# Crustal Structure of Hainan Island and Surrounding Seabed Based on High-Resolution Airborne Gravity
## 5 Discussion  
### Gravity Moho Compared with Previous Studies  
The depth of the Moho interface is an important parameter of the Earth's structure, and many experts have focused on its variations. To evaluate the Moho interface results, we compared the inversion result in this study with the published results. The result is shown in Table 2. [PERSON] et al. [18] demonstrated that the Moho depth reached 25 km from the Baiyan in Leizhou Peninsula to Jianghong in northern Hainan Island with minor spatial fluctuations. The results derived from natural seismic stations in Hainan Island [17] indicate that the Moho depth was deeper in the southern part of Hainan Island, averaging 30 km, and shallower in the northern part, ranging from 26 to 29 km. [PERSON] [16] acquired four deep reflection seismic profiles across Leizhou Peninsula and the northern part of Hainan Island. Their results reveal a localized thickening of Moho [16] within the QiongZhong Strait, with measured depths of 35 km and 45 km. Only two deep reflection seismic profiles exist in the offshore research area. The Moho depth results of the ESP-W profile vary from 31 km to 12 km, with large fluctuations. Our results are consistent with the measurement results obtained by [PERSON] et al. [17] and others' results. Overall, the thickness of the continental crust thins from 30 km to 28 km along the coastal zone. The calculation results in the QDNB are consistent with mechanics analysis [54]. However, our result outlines the contours of the Hainan Uplift more clearly.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Mean Value (km)** & **SD (km)** & **Min Value** & **Max Value** \\ \hline Gravity-derived depth from this paper & 1.76 & 3.96 & \(-6.71\) & 4.38 \\ Gravity-derived depth-crust1.0 & 4.29 & 2.91 & \(-1.83\) & 8.37 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Statistics of the differences between the new Moho depth model and corresponding models from the literature.  
Figure 7: Inverted Moho surface topography from D7 decomposition results.  
The discrepancies between the gravity-derived Moho and seismic-constrained Moho arise from the following factors: The Moho discontinuity obtained by gravity inversion may be smoother and more gradual than that obtained by seismic measurements. On the planar surface, gravity data points are denser, and the gravity grid is filtered through a 5 \(\times\) 5 km window using the Parker inversion method. Secondly, in the basin, there may be density differences caused by a density parameter that is higher or lower than the basin sediment, which could affect the Bouguer gravity anomaly calculation. Thirdly, intense magmatic activity caused by the Hainan Plume exists. Magma from the deep mantle upwells and crystallizes in the lower crust, leading to an increase in the density of the crust. The deviation of the lower crust density would also affect the Moho inversion result. Finally, gravity-derived Moho primarily reflects its structural trend, since it is calculated using Moho density contrasts. In contrast, seismic Moho measurements typically provide the absolute value.  
The Moho uplift in the northern part of the island (Figure 7) is clearly delimited by the WWWJF on the surface. This uplift is consistent with the P-wave velocity structure inversion results, which correspond to low-velocity anomalies [11]. The Hainan Island volcanic rock area is also exposed within this uplift. All these facts support the conclusion that beneath this Moho uplift, there may be a magmatic activity hotspot caused by the Hainan Plume.