Faulting and folding of basement rocks together accommodate convergence within continental orogens, forming complex zones of intraplate deformation shaped by the fault interaction. Here we use the river terraces along the Dongda river to examine the tectonic deformation patterns of the hinterland and the foreland of the eastern North Qilian Shan, a zone of crustal shortening located at the northeast margin of the Tibetan Plateau. Five Late Pleistocene-Holocene terraces of Dongda river are displaced by three major reverse faults: Minle-Damaying fault, Huangcheng-Ta’erzhuang fault, and Fengle fault, from south to north. Based on displaced terrace treads, we estimated vertical slip rates along the Minle-Damaying fault as 0.7–1.2 mm/a, and along Fengle fault as 0.5–0.7 mm/a. Deformed terraces suggest additional uplift of ~ 0.2 mm/a through folding of the Dahuang Shan anticline. Inhomogeneous uplift of the intermontane basins between the Minle-Damaying fault and the Dahuang Shan anticline indicates a 0.9 ± 0.2 mm/a uplift rate along the Huangcheng-Ta’erzhuang fault. Kinematic modeling of this thrust system shows that deformation propagated northward toward the foreland along a south-dipping 10° décollement rooted into Haiyuan fault at the depth of 20–25 km. This system accommodates 2.7–3.8 mm/a total crustal shortening rate. We suggest this broad thrust belt and the relatively high rate of shortening within this part of the eastern Qilian Shan is as a result of the oblique convergence along a restraining bend of Haiyuan fault system. The elevated shortening rate within this area indicates high potential seismic hazard.

To explore the repeating mud volcanoes influences on the seismicity behaviors, we measured the spatial distribution z and b value changes with the time in the mud volcanoes developing area. We find a weak correlation between the b-z values and the mud volcanoes. Generally, the z-values anomalies of the mud volcanoes area show unchanged negative values and indicate the seismic quiescence before a strong earthquake, while the b-values show the frequently periodicity fluctuations around the value of 0.5. It may indicate the conjunct triggering relationships between the mud volcanoes and earthquakes stuck. We infered that the mud volcanoes eruptions help to partition and release part of the regional stress accumulation from the earthquake seismogenic structures, thus balanced the local stress in the strata. Keywords: Mud volcano; SW Taiwan; coulomb stress change; b-z-value; conjunct triggering relationship

Northward indentation of the Qaidam Basin (QB) and southward underthrusting of North China Craton (NCC) lithospheric mantle beneath the Qilian Shan (QLS) are two frequently-cited geodynamic modes for interpreting the evolution of the northeastern Tibetan Plateau. We here aim at understanding the roles of these two dynamic processes in crustal deformation and how they interact during plateau growth in the NE margin by using sandbox experiments that simulate the convergence of the QB-QLS belt through indentation and underthrusting type of boundary conditions individually, alternately or synchronously. Results illustrate that 1) Underthrusting beneath the QLS favors a gently-tapering, one-sided thrust wedge only above the downgoing slab. 2) Indentation of the QB promotes the occurrence of doubly vergent convergent belts with two oppositely-tapering thrust wedges spreading from the slab boundary. 3) Diverse convergence histories lead to distinct deformation patterns for the modelled convergent belts. However, only when indentation and underthrusting occurred synchronously, the modelled thrust wedge resembles current QB-QLS belt in terms of growth sequence, wedge geometry and deformation localization pattern, indicating that bidirectional compression mode maybe the best approximation for the late Cenozoic northeastern Tibetan Plateau. Our experiments further reveal that shift of boundary conditions like alternation of geodynamic drivers and encountered foreland buttress, would result in limited changes in uplift rate of individual structures. Instead, switch between different structural evolutionary stages causes more pronounced variations and should be noted when interpreting thermochronologic data from the northeastern Tibetan Plateau.