Boundary Zones Between Blocks of Continental Crust
Evolution of Faulted Interblock Zones in Continental Seismic Regions
Tech Area / Field
- OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences
- ENV-SEM/Seismic Monitoring/Environment
3 Approved without Funding
Institute of Seismology, NAS, Kyrgyzstan, Bishkek
- Institute of Dynamics of the Geosphere, Russia, Moscow
- New Mexico State University / College of Arts and Sciences, USA, NM, Las Cruces\nScience Applications International Corporation, USA, VA, McLean\nColumbia University / Lamont-Doherty Earth Observatory, USA, NY, Palisades
Project summaryAnnotation. In the tendered project we propose to develop new methods of measurements of mechanical properties of boundaries between blocks of the continental crust. The experience of fault's diagnostic with seismic waves from underground nuclear explosions in Kazakhstan is used as the basis of the technique. In this approach the deformation parameters of cracks and faults are measured from the change of dynamic parameters of seismic waves before and behind a fault. We offer to investigate faults of the Northern Tien-Shan using earthquakes as a source of seismic waves. In addition, measurements of the deformation characteristics of small-scale cracks and laboratory experiments will be used. The technique will be developed with an example analysis of dynamics processes of a continental crust deforming in the Tien-Shan region. For this purpose the complex of experimental data including data of seismic, deformographic and GPS observations, researches of morphology and kinematics of faults, analysis of block structural models at various hierarchic levels will be used, including data on paleo-strains and paleo-earthquakes in Tien-Shan.
The structure of the Earth's crust is not a simple result of destruction of initially solid plates, but permanently evolving system of interacting members - blocks. Numerous publications in the last 20 years have demonstrated convincingly that deformation characteristics of blocky media and propagation of seismic waves are determined by properties of more yielding (in contrast to the material of blocks) faulted inter-block zones and kinematics of inter-block displacement. Various deformation and geological processes, including the origin of earthquakes, are concentrated mainly in the inter-block zones.
The capabilities of modern experimental methods (networks of digital seismic stations, operated in seismo-active regions, GPS measurements, deformographic observations etc.) and development of numerical modeling methods allow us to reveal inter-block displacements to describe the process of Earth's crust deformation at various hierarchic levels. To solve this problem it is necessary to know properties of inter-block boundaries, first, of active faults. In this project, we propose to develop new methods to measure mechanical characteristics of boundaries between blocks of the continental crust at various hierarchic levels.
The basis for the proposed techniques is our experience of fault's diagnostic in Kazakhstan with seismic waves from underground nuclear explosions: parameters of waves passed through the faults have allowed participants of the given project to estimate deformation parameters of faults.
We will concentrate our attention on the Tien-Shan region. Project participants conduct a considerable volume of researches of block structure and fault tectonics for this region. Structural models of the Earth's crust at various scales have been created, the regularity of the earthquake's sources location as well as stages of seismic activity and fluid regimes have been analyzed.
In the project we offer to investigate faults of Northern Tien-Shan, using earthquakes as a source of seismic waves in combination with the research data on deformation characteristics of small-scale cracks and laboratory experimental results. For the analysis of dynamics of the Earth's crust deformation, the complex of experimental data including seismic observations with the KNET network, deformographic measurements in special underground observatories and data of the GPS system, research results on morphology and kinematics of faults, block structural models at various hierarchic levels will be used. In addition we will examine the accumulated information on paleo-strains and paleo-earthquakes in Tien-Shan.
In the project relationships of inter-block boundary deformations will be studied in the view of previously conducted experiments on natural objects of various scales, including underground nuclear explosions. Measured and analyzed data on measurements conducted as in the near-field region (30-1000 m from the shot point) and at considerable distances from the epicenter (10-100 km) will be used.
Block structure of the Earth's crust and properties of boundaries between blocks are formed at the expense of the internal energy of Earth. However, such processes as solar and lunar tides, cyclonic activity, oscillations of atmospheric pressure at the surface of solid Earth can notably influence process of the crust deformation. Small stresses caused by these processes are not able to create inelastic strains in the block material. However, due to non-linear deformation the inter-block zones can slowly accumulate residual strains of a substantial amplitude. One of possible scenarios how vibrations in rock massifs may transform to the translational block motion is an "acoustic fluidization", suggested by H. J. Melosh. Measured parameters of geophysical fields in neighborhoods of faults have revealed high gradients of a microseismic background in the fault zones, which, in turn, can actuate processes of deformation's accumulation. Small oscillations of blocks may result in noticeable increase of mobility of Earth's crust. Using traditional continuum models, this effect may be treated as a considerable decrease of an effective viscosity in the crust. In the project, we offer to investigate the influence of "gentle" permanently operated factors (such as microseisms, seasonal and tidal variations of the stress-strain state etc.) on the non-linear relationship of accumulation and release of elastic energy at inter-block boundaries. At the same time modern deformation processes at the inter-block boundaries occurs as a part of the general seismic process. The ensemble of displacements in the earthquake source zones may be treated as a macro-strain or seismo-tectonic strain (STS) in the continual description of the Earth's crust. The STS intensity is controlled with the release rate of seismic momentum. Other STS characteristics depends on the earthquake mechanism. The special research will be conducted to study the non-ordered characters of displacements in the earthquake sources what reflects fractal nature of the geophysical media. Within the framework of the tendered project, we propose to formulate models of the process of small deformation's accumulation in Earth's crust and on their basis to analyze available for Tien-Shan region seismological and geodynamic data.
Highly qualified specialists of two organizations - Institute of Seismology, Kyrgyz Republic National Academy of Sciences (IS NAS), and Institute for Dynamics of Geospheres, Russian Academy of Sciences (IDG RAS) will execute the project.
The participants of the project - employees of the IS NAS - have a wide experience in the analysis of the Tien-Shan geodynamics with various geologic and geophysical methods.
The specialists from IDG RAS for many years successfully conducted researches of dynamic deformation processes of blocky media in the field conditions, and with methods of laboratory and numerical modeling.
The majority of specialists participating in the project were engaged into problems of geodynamic support of the USSR underground nuclear-weapon tests, directly participating in nuclear tests at the Semipalatinsk and Novaya Zemlia nuclear test sites. This fact directly responds the purposes of the ISTC to train specialists, engaged earlier to problems of nuclear arms, for a new professional activity.
In the project the solution of following problems is envisioned:
1. Research of the evolution stages of deformation processes during the intracontinental orogenesis of Tien-Shan.
2. Development of technique to measure mechanical properties of rock discontinuities in the natural environment.
3. Development of mechanics of rock discontinuity deformations.
4. Construction of models for small deformations accumulation in the Earth's crust.
The project will allow (i) to reveal fundamental, unknown before, objective laws of the origin and development of deformation processes in the Earth, and (ii) to elaborate the technique of analysis of mechanical properties of inter-block zones in Earth's crust. The developed technique can be applied for various seismo-active regions, having a developed network of instrumental observations.