بررسی اثر توپوگرافی بر دامنه امواج لرزه‌ای با استفاده از شبیه‌سازی سه‌بعدی امواج لرز‌ه‌ای در شهر تهران

نوع مقاله: مقاله تحقیقی‌ (پژوهشی‌)

نویسندگان

موسسه ژئوفیزیک دانشگاه تهران، تهران، ایران

چکیده

شهر تهران یکی از مراکز پرجمعیت جهان با خطرپذیری بسیار زیاد زمین‌لرزه است. این شهر با جمعیتی بالغ بر ۱۲ میلیون نفر، مرکز سیاسی­اقتصادی ایران نیز به شمار می‌رود. ساخت و سازهای غیر اصولی و بافت‌های فرسوده در این شهر، موجب افزایش نگرانی‌ها در صورت رخداد یک زمین‌لرزه است و اهمیت مطالعات مختلف در مورد زمین‌لرزه‌های احتمالی آینده را در این شهر دوچندان می‌کند. در این مطالعه، با استفاده از روش المان طیفی شبیه‌سازی گسل محدود برای چند سناریو مختلف زمین‌لرزه در گسل‌های اطراف تهران در بازة بسامدی 01/0 تا 0/1 هرتز، به منظور بررسی اثر توپوگرافی انجام شد. مدل‌سازی‌ها با استفاده از نرم‌افزار SPECFEM3D، که از روش المان طیفی برای انجام محاسبات استفاده می‌کند، انجام شده است. محاسبات نشان داد که بزرگنمایی امواج در سطح شهر تهران وابسته به سناریو زمین‌لرزه است؛ ولی به‌طور میانگین این میزان در قسمت‌های کم ارتفاع شهر بین۱۰ ± درصد و در کوه‌ها و دره‌های شمال تهران بین 30± درصد می‌باشد.

کلیدواژه‌ها


عنوان مقاله [English]

An investigation on the effect of topography on ground motion amplitudes, using 3D simulation of seismic waves in Tehran

نویسندگان [English]

  • Ehsan Karkooti
  • Zaher hossein Shomali
  • Mehrdad Pakzad
Institute of Geophysics, University of Tehran, Tehran, Iran
چکیده [English]

Tehran, the capital of Iran, is located in the foothills of Alborz Mountains in a very seismically active region and is surrounded by many active quaternary faults with the potential for devastating earthquakes. This city has a daytime population of 12 million people and is the political and economical capital of Iran as well. These facts together with the existence of neighborhoods with old buildings that are poorly constructed increases the importance of different studies to better characterize the nature of ground shaking from future probable earthquakes in the city.
With the increasing computational power in recent years, the seismic waveform simulation has become one of the preferred methods for studying the seismic hazard in regions like Tehran. The topography effect, in this regard, is one of the components of site effects that need to be included in hazard assessment studies. It is  a known fact that the surface topography has significant effects on the earthquake ground motion, especially in mountainous areas with ridges and valleys. As has been observed in the annals of past earthquakes and numerical simulations, topography, In general, increases the ground shaking amplitude on mountain tops and reduces the ground motion amplitude in valleys.
The Spectral Element Method, combining the power of Pseudo Spectral methods with the geometrical flexibility of Finite Element Method, is one of the best methods for modeling the seismic wave propagation in  regions such as Tehran, with notable surface topography.
In the present research, the Spectral Element Method was employed in order to simulate three point sources and three extended source earthquake scenarios both within and around Tehran city and to investigate the role of surface topography on the ground shaking inside the city. The topography effect was investigated by comparing the results of simulations with and without incorporating the surface topography in meshes; the resulting amplification was presented as color maps in the region.
Simulations were performed via SPECFEM3D software package which implements the Spectral Element Method to simulate the seismic wave propagation in the region. The first step in using the Spectral element Method was to create quality meshes in the study area; in this regard, CUBIT program is  employed so as to create the hexahedral meshes in the model area. The extent of the model area was 100 x 60 kilometers horizontally and, vertically, from the ground surface to the depth of 60 kilometers with limits of latitude and longitude of 35.5 to 36.5 degrees and 51 to 52 degrees, respectively.
The peak ground acceleration amplification maps were presented for the topography effect in the frequency range of 0.01 to 1 Hz. The findings indicated that the topography effect inside Tehran city is dependent upon the earthquake scenario and the resulting amplification from topography effect inside the city is generally low and negligible. On average, the amplification resulting from the topography inside the city was between -10% to +10% which could reach as high as ±30% in certain earthquake scenarios at certain locations within the city. In mountainous areas near the city, we observed amplification on the peaks and de-amplification in the valleys; the amplification fell between -50% to +50 %.

کلیدواژه‌ها [English]

  • seismic waveform simulation
  • topography effect
  • Tehran
  • Spectral Element Method

بربریان، م.، قریشی، م.، ارژنگ روش، ب. و مهاجراشجعی، ا.، ۱۳۶۴، پژوهش و بررسی ژرف نوزمین‌ساخت، لرزه‌زمین ساخت و خطر گسلش زمین‌لرزه-گسلش در گستره تهران و پیرامون: سازمان زمین‌شناسی کشور، گزارش ۶۱، ۱۹۷ص.

 

Abbasi, A., Nasrabadi, A., Tatar, M., Yaminifard, F., Abbassi, M. R., Hatzfeld, D. and Priestley, K., 2010, Crustal velocity structure in the southern edge of the Central Alborz (Iran): Journal of Geodynamics, 49, 68-78.

Allen, M. B., Ghassemi, M. R., Sharabi, M. and Qoraishi, M., 2003, Accomodation of late Cenozoic oblique shortening in the Alborz range, northern Iran: Journal of Structural Geology, 25, 659 – 672.

Allenbach, P., 1966, Geologie und Petrographie des Damavand und seiner umgebung (central Alborz), Iran: Geol. Mitt. Geol. Inst. Eth univ. Zurich, n. s., 63, 144 pp.

Ambraseys, N. N. and Melville, C. P., 1982, A History of Persian Earthquakes: Cambridge University Press, London. 219 p.

Berberian, M., Qorashi, B., Arzhang-ravesh, A. and Mohajer-Ashjai, A., 1985, Recent tectonics, seismotectonics and earthquake fault hazard investigations in the greater Tehran region: contribution to the seismotectonics of Iran: Part V, Geological Survey of Iran, report 56, 316 pp, 1985.

Berberian, M. and King, G. C., 1981, Towards a paleogeography and tectonic evolution of Iran: Canadian Journal of Earth Science, 18, 210-265.

Berberian, M., 1983, The southern Caspian: A compressional depression floored by a trapped, modified oceanic crust: Canadian Journal of Earth Science, 20, 163-183.

Berberian, M., Qorashi, M., Arzhang-ravesh, B. and Mohajer-Ashjai, A., 1993, Recent tectonics, seismotectonics and earthquake fault hazard investigations in the Greater Tehran region: contribution to the seismotectonics of Iran: part V., Geological Survey of Iran, Report 56, 316 pp.

Berberian, M., and Yeats, R. S., 2001, Contribution of archeological data to studies of earthquake history in the Iranian plateau: Journal of Structural Geology, 23, 563 − 584.

De Martini, P. M., Hessami, K., Pantosi, D., Addezio, G., Alinaghi, H. and Ghafuri Ashtiani, M., 1998, A geologic contribution to the evaluation of the seismic potential of the Kahrizak fault (Tehran, Iran): Tectonophysics, 287, 187 −199.

Dziewonski, A. M. and Anderson, D. L., 1981b, Preliminary Reference Earth Model (PREM): Physics of the Earth and Planetary Interiors, 25, 297-356.

Jackson, J. and McKenzie, D., 1984, Active tectonics of the Alpine–Himalayan Belt between western Turkey and Pakistan: The Geophysical Journal of the Royal Astronomical Society, 77, 185 – 264.

Jackson, J. A., Priestley, K., Allen, M. and Berberian, M., 2002, Active tectonics of the South Caspian Basin: Geophysical Journal International, 148, 214-245.

Jarvis, A., Reuter, H. I., Nelson, A. and Guevara, E., 2008, Hole-filled SRTM for the globe Version 4, available from the CGIAR-CSI SRTM 90m Database. (http://srtm.csi.cgiar.org).

Komatitsch, D. and Vilotte, J. P., 1998, The spectral element method: an efficient tool to simulate the seismic response of 2D and 3D geological structures: Bulletin of the Seismological Society of America, 88, 368-392.

Komatitsch, D. and Tromp, J., 1999, Introduction to the spectral-element method for 3-D seismic wave propagation: Geophysical Journal International, 139(3), 806-822.

Komatitsch, D., Liu, Q., Tromp, J., Stidham, P. C., and Shaw, J. H., 2004, Simulations of ground motion in the Los Angeles basin based upon the spectral-element method: Bulletin of the Seismological Society of America, 94, 187-206.

Komatitsch, D., Erlebacher, G., Göddeke, D. and Michéaa, D., 2010, High-order finite-element seismic wave propagation modeling with MPI on a large GPU cluster: Journal of Computational Physics, 229, 7692–7714.

Naghavi, M., Shomali, Z. H. and Zare, M., 2012, Lg Coda Variations in North-Central Iran: International Journal of Geophysics, Doi: 10.1155/2012/673506.

Olsen, K. B., Archuleta, R. J., and Matarese, J. R., 1995, Three-dimensional simulation of a magnitude 7.75 earthquake on the San Andreas Fault: Science, 270, 1628-1632.

Olsen, K. B., 2000, Site Amplification in the Los Angeles Basin from Three Dimensional Modeling of Ground Motion: Bulletin of the Seismological Society of America, 90(6B), S77-S94. doi:10.1785/0120000506

Sengor, A. M .C., Cin, A., Rowley, D. B. and Nie, S. Y., 1993, Space-time patterns of magmatism along the Tethysides: a preliminary study: Journal of Geology, 101, 51-84.

Tchalenko, J. S., Berberian, M., Iranmanesh, H., Bailly, M. and Arsovsky, M., 1974, Tectonic framework of the Tehran region: Geological Survey of Iran, Report no 29.

Tchalenko, J. S., 1975, Seismotectonics framework of the North Tehran fault: Tectonophysics, 29, 411 – 420.

Tromp, J., Komattisch, D. and Liu, Q., 2008, Spectral-element and adjoint methods in seismology: Communications In Computational Physics, 3(1), 1-32

Vernant, P., Nilforoushan, F., Chry, J., Bayera, R., Djamour, Y., Masson, F., Nankali, H., Ritz, J. F., Sedighi, M. and Tavakoli, F., 2004, Deciphering oblique shortening of Central Alborz in Iran using geodetic data: Earth and Planetary Science Letters, 223, 177-185.

Zanchi, A., Berra, F., Mattei, M., Ghassemi,
M. R., and Sabouri, J., 2006, Inversion tectonics in central Alborz, Iran: Journal of Structural Geology, 28, 2023-2037