Fig. 13

Distribution of \(\chi ^2\) to the variations of d and \(\eta\) in the compressible case. The green cross denoted by C indicates the position, where the \(\chi ^2\) value reaches a minimum, and the green line indicates the 68.27 % confidence level of \((\eta , d)\). The red lines denoted by IC show the results obtained in this study by assuming the incompressible Earth (see Fig. 7), and pink dashed lines indicate the projection of its confidence level to each axis of d and \(\eta\)