 136°5' E.), contains records of paleoenvironmental changes during the Last Glacial and Holocene periods. The Naka-Ikemi Moor stretches about 1.3 km from the west to east. This peculiar shapes and crustal movements had been pointed out by purely from a topographical point of view. And this moor is regarded as a waste-filled valley created by sort of tectonic depression at the eastern part of the Tsuruga Plain. From the stratigraphical examination, some volcanic ashes were detected as follows : Kikai-Akahoya Tephra (K-Ah : 6.3 ka), Aira-Tn Tephra (AT : 24 ka), Daisen Kurayoshi Tephra (DKP : ca. 50 ka). Values of bulk density measurements and radiocarbon dates of core samples indicate that the Naka-Ikemi core samples contain continuous records for the past 50 ka. The average sedimentation rate of Naka-Ikemi Moor was increased after the fall of AT volcanic ash had occurred. The sedimen tation process of Naka-Ikemi Moor has also been clarified by sedimentary facies and value of loss on ignition of core samples. Value of loss on ignition began to increase since the end of Last Glacial, suggesting the increase of organic material caused by environmental changes.
The rates and processes of periglacial mass movement were measured on the vegetation-free debris-mantled slopes in middle reaches of Adventdalen and Reindalen in central Spitsbergen Svalbard (Fig. 1). All slopes are mainly covered with debris of sandstone and shale of Jurassic, Cretaceous and Tertiary age (Fig. 2). A grain size analysis shows that surface layers of these slopes are composed of rubble and frost-susceptible fine materials (Fig. 5). The maximum depth of active layer varies year by year, but the average depth is estimated about 1 meter. Total 17 painted-stone lines were installed nearly horizontally on the slope surface in above 2 areas : 12 lines during the summer, 1988 and -5 during the summer, 1989 in order to detect movement rates of surface materials (Table 1). Eight pieces of flexible glass-fibre tubes (5 mm in diameter) were inserted into the ground vertically in 1988 and 1989. Furthermore measurement of year-round ground temperature and frost heave was achieved at north-facing mountain slope (700 m a.s.l.) of Mt. Skolten, using a data logger at 3-hour intervals from August, 1990 to July, 1991. Sensors were installed at 0, 5, 20, 40, 60 and 100cm in depth. Annual averages of movement rates measured by painted stone-lines are 0.6 cm to 11.2 cm (Table 1). Movement rates of surface rubble and slope gradients have roughly mutual relation (Fig. 3). Deformation of all painted stone-lines were patterns parallel to the base lines, and this occurred on every type of slope materials independently of the thickness and size of surface rubble layer (Fig. 4). The vertical velocity profiles of the excavated tubes fall into three types : straight profile keeping tilt (Fig. 6 JH-1), concave profile indicating the greatest movement at the surface (5-1, S-2, S-4, R-5) and complex (concave/convex) profile indicating relatively larger movement at depth (AD-4, S-3, R-3). The movement of the tops of all tubes averaging 3.4 cm, which similar to the average rate of movement measured by painted stones. This implies that these three types of deformation were formed by the same processes, namely frost creep and gelifluction. Only eleven diurnal freeze-thaw cycles were recorded at the ground surface on the northfacing mountain slope (19°) of Mt. Skolten from August, 1990 to July, 1991 (Fig. 7-a). Maximum and average depth of ground freezing occurred during these short-term cycles were 6.5 cm and 3.2 cm respectively. Frost heave recorded as the average 0.47 cm per 1 event, occurred from middle August to middle September, corresponding to the diurnal freeze-thaw cycles (Fig. 8). On the other hand, the heave caused by seasonal frost occurred from 21 to 27 August and the amount was 3.0cm (Fig. 8). The seasonal heave occurred untill the frost table reached less than 30cm in depth. The cumulative amount of diurnal and seasonal frost-heave is 8.7 cm. Accordingly amount of potential frost creep for the year is calculated to 2.7 cm on the 19 degrees slope. The annual average movement rate which was measured by painted stonelines at the same slope is 4.0 cm. This value is lager than the potential frost creep. Since the movement of painted stone-line resulted from a combination of frost creep and gelifluction, the value (1.3 cm) which deduct potential frost creep from movement by painted line is regarded as movement by gelifluction. An increase of thickness of surface rubble layer without interstitial fine materials is the cause of decrease of rubble movement because ice segregation do not occur in such rubble layer (Fig. 9). Especially the surface rubble attaining more than about 45 cm in thickness suddenly decrease in movement rates by the reason of the layer underlying such thick rubbles maintain the frozen conditions for all the year round.