## 1 Introduction  
The Tibetan Plateau and its adjacent area are the primary part of the intercontinental deformation zone in the India-Eurasia collision system. It is composed of the Tibetan Plateau and the Pamir Plateau. The former is the youngest plateau in the world, while the latter exhibits geodynamic processes comparable to those of the Tibetan Plateau [1; 2; 3; 4; 5; 6; 7]. The Cenozoic tectonic evolutionary processes and kinematic characteristics of the Himalayan-Tibetan orogenic zone are mostly expressed by the development of complex fault systems, folds and blocks [8; 9; 10; 11; 12; 13; 14; 15; 16; 17]. How these structures accommodate the convergence of the Indian and Eurasian plates is the key to understanding both the collision process between the two plates and the mechanisms of tectonic evolution [18; 19; 20; 21]. There is long-term controversy regarding the roles of active faults in the process of tectonic evolution. Some scholars argue that active faults are very important because they separate the crust into a series of rigid blocks, and crustal deformation of the study area is mainly accommodated by activity along these major faults [22; 23; 24; 25]. Others argue that the principal characteristics of crustal deformation in the study area are continuous and widely diffused. Active faults have a very limited role in adjusting the process of present-day crustal deformation [26; 27; 28; 29]. Therefore, the detailed spatial distribution of active faults and structural discontinuities in the lithosphere is the key to understanding the role of active faults in the process of regional crustal deformation and the mechanisms of tectonic evolution.  
At present, the main methods of deep tectonic exploration are geomagnetic, seismic wave, geothermal flow and gravity [30]. Among these, gravity has the advantages of higher efficiency, lower cost and larger observation scale. With the rapid development of satellite gravity technology, the accuracy and efficiency of deep tectonic exploration based on gravity field have greater development potential. The Earth's gravity field is a superposition of geological gravity effects at different depths and with different properties. As the crustal lithosphere and upper mantle make up only a small part of the Earth, their gravity is bound to be strongly perturbed by the background gravity field, making them difficult to identify. Therefore, it is necessary to decompose the observed Earth's gravity field. Wavelet multiscale analysis can decompose the gravity field data into an approximation and details of each order. The approximation corresponds to the background gravity field. Wavelet details with different power spectra could be identified as gravity signals from different depths [31; 32].  
Therefore, we have used the wavelet multiscale decomposition technique to distinguish the contributions of Bouguer gravity anomalies at different depths [31; 33], which can effectively reveal the lateral heterogeneity of the crust at that location. The location of fracture zones within the crust and the boundaries of different geological bodies are usually accompanied by significant density mutations or density discontinuities, resulting in a greater rate of change in gravity anomalies at these locations. We have therefore calculated the total horizontal derivative (THD) of the Bouguer gravity anomaly for each layer as a numerical indicator of the spatial rate of density change and have shown the spatial distribution of active faults and structural discontinuities at different depths in the study area.