The Basic Characteristics Of Main Magnetic Field And Lithospheric Magnetic Field In Mongolia And Its Adjacent

IGRF-11main field model provided by the International Association of Geomagnetism and Aeronomy(IAGA) is used this paper to compute and draw the main magnetic field anomaly map of Mongolia and the adjacent areas(40°-55°N,85°-125°E).Analysis the characteristics of main field,dipole and non-dipole magnetic field, westward drift and long-term changes in the study area. Research shows that the main field, dipole and non-dipole magnetic field,the distributions of X and H are close, the same to Z, F and I, and they are all east-west trending, magnetic are positive,the intensity of X and H are uniformly decreasing from south to north.Z,F and I are contrast,F and D are the north-south,the strength of main field and non-dipole field are increasing from east to west,dipole field in contrast.From1900to2000,the average westward drift speed of D and Z respectively are0.066°/a and0.04°/a,significantly less than the global average west drift which is0.2°/a.The annual change rate of long-term changes is decreasing from southwest to northeast.National Geophysical Data Center (NGDC) provided NGDC-EMM-720-V3magnetic field model, which is used to calculate and draw the lithospheric magnetic values of Mongolia and its adjacent areas.The lithospheric magnetic is decomposed into multi-scale by two-dimensional wavelet transform method.Analysis the lithospheric magnetic characteristics of surface,different heights,different wavelength bands,vertical gradient magnetic anomaly.Discussed the relationship between magnetic anomaly and the regional tectonic,geophysical field.The result showedrthe distributions of AX and ΔH, ΔY and ΔD, ΔZ, ΔF and ΔI display similar distribution pattern which is given priority to ribbon shape positive and negative anomaly alternation and the overall anomaly is comparatively weak;,the whole abnormal strength is weak.1order detail of wavelet decomposition reflects shallow lithospheric magnetic anomalies, and the3to4order combination anomaly can reflects the magnetic materials in the deep lithosphere.With the ascend of height, the local attenuation velocity of magnetic anomaly trends to simple and reduces intensity.The magnetic anomaly of long wavelength band, medium wavelength band and short wavelength band become more complex, reflecting the magnetic source characteristics in the deep, middle and shallow litho sphere respectively. The vertical gradient magnetic anomaly space become smaller and the strength is weaker; the magnetic anomaly roughly reflects the characteristics of the regional structure,but gravity anomaly not fully reflects the magnetic anomaly distribution.The depth of Moho decreases gradually from west to east and magnetic anomaly and the Moho have no corresponding relation.Most earthquakes occur in the magnetic anomaly zone and its gradient zone,abnormal endpoint or turning point and weak abnormal area.Besides, the Pn velocity can’t reflect the distribution of magnetic anomaly.