Geoblocks Recognition and Delineation of the Earthquake Prone Areas in the Tuan Giao Area (Northwest Vietnam)

The goal of the paper is to reveal the hierarchical block structure in the Tuan Giao area (Northwest Vietnam) and, on that base, to identify areas prone to earthquakes with M ≥ 5. Four large geoblocks of the second rank have been delineated on the basis of the joint analysis of geological, geophysical, geomorphic, and remote sensing data. The second rank geoblocks have been divided into smaller sub-blocks of the third rank. The recent geodynamics of the geoblocks have been characterized using geomorphic, seismological, gravity, and GPS data.The system of the delineated geoblocks is viewed as the Geodynamic Blocks model. The areas prone to earthquakes with M ≥ 5 have been identified using the pattern recognition algorithm CORA-3. The objects of the recognition were defined as circular areas, where boundaries of the geoblocks intersect each other. The recognition results confirm high seismic potential of the study region and provide information on potential earthquake sources for seismic hazard assessment: a number of boundary intersections have been identified as areas prone to earthquakes with M ≥ 5, where events of such magnitude have not been recorded up to date. Mordern geothermal activity and anomalies of dissolved methane (up to 10000 nL/L), helium and hydrogen in the hot mineral water springs prove high permeability of the study area and its active seismo-tectonic state.