I’ve spent several weeks in Eastern Kazakhstan this summer for paleoseismological field work. During the first part of this trip we looked at some thrust and strike-slip faults in the Ili Basin and the Saty area. The second part was almost entirely devoted to study the Dzhungarian Fault. I’ll blog about this second part later. Eleanor, David, Austin and me were the UK representatives in our team. We were so lucky to have Kanatbek from Kyrgyzstan and Aydin from Kazakhstan with us. They did not only lead us to all the interesting places and helped us to understand the geology and the tectonics, but they also did a fanatastic job organizing the field trip and dealing with the local surprises, which as you know happen in basically every field trip.
Our first study site was located at the northern boundary of the Ili Basin, where we did some work last year already.
This year we completed our aerial photo survey with the helikite. This involved some intense hiking along an impressive fault scarp which is littered with the most amazing petroglyphs.
Actually, moving the balloon is only one part of the story and can be done by one person. The others are running back and forth, setting up ground control points and measuring their position with DGPS after the balloon has passed them.
Our next target was a fault at the southern Ili Basin, which we thought might be less active, and indeed we didn’t find many interesting things here. At least nothing that points to young deformation…
Later we stopped at a giant scarp completely covered in loess. We did a quick drone survey there to produce a digital elevation model (DEM) using structure-from-motion (SfM).
On our way to the south of the country we passed the Charyn Canyon, where one can see a thrust fault in action, Paleozoic rocks being thrust over Neogene and Quaternary units:
Finally we reached Saty, a town close to the border with Kyrgyzstan. Do you also feel that border areas are always somewhat special? It’s not only the presence of police and the military, it’s often a kind of diffuse feeling of a place being different from other places. Well, I had exactly this inaccurately described feeling there. However, Saty – which my autocorrect now has changed to ‘stay’ for the third time – is located in the epicentral area of the 1889 Chilik earthquake. This was one of the strongest continental earthquakes that ever happend with a magnitude of ~MW8.3, based on macroseismic intensities. Reason enough to have a close look at the faults there! The Saty valley is exceptionally beautiful. A tourist is probably amazed by the high mountains and the weird hills, a geomorphologist is stunned by the landslides, the deformed terraces, the surface ruptures, and the tilted erosional surfaces.
We worked on channels which were offset by a left-lateral fault that also has a vertical component. The fault trace is quite easily visible in the field. We dug pits to sample abandoned alluvial surfaces – by getting to know when they were abandoned we can say something about the fault activity and hopefully measure a slip rate.
In some of the pits we found charcoal and snails which allow us to do 14C dating. In other pits we took loess samples for optical stimulated luminescence (OSL) dating. When sediment containing quartz or feldspars is buried and shielded from cosmic rays, ionizing radiation from the natural radioactive decay will cause charges which are stored in electron traps in these minerals. These charges accummulate over time as long as the sediment doesn’t see the sun. Later in the lab the samples are exposed to light (optically stimulated) and as a consequence, the charges will be released and cause luminescense. By measuring the amount of light emitted, one can determine how long the sample was buried. So we took samples using opaque steel tubes to shield them from sunlight. These samples will tell us when the fan became inactive and covered by the loess.
We also surveyed the area with the helikite and the drone, because we want to build a DEM of the offset morphology.
The helikite was a bit more successful than the drone flight:
We don’t know what caused the drone to crash. What we do know is that it was quite spectacular and thorough.
Our last day in the Saty area was devoted to see some extension cracks on a hill that’s crossed by the fault, probably secondary earthquake effects. Then we hiked up a steep valley to the Kaiyndy lake. Some time ago, a huge landslide blocked the river and a lake formed, drowning the trees on the valley floor. A touristic highlight spiced with interesting geology – the landslide might have been caused by an earthquake…
I will blog about part II of the field trip, soon. Be prepared for some amazing strike-slip geomorphology!
A big thank you goes to Aynagul who made the stay in the field a pleasure by cooking the most delicious food, and to Sagyn who is the king of offroad driving.
We were funded by COMET and the Earthquakes without Frontiers project (EwF). Both are on Twitter (@NERC_COMET, @EwFProject), have great websites, and EwF also has a nice blog!
Andrew Alden | 2015-10-27|23:40 (UTC)
Graben on a hilltop = sackung!
Christoph Grützner | 2015-10-28|00:03 (UTC)
Yeah, we’ve seen this also in Kyrgyzstan as a consequence of the 1992 Suusamyr earthquake: http://paleoseismicity.org/paleoseismological-field-work-in-kyrgyzstan/dsc_0025/
I feel there should be a terminological distinction between slow/gravitational sackungen and secondary earthquake effects due to (strong) ground motion, but there isn’t, right?