Fig. 3: Schematic formation mechanism of I-J and I2-J correlation features.
From: An estimate of absolute shear-wave speed in the Earth’s inner core
a Ray paths of two possible constituents contributing to the formation of the I-J correlation feature, xPKIKP-xPKJKP. These constituents originate from a secondary source (i.e., via the Huygens principle), denoted by the x sign, and propagate as PKJKP and PKIKP waves to receivers R1 and R2. These two rays have the same ray parameter and share first propagation legs in the mantle and outer core. The secondary source x can be a surface reflection of any seismic ray propagating from a distant earthquake with the same ray parameter. The prefix x, whose travel time is canceled out and not sensitive to the I-J feature’s timing, is used in the feature name to generically refer to the arbitrary ray paths before the two final constituents. b Similar to (a), but for a correlation feature with one more PKIKP leg. xPKIKPPKIKP-xPKJKPPKIKP is another example of constituent pairs whose differential travel times contribute to forming the I-J feature. c Similar to (a) and (b) but for many more PKIKP legs before arriving two the two receivers, i.e., xPKIKPPKIKPn-xPKJKPPKIKPn. The last PKIKP legs in common, n = 0–10, are color-coded as in the color bar. d–f Similar to (a–c) panels but for various constituent pairs contributing to forming I2-J correlation features.
