Two earthquakes with magnitude larger than 7.0 occurred in 2008 and 2014 on the southwestern end of the Altyn Tagh Fault, which is located in the northwestern borderland of Tibetan plateau. Occurrences of these two earthquakes provide important insights into regional geodynamics and potential seismic risk. Layered viscoelastic model is employed in the paper to study the interaction between these two events. We find that most of aftershocks were triggered by coseismic stress produced by the 2008 Yutian earthquake, and the effect of this earthquake is insignificant on the occurrence of the 2014 Yutian earthquake. However, stress transfer by viscoelastic relaxation of postseismic deformation is in favor of occurrence of the 2014 Yutian earthquake. The coseismic and postseismic stress transfer produced by the 2014 Yutian earthquake leads to stress increasing on the western segment of the Altyn Tagh Fault. Since the occurrence time of the last major earthquake on the western segment of the Altyn Tagh Fault is tens of years ago, it should have accumulated large moment deficit on the fault segment. The Altyn Tagh Fault should be considered as a fault with high potential seismic risk.

As the most important fault of Late Pleistocene in the Lhasa area,the Nalinlaka Fault is a left-lateral thrust fault,striking NWW,dipping SSW with a high dip angle,and extending over 33km.According to the studies on the latest strata on the Nalinlaka Fault zone,this fault zone has been obviously active since Late Pleistocene and the movement left behind some geomorphologic phenomena on the earth's surface,especially at the sites of the gully west of Cijiaolin and around Xiecun village.For example,some rivers,ridges and terraces are dislocated,forming beheaded gullies,fault escarps and so on.The horizontal displacements since Late Pleistocene at the above two places are 54～87m and 20～67m,respectively.Based on the studies on the 4 trenches along the fault using progressive constraining method,we conclude that there might have occurred 5 paleoearthquake events along the Nalinlaka Fault since 70ka BP,the ages of each paleoearthquake are 8.53,54.40,<41.23,21.96,and 9.86 ka BP,and the average recurrence interval is 14.67ka.Because of the limits of trenches and earthquake events exposed by each trench,no single trench revealed completely all the 5 events.So,there may be some errors in determining the upper and lower limits of some events in this article.

Using remote sensing (RS) data, the major active faults of the eastern margin of Altai Mountains——the Hovd Fault and the Har-Nuur Fault, are studied, the detailed rupture character is analyzed from a viewpoint of topographic features, and the fault geometry and kinematics characteristics are revealed. Preliminary researches indicate the scale, slip-rate and strong seismic activity of active faults along the eastern margin of Altai Mountains are not weaker than those of the southwest’s. The Hovd Fault is of NNW-direction right-lateral strike-slip, with the length of 600 km, the maximal right-lateral displacement of river system of 9km since mid-Pleistocene(Q_p²), the possible slip-rate of 3.8～12.3mm/a,and the approximate average slip-rate of 7.8mm/a; The Har-Nuur Fault is of NNW-direction right-lateral strike-slip, with the length of 480 km. The fault is obviously active since Holocene(Qh), and there are signs of the latest faulting on the alluvial fans of Quaternary. So, the intense neotectonic movement and seismic activity on the eastern margin of Altai Mountains are related to the collision of India-Eurasia plate and maybe to the regional kinematic process.