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توموگرافی دوبعدی سرعت موج ML در ایران | ||
| فیزیک زمین و فضا | ||
| مقاله 4، دوره 42، شماره 2، شهریور 1395، صفحه 263-279 اصل مقاله (1.86 M) | ||
| شناسه دیجیتال (DOI): 10.22059/jesphys.2016.57731 | ||
| نویسندگان | ||
| مهدی ماهری پیرو1؛ عبدالرضا قدس* 1؛ مجید عباسی2 | ||
| 1دانشگاه تحصیلات تکمیلی علوم پایه زنجان | ||
| 2بخش مهندسی نقشه برداری، دانشگاه زنجان | ||
| چکیده | ||
| در این مطالعه به منظور بررسی تغییرات جانبی ضخامت پوسته در ایران، با استفاده از روش توموگرافی لرزه‌ای تغییرات سرعتِ گروه بیشینه دامنه‌ی جابجایی موج برشی ML در پوسته‌ی ایران بدست آمده است. داده‌های استفاده شده در این مطالعه شامل 56152 خوانش سرعتِ ML استخراج شده از شکلموجهای ثبت شده توسط شبکه‌های لرزهنگاری دائم و موقت ایران است. زلزلههای انتخاب شده شامل 2943 رویداد زلزله در قالب 63 خوشه‌ی لرزه‌ای با خطای مکان‌یابی 5 کیلومتر یا کمتر هستند. با استفاده از روش کمترین مربعات مقید، وارون‌سازی مستقیم برای بدست آوردن نقشه‌ی سرعت دوبُعدی موج ML به همراه تصحیحات ایستگاه و چشمه انجام شد. نقشه‌ی سرعت موج برشی بدست آمده از این مطالعه تشابه زیادی با نقشه‌ی سرعت امواج Pnدارد که بیانگر وابستگی شدید سرعت موج Lg به تغییرات ضخامت پوسته و سرعت گوشته‌ی بالایی است. سرعت‌های بیشتر از 4 کیلومتر بر ثانیه برای حوضه‌ی خزر جنوبی و زاگرس نشان‌دهنده انسداد انتشار موج Lg در این مناطق است. مرز سرعتی بین زاگرس و ایران مرکزی به طور قابل ملاحظه‌ای از گسل اصلی زاگرس انحراف دارد که می‌تواند نشان‌دهنده‌ی زیرراندگی بخشی از صفحه‌ی عربی به زیر ایران مرکزی باشد. منطقه‌ی لوت دارای سرعت کم موج Lg است که می‌تواند نشانگر قاره‌ای بودن پوسته لوت باشد. البرز، قسمت اعظم ایران مرکزی و بخصوص منطقه شمال غرب ایران دارای سرعت کم موج Lg هستند که می‌تواند با گرم بودن پوسته در این مناطق در ارتباط باشد. | ||
| کلیدواژه‌ها | ||
| موج Lg؛ سرعت موج برشی؛ توموگرافی لرزه‌ای؛ کمترین مربعات مقید؛ حوضه خزر جنوبی؛ زاگرس | ||
| عنوان مقاله [English] | ||
| ML Velocity Tomography in Iranian Plateau | ||
| نویسندگان [English] | ||
| Mehdi Maheri Peyrov1؛ Madjid Abbasi2؛ | ||
| چکیده [English] | ||
| We useWe use ML shear wave velocity to derive a high resolution 2D ML shear wave velocity map for the Iranian Plateau. The ML amplitudes and arrival times are routinely measured for the calculation of local magnitude. ML shear wave velocity is very sensitive to the lateral change of crustal thickness and switches between the velocity of Lg and Sn waves. An Lg wave will die out as soon as encounter a sudden crustal change in favor of formation of mantle Sn wave. The collected data base is consisted of 56152 ML velocity belong to 2943 precisely relocated events happened during 1996 to 2012. The arrival time of ML amplitudes were read from waveforms of permanent and temporary networks in Iran. Using the arrival time of an ML amplitude and its ray length, we calculate average shear wave velocity for each ray. The selected events are consisted of 63 clusters with epicentral location uncertainty of 5 km or less. The cluster approach adopted in this work allows us to easily calculate empirical velocity error for each summary ray connecting a given observing station to the corresponding cluster. This also reduces drastically the number of initial 56152 rays to just 3107 summary rays and thus significantly reduces the required computation time for the seismic tomography. Except for the Makran region, the summary rays provide a good coverage for most of Iran. Using a constrained direct damped weighted least square inversion scheme, we inverted the ML velocity for a 2D ML shear wave velocity map of Iran along with its cluster and station correction terms. In our tomography, we constrained the velocity of each cell based on the azimuthal coverage of the hitting rays. The input average velocity for each ML ray was also weighted based on its empirical reading spread. The computed ML shear velocity varies mostly between 2.9 and 3.6 km/s, so suggesting that the majority of the rays are indeed Lg rays. The map shows a general similarity with previous maps of Pn velocity indicating that ML shear wave velocity is strongly affected by lateral changes of crustal thickness and upper mantle velocity. Our results show that Caspian Basin, and Zagros regions are Lg blocking regions. We speculate that the blockage of Lg wave in Zagros is related to strong lateral crustal thickness changes caused by the orogenic processes. We also noted that the shear wave velocity border between the Zagros and Central Iran is considerably deviating from Zagros suture line indicating a partial underthrusting of the cold Arabian plate beneath the Central Iran. The Lg blockage in South Caspian basin is either related to its postulated oceanic type crust and/or strong lateral change in its crustal thickness. East of the Caspian Sea shows high velocities likewise its interior, implying the low plain is underlane by either an oceanic type crust or a transitional crust with large lateral variations of crustal thickness. The ML velocity map also shows a velocity in the range of Lg velocity for the Lut block and thus implying a continental nature for the unknown Lut block. Alborz, most of the Central Iran and especially the northwestern Iran show rather low Lg velocities suggesting a warm continental crust. | ||
| کلیدواژه‌ها [English] | ||
| Seismic tomography, Constrained least square, Zagros, South Caspian Basin, Lg wave, Shear wave’s velocity | ||
| مراجع | ||
|
Al-lazki, A., Sandvol, E., Seber, D., Barazangi, M., Turkelli, N. and Mohamad, R., 2004, Pn tomographic imaging of mantle lid velocity and anisotropic at the junction of Arabian, Erusian and African plates, Geophys. J. Int., 158, 1024-1040.
Allen, M. B., Ghassemi, M., Sharabi, M. and Qorashi, M., 2003, Accommodation of late Cenozoic oblique shortening in the Alborz Range, northern Iran, Journal of Structural Geology, 25, 659-672.
Amini, S., Shomali, Z. H., Koyi, H. and Roberts, R. G., 2012, Tomographic upper-mantle velocity structure beneath the Iranian Plateau, Tectonophysics, 554-557, 42-49.
Aziz Zanjani, A., Ghods, A., Sobouti, F., Bergman, F., Mortezanejad, G., Priestley, K., Madanipour, S. and Rezaeian, M., 2013, Seismicity in the western coast of the South Caspian Basin and the Talesh Mountains, Geophys. J. Int., 195(2), 799-814.
Engdahl, E. R., Jackson, J. A., Myers, S. C., Bergman, E. A. and Priestley, K., 2006, Relocation and assessment of seismicity in the Iran region, Geophys. J. Int., 167, 761-778.
Furumura, T. and Kennett, B. L. N., 1997, On the nature of regional seismic phases-II, on the influence of structural barriers, Geophys. J. Int., 129, 221-234.
Ghods, A., Rezapour, E., Bergman, G., Mortezanejad, G. and Talebian, M., 2012, Relocation of the 2006 Mw 6.1 Silakhour, Iran, Earthquake Sequence: Details of Fault Segmentation on the Main Recent Fault, Bull. Seism. Soc. Am., 102, 398-416.
Ghods, A., Shabanian, E., Bergman, E., Faridi, M., Donner, S., Mortezanejad, G. and Aziz Zanjany, A., 2015, The Varzaghan–Ahar, Iran, Earthquake Doublet (Mw 6.4, 6.2): implications for the geodynamics of northwest Iran, Geophys. J. Int, 203(1), 522-540.
Havskov, J. and Otemoller, L., 1999, SEISAN: The Earthquake Analysis Software, version 8.0, Institute of Solid Earth Physics, University of Bergen, Norway.
Hutton, L. K. and Boore, D. M., 1987, The ML scale in southern California, Bull. Seismol. Soc. Am., 77, 2074-2094.
Hermann, R. B. and Kijko, A., 1983, Modeling some empirical vertical component Lg relations, Bull. Seism. Soc. Am., 73, 157-171.
Hessami, K., Jamali, F. and Tabassi, H., 2003, Major active faults of Iran, scale 1:2,500,000, Int. Inst. of Earthquake Eng. And Seismol., Tehran.
Jackson, J., Priestley, K., Allen, M. and Berberian, M., 2002, Active tectonics of the South Caspian Basin, Geophys. J. Int., 148(2), 214-245.
Kadinsky-Cade, K., Barazangi, M., Oliver, J. and Isacks, B., 1981, Lateral variations of high-frequency seismic wave propagation at regional distances across the Turkish and Iranian plateaus, J. Geophys. Res., 86(B10), 9377-9396, doi:10.1029/JB086iB10P09377.
Kaviani, A., Paul, A., Bourova, E., Hatzfeld, D., Pedersen, H. and Mokhtari, M., 2007, A strong seismic velocity contrast in the shallow mantle across the Zagros collision zone (Iran), Geophys. J. Int., 171, 399-410, doi:10.1111/j.1365-246X.2007.03535.x.
Kennett, B. L. N., 1986, Lg waves and structural boundaries, Bull. Seism. Soc. Am., 76, 1133-1141.
Lytle, R. J. and Dines, K. A., 1980, Iterative ray tracing between boreholes for underground image reconstruction, IEEE Trans. Geosci. Remote sensing, 18, 234-240.
Mangino, S. and Priestley, K., 1996, Seismic studies of the Caspian basin and surrounding regions, Geophys. J. Int., 133, 630-648.
Mortezanejad, G., Aziz Zanjani, A., Ghods, A. and Sobouti, F., 2013, Insights into the crustal structure and the seismotectonics of the Talesh region using the local and teleseismic data, Quart. J. Earth Sci., 88.2, 38-47, in Farsi.
Mouthereau, F., Lacombe, O. and Vergés, J., 2012, Building the Zagros collisional orogen: timing, strain distribution and the dynamics of Arabia/Eurasia plate convergence, Tectonophysics 532-535, 27-60.
Nemati, M., Hollingsworth, J., Bolourchi, M. J., Mirzaei, N. and Zhan, Z., 2013, Microseismicity and seismotectonics of the South Caspian Lowlands, NE Iran, Geophys. J. Int., 193(3), 1053-1070, doi: 10.1093/gji/ggs114.
Nilforoushan, F., Masson F., Vernant, P., Vigny, C., Martinod, J., Abbassi, M., Nankali, H., Hatzfeld, D., Bayer, R., Tavakoli, F., Ashtiani, A., Doerflinger, E., Daignières, M., Collard, P. and Chéry, J., 2003, GPS network monitors the Arabia-Eurasia collision deformation in Iran, J. Geodesy, 77, 411-422.
Paul, A., Hatzfeld, D., Kaviani, A., Tatar, M. and Péquegnat, C., 2010, Seismic imaging of the lithospheric structure of the Zagros mountain belt (Iran), Geol. Soc. London. Spec. Pub., 330, 5-18.
Paul, A., Kaviani, A., Hatzfeld, D., Vergne, J. and Mokhtari, M., 2006, Seismological evidence for crustal-scale thrusting in the Zagros mountain belt (Iran), Geophys. J. Int., 166(1), 227-237, doi:10.1111/j.1365-246X.2006.02920.x.
Pei, S., Sun, Y. and Taksoz, M. N., 2011, Tomographic Pn and Sn velocity beneath the continental collision zone from Alps to Himalaya, J. Geophys. Res., 116, B10311, doi:10.1029/2010JB007845.
Press, F. and Ewing, M., 1952, Two slow surface waves across North America, Bull. Seism. Soc. Am., 42, 219-228.
Radjaee, A., Rham, D., Mokhtari, M., Tatar, M., Priestley, K. and Hatzfeld, D., 2010, Variation of Moho depth in the central part of the Alborz Mountains, northern Iran, Geophys. J. Int., 181, 173-184.
Raven, K. J., 2005, The nature of Oceanic basins trapped within the Alpine-Himalayan belt, and their relationship to Tethys. Ph.D. thesis, Earth Sciences, University of Cambridge.
Rodgers, A. R., Ni, J. F. and Hearn, T. M., 1997, Propagation characteristics of short-period Sn and Lg in the Middle East, Bull. Seism. Soc. Am., 87, 396-413.
Rham, D., 2007, The crustal structure of the Middle East, Ph.D. Thesis, University of Cambridge, Cambridge, UK.
Ruzaikin, A. I., Nersesov, I. L., Khalturin, V. I. and Molnar, P., 1977, Propagation of Lg and lateral variations of crustal structure in Asia, J. Geophys. Res., 82, 307-316.
Sandvol, E., Al-Damegh, K., Calvert, A., Seber, D., Barazangi, M., Mohamad, R., Gok, R., Turkelli, N. and Gurbuz, C., 2001, Tomographic imaging of Lg and Sn propagation in the Middle East, Pure appl. Geophys., 158, 1121-1163.
Shad Manaman, N., Shomali, H. and Koyi, H., 2011, New constraints on upper-mantle S-velocity structure and crustal thickness of the Iranian plateau using partitioned waveform inversion, Geophys. J. Int., 184, 247-267. Shearer, P. M., 2002, Introduction to seismology, Cambridge University Press, 115-125.
Sodoudi, F., Yuan, X., Kind, R., Heit, B. and Sadidkhouy, A., 2009, Evidence for a missing crustal root and a thin lithosphere beneath the Central Alborz by receiver function studies, Geophys. J. Int., 177, 733-742.
Stocklin, J., 1968, Structural history and tectonics of Iran. A review, Am. Assoc. Pet. Geol. Bull., 52, 1229-1258.
Takin, M., 1972, Iranian geology and continental drift in the Middle East, Nature, 235, 147-50.
Vanicek, P. and Krakiwsky, E., 1986, Geodesy: the concepts, Elsevier Science Publishing Company, p. 209-213.
Yaminifard, F., Tatar, M., Hessami, K., Gholamzadeh, A. and Bergman, E., 2012, Aftershock analysis of the 2005 November 27 (Mw 5.8) Qeshm Island earthquake (Zagros-Iran): Triggering of strike-slip faults at the basement, Journal of Geodynamics, 61, 138-147.
Walker, R. and Jackson, J., 2004, Active tectonics and late Cenozoic strain distribution in central and eastern Iran, Tectonics, 23, TC5010, doi:10.1029/2003TC001529.
Walker, R. T., Bergman, E. A., Elliott, J. R., Fielding, E. J., Ghods, A.-R., Ghoraishi, M., Jackson, J., Nazari, H., Nemati, M., Oveisi, B., Talebian, M. and Walters, R. J., 2013, The 2010-2011 South Rigan (Baluchestan) earthquake sequence and its implications for distributed deformation and earthquake hazard in southeast Iran, Geophys. J. Int., 193, 349-374.
Walker, R. T., Bergman, E., Jackson, J., Ghorashi, M. and Talebian, M., 2005, The 2002 June 22 Changureh (Avaj) earthquake in Qazvin province, northwest Iran: epicentral relocation, source parameters, surface deformation and geomorphology, Geophys. J. Int, 160(2), 707-720.
Walker, R. T., Bergman, E., Szeliga, W. and Fielding, E. J., 2011, Insights into the 1968-1997 Dasht-e-Bayaz and Zirkuh earthquake sequences, eastern Iran, from calibrated relocations, InSAR and high-resolution satellite imagery, Geophys. J. Int, 187(3), 1577-1603.
Walker, R. T., Khatib, M. M., Bahroudi, A., Rodés A., Schnabel C., Fattahi, M., Talebian M. and Bergman E., 2015, Co-seismic, geomorphic, and geologic fold growth associated with the 1978 Tabas-e-Golshan earthquake fault in eastern Iran, Geomorphology, 237, 98-118. | ||
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