Integrated Geophysical Survey In Former Mountain Fracture Zone Of Longmen Mountains

Fault is the main reason to induce earthquake, and also is a major factor for destruction of city buildings and facilities. Therefore, detection and study of fault is of great importance which can provide important data to predict seismic activity and for housing construction to effectively avoid the faults.In this paper, gravity, magnetic, seismic methods, high-density resistivity method, magnetotelluric (MT) sounding method etc. were used. Detecting a series of measuring lines at part of fault at the middle of fault zone before the Longmen Mountains, including Dujiang Weir, Bailu, Hanwang, An county etc. areas, advanced data processing and interpretation was applied to analysis of data in survey area, combined with previous geological research results, all kinds of geophysical exploration methods fully play advantages to seek the fault at the middle part of the fault zone before Longmen Mountains or the location of concealed faults in the surface and speculate the deep fault tectonics, and analysis of fault activity laid the basis for risk analysis for the city.This paper first described the basic concepts and classification of fault, and introduced a variety of geophysical methods in the role of fault detection. Gravity and magnetic profiles can be measured to find fault or the location of concealed faults in the surface; high density resistivity and shallow seismic methods can be to study the morphological characteristics of fault and fault activity law near the surface; MT method can study the deep structure and activities law of fault.Focuses on the study of the basic principles for the various geophysical exploration methods, for fault model, they were used, such as gravity anomaly, high density resistivity anomaly, MT anomaly and shallow seismic reflection anomaly forward modeling. Systematic analysis was used for the gravity profile anomalies and surface anomaly, characteristics of high-density resistivity fault anomaly, MT apparent resistivity and phase section features, characteristics of the apparent resistivity and phase curves at faults and both sides of faults, and the shallow reflection seismic anomaly cross-section morphology.The integrated geophysicalmethod used at the middle of fault zone before Longmen Mountains detection is a key point in this paper, of which each of the regional geological overview, each exploration methods used in the surveyed area, the used detection instruments were introduced, and finally data for each measured area was processed, combined with geological data to interpret the final results of various exploration methods. And detection was used to part of fault location at the middle of the fault zone before Longmen Mountains and deep structural patterns were inferred. The end result with the surface outcrop has a very good correspondence. It also was showed that a variety of geophysical methods to detect the fault play a different role, reflecting integrated geophysicalmethod in investigation of underground geological structure is very effective.