Study On Scientific Drilling On Wenchuan Earthquake Fault Zone By MT

May 12, 2008 Wenchuan earthquake shocked the world, to people's lives and property it was enormous disaster. Passed and two years ago more than 512 earthquakes, aftershocks are continuing, the unique event of an earthquake, the disaster also brought to people the opportunity of science. Earthquake occurred in the Longmen mountain fault zone, in the fault zone on the implementation of scientific drilling, it is very important for the study of earthquake mechanisms, continue to monitor the aftershocks and the study of Longmen mountain.Scientific Drilling is based on multi-disciplinary observation and test's research, to reveal the deep earthquake fault zone composition, structure and structural properties, remodeling fault zone physical and chemical processes, in order to provide useful information on earthquake early warning. Core drilling can be more intuitive with the underground rock composition, but because of the difficulty and high cost of drilling, well drilling as a result is elusive, so single well for the study of complex geological profile is slightly thin. In the dramatic mountain terrain, seismic wave can't be received easily; DC and time domain sounding are limited by the above reason. Magnetotelluric (MT) can overcome many above factors, to solve certain well site near underground electrical structure within the depth of the fault in the ground characteristics such as the extension and angle. Drilling is the "point" data, Magnetotelluric is the "side" information, "point" can guide the "side" and "side" can serve the "points". They are combined to solve not only the construction of the Longmen mountain deep fault and remodeling the physical process, but also can promote the development of geophysics.To fault (crack) distribution due to differences in physical properties of the premise, the lines should be vertical to the main fault as far as possible, and study the tendency towards deep changes. Three basic Magnetotelluric sounding profiles identified four boreholes near site features underground electrical structure. Qualitative analysis of the frequency of apparent resistivity, phase characteristics, provides the basis for the inversion and interpretation. This also added a new test of the apparent resistivity (Basokur) inversion imaging effects, Carney explained ATV resistivity inversion to provide a reference. 1st and 2nd drilling (WFSD-1, WFSD-2) inversion profile of interpreting, cross-reference verification, precise electrical construction. Comprehensive geological and geophysical interpretation of a key section in Hongkou Township in Dujiangyan central Longmen mountain fault situation the structural characteristics, for further research to provide geophysical basis for the central fault, and the results are more consistent with the actual drilling. For the special geological features (octagonal temple to be at the central Longmen mountain fault zone, the area is brittle - ductile zone, on the plate for the Peng-guan complex on the lower plate for the clastic rock), on the Magnetotelluric inversion profile explain the proposed new point of view: high and low resistance contact with the fault zone, the division of fault plane should be close to the high impedance side. Respectively, we can demonstrate that the view is correct from the numerical simulation and geology. WFSD-3, 3P are on the Longmen mountain fault zone before middle faults, the frequency diagram and inversion results were complicated geological activities in the region early, it is more associated with secondary fracture, showing the characteristics of the Longmen Mountain imbricate thrust faults.Integrated Scientific Drilling, Shi-Fang and Han-Wang Magnetotelluric sounding profiles, inferred on the Longmen Shan fault zone exposed in the section angle are larger, the increase of dip with depth decreases, and in the ground 1-2Km the angle changes faster with the angle reducing about 15°-25°, with the extension of the deeper depth changes will slow down gradually. In fact, this fault dip with depth smaller surface phenomenon, they are also important features for Longmen Mountain imbricate thrust faults.