Fig. 2: Identifications of Martian IC phases.

a, PKKP vespagram constructed from 23 events with distance <40° in Extended Data Table 1, showing two distinct peaks at (about 1,290 s, −8 s per degree) and (about 1,340 s, −7 s per degree). The later arrival is interpreted as PKKP or alternatively as PKKP_MSL, a reflection from the top of the proposed molten silicate layer overlying core^31,32. Orange shading outlines predicted PKKP travel time or slowness at the reference distance of 29° for available velocity models. Top panel shows the envelope stack for the picked PKKP slowness in b. b, Occurrence percentage of grids with energy exceeding 85% of the peak value in the vespagram, with white cross marking the identified PKKP arrival and the associated 1σ errors from Gaussian fitting (Methods and Supplementary Information section A3.2.2.3). c, Synthetic vespagram for the BS_SKS_GD_IC model (Extended Data Table 2, case 8). Orange crosses denote predicted PKKP_CMB and PKKP_MSL for case 6. d–f, Same as a–c, but for PKiKP. White shading in d shows the expected PKiKP slowness range for IC size of 0–900 km. The energy at (600 s, −4 s per degree) has a similar slowness to that of ScS (see Supplementary Information section A3.3 for possible origins of this arrival). g, Polarization analysis on event S0235b confirms PKKP identification: top, bandpass-filtered waveforms (grey line); middle, polarization-filtered waveforms (blue line) with envelopes; and bottom, vertical–horizontal summed FDPA intensity (VRM–HRM) (Methods), showing a strong polarized signal at about 1,348 s with large VRM–HRM. Red dashed lines mark the predicted travel time from the PKKP slowness in c. Black-dashed line marks the mean plus one standard deviation of VRM–HRM values in the 100-s window preceding PKKP. h, Same as g but for event S1015f, showing a PKiKP arrival at about 605 s.