Recent Tectonic Movements Along the Coastal Zone of Tuy Hoa Area (Central Vietnam) and Its Significance for Coastal Hazards in the Case of Sea Level Rise

Abstract

The Tuy Hoa area is part of central coastal zone of Vietnam, which is commonly exposed to natural calamity including several types of geological hazards. The area is underlain by dominantly magmatic rocks and subordinated sedimentary units, which were formed during the Paleozoic to Early Cenozoic. These were variably covered by thin Cenozoic sedimentary cover including subordinate Quaternary volcanics and predominant fluvial, marine and aeolian deposits, which overlying most part of the area. All of the crystalized rocks and unconsolidated sedimentary units are variably affected by regional tectonic deformation, including extensive fracturing, faulting, subsidence and uplift, which were resulted from multiphase paleotectonic and neotectonic activities. Recent recorded earthquake also indicates active ground movement in the area. Local structural elements can be documented on the basis of numerous geological and morphological evidences and qualitative dating of the displaced Quaternary materials, which revealed significant local uplift, subsidence or displacement during recent time in the study area. The northern part of the area has been uplifted at the rate of at least 0.17 mm per year. In contrast, some areas such as Ban Thach River basin and Hao Son Lake are subsided significantly, in which Hao Son Lake area has subsided at the rate of ca. 0.96 mm per year. Incorporating the local uplift and subsidence with the predicted regional sea level rise scenario during next 100 years, most of the coastal area in the north of Tuy Hoa area will be slightly flooded under maximum 0.60 m of sea level rise compared with the prediction of regional ca. 0.77 m of sea level rise. In contrast, the tectonic subsidence will lead to serve flooding by sea water in which Hao Son Lake area will be submerged at least to the depth of 0.9 m and Ban Thach River basin will be also flooded deeply under the sea level during next 100 years. Other hazards including landslides, beach erosion are locally developed along the coastal zone and are controlled by bedrock inhomogeneity, zones of structural weakness, and active tectonic movement. Thus, basement architecture and bedrock fracturing within an area of active tectonic regime are major factors to influence landscape morphology and geological hazards in the coastal zone. Therefore, accurate identification and proper documentation of regional and local structural elements must be properly addressed in order to predict natural hazards, especially in the context of a predicted global sea level change.