BULLETIN OF THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS 
VOL. 19, NO. 1 (JANUARY, 1935), PP. 58-63, 3 FIGS. 
STUDY OF STRUCTURE OF SUWA BASIN NEAR KYOTO, 
JAPAN, BY TORSIUN BALANCE! 
M. MATSUYAMA, Y. FUJITA ann H. HIGASHINAKA? 
Kyoto, Japan 
ABSTRACT 
The origin of the Suwa Basin near Kyoto, Japan, was sought from the geophysical 
standpoint by use of the torsion balance. An isogam map suggests Lake Suwa as a 
crater lake, but this conclusion is not reasonable from a geological standpoint. There- 
fore, the origin of the lake seems to be in subsidence following the eruption of Yatsuga- 
dake Mountain, near by. 
The gravity field of the basin is negative while that of the mountains which surround 
the basin is positive. Hence, from the standpoint of isostasy, the deficiency of the subter- 
ranean mass is clear, and shows that the basin is a result of faulting or subsidence. 
PURPOSE OF RESEARCH 
From the geological standpoint, the origin of the Suwa Basin has 
been studied and the results of the study have been published and 
discussed by geologists. To examine the opinion of the geologists, 
this research was carried out from the geophysical standpoint so as 
to determine the reasons for the occurrence of the Suwa Basin and the 
geological history of Lake Suwa. 
FIELD WORK 
The field work was performed in April, 1927, and again in May 
and June, 1928. The E6tvés original type torsion balance was used 
on these two occasions. The number of observation points was 13 in 
the field work of 1927, and 32 in the field work of 1928, making a total 
of 45 stations. 
COMPUTATION OF RESULTS 
The topographic (including terrane, topographic, and carto- 
graphic corrections) and normal corrections were applied to the ob- 
served values. There are a number of formulas for the computation 
of the topographic correction, but none of them is absolute. The cor- 
? Manuscript received, November 13, 1934. 
2 Kyoto Imperial University. 
718 58 
