Fig. 4

Eigenvectors of the gravity gradient tensor caused by the subsurface model shown in Fig. 3. The maximum eigenvector and minimum eigenvector are shown by red and blue, respectively. a Eigenvectors on the high-density causative body (light green). When the high-density causative body was given in the low-density medium, the maximum eigenvector of the gravity gradient tensor points to the causative body and the minimum eigenvector points to the low-density medium. b Eigenvectors on the low-density causative body (light yellow). When the low-density causative body was given in the high-density medium, the minimum eigenvector of the tensor points to the causative body and the maximum eigenvector points to the high-density medium