SUMMARY

ESR dating of fault gouge in the midstream Thu Bồn river: New evidence of fault movements during late Pleistocene-Holocene

Nguyễn Quốc Hưng, Vũ Anh Đạo, Ngô Xuân Thành, Trần Thanh Hải, Đặng Văn Bát

The main course of the Thu Bồn river system flows through Nam Trà Mi, Bắc Trà Mi, Hiệp Đức, Nông Sơn, Duy Xuyên, Điện Bàn, Hội An and outlets to the sea at Cửa Đại. The river system has been changing drastically its flow in recent years, causing landslide, sedimentation, droughts and floods. The The course of river system is changed due to different causes, of which, endogenous geological activities such as tectonic displacement of the active faults play an important role. Field studies have identified a number of fault systems that exist in the study area, including many large systems, spanning dozens of kilometers across the entire study area. Dynamic analysis shows that four fault systems in the area are part of a regional Riedel right-sided slip system. Three samples in the fault gouge of the fault systems that cut through the midstream Thu Bồn river were collected to determine their faulting age by Electron Spin Resonance (ESR) method, yielding 10282 years, 15409 years and 17689 years. These results show that the movement of the fault systems in the midstream Thu Bồn river occurred during Late Pleistocene - Holocene, in which the last active phase occurred at least 10,000 years ago.

Keywords: Quảng Nam; Thu Bồn river; ERS method; active Fault