COMPARISON OF CRUSTAL DEFORMATION RATES ESTIMATED FROM SEISMIC AND GPS DATA ON THE BISHKEK GEODYNAMIC POLYGON

The Bishkek geodynamic polygon (BGP, 41.5–43.5° N – 73–77° E) is located within the central segment of the North Tien Shan seismic zone, in the junction zone of the Tien Shanorogene and the Turan plate (Fig. 1). In the entire modern structure of Tien Shan lengthwise zones of shearing (with both right- and left-lateral strike-slip faults) are observed, thus Tien Shancan be considered as a transpression zone. Our study aimed at comparing deformation values estimated for the BGP territory from the seismic and GPS data. The modern stress-strain state of the study area was determined from the focal mechanisms of 1287 earthquakes that occurred in the period from 1994 to 2015. The study area was divided into cells with a radius of 0.2° (~20 km). The cell centers were in the nodes of the grid with a spacing of 0.1° (~10 km). A tensor of a seismotectonic deformation (STD) rate within a cell was calculated as a sum of seismic moment tensors normalized for time, volume and shear modulus, assuming that STD is similar at different scale levels. The STD field is shown in Figure 4 at the background given by the deformation intensity pattern. Figure 6 shows the scatter of the sums of the strain rate tensor’s horizontal components estimated from the seismic data. The modern crustal movements were estimated from the geodetic measurements performed on the Central Asian GPS Network. Using the crustal movement velocities for 90 sites in the study area, the deformation processes in the crust were modeled based on the linear part of the Taylorexpansion of the point's-velocity-versus-its-radius-vector function. Then the velocity gradient tensors were estimated for the grid nodes with a spacing of 8.3 km. To estimate tensor's value in every single grid node a system of linear algebraic equations was solved by the weighted least-squares method. The weight of an observation point decreased with an increasing distance to such point, so that the inhomogeneity of the deformation field could be taken into account. From the velocity gradient tensors we calculate the strain rate tensors (Fig. 5) and then the rate of changes of the area (meterage)  (Fig. 7). A comparison of Figures 4 and 5 shows a general coincidence between the directions of compression/shortening axes estimated from the seismic and GPS data. On average, the STD intensity is by two to three orders lower than the deformation intensity assessed from the GPS data. It can be explained by the fact that the horizontal components of the total deformation amounts visible in the GPS data are actually the sums of aseismic and coseismic components, and the deviator part of coseismic component was considered as STD. Comparing the fields of the sums of the strain rate tensor’s horizontal components from the seismic data (Fig. 6) and the GPS data (Fig. 7) reveals an inconsistency for the Suusamyr depression: the GPS data shows a considerable crustal shortening in the horizontal plane, while the seismic data is indicative of a shear deformation. In the central part of the junction zone of the Chu basin and the Kyrgyz ridge, the crustal shortening rate exceeds –50·10^–9 per year, and it is likely that the stress is released by seismicity of a low magnitude, which can be induced by the operations of an electromagnetic prospecting generator in this territory.

1. Bogomolov L.M., Zakupin A.S., Sychev V.N., 2011. Electric Impacts on the Earth Crust and Variations of Weak Seismicity. LAP Lambert Academic Publishing, Saarbrücken, 408 p. (in Russian) [Богомолов Л.М., Закупин А.С., Сычев В.Н. Электровоздействия на земную кору и вариации слабой сейсмичности. Саарбрюкен: LAP Lambert Academic Publishing, 2011. 408 c.].

2. Buslov M.M., Klerkx J., Abdarakhmanov K., Delvaux D., Batalev V.Yu., Kuchai O.A., Dehandschutter B., Muraliev A., 2003. Recent strike-slip deformation of northern Tien Shan. In: F. Storti, R.E. Holdsworth, F. Salvini (Eds.), Intraplate strike-slip deformation belts. Geological Society, London, Special Publications, vol. 210, p. 53–64. https://doi.org/10.1144/GSL.SP.2003.210.01.04.

3. Cobbold P., Davy P., 1988. Indentation tectonics in nature and experiment. 2. Central Asia. Bulletin of the Geological Institutions of the University of Uppsala 14, 143–162.

4. England P., Molnar P., 1997. Active deformation of Asia: from kinematics to dynamics. Science 278 (5338), 647–650. https://doi.org/10.1126/science.278.5338.647.

5. Herring T.A., King B.W., McClusky S.C., 2009. Introduction to GAMIT/GLOBK Release 10.35. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 45 p. Available from: http://www-gpsg.mit.edu/~simon/gtgk/Intro_GG.pdf.

6. Kostyuk A.D., 2008. Deformation changes in the crust of the Northern Tien Shan based on space geodesy data. Bulletin of the Kyrgyz-Russian Slavic University 8 (3), 140–144 (in Russian) [Костюк А.Д. Деформационные изменения земной коры Северного Тянь-Шаня по данным космической геодезии // Вестник Кыргызско-Российского Славянского университета. 2008. Т. 8. № 3. С. 140–144].

7. Kostyuk A.D., Sycheva N.A., Bogomolov L.M., Yunga S.L., Yagi Y., 2010. Deformation of the Earth’s crust in the Northern Tien Shan according to the earthquake local data and satellite geodesy. Izvestiya, Physics of the Solid Earth 46 (3), 230–243. https://doi.org/10.1134/S1069351310030055.

8. Kuzikov S.I., Mukhamediev S.A., 2010. Structure of the present-day velocity field of the crust in the area of Central-Asian GPS Network. Izvestiya, Physics of the Solid Earth 46 (7), 584–601. https://doi.org/10.1134/S1069351310070037.

9. Lukk A.A., Yunga S.L., 1979. Seismotectonic deformation of the Garm district. Izvestiya AN SSSR, seriya Fizika Zemli (10), 24–43 (in Russian) [Лукк А.А., Юнга С.Л. Сейсмотектоническая деформация Гармского района // Известия АН СССР, серия Физика Земли. 1979. № 10. С. 24–43].

10. Makarov V.I., 1977. Modern Tectonic Structure of Central Tien Shan. Nauka, Moscow, 172 p. (in Russian) [Макаров В.И. Новейшая тектоническая структура Центрального Тянь-Шаня. М.: Наука, 1977. 172 с.].

11. Mansurov A.N., 2012. Structural design of the automated system for calculation of the field of crustal deformation rates from GPS data. Problemy Avtomatiki i Upravleniya (Problems of Automation and Control) (2), 120–127 (in Russian) [Мансуров А.Н. Структурное проектирование автоматизированной системы расчета поля скорости деформации земной коры по данным GPS-наблюдений // Проблемы автоматики и управления. 2012. № 2. С. 120–127].

12. Mansurov A.N., 2015. Distribution of modern crustal deformation rates in the Northern Tien Shan, estimated by the triangulation of GPS observation points. In: Modern tectonophysics. Methods and results. Proceedings of the Fourth Youth Tectonophysical Workshop. Schmidt Institute of Physics of the Earth of RAS, Moscow, vol. 1, p. 192–201 (in Russian) [Мансуров А.Н. Распределение скорости современной деформации земной коры Северного Тянь-Шаня, полученное триангуляцией сети точек GPS наблюдений // Современная тектонофизика. Методы и результаты: Материалы Четвертой молодежной тектонофизической школы-семинара. М.: Институт физики Земли им. О.Ю. Шмидта РАН, 2015. Т. 1. С. 192 201].

13. Mansurov A.N., 2016a. Field of modern crustal deformation rates in the Northern and Central Tien Shan according to the observations by the CA-GPS network. Bulletin of the Kyrgyz-Russian Slavic University 16 (1), 157–160 (in Russian) [Мансуров А.Н. Поле скорости современной деформации земной коры Северного и Центрального Тянь-Шаня по данным наблюдений ЦА-GPS-сети // Вестник Кыргызско-Российского Славянского университета. 2016a. Т. 16. № 1. С. 157–160].

14. Mansurov A.N., 2016b. Software package for calculation of crustal deformation from GPS data, SUR_GPS_STRAINS. Certificate No. 2016610153. Legal owner: Federal State Budgetary Institution of Science, Research Station of the Russian Academy of Sciences in Bishkek (RS RAS). Application No. 2015661945; applied on 12.11.2015; published on 20.02.2016. Bulletin No. 2 (112), (Part 1.). 212 Kb (in Russian) [Мансуров А.Н., 2016б. Программа для расчета деформаций земной коры по данным GPS-наблюдений SUR_GPS_STRAINS. Свидетельство № 2016610153. Правообладатель: Федеральное государственное бюджетное учреждение науки Научная станция Российской академии наук в г. Бишкеке (НС РАН). Заявка № 2015661945; заявл. 12.11.2015; опубл. 20.02.2016. Бюл. № 2 (112), (Ч. 1.). 212 Кб. http://www1.fips.ru/fips_servl/fips_servlet?DB=EVM&rn=4014&DocNumber=2016610153&TypeFile=html].

15. Meade B.J., Hager B.H., 2001. The current distribution of deformation in the western Tien Shan from block models constrained by geodetic data. Geologiya i Geofizika (Russian Geology and Geophysics) 42 (10), 1622–1633.

16. Rebetsky Y.L., Sycheva N.A., Sychev V.N., Kuzikov S.I., Marinin A.V., 2016. The stress state of the northern Tien Shan crust based on the KNET seismic network data. Russian Geology and Geophysics 57 (3), 387–408. https://doi.org/10.1016/j.rgg.2016.03.003.

17. Sagiya T., Miyazaki S.I., Tada T., 2000. Continuous GPS array and present-day crustal deformation of Japan. Pure and Applied Geophysics 157 (11–12), 2303–2322. https://doi.org/10.1007/PL00022507.

18. Seber G.A.F., Lee A.J., 2003. Linear Regression Analysis. Wiley, Hoboken, New Jersey, 582 p.

19. Shen Z.K., Jackson D.D., Ge B.X., 1996. Crustal deformation across and beyond the Los Angeles basin from geodetic measurements. Journal of Geophysical Research: Solid Earth 101 (B12), 27957–27980. https://doi.org/10.1029/96JB02544.

20. Sychev V.N., 2008. Study of the Influence of Impulse Energy Effects on the Variations in the Spatial and Temporal Patterns of Seismicity in the Northern Tien Shan. Abstract of PhD Thesis (Candidate of Physics and Mathematics). Schmidt Institute of Physics of the Earth RAS, Moscow, 28 p. (in Russian) [Сычев В.Н. Исследование влияния импульсных энергетических воздействий на вариации пространственно-временных распределений сейсмичности на территории Северного Тянь-Шаня: Автореф. дис. … канд. физ.-мат. наук. М.: Институт физики Земли им. О.Ю. Шмидта РАН, 2008. 28 с.].

21. Sychev V.N., Avagimov A.A., Bogomolov L.M., Zeygarnik V.A., Sycheva N.A., 2008. On the trigger effect of electromagnetic impulses on weak seismicity in connection with the problem of release of excessive tectonic stresses. In: Geodynamics and stress state of the Earth interior. Institute of Mining SB RAS, Novosibirsk, p. 179–188 (in Russian) [Сычев В.Н., Авагимов А.А., Богомолов Л.М., Зейгарник В.А., Сычева Н.А. О триггерном влиянии электромагнитных импульсов на слабую сейсмичность в связи с проблемой разрядки избыточных тектонических напряжений // Геодинамика и напряженное состояние недр Земли. Новосибирск: Институт горного дела СО РАН, 2008. С. 179–188].

22. Sychev V.N., Bogomolov L.M., Sycheva N.A., Borovsky B.V., 2010. On the synchronization of seismic activity variations in the Northern Tien Shan with the regime of electromagnetic probing of the crust. In: Geodynamics and stress state of the Earth interior. Institute of Mining SB RAS, Novosibirsk, p. 83–90 (in Russian) [Сычев В.Н., Богомолов Л.М., Сычева Н.А., Боровский Б.В. О синхронизации вариаций сейсмической активности на территории Северного Тянь-Шаня с режимом электромагнитных зондирований земной коры // Геодинамика и напряженное состояние недр Земли. Новосибирск: Институт горного дела СО РАН, 2010. С. 83–90].

23. Sycheva N.A., 2005. Study of the Features of Earthquake Focal Mechanisms and Seismotectonic Deformation in the Northern Tien Shan Based on the Data from the Digital Seismic Network KNET. PhD Thesis (Candidate of Physics and Mathematics). Schmidt Institute of Physics of the Earth of RAS, Moscow, 189 p. (in Russian) [Сычева Н.А. Исследование особенностей механизмов очагов землетрясений и сейсмотектонических деформаций Северного Тянь-Шаня по данным цифровой сейсмической сети KNET: Дис. … канд. физ.-мат. наук. М.: Институт физики Земли им. О.Ю. Шмидта РАН, 2005. 189 с.].

24. Sycheva N.A., Bogomolov L.M., Mukhamadeeva V.A., Yunga S.L., 2005. Determination of seismotectonic crustal strains in Northern Tien Shan using focal mechanisms from data of the KNET digital seismic Network. Izvestiya, Physics of the Solid Earth 41 (11), 916–930.

25. Sycheva N.A., Bogomolov L.M., Yunga S.L., Makarov V.I., 2008. Seismotectonic deformations and recent tectonics of the Tien Shan. Izvestiya, Physics of the Solid Earth 44 (5), 351–363. https://doi.org/10.1134/S1069351308050017.

26. Sycheva N.A., Ges’ V.P., 2016. Updated estimates of the average rate of seismotectonic deformation in the Bishkek geodynamic polygon. In: V.A. Mukhamadeeva, O.B. Zabinyakova (Eds.), Modern techniques and technologies in research. Research Station of RAS, Bishkek, p. 246–251 (in Russian) [Сычева Н.А., Гесь В.П. Обновленные оценки величины среднегодовой скорости сейсмотектонической деформации Бишкекского геодинамического полигона // Современная техника и технологии в научных исследованиях / Ред. В.А. Мухамадеева, О.Б. Забинякова. Бишкек: Научная станция РАН в г. Бишкеке, 2016. С. 246–251].

27. Sycheva N.A., Mansurov A.N., 2016. Comparison of crustal deformation rates in the Northern and Central Tien Shan, estimated from seismic and GPS data. Bulletin of the Kyrgyz-Russian Slavic University 16 (1), 178–182 (in Russian) [Сычева Н.А., Мансуров А.Н. Сравнение оценок деформации земной коры Северного и Центрального Тянь-Шаня, полученных на основе сейсмических и GPS-данных // Вестник Кыргызско-Российского Славянского университета. 2016. T. 16. № 1. С. 178–182].

28. Sycheva N.A., Mansurov A.N., Sychev V.N., 2016. Dynamic parameters of earthquakes in the Bishkek geodynamic polygon. In: Tectonophysics and top issues in Earth sciences. The fourth tectonophysical conference. Schmidt Institute of Physics of the Earth RAS, Moscow, vol. 1, p. 554–561 (in Russian) [Сычева Н.А., Мансуров А.Н., Сычев В.Н. Динамические параметры землетрясений Бишкекского геодинамического полигона // Тектонофизика и актуальные вопросы наук о Земле. Четвертая тектонофизическая конференция. М.: Институт физики Земли им. О.Ю. Шмидта РАН, 2016. Т. 1. С. 554–561].

29. Yudakhin F.N., 1983. Geophysical Fields, Deep Structure and Seismicity of Tien Shan. Ilim, Frunze, 246 p. (in Russian) [Юдахин Ф.Н. Геофизические поля, глубинное строение и сейсмичность Тянь-Шаня. Фрунзе: Илим, 1983. 246 с.].

30. Yunga S.L., 1990. Methods and Results of Seismotectonic Deformation Studies. Nauka, Moscow, 191 c. (in Russian) [Юнга С.Л. Методы и результаты изучения сейсмотектонических деформаций. М.: Наука, 1990. 191 c.].

31. Yunga S.L., 1997. Classification of seismic moment tensors on the basis of their isometric mapping on a sphere. Tran¬sactions (Doklady) of the Russian Academy of Sciences / Earth Science Sections 352 (1), 108–110.

32. Yunga S.L., 2002. Study of Crustal Surface Movements and Deformation in the Central Tien Shan, Kazakh Platform and Altai; Development of Software for Seismic Data Processing; Data Processing. Research report. Obninsk, 41 p. (in Russian) [Юнга С.Л. Изучение движений поверхности и деформаций земной коры на территории Центрального Тянь-Шаня, Казахской платформы и Алтая; создание программ обработки сейсмологических данных, проведение обработки. Отчет о научно-исследовательской работе. Обнинск, 2002. 41 с.].

33. Zubovich A.V., 2001. Study of the Field of Modern Crustal Movement Velocities in the Central Tien Shan by Space Geo¬desy Methods. PhD Thesis (Candidate of Physics and Mathematics). Schmidt Institute of Physics of the Earth of RAS, Moscow, 95 p. (in Russian) [Зубович А.В. Изучение поля скоростей современных движений земной коры Центрального Тянь-Шаня методами космической геодезии: Дис. … канд. физ.-мат. наук. М.: Институт физики Земли им. О.Ю. Шмидта РАН, 2001. 95 с.].

34. Zubovich A.V., Trapeznikov Yu.A., Bragin B.D., Mosienko O.I., Shchelochkov G.G., Rybin A.K., Batalev V.Yu., 2001. Deformation field, Earth's crust deep structure, and spatial seismicity distribution in the Tien Shan. Geologiya i Geofizika (Russian Geology and Geophysics) 42 (10), 1634–1640.