# Crustal Structure of Hainan Island and Surrounding Seabed Based on High-Resolution Airborne Gravity
## 6 Conclusions  
In this study, we investigated the crustal structure of Hainan Island and surrounding seabed using newly acquired airborne gravity data. Multiscale wavelet analysis, the Parker-Oldenburg inversion method, and the radial averaged logarithmic power spectra analysis method were used to extract gravity anomaly information for crustal deformation and density structure. Through combining the decomposed result with seismic data, the relationship between the crustal structural architecture and seismicity patterns is also discussed. The key findings are summarized as follows:  
1. The results of the wavelet-based multiscale analysis reveal the crustal structure at depth. The results show that there are NE-trending banded anomalies in the middle and lower crust, interpreted as remnants of the subduction of the Mesozoic paleo-Pacific plate subduction. These findings provide critical evidence for Hainan Island's tectonic evolution within the Paleo-Pacific tectonic domain system during the Mesozoic era.
2. The Moho depth is obtained by gravity data inversion. The average depth of the Moho surface in the study area is about 24.94 km, and the Moho surface fluctuates greatly in the range of 16.2-31.4 km. There are two significant Moho depression areas and three local uplift zones of the Moho surface, among which the Qiongbei Moho uplift exhibits a direct spatial correlation with the Hainan mantle plume. This specific uplift is interpreted as a surface manifestation of the upper mantle material ascent driven by plume-related thermochemical processes.  
Figure 8: Schematic plot of seismogenic tectonic environment model of northern Hainan Island modified from [20; 59; 60]. The black circles denote earthquakes, and the gravity Moho depth derives from Figure 7. The surface is part of D5 covered with faults and the earthquake epicenter. HNI, Hainan Island; QZS, Qiongzhou Strait; LQP, Leiqiong Peninsula. The white line represents the coastline.  
3. The results of the decomposed gravity anomalies and natural earthquake distribution reveal that the regional seismic activity is primarily controlled by the left-lateral strike-slip motion of the YGHF and thermomechanical processes associated with the Hainan Plume. Most of the seismic activities in the north and southeast of Hainan Island may be related to the deep-sourced mantle upwelling of the Hainan Plume along the Mesozoic fault gap.  
We conclude that the airborne gravity survey is an important remote sensing method to provide a new view of revealing the deep crustal structure across both offshore and onshore regions.  
Conceptualization, X.L., X.Z., W.Z. and H.W.; data curation, X.L. and R.W.; formal analysis, X.L. and X.Z.; funding acquisition, X.Z. and H.W.; investigation, X.L.; methodology, X.L., X.Z., W.Z. and Y.S.; supervision, H.W.; visualization, X.L. and R.W.; writing--original draft, X.L.; writing--review and editing, X.L. and G.Y. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Programs of China Geological Survey (Grant No. DD20243057; DD20221715; DD20240090; DD20243216) and the National Natural Science Foundation of China (Grant No. U2344203).  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.  
We are grateful to the editors and anonymous reviewers for their constructive comments on the manuscript.  
The authors declare no conflicts of interest.