SUMMARY

Bắc Yên M4,7 and Mai Sơn M4,2 earthquakes in November 26, 2009

Cao Đình Triều, Ngô Gia Thắng, Mai Xuân Bách,

Phạm Nam Hưng, Bùi Anh Nam

In this paper, the authors present some new results about earthquakes and tectonic investigation in the source area of Bắc Yên and Mai Sơn November 26 earthquakes. On the basis of the obtained results some conclusions can be made:

1. The Bắc Yên earthquake occurred in November 26, 2009 at 11:47:02 AM (local time), with the location of the epicenter: lat. 21.29 N and long. 104.27 E; focal depth: 15 km; and M_S = 4.7. This earthquake occurred in the Bắc Yên - Phú Yên Fault zone, with the following parameters: depth of penetration: 20 km; dip angle: 70-80⁰.

2. The Mai Sơn earthquake occurred in November 26, 2009 at 20:59:01 PM (local time), with the location of the epicenter: lat. 21.25 N and long. 104.25 E, focal depth: 15 km; and M_S = 4.2. This earthquake occurred in the Bản Hộc - Bản Chen Fault zone, with the following parameters: depth of penetration: 15 km; dip angle: 50-70⁰.

3. The great contrast of tectonic movement between structural blocks of West Bắc Bộ in present day, especially between strongly uplifted blocks, such as Tú Lệ - Phan Si Pan, Tạ Khoa Blocks, and Sông Đà, Mường Bú - Pa Vinh basins, is the reason of the seismic activity in the studied area.

4. The maximum magnitude of earthquakes possibly to occur in the studied area can be predicted as follows: M6.8 for the Pa Vinh and Bắc Yên - Phù Yên Fault zone; M6.6 for Bản Cua Mường - Bản Vàn Fault zone; M6.5 for Bản Hộc Fault zone; and M6.3 for Bản Vàn Xay Fault zone. The earthquakes occurring in November 26, 2009 are not the biggest. The magnitude of the maximum earthquake possibly to occur in this area can reach the value of 6.8.

Người biên tập: Trần Văn Thắng