Earth Crust Deformations
Strain Accumulation and Triggering of Strain Release in the Earth’s Crust by Weak Disturbances
Tech Area / Field
- ENV-SEM/Seismic Monitoring/Environment
- OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences
3 Approved without Funding
Institute of Seismology, NAS, Kyrgyzstan, Bishkek
- Joint Institute for High Temperatures RAS / High Energy Density Research Center, Russia, Moscow\nInstitute of Dynamics of the Geosphere, Russia, Moscow
- Lawrence Livermore National Laboratory, USA, CA, Livermore\nColumbia University / Lamont-Doherty Earth Observatory, USA, NY, Palisades
Project summaryThe purpose of this project is the development of physically reasonable models and investigation of possible mechanisms of the effect of weak disturbances on evolution of deformation in the Earth’s crust.
The problem of triggering the geodynamic processes by weak disturbances has been influenced by the well-known Landers earthquake (28.06.1992, M=7.3), after which seismic events were registered for tens of hours at distances up to 1250 km from the epicenter. The origin of these events is attributed to a trigger effect. In spite of a great number of experimental evidences of the effect of weak disturbances on deformation processes in the Earth's crust, the physical mechanics of this phenomenon has not been developed yet. The reason is that so far there are no models that adequately describe the regularities of dynamic deformation of rock discontinuities – faults of different hierarchical levels.
The seismic method of estimation of deformation parameters of rock discontinuities has been developed recently in IDG RAS. The basis of this technique is the analysis of dynamic parameters of seismic waves registered in a neighbourhood of a fault or crack. The method has been tested recently and a number of useful results were identified. In particular, it has been demonstrated that a non-linear relation between stresses and deformations is characteristic for the investigated discontinuities, the non-linearity being traced to very small deformations of about 10-9 m/m.
The experimental data allows us to proceed to the development of a nonlinear model of inter-block zone deformation, which is one of the tasks of the proposed project. We plan to develop applicable analytical and numerical models to describe nonlinear processes of static and dynamic deformation of discontinuities in rock. An extensive set of experimental data previously obtained by the authors will be used in the model development. Additional new experiments on the dynamic deformation of discontinuities of different types will be conducted. In these experiments the direct precise measurements of dynamic and residual interblock displacements will be performed (accuracy up to 0.05 mm in the frequency range of 0-10 kHz), which will allow us to reveal more exact constitutive laws of the accumulation of small residual displacements in a blocky medium under weak disturbances. The distinctive feature of the above models will be the ability to adequately describe the process of nonlinear interaction of seismic waves with discontinuities in a stressed block massif. The developing models create the basis for processing various observational and experimental data from the unified methodological viewpoint.
The Institute for Dynamics of Geospheres of the Russian Academy of Sciences is, perhaps, the only institution in the world that for many years has conducted systematic instrumental observations of interblock movements produced by large-scale underground explosions (including the nuclear ones). A wide range of explosion yields and epicentral distances allow us to study the interblock movements at different hierarchical levels – from tens of centimeters to hundreds of meters, and sometimes to kilometres. Though the main parts of interblock displacements were usually accumulated during tens of milliseconds, in some tests slow post-shot block displacements were observed for tens of hours. In fulfilling the project, we are planning to use an extensive set of data acquired from aftershocks of underground nuclear explosions. Numerical simulations of the mechanical effect of an explosion in a non-uniform block medium are planned to be done to estimate the values of residual post-shot stresses and strains localized in the vicinity of neighbouring discontinuities and hypocenters of the main aftershocks.
Similar measurements were also conducted at some mining enterprises. The authors of the project have also collected data on systematic long-term precise geodetic measurements conducted at the mines of the Kola Peninsula, together with deformation and inclination measurements, as well as results of the simultaneous recording of seismic emissions.
The model of non-linear deformation of inter-block zones will allow us to analyse, from the new point of view, the available data on the possible trigger effect of distant earthquakes and nuclear explosions on the evolution of deformation processes in the Earth crust. One of the indicators of such effects is the local change of a seismic regime. This work requires a thorough multi-factor statistical analysis of seismic catalogues for the period of nuclear test performance as well as for the following decade. First of all, this analysis will be conducted for the Northern Tien Shan, since the participants of the project have performed a considerable number of investigations of block structure of Northern Kyrgyzstan, have developed structural models of the Earth’s crust at different hierarchical levels, and have analyzed the regularities of earthquake source location and stages of seismic activity. The region is located about 1000 km away from the Semipalatinsk Test Site, where more than 300 underground nuclear explosions were performed during the period of 1961-1989. Since we possess the necessary data on characteristics of each explosion and the results of registering the parameters of seismic waves from many explosions, we plan to make estimations of dynamic stresses and strains that originate in the region during transmission of the explosion seismic waves.
The participants of the project from the Institute of Seismology of the National Academy of Sciences of Kyrgyz Republic plan to compile an updated unified catalogue of Tien Shan earthquakes. Availability of a rather dense network of digital seismic stations in the Northern Tien Shan provides an opportunity to try to detect, in the nearest vicinity of a station, the weak seismic disturbances and micro-earthquakes triggered by passing seismic waves from strong remote earthquakes – in particular, by deep-focus earthquakes of the Pamirs-Hindu Kush tectonic plate. For this purpose we plan to develop specialized software that will allow us to distinguish local events from exogenous effects or remote seismic events, as well as comprehensively detect their standard parameters. A catalogue will be compiled of micro-earthquakes occurring in the vicinity of each zone of deep faults of Northern Tien Shan since the beginning of operation of each station of the KNET array.
Beside investigations of the mechanics of a possible trigger effect of dynamic events, an analysis of the results of triggering geodynamic processes by long-term anthropogenic effects will be done in a course of the project. Here, we plan to analyse the available data on three locations: (i) the Gazli gas field (catastrophic earthquakes on April 8, 1976, M=6.8, May 17, 1976, M=7.3, March 20, 1984, M=7.2, that occurred, as it is supposed, due to gas recovery); (ii) the Romashkinskoye oilfield in Tatarstan – a good example of activation of seismic and tectonic processes in seismically quiet regions due to oil recovery; (iii) one of the most seismically dangerous mining enterprise in Russia – the Severouralskoye bauxite deposit, where powerful rock and tectonic events are observed regularly (magnitudes of up to 4.3). For all these locations, we have catalogues of seismic events and information about the geological structure and regimes of human activities. In this part of the project, we plan to reveal common features and differences of the development processes of anthropogenic seismicity of different origins and to investigate the spatial and temporal structuring of deformation processes in the region of human activities.
In parallel with the mechanical effects, the process of rock dynamic deformation is accompanied by electromagnetic phenomena. Measurement of the electric and magnetic fields carried out simultaneously with observations of seismic signals and rock deformation can give additional information about the character of dynamic processes in the terrestrial crust. Experimental and theoretical investigations of generation of electrical and magnetic fields during deformation of a rock massif with discontinuities in situ and in laboratory are planned to be carried out in the course of this project. Explosions of chemical explosives and detonation of air-fuel mixtures inside wells drilled in rock will be used as the sources of pulse effects.
We plan to investigate in the course of the project the effect of powerful electromagnetic pulses on the seismic regime. This part of the project will engage the data obtained in monitoring the electric conductivity of terrestrial crust in two of the most seismically active regions of Central Asia – in the limits of Southern Tien Shan and Tajik depression, and in the Northern Tien Shan and Chu basin. For this purpose, the crust was probed with electric current pulses using magneto-hydrodynamic (MHD) generators. Preliminary analysis of the results has demonstrated that appreciable spatial and temporal changes of the seismic regime occur. The nature of this phenomenon is still very uncertain. One can only assume that the inhomogeneous zones, which contain fluids, play an important role in realization of the mechanism of triggering deformation processes by electromagnetic pulses. Experimental and theoretical studies aimed to reveal the nature of this phenomenon will be done in the course of the proposed project. In particular, experiments will be conducted on deformation of heterogeneous models of blocky media under long-term quasi-static load and external pulse electric action.
The seismic catalogues compiled in course of the project will be used for a multi-factor statistical analysis of the effect of distant earthquakes, nuclear explosions and operation of MHD-generators on the temporal characteristics of seismicity. In our opinion, this work will provide an opportunity either to detect a reliable correlation between weak external effects and local changes of seismic regime, or to demonstrate the lack of real connections between these phenomena.
In our opinion, the proposed project will improve our understanding of the evolution of deformation processes in the Earth crust and create models suitable for adequate description of some important characteristics of these processes.
Scientists and specialists from the Institute for Dynamics of Geospheres of Russian Academy of Sciences, the Institute of Thermal Physics of Extreme State of the United Institute of High Temperatures of Russian Academy of Sciences, and the Institute of Seismology of the National Academy of Sciences of Kyrgyz Republic will take part in this work.
The project is aimed at solution of the following problems:
1. Development of the model of dynamic deformation of rock discontinuities.
2. Investigation of the dynamics of deformation processes in Northern Tien Shan.
3. Studying the generation of electrical and magnetic fields during deformation of rock with discontinuities.
4. Investigation of possible mechanisms of the effect of electromagnetic pulses on geodynamic processes.
5. Development of mechanical models to describe the effect of weak disturbances on deformation processes in the terrestrial crust.
A database of deformation processes in the Northern Tien Shan, including an updated earthquake catalogue, data of geodetic observations, improved structural block models, and information about anthropogenic dynamic events and accompanying phenomena, will be compiled.
New experimental data will be obtained on generation of electrical and magnetic field signals in hard rock subjected to dynamic load in situ.
The mechanism of the effect of powerful electromagnetic pulses on deformation processes in the Earth crust will be investigated.
Summarizing the data will allow to understand the mechanism of the effect of weak dynamic disturbances on deformation processes in the terrestrial crust.
Realization of the project will thus noticeably improve understanding of the evolution of deformation processes in the Earth’s crust.