## 2 Data and Methods
### 3D Geological Modeling Scheme
#### 2.3.1 Standard Stratigraphic Sequence  
Standard stratigraphy refers to a set of strata and their sequences with a unified temporal and spatial arrangement, capable of comprehensively representing the evolutionary process of strata in the study area. The standardization of strata in the study area is based on the standard stratigraphy, where all data involved in modeling undergo standardization under a unified constraint framework. This process provides normative modeling data and topological foundations imbued with geological significance for subsequent 3D geological modeling. Strata standardization is one of the key and challenging aspects in urban 3D geological modeling research. It is not only a decisive factor in model accuracy, but also influences the workload involved in model construction and revision. Especially for 3D geological modeling with immense data volumes, strata standardization can even determine the success or failure of the modeling effort.  
Previous research on strata standardization has largely relied on manual editing, which is not only time-consuming and labor-intensive, but also necessitates the generalization of a vast amount of geological information. For modeling involving large data volumes, the standardization of strata often requires the division of labor among multiple individuals, inevitably leading to varying degrees of subjective inconsistencies. To address this issue, this study proposes an automated strata standardization scheme based on multi-scale stratigraphic sequences, as illustrated in Figure 4.  
Firstly, a statistical analysis is conducted on the borehole database to obtain all stratigraphic types and sequences. Subsequently, from the large scale to the small scale, all stratigraphic names are uniformly revised following the order of Period (System)--Epoch (Series)--Age (Stage)--Formation. Next, the revised stratigraphic types are counted and arranged in sequence according to the geological time scale to determine the standard stratigraphy of the study area. Finally, based on the standard stratigraphy, all modeling data are standardized.  
A total of 236,000 borehole data were collected for this modeling, covering 11 \"Period (System)\" levels, 14 \"Epoch (Series)\" levels, and 26 \"Formation\" levels of strata. Given the exceptionally thin Quaternary unconsolidated strata in the study area, coupled with the similarity in genesis and lithofacies characteristics across different Quaternary epochs, the modeling of Quaternary strata in this research is confined to four \"Epoch\"-level strata: the Holocene (Q\(\mu\)_I_), Late Pleistocene (Q\(p\)_3_), Middle Pleistocene (Q\(p\)_2_), and Early Pleistocene (Q\(p\)_1_), due to the insufficient modeling data required to achieve a \"Formation\"-level refinement.  
With regard to the bedrock, considering the intricate geological tectonic evolution history in the study area and the significant variations in genesis, spatial structural characteristics, and lithology among different \"Formation\"-level strata, the modeling of bedrock strata necessitates a refinement to the \"Formation\"-level to comprehensively capture the 3D spatial structural features of the bedrock strata in the entire study area. The final determination of the standard stratigraphy in the study area includes 4 Quaternary strata and 22 bedrock strata, as detailed in Figure 5.