The characteristics of the anomaly level, variability and distribution of monthly mean precipitation have been investigated at 4 different weather stations on Cheju Island, Korea. The results of this study are as follows : 1) The SE area of Cheju Island turns out to be the heavy rain area from February to July than the NW area of the island. The heavy rain area migrates from the SE area to the NE area during the period from August to January. 2) The rainy season, in which monthly mean precipitation is more than 180mm, appears in Cheju City and Sungsan from June to August, in Seoguipo from April to August, and in Daejung from June to July. On the other hand, the dry season, in which monthly mean precipitation is less than 100㎜, appears in Cheju City from October to May, in Sungsan from December to February in Seoguipo from October to February, and in Daejung from October to March. 3) The variability of precipitation on Cheju Island appears high during the 'Changma' spell and it is also high in autumn, particularly in October, and appears low in March and April. 4) The frequency of the anomaly level shows maximum not only on the normal level but the lower normal level and the upper normal level in monthly precipitation. The annual frequency distribution of each anomaly level shows maximum on the normal level, and the frequency of the lower normal level is a lot higher than the lower normal level. 5) The precipitation of the summer season acts as an important variable in deciding between the dry year and the moisture year. In particular, this applies to the large precipition of June in the moisture year and the small precipitation of July and August in the dry year.
The physical properties of sedimentary rocks in the coal fields were studied. Sandstones and shales are major samples among the core samples from Samchuck and Boeun coal fields. The measured properties were seismic velocities (P and S-wave), electrical resistivity, density and porosity. The relationships between physical properties were analyzed by using the cross plots. Summarized results are as follows : 1. Compressional wave velocity is approximately linearly related to shear wave velocity and the velocity ratio Vp/Vs of shales has slightly larger value than that of sandstone. And with increasing Vp, the velocity ratio Vp/Vs decreases because the effect of porosity and clay content on Vs is larger than on Vp. 2. In the case of sandstones, as porosity increases, P-wave velocity decreases slowly, but effect on the density is not apparent. In the case of shales, as porosity increases, both P-wave velocity and density decrease. 3. The values and variation range of density of sandstones are relatively small as compared to those of shales. But the range of elastic wave velocities of both rocks are appeared to be similar. 4. Seismic velocity is power-functionally related to electrical resistivity, and the value of the power is appeared to be larger for sandstones than for shales. 5. Because samples from Boeun field are slightly metamorphosed, the values of electrical resistivity are larger than those of samples from Samchuk field.
The principal consisting rocks of study area are Precambrian metasedimentary bedrocks, Cambro-ordovician sedimentary rocks and Samhwa granite which have intruded these metasedimentary and sedimentary rocks. The reddish K-feldspar bearing Samhwa granite presettts miarolitic texture and graphic intergrowth between quartz and K-feldspar. The granite, homogeneous in chemical composition of major elements, belongs to Calc-alkali rocks of subalkali series. According to AMF diagram, the granite was crystallized at the latest stage of the differentiation of magma. The Samhwa granite belongs to I-type granitoids and magnetite-series granitoids. Especially, this granite is thought to be crystallized in the epicrust with high oxygen fugacity. The Samhwa granite has similar characteristics to masanite of cretaceous granitic rocks of Gyeongsang basin in the petrological and petrochemical properties. The biotite age of the granite by K-Ar age dating is 50.1±1.5. Finally, contact metamorphic zone of limestone by granite intrusion contains distinct minerals such as diopside, brucite, tremolite and muscovite, which indicate low temperature metamorphic grade.