# Three-Dimensional Modeling of the Xichang Crust in Sichuan, China by Machine Learning
## 4 Morphology of Active Fault
### Initial Fault Model  
By collecting carefully the distribution characteristics of earthquakes and the deep faults exposed in this region, we have analyzed eight deep fault zones, such as Longmanshan fault, Xianshuibe fault, Anninghe fault, Daliangshan fault, Xiaojianghe fault, Qinghe fault, Mopanshan fault, and Zemuhe fault. These faults occurred in the intermediate transition position of the Xianshuibe-Xiaojiang fault system and spread in a spindle shape near Shimian, and cut the Xichang area into multiple structural units. By referring to the basement fault data published in CSES [4], combined with the latest research results and 1:500,000 geological map of the region, the fault linear feature and occurrence information were extracted to constrain the morphological fault characteristics on the shallow surface. The details of the initial model parameters are shown in Table 2.  
The focal mechanism is very important in describing geometric characteristics of faults, evaluating stress disturbance and evaluating aftershock mode. It contains the dislocation information of source rupture, and can also constrain the occurrence of a deep fault plane and distinguish the fault dislocation type. [PERSON] et al. (2019) [7] analyzed the spatial distribution characteristics of the tectonic stress field in this area by using the focal mechanism solution and considering that the regional earthquake fault type is left-lateral strike-slip type. Along the Xianshuibe-Xiaojiang Fault Zone on the east boundary of the Sichuan-Yunnan block, the principal compressive stress gradually changes from NWW to NW with a clockwise rotation of about 50\({}^{\circ}\). Moreover, the angle between the principal compressive stress axis and the fault strike on the east boundary remains nearly the same [7]. Because of one of the interfaces in the focal mechanism, the solution may be approximately parallel to the fault plane. Therefore, we can extract the focal mechanism  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Faults** & **Length (km)** & **Strike** & **Dip** & **Dip Angle** & **Fault Property** & **Data Sources** \\ \hline Xianshuibe Fault (Moxi) & 600 & 340\({}^{\circ}\) & 70\({}^{\circ}\) & 85\({}^{\circ}\) & Strike-slip & [PERSON] et al., 2014 [36] \\ Longmanshan Fault & 600 & 3\({}^{\circ}\) & 273\({}^{\circ}\) & 80\({}^{\circ}\) & Thrust & Lu, 2019 [5] \\ Xiaojinhe Fault & 300 & 45\({}^{\circ}\) & 315\({}^{\circ}\) & 70\({}^{\circ}\) & Strike-slip & [PERSON] et al., 2014 [36] \\ Qinhe Fault & 200 & 5\({}^{\circ}\) & 275\({}^{\circ}\) & 70\({}^{\circ}\) & Strike-slip & Lu, 2019 [4] \\ Mopanshan Fault & 300 & 178\({}^{\circ}\) & 268\({}^{\circ}\) & 83\({}^{\circ}\) & Strike-slip & [PERSON], 2019 [4] \\ Anning Fault & 300 & 173\({}^{\circ}\) & 83\({}^{\circ}\) & 80\({}^{\circ}\) & Strike-slip & [PERSON] et al., 2007 [34] \\ Zemuhe Fault & 300 & 330\({}^{\circ}\) & 45\({}^{\circ}\) & 70\({}^{\circ}\) & Strike-slip & [PERSON] et al., 2014 [36] \\ Daliangshan Fault (N) & 300 & 160\({}^{\circ}\) & 250\({}^{\circ}\) & 55\({}^{\circ}\) & Strike-slip & [PERSON] et al., 2014 [36] \\ Daliangshan Fault (S) & 300 & 180\({}^{\circ}\) & 270\({}^{\circ}\) & 55\({}^{\circ}\) & Strike-slip & [PERSON] et al., 2016 [38] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Initial parameters of the fault model.  
solution within 5 km of the fault by means of buffer analysis, combined with the extended azimuth of the fault plane. We select the focal node information consistent with the fault plane (Table 3), and by doing so one can restrict the position of the deep fault plane.