The Crustal Structure Beneath Leiwuqi-Yushu-Maduou Region From Gravity Inversion

Two-dimensional gravity modeling is applied to the contact of the Bayankala segment and the Qiangtang segment as a contribution to solving structural and tectonic relations in this area characterized by very complex relations. The purposes of this study are inversing the crustal interfaces and discussing the causes of Yushu earthquake. An interpretation procedure, which improves the resolution of gravity modeling by the use of seismic refraction data, has been developed. On the Leiwuqi-Yushu-Maduo profile, active seismic studies gave first, but not in all details consistent, structural results useful for supporting gravity modeling. A2-D gravity modeling was carried out on the profile for the purpose of determining the structural relations. Gravity interpretation was based on a gravity line (from Leiwuqi to Yushu to Maduo, surveyed in2010). The anomalies range from-520mGal (Leiwuqi) to-470mGal (Maduo). The Model comprises four layers-sediments and three heterogeneous layers in the crystalline crust. Different from traditional methods of inversing the multi-layer density interface, this paper presents a new method of simultaneous inversion in space domain. Using a novel approach based on the smooth constraint of density distribution, this procedure achieved the same effect as field separation but preserved the long wave length components of the shallower interface. The computed gravity anomaly fits the low frequency part of the observed one, which is controlled by variations in crustal interfaces. The final model clear up the crustal structure of Leiwuqi-Yushu-Maduo profile and can give several geological evidences.