The Sound Velocity and Attenuation Coefficient of the Marine Surface Seciments in the nearshore area, Korea

韓半島 沿近海底 表層堆積物에서의 音波傳達速度와 減衰係數

The sound velocity (compressional wave) and attenuation coefficient in the marine surface sediments in the nearshore areas off the Pohang, Pusan, Yeosu and Kunsan were investigated in terms of the geotechnical properties of the marine surface sediments in the water depth range of 10-50 meters. The marine surface sediments in the study areas are variable, that is, sand to clay. Due to the various four different study area, the sound velocities and attenuation coefficients in the surface sediment facies vary 1,44m/sec to 1,510m/sec in velocity and 0.82dB/m to 3.70dB/m in coefficient respectively. In fact, the sound velocity increases with increasing of density and mean grain sizes of the sediments, and however, with decreasing of porosith. The correlation equations between the sound velocith and geotechnical properties of mean grain size, density, and porosity were expressed as the following: Vp=1512.28406-9.16083(Mz)＋0.20795(Mz)$\^$2/, Vp=1876.15527-597.50397(d)＋210.48375(d)$\^$2/, Vp=1559.47217-2.09266(n)$\^$2/. where Vp is sound velocity, Mz is mean grain size, d is density, and m is porosity, respectively. However, the relationship between the attenuation and geotechnical properties were different from that of sound velocity and geotchnical properties. Furthermore, the correlation equations between attenuation coefficient and geotechnical properties were expressed as the following: a=1.85217＋0.67197(Mz)-0.09035 (Mz)$\^$2/, a=48.87859＋58.21721(d)-16.3.143(d)$\^$2/, a=2.06765＋0.07215(n)-0.00111(n)$\^$2/, where a is attenuation coefficient. The high attenuation appeared in the silty sand through fine sand facies in sediment and k values in these facies were in the range of 0.86 to 0.89 dB/m/KHz.

음원과 3개의 수진기를 사용하여 포항,부산,여수 및 군산연근해 수심 10~50m 의 표층퇴적물에서 음파전달속도(Sound velocity)와 감쇠계수(attenuation coefficient)를 구하였다. 연구지역에서의 층퇴적물에서 측정된 음파전달속도는 1,444 ~1,510m/sec, 감쇠계수는 0.82~3.70dB/m로 나타나고 있다. 퇴적물과의 관계는 입 도와 공치율이 감소함에 따라, 또한 밀도가 증가함에 따라 음파전달속도가 증가한 다. 음파전달속도와 퇴적물의 물성간에는 다음과 같은 관계식을 가진다. Vp=1512.28 406-9.16083(Mz)＋0.20795(Mz)$^{2}$, Vp=1876.15527-597.50397(d)＋210.48375(d)$^{2}$, Vp=1559.47217-2.09266(n)$^{2}$. 여기서 Vp는 음파전달속도, Mz는 퇴적물의 평균 입도, d는 밀도 그리고 n은 공치율이다. 그러나 감쇠계수와의 관계는 그 양상이 다 르게 나타난다. 입도와 밀도가 증가하거나 공치율이 감소함에 따라 감쇠계수는 커 졌다가 다시 작아지는 곡선관계를 보이는데 이를 2차회귀방정식으로 나타내면 다음 과 같다. a=1.85217＋0.67197(Mz)-0.09035 (Mz)$^{2}$, a=48.87859＋58.21721(d)-16.3.143(d)$^{2}$, a=2.06765＋0.07215(n)-0.00111(n)$^{2}$.여기서 a는 감쇠계수 Mz는 평균입도, d는 밀도, n은 공치율이다. 감쇠현상이 가장 심한 퇴적상은 실트질 砂~細砂로서 k값은 0.86dB/m/KHz이다.