A palaeoearthquake event and its age revealed by the travertine layer along the Litang fault in the southeastern margin of the Qinghai-Tibetan plateau

Abstract

The Litang fault (LTF), located in the southeast of the Qinghai-Tibetan Plateau, is known for its high level of present-day seismicity, whereas its Pleistocene activity has been scarcely documented. This study focused on a tract of banded travertine deposits precipitated from thermal waters along the NW–SE-trending LTF trace. The role of travertine deposits in recording neotectonic activity has been studied by identifying their internal structure. Typical soft-sediment deformation structures observed within the banded travertines include micro folds, liquefied breccia, and liquefied diapirs. These deformed structures, which are restricted to a single unit separated unconformably by undeformed layers, can be traced for tens of meters, indicating that they were formed by seismic shaking triggered by LTF activity. The deformation of the banded travertine layers is attributed to the combined effects of seismic shaking, liquefaction, and fluidization, and it can be related to a paleo earthquake event with a magnitude of M_S ​> ​5. The U-series ages obtained from the banded travertine deposits perturbed by the earthquakes are in the range of 130.59–112.94 ka, indicating an important fault-assisted neotectonic activity that occurred during the Middle–Late Pleistocene. Analysis of such structures, in combination with the use of U-series dating methods, can yield a reliable timing of neotectonic activity and provide new evidence for understanding the seismotectonic setting of the Litang area.