The Uplift and Seismic Structure of the Greater Caucasus
Tech Area / Field
- ENV-SEM/Seismic Monitoring/Environment
- OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences
6 Project underway
Senior Project Manager
Institute of Geological Sciences, Armenia, Yerevan
- University of Missouri, USA, MO, Columbia\nOregon State University, USA, OR, Corvallis\nMichigan State University / College of Natural Science, USA, MI, East Lansing\nLawrence Livermore National Laboratory, USA, CA, Livermore
Project summaryContinental collision zones are dynamic environments where the continental crust and lithosphere are created, destroyed, and modified. One of the best regions, if not the best place, on the planet to study early stages of mountain building is the Greater Caucasus where most of the volcanism and uplift appears to be on the order of 5 Ma. The Greater Caucasus mountain belt contains the highest topography of the Eurasia-Arabia plate boundary.
We propose to conduct a large-scale multi-national passive seismic experiment that would cover most of the Greater Caucasus. The passive seismic experiment will have two major components: a distributed network throughout the Caucasus to supplement the regional stations (Linear Array), and a dense linear profile of stations bisecting the entirety of the Greater Caucasus and much of the Lesser Caucasus (Large Scale 2D Array).
The goals of the proposed Project, and particularly, of a passive source seismic experiment, are to test the following hypotheses:
(1) A broad zone of horizontal shortening is due to the convergence of the Arabian plate into the stable Eurasian plate;
(2) The high topography in the Greater Caucasus is supported by a corresponding crustal root;
(3) Recent delamination or slab break-off events have led to an asthenospheric upwelling that is supporting the high topography in the Greater Caucasus;
(4) There is ongoing subduction beneath the Greater Caucasus that is an extension of the subduction of the South Caspian basin and that has led to the recent uplift of the high topography in the region.
The current status in the area of study. The collisional belt between the Eurasian and Arabian plates forms a very young, diffuse plate boundary and has important similarities and differences with the India-Eurasia collision zone.
The central Caucasus is characterized by a broad plateau, with the Lesser Caucasus to the south; both are within the seismically active but diffuse boundary. Thus far very few broadband seismic data have been available from the Greater Caucasus and, therefore, velocity models are poorly defined and little is known about the subsurface structure. For example, only recently have hypocentral depths become well enough constrained to demonstrate that there are intermediate depth earthquakes beneath the eastern Greater Caucasus. Recently, seismic networks in the region (Azerbaijan, Armenia, Georgia, and southern Russia) have added proprietary broadband seismic stations, including three ocean bottom seismometers on the Caspian seafloor, and the proposed project would help make these data available to the larger scientific community. Currently there are collaborative agreements with the operators of all of these networks and all have agreed to participate in this proposal.
Impact of the proposed Project on the progress in the considered field. This will be the first research project of its kind in this region. A large scale multi-national passive seismic experiment will allow us to create robust models of 3D seismic velocity structure and determine very accurate hypocentral earthquake locations for the Caucasus-Caspian region in order to better understand the uplift mechanism for the Greater Caucasus, the origin of large earthquakes in the region, and the early stages of mountain building in general. Recent work has shown that there is a cluster of deep earthquakes beneath the eastern Greater Caucasus. The deep earthquakes suggest the presence of either a delaminating or subducting piece of southern Caspian Sea lithosphere beneath this part of the mountain belt.
Expected results and their application
The proposed Linear Array will obtain the following: (1) The detailed crustal P and S velocity structure and intrinsic attenuation; (2) The Moho topography and the upper mantle velocity gradient; (3) The location of any pockets of partial melt or partially molten lower crust; (4) The depth of any major crustal detachments or ramps; (5) The relationship of local seismicity and uplift rates to the imaged crustal/upper-mantle structure.
The proposed Large Scale 2D Array will obtain the following: (1) Three dimensional P and S-wave velocity variations (resolution of approximately 50 km); (2) Seismic attenuation structure using both t-star (from local earthquakes) and high frequency regional waves; (3) A two and a half dimensional model of the seismic anisotropy.
The proposed collaborative research will result in an improved image of the crustal and upper mantle structure beneath the Caucasus that will reveal important aspects of this major intra-continental mountain belt that is directly relevant to our understanding of diffuse plate boundary seismic zones or mountain building. This has implications for seismic hazard reduction in Armenia, Azerbaijan Georgia, and Russia, as well as in USA, since there are a number of diffuse and intraplate seismic zones including the Basin and Range and Rocky Mountains.
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