بررسی کاهندگی امواج برشی و کدا در منطقه جنوب شرقی تهران

نوع مقاله : Articles

نویسندگان

1 دانشگاه پیام نور، تهران

2 پژوهشگاه بین‌المللی زلزله‌شناسی و مهندسی زلزله

چکیده

همگرایی صفحات عربی و اوراسیا، باعث ایجاد سامانه‌های پیچیده‌ی تکتونیکی در ایـران شده است و در ایـن میـان شهـر تهران در دامنه رشتـه‌کوه‌هـای البرز، بر روی یک پهنه‌ی ناپایدار قرار دارد و به‌دلیل وجود گسل‌های فراوان مستعد زمیـن‌لــرزه می‌باشد. با توجــه به اهمیت شهـر تهـــران و شناسایـی هـرچــه بهتـر خصوصیات لرزه‌ای این منطقه، پارامتر کیفیت و خصوصیات کاهندگی امواج برشی و کدا (دنباله) در منطقه جنوب شرقی تهران بر اساس 22 شتاب‌نگاشت ثبت‌شده از زلزله‌های محلی که عموماً شتاب‌نگاشت‌های زمین‌لرزه‌ی 25 مهرماه 1388 شهرری با بزرگی 4 و دارای عمق کم می‌باشند، مورد پردازش قرار گرفته‌اند. ضریب کیفیت امواج S (Qs) با روش توسعه‌یافته کدای بهنجار و ضریب کیفیت امواج کدا (Qc) با روش تک‌پراکنش به عقب در بازه‌ فرکانسی 5/1 تا 24 هرتز برآورد شده است. رابطه‌ فرکانسی ضریب کیفیت که برای این منطقه برآورد شده عبارت است از Qs=(92±16)f (0.98±0.15) وQc=(114±5)f(1.12±0.04) . مقادیر کم به‌دست‌آمده Q­o (Q در فرکانس 1 هرتز) در ایستگاه‌های منطقه و مقایسه با مناطق آرام و فعال لرزه‌ای جهان مشاهده می‌شود که منطقه‌ مورد مطالعه ناحیه‌ای با ناهمگنی و فعالیت تکتونیکی بالا می‌باشد. این ناهمگنی‌ها می‌تواند به‌سبب خردشدگی حاصل از گسل‌های منطقه باشد. در شهر تهران به دلیل کمبود زلزله‌های ثبت شده، نتایج این مطالعه به کمک نگاشت‌های یک زلزله به دست آمده است و برای کاهش عدم قطعیت می­توان از زلزله­های متفاوت استفاده نمود.Estimation of S and Coda Waves Attenuation in the SE-Tehran Shima Taheri1*, Majid Mahood21. Instructor, Department of Civil Engineering, Payam-e Noor University, *Corresponding Author, e-mail: Shima.tahery@gmail.com.2. Assistant Professor, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran.The Iranian Plateau, characterized by active faulting, active folding, recent volcanic activities, mountainous terrain, and variable crustal thickness, has been frequently struck by earthquakes resulting in the massive loss of life. Studying the seismic hazard as well as evaluating and predicting the strong ground motions require the knowledge of seismic wave attenuation. The complex structure of the Earth’s medium affects seismic wave propagation. Attenuation quantifies the behavior of the seismic energy propagation in the lithosphere and can be utilized for seismic hazard mitigation. Local seismicity makes a large body of data, which provides a unique opportunity to estimate the seismic attenuation. Data from the strong-motion network installed in Tehran region was used to study the seismicity and the frequency-dependent attenuation of the crust. 22 local accelerograms recorded at 14 stations were utilized for the present study. It is estimated that the quality factor of coda waves (Qc) and shear waves (Qs) in the frequency band of 1.5–24 Hz by applying the single backscattering method of S-coda envelopes and the extended coda normalization method, respectively. The values of Qc and Qs show a dependence on frequency in the range of 1.5–24 Hz for this region. Considering records from Shahr-e Rey earthquake (Ml 4, 1388), the estimated values of Qc and Qs vary from 151 ± 49 and 93 ± 14 at 1.5 Hz to1994 ± 124 and 1520 ± 123 at 24 Hz, respectively. The average frequency-dependent relationships estimated for the region are Qs=(92±16)f (0.98±0.15)  and Qc=(114±5)f (1.12±0.04). These results evidenced a frequency dependence of the quality factors Qc and Qs, as commonly observed in tectonically active zones characterized by a high degree of heterogeneity, and the low value of Q indicated an attenuative crust beneath the entire region. The experimental results show that lower Q values can be observed for near main shock epicenter stations and higher Q values for distant stations. The quality factor Q is affected significantly by the presence of cracks, and that Q is sensitive to cracks. The environment of the epicenter is more affected by the released energy, and seismic waves recorded in the near field are propagated in the filled crack area. This paper makes a significant contribution to the understanding of crustal attenuation and provides data to fill an important gap in the knowledge of attenuation in this region.Keywords: Attenuation, Shear Wave, Seismic Coda, Quality Factor, Tehran.

کلیدواژه‌ها


- Motaghi, K., Ghods, A., and Siahkoohi, H. (1390) Determination of seismic wave attenuation in Tehran region. Earth Science J., 79, 61-66 (in Persian).
- Daneshdoost, M., Yaminifard, F., and Gheytanchi, M. (1389) Determination of quality factor for Tehran. Earth, 3, 49-33 (in Persian).
- Hessami, K., Jamali, F., and Tabassi, H. (2003) Major Active Faults of Iran (map). Ministry of Science, Research and Technology, International Institute of Earthquake Engineering and Seismology.
- Aki, K. (1980) Attenuation of shear waves in the lithosphere for frequencies from 0.05 to 25 Hz. Phys. Earth Planet. Inter., 21, 50-60.
- Sato, H. and Fehler, M. (1998) Seismic Wave Propagation and Scattering in the Heterogeneous Earth. New York: Springer, 1-308.
- Hoshiba, M. (1993) Separation of scattering attenuation and intrinsic absorption in Japan using the multiple lapse time window analysis of full seismogram envelope. Journal of Geophysical Research, 98, 15809-24.
- Hamzehloo, H., Sinaeian, F., Mahood, M., Mirzaei Alavijeh, H., and Farzanegan, E. (2009) Determination of causative fault parameters Ray-Tehran earthquake, using near-field SH-wave data. JSEE, 11,121-131.
- Yoshimoto, K., Sato, H., and Ohtake, M. (1993) Frequency-dependent attenuation of P and S waves in the Kanto area, Japan, based on the coda normalization method. Geophysical Journal International, 114, 165-174.
- Aki, K. and Chouet, B. (1975) Origin of coda waves: source, attenuation and scattering effects. Journal of Geophysical Research, 80, 3322-3342.
- 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.
- Mahood, M. (2014) Attenuation of high-frequency seismic waves in Eastern Iran. Pure Appl. Geophys., 171, 2225-2240.
- Rahimi, H. and Hamzehloo, H. (2008) Lapse time and frequency-dependent attenuation of coda waves in the Zagros continental collision zone in Southwestern Iran. J. Geophys. Eng., 5, 173-185.
- Farrokhi, M., Hamzehloo, H., Rahimi, H., and Allameh Zadeh, M., (2015) Estimation of Coda wave attenuation in the central and eastern Alborz, Iran. Bull. Seis. Soc. Am., 105, 1756-1767.
- Farrokhi, M. and Hamzehloo, H. (2016) Body wave attenuation characteristics in the crust of Alborz region and North Central Iran. J. Seismol., 1-16.
- Zafarani, H., Hassani, B., and Ansari, A. (2012) Estimation of earthquake parameters in the Alborz seismic zone, Iran using generalized inversion method. Soil Dynam. Earthq. Eng., 42, 197-218.
- Motaghi, K. and Ghods, A. (2012) Attenuation of ground-motion spectral amplitudes and its variations across the central Alborz Mountains. Bull. Seis. Soc. Am., 102, 1417-1428.
- Campbell, K.W., Eeri, M., and Bozorgnia, Y. (2014) NGA-West2 ground motion model for the average horizontal components of PGA, PGV, and 5 % -damped linear acceleration response spectra. Earthquake Spectra, 30(3), 1-38.
- Chiou, B.S.J., and Youngs, R.R. (2014) Update of the Chiou and Youngs NGA model for the average horizontal component of peak ground motion and response spectra. Earthquake Spectra, 30(3), 1117-1153.
- Boore, D.M., Stewart, J., Seyhan, E., and Atkinson, G.M. (2014) NGA-West2 equations for predicting response spectral accelerations for shallow crustal earthquakes. Earthquake Spectra, 30, 1057-1086.
- Rahimi, H., Hamzehloo, H., Vaccari, F., and Panza, G.F. (2014) Shear-wave velocity tomography the lithosphere–asthenosphere system beneath the Iranian Plateau. Bull. Seismol. Soc. Am., 104, 2782-2798.
- 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 Geophysica, 58, 244-268.
- Shoja-Taheri, J., Naserieh, S., and Ghofrani, H. (2007) ML and MW scales in the Iranian Plateau based on the strong-motion records. Bull. Seismol. Soc. Am., 97, 661-669.
- Safarshahi, M., Rezapour, M., Hamzehloo, H. (2013) Stochastic finite-fault modeling of ground motion for the 2010 Rigan Earthquake, southeastern Iran. Bull. Seismol. Soc. Am., 103(1), 223-235.
- Shengelia I., Javakhishvili, Z., and Jorjiashvili, N. (2011) Coda wave attenuation for three regions of Georgia (Sakartvelo) using local earthquakes. Bull. Seismol. Soc. Am., 101(5), 2220–2230.
- Nowroozi, G. (2006) Seismological Constraints on the Crustal Structure of NE-Iran. Ph.D. Thesis. International Institute of Earthquake Engineering and Seismology.
- Padhy, S., Subhadra, N., and Kayal, J.R. (2011) Frequency-dependent attenuation of body and coda waves in the Andaman Sea basin. Bull. Seismol. Soc. Am., 101(1), 109-125.
- Hellweg, M., Spandich, P., Fletcher, J.B., Baker, L.M. (1995) Stability of coda Q in the region of Parkfield, California: view from the U.S. Geological Survey Parkfield dense seismograph array. Journal of Geophys. Res., 100, 2089-2102.
- Gupta, S.C., Singh, V.N., and Kumar, A. (1995) Attenuation of coda waves in the Garhwal Himalaya, India. Phys. Earth. Planet. Inter., 87, 247-253.
- Gupta, S.C., Teotia, S.S., and Gautam, N. (1998) Coda Q estimates in the Koyna region, India. Pure Appl. Geophys., 153, 713-731.
- Kumar, N., Parvez, I.A., and Virk, H.S. (2005) Estimation of coda wave attenuation for NW Himalayan region using local earthquakes. Phys. Earth Planet Inter., 151, 243-258.
- Pulli, J.J. (1984) Attenuation of coda waves in New England. Bull. Seismol. Soc. Am., 74, 1149-1166.
- Pujades, L., Canas, J.A., Egozcue, J.J., Puigvi, M.A., Pous, J., and Gallart, J. (1991) Coda Q distribution in the Iberian Peninsula. Geophys. J. Int., 100, 285-301.
- Ramakrishna Rao, C.V., Seshamma, N.V., and Mandal, P. (2007) Attenuation studies based on local earthquake coda waves in the southern Indian peninsular shield. Nat. Hazards, 40(3), 527-536.
- Singh, S.K. and Herrmann, R.B. (1983) Regionalization of crustal coda Q in the continental United States. J. Geophys. Res. 88, 527-538.
- Joshi, A., Kumar, P., Mohanty, M., Bansal, A.R., Dimri, V.P., and Chadha R.K. (2012) Determination of Qβ(f) at different places of Kumaon Himalaya from the inversion of spectral acceleration data. Pure Appl. Geophys., 169, 1821-1845.
- Kumar, P., Joshi, A., Sandeep Kumar, A., and Chadha, R.K. (2015) Detailed attenuation study of shear waves in the Kumaon Himalaya, India, using the inversion of strong-motion data. Bull. Seismol. Soc. Am., 105(4).
- Zafarani, H., Rahimi, M., Noorzad, A., Hassani, B., Khazaei, B. (2015) Stochastic simulation of strongmotion records from the 2012 Ahar-Varzaghan dual earthquakes, northwest of Iran. Bull. Seismol. Soc. Am., 105, 1419-1434.
- Sharma, B., Gupta, K.A., Devi, K.D., Kumar, D., Teotia, S.S., and Rastogi, B.K. (2008) Attenuation of high-frequency seismic waves in Kachchh region, Gujarat, India. Bull. Seism. Soc. Am., 98(5), 2325-2340.
- Mahood, M. and Hamzehloo, H. (2009) Estimation of coda wave attenuation in east central Iran. Journal of Seismology, 13, 125-139.