Abstract: Numerous hypocenters’ spatial data were used to characterize the crustal structure in the southern section of the North-South seismic belt. The results show a variation, corresponding to the tectonic features of the distribution of hypocenters’ density along latitudes in study area. According to the Hypocenters’ density distribution on the profiles, seismogenic layers distribute widely in middle and lower crust. Spatial distribution of hypocenters can also be considered as a geophysical feature of continental crust. It is found that the seismogenic layers are usually at the top of low velocity and resistivity layers, which are assumed to be detachment shear zones between ductile lower crust and brittle upper crust. The low velocity and resistivity layer are possibly related with partial melting, rheological fluid containing etc. Seismogenic layer is corresponding to the hard brittle upper crust, which is prone to result in sudden ruptures and earthquakes. As a result, the more active of the low-velocity & resistivity layer, the higher the density of hypocenters of the seismogenic layer. Tectonic activities, including tremender earthquakes, are controlled by differential movements between different layers and blocks in the crust of southern section of the North-South seismic belt, and the most important factor is the differential movement between flowable lower crust and brittle upper crust which occurred in the detachment shear zone in middle crust.

Key words: crust structure, hypocenter distribution, seismogenic layer, north-south seismic belt, tectonics