|Budget Amount *help
¥1,800,000 (Direct Cost : ¥1,800,000)
Fiscal Year 1992 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1991 : ¥1,300,000 (Direct Cost : ¥1,300,000)
The aim is to establish the empirical equations to express the rates of weathering of bedrocks defined as dZ/dt, where Z is the thickness of weathered materials in the direction perpendicular to ground surface and t is the time elapsed since the surface of fresh bedrock was last eroded. The data were obtained for the weathered materials of bedrocks under the dated fluvial and marine erosional terrace surfaces arount Tokyo, Japan. The studied terraces are 1)divided into the 21 sequential series ranging from 70 to 70,000 yr.B.P.in the age assumed to be equal to the time t, 2)composed of the Tertiary sedimentary rocks, and 3) covered with gravels or sand veneer ranging from 0.2 to 3 m thick.
The weathering profiles were investigated at 56 sites on 14 series of the terraces with the combined methods of test pits, borings and seismic prospectings, and were divided into four weathering zones different in weathering grades : highly weatheredzone (H), moderately (M), slightly (S) and faintly (F). The boundaries between the four zones were confirmed by the differences in the pore-size distribution and penetration hardness. The thickness of weathered materials from the base of terrace veneer to each base of the four zones are denoted as Z_H, Z_M, Z_S and Z_F, respectively.
The relationships between these Z's and t are expressed as Z=alphat^<beta>, where alpha and beta are constatns. The values of slpha are 0.48, 1.2 and 3.2 mm/yr for Z_H, Z_M and Z_S, respectively, whereas beta shows an almost uniform value of 0..75 for the three different zones. This fact indicates that the weathering rates, dZ/dt, decrease with the time t.