SUMMARY
Features of main faults in Quỳnh Nhai - Than Uyên area, West Bắc Bộ
Vũ Văn Chinh, Nguyễn Ngọc Thủy, Bùi Công Hóa
The Quỳnh Nhai - Than Uyên area belongs to the West Bắc Bộ tectonic region,
where the main structure is of northwest - southeast trend. The use of a complex
of tectonic structural methods allows to
determine that in this area, there are two main faults including the Sông
Đà fault of northwest - southeast direction and the submeridian Than Uyên fault.
These are major faults and appear to be the boundary of structure zones.
The activities of Sông Đà fault began since Late Paleozoic, and of Than Uyên
fault since Late Jurassic; they are continuing up to present time. The Sông Đà
fault has the slip surface dipping northeastward (70-800),
whereas the Than Uyên fault has vertical slip surface or dipping eastward.
Neotectonic activities of both mentioned faults consist of two phases in
strike-slip stress field. In Eocene-Miocene phase the Sông Đà fault shown to be
a left-lateral strike-slip, and the Than Uyên fault was
a thrust fault playing the role of west boundary of Tú Lệ Massif. In
Pliocene-Quaternary phase the Sông Đà fault seems to be right-lateral
strike-slip and the Than Uyên fault shown as an extension zone.
Recent activities of the Sông Đà fault have been leading to the exposure of
mineral water and weak earthquake, and activities of the Than Uyên fault have
been causing land slide in many localities, especially in the He Luang - Than
Uyên band.
Người biên tập: Lê Như Lai