ارزیابی همبستگی آماری و مکانی بین پارامترهای لرزه‌خیزی و بی‌هنجاری بوگه در ایران

نوع مقاله : مقاله پژوهشی‌

نویسنده

استادیار زمین شناسی، دانشکده‌ علوم زمین، دانشگاه دامغان، ایران

چکیده

در این تحقیق، همبستگی آماری و مکانی بین متغیرهای معرف بی هنجاری گرانی بوگه و پارامترهای لرزه خیزی در گستره ایران مورد ارزیابی قرار گرفته است. به این منظور، داده های بی هنجاری بوگه و لرزه خیزی این گستره در بازه زمانی 2021-1975،  بررسی شده است. در این راستا، ابتدا ناحیه مورد مطالعه به چهارگوش هایی با ابعاد 5/0 در 5/0 درجه جغرافیایی تقسیم بندی شده و سپس متغیرهای معرف لرزه خیزی و بی هنجاری بوگه برای هر سلول محاسبه شد. با استفاده از نرم افزارهای آماری، ضریب همبستگی پیرسون بین این متغیرها تعیین شده و سپس مورد اعتبارسنجی  قرار گرفت. همچنین، نقشه های معرف الگوی توزیع مکانی این متغیرها تهیه شده است. در ادامه، نمودارهای واریوگرام برای هر متغیر  ترسیم شده و این نمودارها مورد تحلیل و تفسیر قرار گرفت. با تفسیر نمودارهای واریوگرام، ارتباط و همبستگی مکانی این متغیرها مورد ارزیابی قرار گرفته است. بر اساس یافته های این تحقیق می توان چنین گفت که همبستگی قابل توجه و معنادار مشاهده شده بین متغیر بیشینه تغییرات بی هنجاری بوگه و متغیرهای معرف لرزه خیزی، بخصوص متغیرهای مرتبط با فراوانی رخداد زلزله ها، نشان می دهد تغییرات بی هنجاری گرانی بوگه می تواند از عوامل مؤثر بر رخداد زلزله ها در این گستره به شمار آید. همچنین، می توان چنین نتیجه گیری نمود که نیروهای گرانی و بخصوص نیروهای ناشی از عدم تعادل ایزوستازی، می توانند نقش مهمی در رخداد زلزله های این گستره،  ایفا نمایند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Evaluation of the statistical and spatial correlation between seismicity parameters and Bouguer anomaly in Iran

نویسنده [English]

  • Seyed Naser Hashemi
Assistant Professor, School of Earth Sciences, Damghan University, Damghan, Iran
چکیده [English]

In this research, the spatial correlation between the variables representing Bouguer gravity anomaly and seismicity in Iran is evaluated. For this purpose, the gravity anomalies and seismicity data of this region have been analyzed statistically as well as geostatistically, for the period 1975-2021. Based on the findings of this study, it can be concluded that the significant correlation observed between the variables of gravity anomaly variations and the seismicity-related variables, especially the variables related to the frequency of earthquake occurrences, suggests that the gravity anomaly variations can be considered as an affective factor in seismic activity of this region.
The Iranian Plateau is one of the most seismically active regions on the Earth because of its geologic and tectonic setting. This plateau is marked by high topography relief and also by great changes in gravitational and isostatic anomalies across it. Many researchers have studied the variations of gravitational anomalies across Iran, and some have pointed to the relationships between these anomalies and seismicity in this region. The Bouguer gravity anomaly is obtained by making the necessary corrections to measurements taken directly from the ground stations, and well reflects the deep density variations in the crust. This anomaly can also clearly show changes in crustal thickness in different regions, such that areas with high crustal thicknesses show negative anomalies and areas with low crustal thicknesses show positive anomalies.
In this study, at first, the study region was divided into rectangles with dimensions of 0.5 by 0.5 geographical degrees and then the variables related to the seismicity and gravity anomalies were calculated and computed for each cell. Pearson correlation coefficients between these variables were computed and validated using statistical software Minitab (ver. 16.2.2). Also, maps representing the spatial distribution pattern of these variables were prepared. The remarkable similarity between the spatial patterns of variations of these variables indicates a strong correlation between the Bouguer gravity anomaly and seismicity in this region. The Pearson correlation coefficient values calculated between the variables also confirm this correlation. These values indicate that both variables of average Bouguer anomaly and the range of variations of this anomaly show a significant positive correlation with the seismicity-related variables. This degree of correlation is stronger for the variable of the Bouguer anomaly variation and moreover, this variable is more correlated with the seismicity variables associated with the frequency of earthquakes. In the next step, variograms were prepared.
     The results obtained show that among the seismicity-related variables of the region, the b seismicity parameter (from the Gutenberg-Richter relation) has more spatial variability and show high spatial autocorrelation up to long distances. On the other hand, the other variables related to earthquake frequency and magnitude of earthquakes show less spatial autocorrelation. The variograms provided for the two variables representing the bouguer anomaly also show remarkable similarity to the seismicity-related diagrams. This similarity is more pronounced for the variable of the Bouguer anomaly variation. The remarkable similarities of the variograms, along with the similarities of the spatial distribution maps of these variables, may indicate a close relationship between these two series of variables. Finally, it can be concluded that gravitational forces, especially forces caused by isostatic imbalances, can play an important role in the process of earthquake occurrences in Iran.

کلیدواژه‌ها [English]

  • Seismotectonics
  • spatial analysis
  • seismicity parameters
  • gravity anomalies
  • spatial correlation
  • spatial statistics
خسروی، ی. اسمعیلی، ع. 1394، تحلیل فضایی داده‌های محیطی با زمین‌آمار. چاپ اول، انتشارات آذر کلک.
هاشمی، ن.، کولیوند، ف.، 1397، تحلیل مکانی لرزه خیزی در ناحیه زاگرس با استفاده از مدل سازی واریوگرام. هجدهمین کنفرانس ژئوفیزیک ایران، 20-18 اردیبهشت 1397، دانشگاه تهران، تهران.
هاشمی، س.ن.، عسکری، ل.، 1391، استفاده از روش زمین آماری تحلی واریوگرام ها در بررسی تغییرات مکانی ناهنجاری گرانشی بوگه در ناحیه زاگرس. شانزدهمین همایش انجمن زمین شناسی ایران، 14 تا 16 شهریور ماه 1393، دانشگاه شیراز، شیراز.
Abdelrahman, E.M., El-Araby, H.M., El-Arabym, T.M., Abo-Ezz, E.R., 2003. A least-squares derivatives analysis of gravity anomalies due to faulted thin slabs. Geophysics, 68: 535–543.
Benvenuti, M. and Caputo, M., 1982. Pattern recognition of a gravity anomaly-seismicity relationship. Atti Accad. Naz. Lincei, 72(l): 360-372.
Berberian, M., 1976. Contribution to the Seismotectonics of Iran (Part II). Geological Survey of Iran, Report No. 39, p. 517.
Berberian, M., 1995, Master blind thrust faults hidden under the Zagros folds: active basement tectonics and surface morphotectonics, Tectonophysics, 241,193-224.
Bora, D.K., Borah, K., Mahanta, R., Borgohain, J.M., 2018. Seismic b-values and its correlation with seismic moment and Bouguer gravity anomaly over Indo-Burma ranges of northeast India: Tectonic implications. Tectonophysics, 728-729, 130-141.
Caputo, M., Milana, G. and Rayhorn, J., 1984. Topography and its isostatic compensation as a cause of seismicity of the Apennines. Tectonophysics, 102, 333-342.
Caputo, M., Manzetti, V. and Nicelli, R., 1985. Topography and its isostatic compensation as a cause of seismicity: a revision. Tectonophysics, 111, 25-39.
Davis, J.C., 2002. Statistics and Data Analysis in Geology, Third Edition. John Wiley and Sons, New York, 638 p.
Dehghani, G.A. and Makris, J., 1983. The gravity field and crustal structure of Iran. Geological Survey of Iran, 51, 51-68.
Deutsch, C.V., 2002. Geostatistical Reservoir Modeling, Oxford University Press, Oxford.
Ghosh, G.K., 2019. Interpretation of gravity anomaly to delineate thrust faults locations at the northeastern part of India and its adjacent areas using source edge detection technique, tilt derivative and Cos(θ) analysis. Acta Geophysica, 67, 1277–1295.
Ghosh, G.K., Dasgupta, R., Reddy, B.J., Singh, S.N., 2015. Gravity data interpretation across the Brahmaputra Thrust and Dauki Fault in the north-Eastern India. Journal of Geophysics, 7(1):31–38.
Hessami, K., Jamali, F., Tabasi, H., 2003. Major Active Faults map of Iran, Scale 1:2500000, International Institute of Earthquake Engineering and Seismology (IIEES), 1 sheet.
International Seismological Centre (2023), On-line Bulletin, https://doi.org/10.31905/D808B830
Jacoby, W., Smilde, P.L., 2009. Gravity Interpretation: Fundamentals and Application of
Gravity Inversion and Geological Interpretation. Springer, Berlin, 395 p.
Jimenez-Munt, I., Fernandez, M., Saura, E., Verges, J. and Garcia-Castellanos, D., 2012. 3-D lithospheric structure and regional/residual Bouguer anomalies in the Arabia–Eurasia collision (Iran). Geophys. J. Int., 190, 1311–1324.
Khan, P.K., Chakraborty, P.P., 2007. The seismic b-value and its correlation with
Bouguer gravity anomaly over the Shillong Plateau area: tectonic implications.
Journal of Asian Earth Sciences, 29, 136–147.
Mallick, K., Vasanthi, A., Sharma, K.K., 2012. Bouguer gravity regional and residual separation: Application to geology and environment. 1th edn., Springer, New York.
McKenzie, D.P., 1972. Active tectonics of the Mediterranean region. Geophys. J. R. Astron. Soc., 30, 109-185.
McKenzie, D. P,. 1987. Active tectonics of the Alpine-Himalayan belt: the Aegean Sea and    surrounding    regions.   Geophysical
 
     Journal of the Royal Astronomical Society, 55, 217-254.
Noreus, J.P., Nyborg, M.R., Hayling, K.L., 1997. The gravity anomaly field in the Gulf of Bothnia spatially characterized from satellite altimetry and in situ measurements. J. appl. Geophys., 37, 67-84.
Pamukçu OA, Doğru F, Çirmik A, Göneş D., 2021. Seismic a and b-values and crustal parameters of Samos Island-Aegean Sea, Lesvos Island-Karaburun, Kos Island-Gökova Bay earthquakes. Turkish Journal of Earth Sciences, 30: 833-850, doi:10.3906/yer-2107-13
Sarkarinejad, K., Mehdi Zadeh, R., Webster, R., 2013. Two-dimensional spatial analysis of the seismic b-value and the Bouguer gravity anomaly in the southeastern part of the Zagros Fold-and-Thrust Belt, Iran tectonic implications, Journal of Asian Earth Sciences, 62, p.308-316.
Stocklin, J., 1968. Structural history and tectonics of Iran. American Association of Petroleum Geologists Bulletin, 52, 1229-1258.
Swan, A.R.H., Sandilands, M., 1995. Introduction to Geological Data Analysis. Blackwell Sciences, Oxford, 446 p.
Tobing, A. A. L., Sukarasa, I. K., & Yusuf, M., 2021. Analysis of gravity anomaly and seismicity in Bali region. International Journal of Physical Sciences and Engineering, 5(3), 34-43. https://doi.org/10.53730/ijpse.v5n3.1723
Vernant, Ph., Nilforoushan, F., Hatzfeld, D., Abbassi, M. R., Vigny, C., Masson, F., Nankali, H., Martinod, J., Ashtiani, A., Bayer, R., Tavakoli, F., Chéry, J., 2004. Present-day crustal deformation and plate kinematics in the Middle East constrained by GPS measurements in Iran and northernOman. Geophysical Journal International, 157(1), 381-398.
Webster, R., Oliver, M.A., 2007. Geostatistics for Environmental Scientists, Second Edition, John Wiley & Sons, Ltd.
Zamani, A. and Hashemi, S.N., 2000. A comparison between seismicity, topographic relief, and gravity anomalies of the Iranian Plateau. Tectonophysics, 327, 25-36.
Zhan, F.B., Zhu, Y., Ning, J., Zhou J., Liang W., Xu Y., 2011. Gravity changes before large earthquakes in China: 1998–2005. Geo-spat. Inf. Sci. 14, 1–9. https://doi.org/10.1007/s11806-011-0440-0.