Crustal Swave velocity beneath the northeastern Tibetan plateau inferred from teleseismic Pwave receiver functions
ZHANG Hong-Shuang1,2, GAO Rui1,2, TIAN Xiao-Bo3, TENG Ji-Wen3, LI Qiu-Sheng1,2, YE Zhuo1,2, LIU Zhen3, SI Shao-Kun3
1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China; 2. Key laboratory of Eearth Probe and Geodynamics, Ministry of Land and Resources of the People's Republic of China, Beijing 100037, China; 3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Abstract：The northeastern (NE) Tibetan Plateau is an ideal place for investigating the far field effects of collision between the Indian and Eurasian plates. By what ways the Tibetan crust is thickened and extended is a long-term debated issue for absence of convincing evidence for proving the existence of the inner-crustal low velocity zone and its role. Using teleseimic P wave data from the China Seismograph Network in Qinghai and Gansu provinces recorded from 2007 to 2009, the crustal S-wave velocity structure beneath the NE Tibet plateau is resolved.#br#The receiver function waveform inversion technique (PROGRAM330) is used to analyze the crustal S-wave velocity structure below seismic stations. The receiver functions are estimated by a time-domain iterative deconvolution method of Ammon (1991) with four different Gaussian coefficients (α=1.0, 1.5, 2.0 and 2.5). Firstly, receiver functions, which are much similar in waveforms and within a narrow range of back-azimuth (less than 10°) and ray parameter (less than 0.002), are stacked to enhance the main signal characteristics. To maintain the intrinsical details of the receiver functions, they are stacked without normal moveout. Results of Tian et al. (2013) and Li et al. (2006) are used as the constraints in the inversion process to reduce the uncertainty.#br#The results show thata relatively low velocity layer (LVL) exists between the upper and lower crust in the region between the East Kunlun fault and the Haiyuan fault. The depth of the LVL shallows northeastward from ~35 km to ~20 km along the surface movement direction, while the Moho uplifts. The variation in thickness of the upper crust is more obvious than the lower crust. The thickness of the lower crust (15~20 km) beneath the Kunlun-west Qinling orogenic belt is thinner than that beneath the adjacent Qilian block (25~30 km). Beneath the NE Tibetan plateau, as well as the Alashan and Ordos blocks, the S-wave velocity in the lower crust increases with depth.The whole crustal S-wave velocity increases with depth beneath the eastern part of the west Qinling orogenic belt, the Ordos and Alashan blocks.#br# It can be concluded that the observed LVL in the NE Tibetan plateau can act as an intra-crustdecollement/detechment to decouple the deformation between the upper and lower crust. The geometry of the LVL and the Moho indicates that the NE Tibetan crust is growing northeastward, and is predominated by upper-crustal thickening at present.The lower crust of the Kunlun-west Qinling orognic belt may be more rigid than the adjacent Qilian block and thus has experienced less deformation and crustal thickening. The lower crust of the NE Tibetan plateau is normal and possess high viscosity, so that is not conducive to the flow of the lower crust.
Ammon C J, Vidale J E. 1993. Tomography without rays. Bulletin of the Seismological Society of America, 83(2): 509-528. Bai D H, Unsworth M J, Meju M A, et al. 2010. Crustal deformation of the eastern Tibetan plateau revealed by magnetotelluric imaging. Nature Geoscience, 3: 358-362, doi: 10.1038/NGEO830. Chen J H, Liu Q Y, Li S C, et al. 2005. Crust and upper mantle S-wave velocity structure across Northeastern Tibetan Plateau and Ordos block. Chinese J. Geophys. (in Chinese), 48(2): 333-342. Clark M K, Royden L H. 2000.Topographic ooze: Building the eastern margin of Tibet by lower crustal flow. Geology,28(8): 703-706. Cui Z Z, Li Q S, Wu C D, et al. 1995. The crustal and deep structures in Golmud-Ejin Qi GGT. ActaGeophys.Sinica (in Chinese), 38(Suppl. II):15-28. Enkelmann E, Ratschbacher L, Jonckheere R, et al. 2006. Cenozoic exhumation and deformation of northeastern Tibet and the Qinling: Is Tibetan lower crustal flow diverging around the Sichuan Basin?.GSA Bulletin, 18(5-6):651-671, doi: 10.1130/B25805.1. Galvé A, Hirn A, Jiang M, et al. 2002. Modes of raising northeastern Tibet probed by explosion seismology. Earth and Planetary Science Letters, 203(1):35-43. Gan W J, Zhang P Z, Shen Z K, et al. 2007.Present-day crustal motion within the Tibetan Plateau inferred from GPS measurements. J. Geophys. Res.,112:B08416, doi: 10.1029/2005JB004120. Gao R, Ma Y S, Li Q S, et al. 2006. Structure of the lower crust beneath the Songpan block and West Qinlingorogen and their relation as revealed by deep seismic reflection profiling. Geological Bulletin of China (in Chinese), 25(12): 1361-1367. Gao R, Wang H, Yin A, et al. 2013. Tectonic development of the northeastern Tibetan Plateau as constrained by high-resolution deep seismic-reflection data. Lithosphere, 5(6): 555-574. Hu J F, Xu X Q, Yang H Y, et al. 2011.S receiver function analysis of the crustal and lithospheric structures beneath eastern Tibet.EarthPlant. Sci. Lett.,306(1-2):77-85, doi: 10.1016/j.epsl.2011.03.034. Jia S X, Zhang X K, Zhao J R, et al. 2010. Deep seismic sounding data reveal the crustal structures beneath Zoigê basin and its surrounding folded orogenic belts. Sci. China-Earth Sci., 53(2):203-212, doi: 10.1007/s11430-009-0166-0. Karplus M S, Zhao W, Klemperer S L, et al. 2011.Injection of Tibetan crust beneath the south Qaidam Basin: Evidence from INDEPTH IV wide-angle seismic data. J. Geophys. Res.,116:B07301, doi: 10.1029/2010JB007911. Kennett B L N, Engdahl E R. 1991. Traveltimes for global earthquake location and phase identification.Geophys.J. Int.,105(2):429-465. Klemperer S L. 2006.Crustal flow in Tibet: geophysical evidence for the physical state of Tibetan lithosphere, and inferred patterns of active flow. Geological Society, London, Special Publications, 268(1):39-70. Li Q S, Peng S P, Gao R, et al. 2004. Deep tectonic background of the 8.1MS Earthquake in the East Kunlun. Acta Geoscientica Sinica (in Chinese), 25(1): 11-16. Li S L, Mooney W D, Fan J C. 2006.Crustal structure of mainland China from deep seismic sounding data.Tectonophysics, 420(1-2):239-252. Li Y H, Wu Q J, An Z H, et al. 2006. The Poisson ratio and crustal structure across the NE Tibetan Plateau determined from receiver functions. Chinese J. Geophys.(in Chinese), 49(5): 1359-1368. Ligorría J P, Ammon C J. 1999.Iterative deconvolution and receiver-function estimation.Bulletin of the Seismological Society of America, 89(5):1395-1400. Liu M J, Mooney W D, Li S L, et al. 2006. Crustal structure of the northeastern margin of the Tibetan plateau from the Songpan-GanziTerrane to the Ordos Basin.Tectonophysics, 420(1-2): 253-266. Liu Q Y, Kind R, Li S C. 1996. Maximal likelihood estimation and nonlinear inversion of the complex receiver function spectrum ratio. Acta Geophysica Sinica (in Chinese), 39(4): 500-511. Liu Q Y, van der Hilst R D, Li Y, et al. 2014. Eastward expansion of the Tibetan Plateau by crustal flow and strain partitioning across faults. Nature Geoscience, 7(5): 361-365, doi: 10.1038/ngeo2130. Meyer B, Tapponnier P, Bourjot L, et al. 1998. Crustal thickening in Gansu-Qinghai, Lithospheric mantle subduction, and oblique, strike-slip controlled growth of the Tibet plateau.Geophys.J. Int.,135(1): 1-47. Pan S Z, Niu F L. 2011. Large contrasts in crustal structure and composition between the Ordos plateau and the NE Tibetan plateau from receiver function analysis. Earth and Planetary Science Letters, 303(3-4):291-298. Tapponnier P, Xu Z Q, Roger F, et al. 2001. Oblique stepwise rise and growth of the Tibet plateau. Science, 294(5547):1671-1677, doi: 10.1126/science.105978. Teng J W. 1974. Deep reflected waves and the structure of the earth crust of the eastern part of Chaidambasin. Acta Geophys. Sinica (in Chinese), 17(2): 122-135. Tian X B, Zhang Z J. 2013.Bulk crustal properties in NE Tibet and their implications for deformation model. Gondwana Research, 24(2):548-559. Unsworth M J, Jones A G, Wei W, et al. 2005.Crustal rheology of the Himalaya and southern Tibet inferred from magnetotelluric data. Nature, 438(7064):78-81. Vergne J, Wittlinger G, Hui Q, et al. 2002. Seismic evidence for stepwise thickening of the crust across the NE Tibetan plateau. Earth Planet.Sci. Lett.,203(1):25-33. Wang Q, Gao Y, Shi Y T, et al. 2013. Seismic anisotropy in the uppermost mantle beneath the northeastern margin of Qinghai-Tibet plateau: evidence from shear wave splitting of SKS, PKS and SKKS. Chinese J. Geophys. (in Chinese), 56(3): 892-905, doi: 10.6038/cjg20130318. Wang Y X, Mooney W D, Han G H, et al. 2005. Crustal P-wave velocity structure from AltynTagh to Longmen mountains along the Taiwan-Altay geoscience transect. Chinese J. Geophys.(in Chinese), 48(1): 98-106. Wang Y X, Mooney W D, Yuan X C, et al. 2013. Crustal structure of the northeastern Tibetan plateau from the southern Tarim basin to the Sichuan basin, China. Tectonophysics, 584:191-208. Xu L L, Rondenay S, Van der Hilst R D. 2007. Structure of the crust beneath the Southeastern Tibetan Plateau from teleseismic receiver functions. Phys. Earth Planet.Int.,165(3-4): 176-193, doi: 10.1016/j.pepi.2007.09.002. Yao H J, Beighein C, Van der Hilst R D. 2008.Surface wave arraytomography in SE Tibet from ambient seismic noise and two-station analysis-II.Crustal and upper-mantle structure.Geophys.J. Int.,173(1):205-219, doi: 10.1111/j.1365-246X.2007.03696.x. Yin A, Dang Y Q, Wang L C, et al. 2008.Cenozoic tectonic evolution of Qaidam basin and its surrounding regions. Geological Society of America Bulletin, 120(7-8): 813-846. Zeng R S, Ding Z F, Wu J Q. 1994. A review on the lithospheric structure in Tibetan plateau and constraints for dynamics. Acta Geophysica Sinica (in Chinese), 37(Supp.1): 99-116. Zhang H, Gao Y, Shi Y T, et al. 2012. Tectonic stress analysis based on the crustal seismic anisotropy in the northeastern margin of Tibetan plateau. Chinese J. Geophys. (in Chinese), 55(1): 95-104, doi: 10.6038/j.issn.0001-5733.2012.01.009. Zhang H S, Teng J W, Tian X B, et al. 2012. Lithospheric thickness and upper-mantle deformation beneath the NE Tibetan plateau inferred from S receiver functions and SKS splitting measurements. Geophys.J. Int.,191(3):1285-1294. Zhang P Z, Zheng D W, Yin G M, et al. 2006. Discussion on late Cenozoic growth and rise of northeastern margin of the Tibetan plateau. Quaternary Sciences (in Chinese), 26(1): 5-13. Zhang X K, Yang Z X, Xu Z F, et al. 2007. Upper crust structure of eastern A'nyemaqên suture zone: results of Barkam-Luqu-Gulang deep seismic sounding profile. Acta Seismologica Sinica, 20(6): 628-640. Zhang Z J, Bai Z M, Klemperer S L, et al. 2013. Crustal structure across northeastern Tibet from wide-angle seismic profiling: Constraints on the Caledonian Qilian orogeny and its reactivation. Tectonophysics, 606:140-159, doi: 10.1016/j.tecto.2013.02.040. Zhang Z J, Klemperer S, Bai Z M, et al. 2011. Crustal structure of the Paleozoic Kunlun orogeny from an active-source seismic profile between Moba and Guide in East Tibet, China. Gond.Res.,19(4):994-1007, doi: 10.1016/j.gr.2010.09.008. Zhang Z J, Yuan X H, Chen Y, et al. 2010. Seismic signature of the collision between the east Tibetan escape flow and the Sichuan Basin. Earth and Planetary Science Letters, 292(3-4):254-264. Zhao G, Tang J, Zhan Y, et al. 2005. Relation between electricity structure of the crust and deformation of crustal blocks on the northeastern margin of Qinghai-Tibet Plateau. Science ChinaEarth Sciences, 48(10): 1613-1326. Zheng Y, Yang Y J, Ritzwoller M H, et al. 2010. Crustal structure of the northeastern Tibetan plateau, the Ordos block and the Sichuan basin from ambient noise tomography. Earthq.Sci., 23(5): 465-476.
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