Terrain Proxy-Based Site Classification For Seismic Zonation In North Korea Within A Geospatial Data-Driven Workflow

Numerous seismic activities occur in North Korea. However, it is difficult to perform seismic hazard assessment and obtain zonal data in the Korean Peninsula, including North Korea, when applying parametric or nonparametric methods. Remote sensing can be implemented for soil characterization or spatial zonation studies on irregular, surficial, and subsurface systems of inaccessible areas. Herein, a data-driven workflow for extracting the principal features using a digital terrain model (DTM) is proposed. In addition, geospatial grid information containing terrain features and the average shear wave velocity in the top 30 m of the subsurface (V-S(30)) are employed using geostatistical interpolation methods; machine learning (ML)-based regression models were optimized and V-S(30)-based seismic zonation in the test areas in North Korea were forecasted. The interrelationships between V-S(30) and terrain proxy (elevation, slope, and landform class) in the training area in South Korea were verified to define the input layer in regression models. The landform class represents a new proxy of V-S(30) and was subgrouped according to the correlation with grid-based V-S(30). The geospatial grid information was generated via the optimum geostatistical interpolation method (i.e., sequential Gaussian simulation (SGS)). The best-fitting model among four ML methods was determined by evaluating cost function-based prediction performance, performing uncertainty analysis for the empirical correlations of V-S(30), and studying spatial correspondence with the borehole-based V-S(30) map. Subsequently, the best-fitting regression models were designed by training the geospatial grid in South Korea. Then, DTM and its terrain features were constructed along with V-S(30) maps for three major cities (Pyongyang, Kaesong, and Nampo) in North Korea. A similar distribution of the V-S(30) grid obtained using SGS was shown in the multilayer perceptron-based V-S(30) map.