Abstract
The publication presents results of the study aimed at reconstruction of recent crustal stresses for Central and South-Eastern Asia with application of the method of cataclastic analysis of displacements caused by ruptures, which was proposed by Yu.L. Rebetsky. Two sources of seismic data were referred to: (1) the catalog comprising data from publications covering the period from 1904 to 1992, and (2) the Global Centroid Moment Tensor (CMT) Database of earthquake mechanisms ( http://earthquake.usgs.gov/eqarchives/sopor ), which covers the period from 1978 to 2010. The method of cataclastic analysis in its earliest version was applied in 1996 and 1997 when seismic data from the first catalog were analyzed, and it yielded only parameters of stress ellipsoids; the reconstructions were published in a Russian-Chinese journal (it does not exist now). In this paper, these reconstructions are presented in new graphical formats of GIS. Data from the Global CMT Database were analyzed by the method of cataclastic analysis in the new revision with application of its stages 1 and 2. Based on the calculations, orientations of axes of principal stresses, types of ellipsoids, correlations between spherical and deviatoric components of stress tensors, and reduced stresses were determined. The two sets of reconstructions are compared in this paper. The catalog of earthquake focal mechanisms for the period from 1904 to 1992 consolidated information provided by different authors, and thus focal data for many seismic events were highly inconsistent; therefore, the reliability of reconstructions based on such data seems to be lower than that on the basis the Global CMT Database for the period from 1978 to 2010. Some of the reconstructed stress tensor parameters are mapped. For the areas which data are given in the Global CMT Database and considered as more reliable, mapping is based on stress parameters calculated from such data. For the areas that are not covered by the Global CMT Database, reconstructions based on the first catalog are mapped. In the maps showing consolidated patterns of the state of stresses, spacious areas of horizontal extension of the crust in Tibet are clearly identified. In the south, such areas are bordered by regions of horizontal compression of the crust in Himalaya; in the north and north-east, they are bordered by regions of horizontal shear of the crust in East Kunlun. According to results of calculations at stage 2 of the method of cataclastic analyses, the crust in the central part of Tibet is subject to intensive confining pressure and lateral compression that is reduced in the neighboring regions. The crust in the southern and northern parts of Pamir is also subject to horizontal extension and shear. Regions of horizontal compression are located to the north, west and south of Pamir. Regulations of the field of recent tectonic stresses of Tibet and Pamir, which are revealed in this study, can be explained by the concept of ‘tectonic spreading’ of these regions due to gravity, which causes intensive horizontal spreading of the crust in Himalaya when the southern boundary of Tibet bends outwards and spreads over the Indian ‘indenter’ moving in the north–north-eastern direction. It is suggested by the data on horizontal extension of the crust in Tibet and underthrusting shear stresses over the horizontal zones that the impact Indian ‘indenter’ does not go beyond the crust of Pamir and the crust of the central parts of Tibet which is located above the long-term active mantle plume.
Highlights
Аннотация: В работе представлены результаты реконструкции современных напряжений в коре Средней и Юго Восточной Азии при использовании метода катакластического анализа разрывных смещений Ю.Л
Название тектонических провинций по работам [Stuwe, 2007; Kunin et al, 1988; Burtman, 2012; Levi, Sherman, 2005; Laverov et al, 2006]
Два других параметра – распределение поддвиговых касательных напряжений на горизон тальных площадках и площадное распределение эф фективного давления и редуцированных латеральных напряжений – в этих работах не рассматривались
Summary
В изучении природных напряжений, действующих в земной коре сейсмоактивных областей, в последние годы наметился существенный прогресс, так как полу чили развитие подходы не только по расчету ориента ции главных осей тензора напряжений, но и по оценке величин напряжений [Angelier, 1989; Michael, 1984; Hardebeck, Hauksson, 2001; Rebetsky, 1994, 2003, 2005]. В настоящей работе будут представлены результа ты реконструкции напряженного состояния для коры Средней и ЮгоВосточной Азии В тектонофизике осо бенности параметров напряженного состояния в точке среды, полученные тем или иным способом (прямая или обратная задача тектонофизики), представляют на основе данных об ориентации осей главных напряже ний, при этом термин «тип напряженного состояния» здесь применяется совершенно не так, как это делается в механике. Подобные различия в механизмах одних и тех же землетрясений приводили к необходимости их учета при реконструкции напряжений, что отражалось в ал горитмах расчета ориентации главных осей напряже ний [Gushchenko et al, 1990, 1991; Petrov et al, 1994]. Именно в таких условиях в середине 90х годов прошлого века была выполнена реконструкция при родных напряжений по данным о механизмах очагов землетрясений для мегарегиона ЮгоВосточной Азии и Океании [Rebetsky et al, 1997]. В нашей работе будет проведено сопоставление ре зультатов исследований современного напряженного состояния, полученного в предыдущих работах, с на шими новыми результатами реконструкции напряже ний
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