We determined a new 3-D P-wave velocity model of the upper mantle beneath eastern Tibet using 112,613 high-quality arrival-time data collected from teleseismic seismograms recorded by a new portable seismic array in Yunnan and permanent networks in southwestern China. Our results provide new insights into the mantle structure and dynamics of eastern Tibet. High-velocity (high-V) anomalies are revealed down to 200 km depth under the Sichuan basin and the Ordos and Alashan blocks. Low-velocity (low-V) anomalies are imaged in the upper mantle under the Kunlun-Qilian and Qinling fold zones, and the Songpan-Ganzi, Qiangtang, Lhasa and Chuan-Dian diamond blocks, suggesting that eastward moving low-V materials are extruded to eastern China after the obstruction by the Sichuan basin, and the Ordos and Alashan blocks. Furthermore, the extent and thickness of these low-V anomalies are correlated with the surface topography, suggesting that the uplift of eastern Tibet could be partially related to these low-V materials having a higher temperature and strong positive buoyancy. In the mantle transition zone (MTZ), broad high-V anomalies are visible from the Burma arc northward to the Kunlun fault and eastward to the Xiaojiang fault, and they are connected upward with the Wadati-Benioff seismic zone. These results suggest that the subducted Indian slab has traveled horizontally for a long distance after it descended into the MTZ, and return corner flow and deep slab dehydration have contributed to forming the low-V anomalies in the big mantle wedge. Our results shed new light on the dynamics of the eastern Tibetan plateau.

We present a new anisotropic tomographic model of the uppermost mantle around eastern Tibet using Pn traveltime data from a newly deployed temporary seismic array and recent observation bulletins of Chinese provincial networks. Our results are generally consistent with previous results but provide new insights into the dynamics of Tibetan plateau. Prominent high‐velocity (high‐V) anomalies are visible under Alashan block and Qaidam and Sichuan basins, which clearly outline their tectonic margins. A distinct high‐V zone representing the double‐sided subduction of Indo‐Eurasian plates is imaged from Lhasa block to the south of Qaidam basin. A pronounced low‐velocity (low‐V) zone is observed from Songpan‐Ganzi block to southern Chuan‐Dian diamond block, suggesting the existence of hot material upwelling there. Crustal strong earthquakes frequently occurred around high‐V anomalies or transition zones from high‐V to low‐V anomalies, suggesting that these earthquakes could be related to lateral heterogeneities in the mantle. The Pn fast direction approximately rotates around Eastern Himalayan Syntaxis, and it is tangential to the margins of Sichuan basin, suggesting that the mantle material flow of Tibetan plateau may have affected east China. In the Yunnan region to the south of 26°N, the Pn fast direction is different from SKS splitting results, indicating that the mantle lithosphere could be mechanically decoupled at certain depth below the uppermost mantle, which might be attributable to the subduction of Indian (or Burma) slab. Although the correlation between anisotropy and velocity is complicated, anisotropy strength could be associated with the pattern of velocity anomalies in the region.

In order to have a better understanding of the lithosphere formation and modification of the Tien Shan orogenic belt, we construct a well‐defined shear wave velocity model of the crust and upper mantle with full‐wave ambient noise tomographic method. High‐quality empirical Green's functions at periods of 7–200 s are extracted from the cross correlation of the vertical component of continuous seismic data at 108 stations during 2012–2014. Our tomographic results show remarkable velocity variations between and within the major tectonic units from the crust down to the upper mantle. We observe very slow upper crust beneath the Tarim and Junggar sedimentary basins. The interior of the Tarim Basin shows strong seismic heterogeneities. The high‐velocity mantle lithosphere of the Tarim Basin underthrusts northward toward the central Tien Shan. Lithosphere underthrusting could trigger intrusion of hot mantle material and partial melting, in correspondence with the prominent low‐velocity anomalies observed in the lower crust and uppermost mantle of the central Tien Shan. In contrast, the connected high‐velocity upper mantle structure from Tarim Basin across eastern Tien Shan to Junggar Basin may reflect the convergent effect between the Tarim and Junggar Basins, which consequently prevents the asthenosphere upwelling. We observe low‐velocity anomalies in the upper mantle of the western Tien Shan, indicating continental crust of the Eurasia lithosphere that has been subducted toward the western Tien Shan. The observed structural variations along the Tien Shan orogenic belt suggest different tectonic mechanisms for the lithosphere formation and modification of the three segments along strike.

To better understand the Wudalianchi intraplate volcanism and mantle dynamics in NE China, we collect abundant teleseismic waveform data during 2008 to 2018 recorded at 259 seismic stations around the Wudalianchi volcano. These stations include 148 WAVESArray portable stations, 66 NECESSArray portable stations and 45 Chinese provincial stations. Our newly deployed WAVESArray makes the station intervals of ~20–30 km around the Wudalianchi volcano. Using the minimum transverse‐energy grid‐search method, we make effective SKS splitting measurements at 192 stations. Our results show that the fast direction in the study region is mainly NW‐SE, but there are obvious contrasts within and between different tectonic units. To the east of the North‐South Gravity Lineament, around the Wudalianchi volcano, our SKS splitting measurements show a southeastward opening U‐shaped pattern in the fast direction and splitting time. Such a pattern of seismic anisotropy could be caused by horizontal and vertical flows in the big mantle wedge due to the deep subduction, long stagnancy, and deep dehydration of the Pacific slab in the mantle transition zone. The horizontal flow in the big mantle wedge could be obstructed by the thicker lithosphere under the Great Xing'an range and disturbed by hot and wet upwelling flow under the Wudalianchi volcano. Around the Nuominhe and Halaha volcanic groups, variations in the splitting parameters may also be associated with lithospheric deformation and delamination, though they are located at the edge of our study region. These results shed new light on the intraplate volcanism and mantle dynamics in NE China.