# Crust and Upper Mantle Structure of Mars Determined from Surface Wave Analysis
## 2 Data, Methodology, and Results  
In the present study, the event S1094b (Supplement S1) recorded at the InSight seismic station (Supplement S2) has been revisited with the application of other filtering techniques [7], which have proven to be very useful techniques in several regions on Earth (e.g., [8]). This filtering analysis consists of a combination of the Multiple Filter Technique (MFT; [9]) and Time-Variable Filtering (TVF; [10]), as described by [PERSON] et al. [7], in which the MFT has been used to obtain the group-velocity dispersion curve from the time signals. The records of the vertical (Z), radial (R), and transverse (T) components of S1094b are obtained from its records in the three non-orthogonal components--UVW--of the seismic sensor [11], after instrument correction and removal of possible glitches [12]. Each of the ZRT records is a linear combination of all the UVW records, and all ZRT records have been analyzed in the present study, but the R and T records were discarded because they were affected by strong scattering. Thus, only the Z record (Figure 1, grey line) has been considered to determine the surface wave dispersion. Figure 2a (magenta points) and Figure 3 (black points) shows the initial group velocities calculated with the MFT, and applied to this record. TVF has been used to determine the smooth L- and R-signals shown in Figure 1 (black line), which are the time-variable filtered seismograms calculated from the original seismogram (Figure 1, grey line) and the initial group velocity (Figure 3, black points). Figure 3 (black line) shows the final group velocities calculated with the MFT (Figure 2b,c), applied to the L- and R-signals shown in Figure 1 (black line). The final dispersion curves for Love and Rayleigh waves shown in Figure 3 (black line) are considered as the observed data for the inversion process to be followed to calculate the S-velocity model, beneath the area crossed by the waves (Figure 4, [13]). The errors in the observed data are assumed as 0.1 km/s [7]. The initial model for this inversion process is listed in Supplement S3. This model has been prepared considering the previous models determined for the crust and mantle of Mars [3,6,14]. Figures 5 and 6 show the inversion process for Love and Rayleigh waves, respectively [7]. The S-velocity models (Figures 5a and 6a) and the resolving kernels (Figures 5b and 6b) are plotted only for depths above 100 km, due to the poor resolution obtained for greater depths. The inversion process for Love wave dispersion gives an S-velocity model (Figure 5a), which is different to that calculated for the Rayleigh wave dispersion (Figure 6a), for the depth range of 0 to 15 km, i.e., the S-velocity model that satisfactorily fits the Love wave dispersion does not fit the Rayleigh wave dispersion (Figure 5c), and conversely, when the Rayleigh wave dispersion is properly fitted, the Love wave dispersion is not fitted (Figure 6c). The Love and Rayleigh wave dispersion are not compatible with a unique isotropic model (i.e., there is Love-Rayleigh discrepancy), and it is necessary to consider the existence of seismic anisotropy in the depth range of 0 to 15 km (Figures 5a and 6a), defining an anisotropic model with hexagonal symmetry (i.e., azimuthal isotropy or transverse isotropy [15]). This model is calculated as described by [PERSON] [16]. In this methodology, the phase velocities are considered as observed data, and an isotropic model must be defined to calculate the anisotropic model, as a small perturbation of this isotropic model. In the present study, the [PERSON] and [PERSON] phase velocities (Figure 7, black rectangles) are calculated from the models shown in Figures 5a and 6a by forward modelling [17; 18], and it is selected as an isotropic model (Supplement S4) that is calculated from the inversion of the Rayleigh group velocities (Figure 6a).