Uppermost Mantle Velocity and Anisotropy Beneath Mongolia and Its Adjacent Regions

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

In order to image the lateral variations of seismic velocity and anisotropy within the uppermost mantle underneath Mongolia and the adjacent regions, travel times of 198,390 Pn arrivals from earthquake at regional distances are inverted. Our model resolution width of 2°×2° are achieved in the study region, with the capacity of distinguishing small-scale geological features. The average velocity of the mantle lid is 8.18 km/s, substantially faster than the global average. We also measured azimuthal anisotropy in the upper and lower mantle lid by grouping the travel time data into two different epicentral distance ranges. Strong lateral variations in Pn velocity of the uppermost mantle underneath the most active zone of Baikal rift is presented. In the Southern and Northern Baikal rift, clear low Pn velocity is observed, whereas Pn velocity is high in the Central Baikal rift, indicating a strong variation in the amount of lithospheric thinning that has taken place across the Baikal Rift. The obvious depth dependence of Pn anisotropy models within the upper mantle beneath the Hentey Mountains suggests different origins for different fabrics; the deeper anisotropy likely results from asthenospheric flow while the shallower fabric may result from preserved lattice preferred orientation (LPO) anisotropy in the uppermost mantle. Depth-dependent anisotropic structures and significantly low velocity are found beneath the Tien Shan orogenic belt, indicating that the lithospheric mantle is thinning due to delamination or a local asthenospheric upwelling.

Presenting Author: Jing He

Authors