여수시 묘도 일대에 분포하는 안산암과 퇴적암 지역에서 물리검층 종류인 부유식 P S파 속도검층과 밀도검층을 실시하였다. 연구목적은 이 지역에 분포하는 두 암상에 대해 깊이에 따른 탄성파속도 및 밀도분포를 찾아내어 시추조사를 통해 얻은 지반정보인 암상과 RQD 값을 비교하여 암석 종류에 따른 상호간에 상관관계를 파악하는 것이다. 연구지역에서 두 암석에 대한 탄성파 속도 분포는 깊이에 따라 P파가 약 2,000m/sec 내외이며, S파가 1,500m/sec 내외의 차이를 보였으며, 밀도는 깊이에 따라 약 0.35g/cm3의 차이로 비교적 넓은 폭으로 나타났다. 이러한 결과는 암석 종류에 대한 차이보다 풍화 정도에 따른 것으로 해석된다. 그러나 RQD, 탄성파속도 및 밀도의 상관성 분석은 비교적 높은 관계를 보이므로 물리 검층자료의 결과를 이용하여 RQD에 관련된 불연속면의 빈도를 유추할 수 있다고 본다.

The physical characteristics of the sedimentary rocks developed in the Gyeongsang basin have been studied based on the geophysical logs which include SP, single electrode resistance, gamma ray, density and caliper logs. The rock sequences penetrated by the borehole, located in the Namji area, are portions of the Chilgok Formation and Jinju Formation which are the base of the Hayang Group and the top of the Sindong Group respectively. Although five different rock types are described on the core log, the boundaries between such rocks are not clearly indicated on the geophysical logs. It is quite apparent that such poorly sorted sediments have non-marine origin and have been severely compacted and almost completely cemented through the diagenesis process. The gamma and SP logs show that the clay content of the formation slightly increases with depth. The organic rich black shale zone of 4m thickness is clearly identified on the gamma-ray log in the top part of the Jinju Formation. The bulk density determined from the density log is about 2.6g/㎤ and does not show much variation between different rock types. This value is close to the expected matrix density of the rock sequences and the rocks are appeared to have very low porosity. The resistivity curve also does not show any clear differences according to the described rock types. This fact also indicates that both shales and sandstones have been severely altered through the diagenesis. The low resistivity peaks and the corresponding large SP deflections are appeared against the fracture zones which are clearly identified on the caliper log. The dominance of such electrokinetic potential over the electrochemical potential also indicates that the permeability of the rocks is very poor.