Fig. 1: Raypaths for different Martian core seismic phases.

a,b, Models without (a) and with (b) an IC are compared. Here, P′P′r represents rays leaving from the event towards the station along the major arc and sampling different depths of the core, whereas P′P′n represents a ray taking off along the minor arc. In the presence of an IC, the PKiKP phase reflects at the ICB (red curve in b). In b, the labelled PKKP phase transiting the IC should be PKIKKIKP, but we use PKKP here for consistency with a model without IC. Moreover, an extra P′P′r_df phase (green dashed curve) transits the faster IC and arrives much earlier than the P′P′r_ab (blue dashed curve). The red star and black triangle denote a marsquake at a depth of 33 km and a seismometer at an epicentral distance of 27°, respectively. c, Locations of the marsquakes used in vespagram analysis (Methods) (white circles), two impacts (red circles), four large-distance events (magenta and blue circles) and the InSight seismometer (red triangle). The red and orange diamonds represent the bouncing points of PKiKP at the inner-core boundary and P′P′ at the surface near the antipode of the InSight location (Fig. 1b), respectively. White lines mark equal-distance circles around InSight with epicentral distances of 20°, 40°, 70° and 90°. Most Martian seismicity is at the epicentral distance range of 27°–40° (blue-shaded region in Extended Data Fig. 1). The thin blue and orange lines denote the great circle paths for event S0235b PKiKP and PKKP phases, respectively. The locations of the marsquakes are plotted based on ref. ⁴⁸. The heavy green line marks the equatorial dichotomy boundary on Mars based on ref. ⁴⁹.