The first part of my report on the field work that I did in Kazakhstan this year focussed on the stuff we had done in the South. Here is part II which is all about the Dzhungarian Fault. You’ve never heard about this fault? That’s easily possible. There are only very few papers that deal with this fault. In the 1960s Soviet geologist V.S. Voytovich published results from extensive field work on this fault (Voytovich, 1965; 1969). 40-50 years later a few studies on geodesy and geodynamics covered the broader study area and Shen et al. (2003) did some work in the Chinese part of the fault, but it took until 2013 before Campbell et al. revisited the Kazakh side and came up with new field data. They focussed on the tectonic geomorphology of this structure and determined a slip rate. Given this little amount of research done one would assume that the fault is not very large and of minor importance, but the opposite is true. The fault is around 300 km long in its Kazakh section and probably twice as long in total!
It’s a right-lateral strike slip fault with a large thrust component, it’s clearly active (slip rate probably more than 2 mm/yr), and it forms the Dzhungarian Gate, basically the only gateway between China and Central Asia. This gate is known as part of the ancient Silk Road and it probably played a major role in human and animal migration.
All this is enough reason to have a closer look, to continue Campbell et al.’s work, and to find out what role the Dzhungarian Fault plays in the tectonics of Central Asia. More precisely, we wanted to find out if the fault slip rate changes along strike, when the last earthquakes did happen, and how strong earthquakes can get.
We therefore investigated sites where geological markers were offset by the fault – alluvial fans, terrace risers, streams, and ridges. Then we measured the displacement by DGPS. In some places we also used the helium balloon to collect aerial imagery, which allows us to produce a high-resolution digital elevation model (DEM) of the study site.
We dug pits in terraces and alluvial fans to find out when they have been abandoned. Organic material for 14C dating was rather rare, so often we had to sample rocks that were covered by carbonate crusts. These crusts form when soil formation starts, so they give us an idea on when the alluvial fan or the river terrace became stable, i.e., inactive. We will date the carbonate rinds with U-Th series. In the northwestern part of the fault we found enough fine-grained material for OSL dating.
The first few days were spent on reconnaissance, which included loooong drives on rather bad roads parallel to the mountain range. We needed to find suitable study sites and promising targets.
We spent the following days digging pits, sampling terraces and alluvial fans, walking the DGPS and the balloon, and trying to avoid encounters with bears and spiders.
Most of the time we were quite lucky with the weather, which can be miserable in September. However, there were rainy days as well and we survived one storm that brought my tent close to collapse.
When the rain was gone, we continued the field work.
References and further reading:
Campbell, G. E., Walker, R. T., Abdrakhmatov, K., Schwenninger, J. L., Jackson, J., Elliott, J. R., & Copley, A. (2013). The Dzhungarian fault: Late Quaternary tectonics and slip rate of a major right‐lateral strike‐slip fault in the northern Tien Shan region. Journal of Geophysical Research: Solid Earth, 118(10), 5681-5698.
- Shen, J., Y.-P. Wang, Y.-Z. Li, H. Jiang, and Z.-Y. Xiang (2003), Late Quaternary Right-Lateral Strike-Slip Faulting Along The Bolokenu-Aqikekuduke Fault In Chinese Tian Shan, Seismol. Geol., 25(2), 183–194.
Voytovich, V. S. (1965). Development of Dzhungar deep fault. International Geology Review, 7(5), 874-883.
- Voitovich, V. S. (1969), Nature of the Dzungarian deep fault (in Russian), Tr. Geol. Inst., 183, 189.