Constraint on Tien Shan structure and dynamics from integrative modelling of new satellite gravity-, GNSS-, SAR- and seismic data

Duration: September 2009 – December 2011

Summary
The main goal of the study is construction of an integrated model of the Central Tien Shan, which is based on a joint analysis of the gravity, geodetic and other geophysical data. The obtained model should open a way for understanding of the ongoing tectonic processes forming this structure. In particularly, a new density model of the crust and upper mantle will be obtained in a joint inversion of the gravity field (including the GOCE data) and the new seismic data. Next, we are going to construct a rheological model of the lithosphere, which will be employed for analysis of surface deformations and stresses within the lithosphere. Real surface deformations will be derived using modern geodetic observations. The observed deformations will be analysed together with predicted deformations given by a rheological model, which enables us to develop a reliable model of the Tien Shan tectonics and evolution.

Main problems
Tien Shan is one of the most active intraplate orogens in the world, located ~1500 km north of the convergence between Indian and Eurasian plate, and surrounded by the stable Kazakh platform to the north and the Tarim block and Parim block to the south - southwest. Despite this area was extensively studied during last decades, several principal problems, related to its structure and tectonics, remain unsolved up to now:  

1. The most principal question is to understand a geodynamic scenario of the Tien Shan evolution. Several scenarios have been discussed so far, such as a direct “crustal shortening”, intracontinental subduction and some others, but no clear evidences for any of them have been found.
2. A striking disagreement exists between the shortening rates of ~20 mm/yr (from GPS measurements) and ~10 mm/yr (from seismic moments of large crustal earthquakes).
3. The Tien Shan range consists of several parts (e.g. Eastern, Central and Western). Even there recognized some differences between them, they are usually considered as one tectonic unit. However, some data (chiefly seismic) obtained last decade evidence for some principal differences, which might relate to different style of tectonics.
4. Still it is not clear why Tien Shan grows so far from the plate boundary and Himalayan collision zone. This problem is connected to a relation of the inherited structures of the Tien Shan tectonic history to its present structure and dynamics.

Answering these questions is principal to forecast future behavior of the entire geological system. Such predictions are highly relevant to the current and future needs of the humanity regarding the assessment of natural hazards, water supply damage, environmental degradation potential and disaster mitigation. For example, almost no strong earthquakes were instrumentally observed in Central Tien Shan. There might be two opposed explanations. First, this type of tectonics doesn’t lead to a significant stress concentration within the crust in this area. Second, the lithosphere still accumulates these stresses, which might be released in future. Obviously, it is important to answer this question.