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Rupture mechanisms of major earthquakes

#KR-2011


Seismic hazard assessment of Kyrgyzstan through the integrated study of focal mechanisms of major earthquakes and seismic trenching

Tech Area / Field

  • OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences

Status
8 Project completed

Registration date
15.03.2012

Completion date
29.03.2016

Senior Project Manager
Turebayev A

Leading Institute
Kyrgyz-Russian Slavonic University, Kyrgyzstan, Bishkek

Collaborators

  • University of Texas at El Paso, USA, TX, El Paso\nUniversity of Colorado / Department of Geological Sciences and Cooperative Instiute for research In Environmental Sciences (CIRES), USA, CO, Boulder

Project summary

Project objective. Assess seismic hazards in Kyrgyzstan through the integrated study of focal mechanisms of major earthquakes and seismic trenching over active faults responsible for historical earthquakes.
Research status. Located in the western part of Tien Shan, the Kyrgyz Republic is one of the world’s seismically most hazardous regions; more than half of India’s convergence with Eurasia is absorbed by deformation across the western Tien Shan. According to the New Catalog of Strong Earthquakes (Editors-in-Chief N.V. Kondorskaya and N.V. Shebalin, 1982) and Institute of Seismology of NAS KR, over the past 125 years (from 1885 to 2010), the Tien Shan has been shaken by many major earthquakes: the Belovodskoye earthquake (9-10 intensity) in 1885, Vernenskoye earthquake in 1887 (9-10 intensity), Chilik earthquake in 1889 (10 intensity), Kashgar earthquake in 1902 (10 intensity), Kemin earthquake in 1911 (10-11 intensity), Kemin-Chui earthquake in 1938 (8-9 intensity), Chatkal earthquake in 1946 (9-10 intensity), Sarykamysh earthquake in 1970 (8-9 intensity), Isfara-Batken earthquake in 1977 (8 intensity), Jalanash-Tyuo earthquake in 1978 (8-9 intensity), Daraut-Kurgan earthquake in 1978 (8 intensity), Suusamyr earthquake in 1992 (9-10 intensity), Kochkor earthquake in 2006 (7-8 intensity), Alai earthquake in 2008 (8 intensity), and other less strong earthquakes. Moreover, every year the regional seismic network records over 1,500 earthquakes with magnitude ≥1.0 in the Kyrgyzstan.
The major earthquakes listed above have killed many people and resulted in colossal economic losses. These destructive earthquakes, some of which occurred shortly after one another, indicate that this region is one of the world’s seismically hazardous regions. Finding solutions to seismological problems there is indisputably of immediate interest. Preliminary studies in this region have revealed evidence of both ancient and historical earthquakes that have occurred in Kyrgyzstan.
Unlike recent strong earthquakes, for which source parameters (epicenter, foci depth, magnitude, and intensity) can be determined using measurements from modern high-precision seismic stations, the same data for the ancient earthquakes can be assessed only approximately with detailed study of natural phenomena such as: paleoseismic deformation, deformation of young alluvial terraces, seismogenic contortions of lacustrine deposits, disruptions of drainage patterns, etc. From assessments of geologic and geomorphologic characteristics of such phenomena during focused field investigations, one can determine epicenter zones, ages, and energy release associated with ancient earthquakes, which are important for the comparative analysis with the recent earthquakes. Strong earthquakes commonly are felt over an area of a few thousand square kilometers. They have left obvious morphological traces in relief, which will be studied in detail in close collaboration with our American collaborators.
Among our approaches, we will map profiles of deformed terraces using high-precision differential GPS equipment and experience of our collaborators from … Universities. Together with dates of the terraces, we will calculate rates at which they have been faulted and folded. We will collect geological samples from the lacustrine and alluvial terraces for dating of them, and we will use radiocarbon and OSL dating techniques. The data obtained will allow us to calculate the dates of the strong ancient earthquakes. To determine intervals between strong earthquakes, we will dig and log trenches across active faults, and we will date layers that have been offset using radiocarbon. Previous work by Thompson et al. [2002] demonstrates that all of these methods can be applied successfully in Kyrgyzstan.
In our study of the ancient earthquakes, we also will exploit methods of archeoseismology. We will study ancient destroyed cities and monuments in Kyrgyzstan to quantify intensities of shaking and, where they can be dated, to determine when past earthquakes occurred. Again we will use methods of the absolute dating, such as radiocarbon, as well as other archeological methods. We will then compare inferences based on these data with those for recent strong earthquakes.
This project will bring improved methods of investigations in the field of geologic, geomorphologic, seismologic and paleoseismologic sciences to Kyrgyzstan. We will apply these investigations to seismic hazard assessment of the Kyrgyzstan territory, but obviously the results that they bring will be applicable to other problems. Our objective, however, will be the compilation of a new Map of the Seismic Hazard of Kyrgyz Republic.
Currently the regional network of digital seismic stations enables the determination not only of locations and magnitudes of earthquakes in the Tien Shan, but also focal mechanisms of earthquakes with magnitudes ≥3.5. These data are widely used to resolve seismic zoning issues, earthquake forecasts, and seismic risk problems in the mountainous areas of Kyrgyzstan. However, the analysis of available seismic data showed the following deficiencies:
1. There is no single, widely used format for describing focal mechanisms of earthquakes in the Tien Shan, which complicates their use in solving problems relating to the state of stress in the earth’s crust. We conducted a detailed analysis of results of focal mechanism solutions of earthquakes in the Tien Shan, Kyrgyzstan during 1946-2008. The mechanisms were determined by different authors using P-waves first arrivals data, registered mainly by a regional seismic network and analyzed manually with use of Wulff net. Results of focal mechanisms, however, can be presented differently, with resulting differences in interpretations. For example, some authors consider azimuths of the dip directions instead of strikes of nodal planes, others cases plot angles between strain axes, etc. This variety of presentation creates problems in interpretations. Hence, the data must be summarized and presented uniformly and completely.
2. Most focal mechanisms of the Kyrgyzstan earthquakes have been determined manually. Only recently have we used computer software for this purpose. Determining the focal mechanism of one earthquake requires at least 1 hour, but a computer it needs only 4-5 minutes. 3. We lack of modern, applicable software for determining earthquake focal mechanisms, which makes it difficult to undertake an extensive computer-aided examination of earthquake focal mechanisms. At present time mass determination of the Tien Shan foci parameters is conducted with use of two computer software mentioned above: American «FPFIT» and Japanese «SOURCE MECHANISM». Both software are very good and they provide by similar results.
1) We would like to compile a catalog of the focal mechanisms of the Tien Shan during period of 1946-2012 using their computer determination. An analysis has shown that the focal mechanisms of the strong earthquake during mentioned period were determined mainly by manual (graphical) method. Results of their solutions are represented in different formats. We would like to introduce an international format for presentation of results of a solution of the focal mechanism of each earthquake, which will be available for everybody
2) We have adopted two (FPFIT and SOURCE MECHANISM) computer programs to our conditions – conditions of the Tien Shan: we have introduced new velocity models of the earth crust, calculated angles of seismic rays’ appearance etc. We have now to determine focal mechanisms of the earthquakes not manually, but with the computer help and to compile a new catalog of the focal mechanisms of the Tien Shan earthquakes in the international format
3) We would like to note that a method of determination of earthquakes focal mechanisms by signs of the P-waves first arrivals needs data of numerous seismic stations which have to surround an earthquake epicenter. At many cases the seismic stations are located in one or two quadrangles compare with source position. In these cases it is hard to determine the earthquake focal mechanism. Such situation took place in region of the Tibetan Plate [V.Levin, Guo-chin Dino Huang, S.Roecker, 2012]. Steve has suggested us a mothod of inversion for determination of the local tensor of the centroid moment (rCMTI).
The application of new technology for examination of focal mechanisms of earthquakes in Tien Shan, where earthquakes are common, would enable us to exploit focal mechanisms as a tool in seismic hazard assessment. Thus we plan to:
1) Collect and systematize focal mechanisms of earthquakes in Tien Shan using a single method and develop appropriate algorithms and software;
2) Develop an earthquake focal mechanism database to address earthquake focus and physics problems;
3) Ensure efficient and high quality data processing, generation, and interpretation for future problems that we have not yet posed;
Exploit the catalogue of focal mechanisms to determine strain rates across the region, by using Kostrov's (1974) method.
4) Study of the foci mechanisms will give us information about parameters of the earthquakes, occurred during last tens of years. However for the conditional seismic hazard assessment it is necessary seismic record lasted onto hundreds and thousands years. Paleoseismological method (together with studies in historical and archeoseismology) can provide data during this long time interval. With use of mentioned method we plan to conduct:
- Interpretation of air photographs and satellite images in order to reveal active fault lines and seismic deformations tied with them.
- Collection of all available published and archival data on recent tectonic activity.
- Creation of GIS data base where all revealed faults and deformations will be placed.
- Digging of trenches across the fault scarps and lineaments displacing laterally the relief forms. Logging of the trench walls with a purpose to reveal seismic ruptures and colluvial wedges. Collection of samples for the absolute dating.
- Interpretation of trenching data, determination of paleoearthquakes parameters, strong earthquake reoccurrence intervals and active faults segmentation.
Contribution of the proposed project to progress in this area. Proposed technologies that enable determination of earthquake focal mechanisms and the use of those methods offer the potential of improving assessments of seismic hazards in Kyrgyzstan and will facilitate the progress of seismology in other methodological and practical aspects.
Expertise of project participants. The project participants have many years of experience in solving seismological problems: seismic hazard assessment and seismic zoning of the Kyrgyz Republic, earthquake forecasting, determination of earthquake focus parameters, seismic risk assessment, etc., which is confirmed by publications and conference reports.
Expected Results and Their Application. A technology enabling the use of focal earthquakes of major earthquakes in Tien Shan for seismic hazard assessment of Kyrgyzstan will help increase the efficiency of data collection, processing, and storage by >5 times, improve labor efficiency by 3 times and increase the reliability and accuracy of research findings through the use of cumulative data from the regional seismic network. Paleoseismological trenching will allow to obtain lacking data on ancient earthquakes (paleoearthquakes parameters, strong earthquake reoccurrence intervals and active faults segmentation) necessary for the complete seismic hazard assessment
The project may bring profit from:
- Sale of database
- Sale and use of the system and technology.


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