SUMMARY

Investigation on the deep geoelectric structure of the Lai Châu - Điện Biên fault zone by magnetotelluric sounding

Lê Huy Minh, Phạm Văn Ngọc, Danièle Boyer,
Nguyễn Ngọc Thủy, Lê Trường Thanh, Ngô Văn Quân, G. Marquis

This paper presents the magnetotelluric sounding results in the Điện Biên Phủ basin in order to have the deep geoelectrical image of the Lai Châu - Điện Biên active fault. The impedance tensor decomposition by Groom & Bailey shows that the geoelectrical structural property of the Điện Biên Phủ basin is complicated; the strike direction is North-South, but varies from area to area in about ±20^o; the twist and shear angles are <±20^o, but in some areas they reach 40^o. The magnetotelluric geoelectrical section obtained by 2D inversion shows that the Lai Châu - Điện Biên fault dip in the Điện Biên basin is about 90^o, and this fault cuts through the terrestrial crust. The existance of conductive zone along the fault from the depth of about 10 km to more than 30 km may be explained by an abundant fluid content (because free water can be released from hydrated minerals during metamorphism) and partial melting in the lower crust. The lower crut from a depth of 20-30 km to the Moho could be in the ductile regime. The MT results obtained in this paper yield the electrical image of the Lai Châu - Điện Biên active fault and confirm the important role of the MT data in seismotectonic studies.

Ngày nhận bài: 15/9/2008

Người biên tập: Trần Văn Trị