برآورد ضریب کیفیت موج‌های برشی و فشاری در پوسته شمال غرب ایران

نوع مقاله : مقاله پژوهشی‌

نویسندگان

1 مؤسسه ژئوفیزیک، دانشگاه تهران

2 موسسه ژئوفیزیک دانشگاه تهران

چکیده

در مطالعات مرتبط با زلزله‌شناسی مهندسی برای برآورد خطر لرزه‌ای در مناطق مختلف و همچنین تعیین دقیق بزرگا، شبیه‌سازی جنبش نیرومند زمین و مطالعه انرژی مخرب حاصل از زمین‌لرزه در حوزه نزدیک تا متوسط، تخمین ضریب کیفیت امواج برشی و فشاری نقشی اساسی دارد. بدین منظور با توجه به قرار گرفتن چندین شهر بزرگ در پهنه شمال غربی فلات ایران، ضریب کیفیت امواج فشاری و برشی با استفاده از داده‌های هفده ایستگاه لرزه‌نگاری با بیش از 13000 زمین‌لرزه ثبت شده در شبکه مرکز لرزه‌نگاری کشوری (IRSC) و شبکه ملی لرزه‌نگاری نوارپهن ایران (INSN) برآورد شد. برای سه گروه داده به‌ترتیب با فاصله رومرکزی کمتر از 100 کیلومتر، از 100 تا 200 کیلومتر و صفر تا 200 کیلومتر بررسی تغییرات جذب امواج حجمی در نُه نوار بسامدی، با بسامدهای مرکزی در 3، 5، 7، 10، 14، 20، 28، 38 و 47 هرتز انجام گرفت و برای هرکدام از ایستگاه‌ها برای بسامدهای مختلف به‌طور جداگانه ضریب کیفیت تخمین ‌زده‌شد. در این مطالعه از روش کُدای بهنجارشده برای برآورد ضریب جذب امواج فشاری و برشی حاصل از زمین‌لرزه به‌عنوان روشی قابل اعتماد با توجه به حذف شدن اثرات چشمه و ساختگاه در مدل‌سازی انجام گرفته، استفاده شد. برای پهنه شمال غربی ایران مقادیر وابستگی بسامدی ضریب کیفیت امواج فشاری و برشی در همه ایستگاه‌ها برآورد شد به‌طوری‌که مقدار متوسط آن برای محدوده شمال غرب فلات ایران از  و  پیروی می‌کند. با توجه به مقادیر پایین و لذا جذب بالای امواج برشی و فشاری در پهنه شمال غرب ایران دامنه امواج حین عبور از زمین به‌شدت تضعیف می‌شود که این اثر جذب امواج لرزه‌ای، باعث کاهش خسارات ناشی از زمین لرزه‌ها در فواصل مناسب از گسل‌ها در زمان وقوع زمین‌لرزه خواهد شد.
 

کلیدواژه‌ها


عنوان مقاله [English]

Estimation of compressional and shear wave quality factor in North West of Iranian Plateau

نویسندگان [English]

  • Mojtaba Naghavi 1
  • Habib Rahimi 2
  • Ali Moradi 1
1 Institute of Geophysics, University of Tehran
2 Institute of Geophysics, University of Tehran
چکیده [English]

The purpose of this study is to estimate compressional and shear wave quality factors of seismic waves by using local earthquakes occurred in the NW of Iranian Plateau. In seismological engineering studies, quality factor estimation of body and shear waves plays an important role in seismic risk assessment of different areas, determining the exact magnitude of the earthquake, strong ground motion simulation and study of destructive energy of earthquake from near to intermediate region. In this study, earthquakes recorded in the Iranian Seismological Center (IRSC) and Iranian National Broadband Seismic Network (INSN) for the longitudinal band from 43°E to 53°E and the latitude band from 36°N to 40°N were used. Among the 17 stations, 14 stations belong to the IRSC and the rest belong to the INSN. Due to the presence of some big cities in the northwestern part of Iranian Plateau, quality factors of body and shear waves were estimated by using the data of 17 seismological stations including 13000 recorded earthquakes of the IRSC and INSN.
This region of intense deformation is situated between two thrust belts of the Caucasus to the north and the Zagros Mountains to the south. The NW of Iranian Plateau is a part of Turkish–Iranian plateau and includes historical and destructive earthquakes and two volcanoes with lots of thermal springs around. The North Tabriz Fault (NTF) is one of the active faults in NW Iran that has a clear surface expression.
Seismic quiescence and large historical earthquakes in the region in more than the two last centuries have increased the seismic risk of this region. To estimate seismic hazard in an area, a two-step process is needed. First, we must understand the nature of the earthquake sources that generate potentially hazardous ground motion. This includes knowledge of the distribution of seismic source zones, predominant fault mechanisms and return times of large events. Second, we must understand the effects of the transmitting medium (the Earth) on the seismic waves. A synthesis of the source and path effects will allow us to calculate the ground motion at a given site. Seismic attenuation is also caused by intrinsic mechanisms that convert the wave energy to heat through friction, viscosity, and thermal relaxation processes. Scattering redistributes wave energy within the medium but does not remove energy from the overall wavefield. In contrast, intrinsic attenuation mechanisms convert the wave energy to heat through friction, viscosity, and thermal relaxation processes. Energy loss caused by inelastic behavior is called inherent or internal attenuation and is determined by the inverse of the Q parameter. Large values of quality factor mean that attenuation is low and when Q is equal to zero, attenuation is very high.
Aki (1980) used the normalized Coda for the first time in order to estimate absorption amplitude of the S waves. Since then, this method has frequently been used in seismological studies for estimation of the absorption parameters of seismic waves (see, for example, Yoshimoto, 1993; Hatzidimitriou, 1995).
For three categories of data with epicentral distances less than 100 km, from 100 to 200 km and 0 to 200 km, attenuation variation investigation of body waves was carried out in 9 frequency bands with central frequencies of 3, 5, 7, 10, 14, 20, 28, 38 and 47 Hz and the quality factor was estimated in different frequencies for each station, separately. For the northwesern part of Iran, the frequency dependence of the body and shear wave quality factors in all stations were estimated so that their average values are quantified as Qp=55f 0.84 and
Qs=38f 0.93 , respectively. Due to the low values of the Q parameter and thus high attenuation values of body and shear waves in North West of Iranian Plateau, the amplitude of the propagated waves are decreased severely in the interested area when these waves pass through it. The attenuation effect of seismic waves would reduce the damages caused by the earthquakes at appropriate distances from the faults at the time of probable earthquake occurence.
 

کلیدواژه‌ها [English]

  • Compressive and shear waves
  • NW of Iranian Plateau
  • Attenuation
  • Quality factor
آقانباتی، س، ع.، 1383،  زمین­شناسی ایران: سازمان زمین‌شناسی کشور.
حسامی آذر، خ.، سلیمانی آزاد، ش.، و فیلیپ، هـ..، 1386، بررسی­های دیرینه‌لرزه‌شناسی بر روی قطعه جنوب خاوری گسل شمال تبریز: پژوهشگاه بین‌المللی زلزله‌شناسی و مهندسی زلزله.
حیدری، ط.، 1394، محاسبه ضریب کیفیت موج برشی در شمال غرب ایران: پایان­نامه کارشناسی ارشد، دانشگاه تحصیلات تکمیلی علوم پایه زنجان.
درویش‌زاده، ع.، 1372،  زمین­شناسی ایران: انتشارات نشر دانش امروز.
راستگو، م.، حمزه­لو، ح.، رضاپور، م.، و رحیمی، ح.، 1390، برآورد ضریب کیفیت امواج برشی و کدا در ناحیه هرمزگان، جنوب ایران: مجله ژئوفیزیک ایران، 5، 111-131.
قاسمی، ه.، کمالیان، ن.، حمزه‌لو، ح.، و بیت‌الهی، ع.، 1384، تعیین فاکتور کیفیت امواج برشی مستقیم ، در منطقه البرز به کمک داده‌های میدان نزدیک حرکت نیرومند زمین‌لرزه کجور در محدوده بسامدی 1 تا 32 هرتز: نشریه فیزیک زمین و فضا، 31، 103-112.
متقی، خ.، قدس، ع.، و سیاهکوهی، ح.، 1388، تعیین روابط کاهندگی دامنه امواج لرزه­ای در ناحیه تهران: مجله علوم زمین، 79، 61-66.
نظام الاسلامی، ح .، 1382 ،  تعیین فاکتور کیفیت برای پیرامون تبریز: پایان­نامه کارشناسی ارشد، مؤسسه ژئوفیزیک دانشگاه تهران.
Aki, K., 1969, Analysis of the seismic coda of local earthquakes as scattered waves: J. Geophys. Res., 74, 615–631.
Aki, K., 1980, Scattering and attenuation of shear waves in the lithosphere: J. Geophys. Res., 85, 6496–6504.
Aki, K., and Chouet, B., 1975, Origin of coda waves: Source, attenuation, and scattering effects: J. Geophys. Res., 80, 3322–3342.
Akinci, A., Del Pezzo, E., and Ibáñez, J., 1995, Separation of scattering and intrinsic attenuation in southern Spain and western Anatolia (Turkey): Geophys. J. Int., 121, 337–353.
Bianco, F., Del Pezzo, E., Castellano, M., Ibáñez, J. and Di Luccio, F., 2002, Separation of intrinsic and scattering seismic attenuation in the Southern Apennine zone, Italy: Geophys, J. Int., 150, 10–22.
Campillo, M., 1990, Propagation and attenuation characteristic of the crustal phase Lg: Pure Appl. Geophys., 132, 1–19. Chung, T. W., and Sato, H., 2001, Attenuation of high-frequency P and S waves in the crust of Southeastern South Korea: Bull. Seism. Soc. Am., 91(6), 1867–1874.
Copley, A., and Jackson, J., 2006, Active tectonics of the Turkish–Iranian Plateau: Tectonics, 25, TC6006, DOI: 10.1029/2005TC001906.
Frankel, A., 1991, Mechanisms of seismic attenuation in the crust: Scattering and inelasticity in New York State, South Africa, and Southern California: J. Geophys. Res., 96, 6269–6289.
Hamada, G. M., 2004, Reservoir fluids identification using Vp/Vs ratio: Oil & Gas Science and Technology – Rev., IFP, 59, 649–654.
Hamzehloo, H., Rahimi, H., Sarkar, I., Mahood, M., Mirzaei Alavijeh, H. and Farzanegan, E., 2009, Modeling the strong ground motion and rupture characteristics of the March 31, 2006, Darb-e-Astane earthquake, Iran, using a hybrid of near-field SH-wave and empirical Green’s function method: J. Seismol., 14, 169–195. DOI: 10.1007/s10950-009-9159-x.
Hassani, B., Zafarani, H., Farjoodi, J., and Ansari, A., 2011, Estimation of site amplification, attenuation and source spectra of S-waves in the East-Central Iran: Soil Dynamics and Earthquake Engineering, 85, 17–30,
Hoshiba, M., 1993, Separation of scattering attenuation and intrinsic absorption in Japan using the multiple lapse time window analysis of full seismogram envelope: J. Geophys. Res., 98, 15809–15824.
Kamalian, N., Hamzeloo, H., and Ghasemi, H., 2007, S-wave attenuation and spectral decay parameter for the Avaj region, Iran: Iranian J. Science and Technology, 31, 63–71.
Hatzidimitriou, P. M., 1995, S-wave attenuation in the crust in northern Greece: Bull. Seism. Soc. Am., 85, 1381–1387.
Kim, K. D., Chung, T. W., and Kyung, J. B., 2004, Attenuation of high frequency P and S waves in the crust of Choongchung provinces, Central South Korea: Bull. Seism. Soc. Am., 94, 1070–1078.
Kinoshita, S., 1994, Frequency-dependent attenuation of shear waves in the crust of the southern Kanto area: Bull. Seism. Soc. Am., 59, 1387–1396.
Lay, T. and Wallace, T. C.,  1995, Modern Global Seismology: Academic Press, 521 pp.
Ma’hood, M., Hamzehloo, H., and Doloei, G. J., 2009, Attenuation of high frequency P and S waves in the crust of the East-Central Iran: Geophys. J. Int., 179, 1669–1678.
Masson, F., Van Gorp, S., Chery, J., Djamour, Y., Tatar, M., Tavakoli, F., Nankali, H., Vernant, P., 2006, Extension in NW Iran driven by the motion of the South Caspian Basin: Earth Planet. Sci. Lett., 252, 180–188.
Ou, G. and Herrmann, R., 1990, A statistical model for peak ground motion from local to regional distances, Bull. Seism. Soc. Am., 80, 1397–1517.
Pearce, J. A., Bender, J. F., De Long, S. E., Kidd, W. S. F., Low. P. J., Güner, Y., Şaroğlu, F., Yılmaz, Y., Moorbath, S., and Mitchell, J. G., 1990, Genesis of collision volcanism in Eastern Anatolia, Turkey: J. Volcanol. and Geothermal Res., 44, 189–229.
Polatidis, A., Kiratzi, A., Hatzidimitriou, P., and Margaris, B., 2003, Attenuation of shear- waves in the back-arc region of the Hellenic arc for frequencies from 0.6 to 16 Hz: Tectonophysics, 367, 29–40.
Pulli, J. J., 1984, Attenuation of coda waves in New England: Bull. Seism. Soc. Am., 74, 1149–1166.
Rahimi, H., Hamzehloo, H., and Kamalian, N., 2010, Estimation of coda and shear wave attenuation in the volcanic area in SE Sabalan Mountain, NW Iran: Acta. Geophys., 58, 244–268.
Rautian, T. G., and Khalturin, V. I., 1978, The use of the coda for determination of the earthquake source spectrum: Bull. Seism. Soc. Am., 68, 923–948.
Safarshahi, M., Hamzeloo, H., Rezapour, M., Sinaeian, F., Farzanegan, E., and Mirzaei, H., 2011, Estimation of QS in southern Iran, using strong motion data of Rigan earthquakes (2010 & 2011): 1st International Conference of Urban Construction in the Vicinity of Active Faults, Tabriz, Iran.
Samaei, M., Miyajima, M., Tsurugi, M., and Fallahi, A., 2013, Source and path parameters for recorded earthquakes in Tehran Province, Iran: J Japan Soc. Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), 69, I 980–I 988.
Tsujiura, M., 1978, Spectral analysis of the coda waves from local earthquakes: Bull. Earthq. Inst. Univ. Tokyo, 53, 1–48.
Vernant, P., Nilfroushan, F., Hatzfeld, D., Abbassi, M., Vigney, C., Masson, F., Nankali, H., and Martinod, J., 2004, Contemporary crustal deformation and plate kinematics in Middle East constrained by GPS measurements in Iran and North Oman, Geophys. J. Int., 157, 381–398.
Yoshimoto, K., Sato, H. and Ohtake, M., 1993, Frequency-dependent attenuation of P and S waves in Kanto area Japan based on the coda-normalization method: Geophys. J. Int., 114, 165–174.
Udias, A., 1999, Principles of Seismology: Cambridge University Press, 492 pp.
Zafarani, H., Mousavi, M., Noorzad, A., and Ansari, A., 2008, Calibration of the specific barrier model to Iranian plateau earthquakes and development of physically based attenuation relationships for Iran: Soil Dynamics and Earthquake Eng., 28, 550–576.