Surface textures of quartz grains taken from about 250 samples of fault gouges in faults in length in ranging from several meters to several tens of meters and faults extending several tens to several hundreds of kilometers in length are examined by means of the scanning electron microscope and are categorized into four gouges from I to IV, judging from the smoothness of the surface, degree of undulation and development of cavities, as mentioned in the previous paper. Based on surface features of quartz grains from faults for which the geological age of their movement is known, the groups I to IV are tentatively related to the age of formation of quartz grains and the period of formation of surface textures. River pattern, striations, granular fracture surfaces, and dimple-like textures are observed to appear on less corroded surfaces of quartz grains from fault gouges. Fractographic analysis of these surfaces of quartz grains should be a clue to revealing the mode of fracture of the fault movement which released the quartz grains into the fault gouge.

View full abstract

The weathering crust of granitic rocks in Antioquia, Colombia, can be divided into eleven zones. Since zone IX that has been formed by wind-bourne loess is not a weathering crust in situ, it was excluded from the study. Zones X and XI, being soil, were also excluded. The grain distribution was mechanically analyzed for the samples from zones V-VIII. The change from “masa” A (zone V) to “masa” B (zone VI) is characterized by transformation of pebble to sand, the change from “masa” B to red “masa”(zone VII) is characterized by transformation of silt to clay and the change from red “masa” to “shimofuri” clay (zone VIII) which does not show noticeable alteration of the silt-size grains to clay-size grains is characterized by transformation only of sand to silt.
Mineralogical composition of weathering zones are identified by the X-ray diffraction method. The presence of quartz was confirmed in all the weathering zones. K-feldspar begins to alter from weathered granite A (zone III) and completely disappears in “masa” A. Plagioclase and biotite disappearsalmost completely in the initial stage of weathering. Of the secondary minerals by the weathering action, chlorite, illite, halloysite and gibbsite are seen. The existence of kaolinite is observed very conspicuously in red “masa” and “shimofuri” clay.
Chemical analysis was carried out by X-ray fluorescence spectrometer. The transfer of CaO and Na₂O shows the tendency of decrease in a convex-shaped curve in the weathering crust in Japan but in a concave-shaped curve in Colombia. The transfer of K₂O and MgO shows almost no change in the weathering crust in Japan but a tendency of rapid decrease in Colombia in “masa” B. SiO₂ decreases with the progression of weathering but resumes an increase in red “masa”. This also well corresponds with the presence of gibbsite until “masa” B which transforms to kaolinite in red “masa”. Although literatures have shown that the progression of weathering induces reduction of SiO₂ with the result of final formation of gibbsite, the new finding obtained in the present study shows that further progression of weathering to red “masa” or “shimofuri” clay induces, on the contrary, infusion of SiO₂ with the consequence of kaolinite formation from gibbsite.

View full abstract

Since the start of the Seikan Undersea Tunnel construction, long horizontal exploratory borings have been employed in order to forecast geological conditions ahead of tunnel face.
This article describes how the geological charts were produced beforehand from the accumulateddata of the advanced borings, and the comparisons are made with the factual geological maps obtained at the excavation site.
This paper also presents the evaluation method for estimating of the rock condition and the water inflow.

View full abstract

A direct current is sent to the earth, and the current is shut off. The difference between transient potentialand the potential of immedietly before breaking contact is measured, and the ratio is shown in percentage. Thusthe distribution of chargeability is gotten.
The minimum chargeability shows a boundary of strata, a large dielectric constant shows the layer of subterraneanwater. The maximum shows the upper limit and the minimum the lower limit of the water layer.
It is reported that the investigations are classified as three typical kinds mentioned below.
1. The investigation of the subterranean water in Alluvial Epoch stratum.
2. The investigation of the subterranean water in Tertiary Period stratum.
3. The investigation of the cavern water in limestone.
The result of the investigations shows that a large chargeability is observed at the subterranean water layerin each stratum.

View full abstract

In August, 1981, many collapses occurred in Yamanashi Pref. owing to Typhoon 15. In this report, the types and features of collapses are described from a geological point of view, based on the field investigationtionsat the stricken areas (South Alps Super Drag Road, Norogawa Drag Road, Sakeishi Drag Road, and Magi Drag Road).
The results obtained from these investigations are as follows:
(1) The types and features of collapses are decided by the lithic characters.
(2) In case of Masa (weathered Granite) and Talus deposit, collapses are generally occurred at the head of1st order valleys or within O-order valleys, and the debris frequently run down valleys in the form ofmud-flow. In the former case the types of the collapse are mostly circular slide, and in the latter, mostcollapses are of the type that slide along the surface of the bedrocks.
(3) In case of lutaceous rocks, the collapses are generally occurred at the fracture zones, and concequently, their breaking points have nothing to do with valley order.

View full abstract