The complexity feature of crust-mantle boundary in Zhangbei seismic region and its tectonic implication

Abstract

The PmP waveform data obtained from a deep seismic sounding profile, which ran through Zhangbei seismic region, were processed by means of both seismic wave complexity coefficient and frequency spectrum analysis methods, and the complexity characteristics of crust-mantle boundary beneath the studied area and its adjacent region were determined. The results show that the place below epicenter can be taken as boundary, the northern side of which is Inner Mongolia axis with small complexity coefficient and the southern side of which is Huai’an basin with large complexity coefficient. The different spectrum patterns at the two sides of the epicenter were inferred from spectrum analysis. In the epicentral area, there have been multi-period magmatic eruptions since Meso-Cenozoic and craters exist at the surface. From the velocity imaging of middle and upper crust in Zhangbei seismic region it can be found that there are crustal low velocity bodies around the craters and also there are low velocity zones, which went into deep crust. It is suggested that the distinct zones of crust-mantle boundary complexity may be the margin, where the magma had intruded due to magma activity in Meso-Cenozoic. The southern side with large complexity coefficient is deep magmatic activity area and the northern side with small complexity coefficient is stable crust-mantle tectonics. The difference of crust-mantle complexity provides deep background for the development of strong earthquake.