تحلیل ارتباط نئوتکتونیک و لرزه ‌خیزی در زون بخاردن-قوچان

زون گسلی بخاردن-قوچان در قسمت مرکزی کمربند چین‌خورده-رورانده کپه داغ در شمال‌شرق ایران ، در مجاورت مرز ایران و ترکمنستان قرار دارد. با آرایه ای از گسل‌های فعال امتدادلغز راست‌گرد با روند شمال‌غرب-جنوب‌شرق بوده که پایانه انتهایی آنها خمیدگی پیداکرده و به گسل‌های کور متصل شده اند. تغییر سازوکار گسل‌ها از امتدادلغز به معکوس همراه راندگی باعث افزایش استرس، کوتاه ‌شدگی و گسلش راندگی در خمیدگی انتهایی شده اند. ارتباط ساختاری این گسل‌ها از طریق پهنه انتقالی راندگی مشکان که موتور محرکه اصلی گسل‌های این زون است، به‌طور مداوم تحت‌تاثیر تنش‌های نئوتکتونیکی ناشی از هم‌گرایی صفحه عربی نسبت به اوراسیا از زمان آخرین فاز کوه زایی آلپی تاکنون بوده اند. بیشتر زمین لرزه های تاریخی و دستگاهی در اطراف سامانه های گسلی زون بخاردنقوچان توزیع شده اند. نتایج بررسی لرزه‌خیزی این زون با استفاده از خرد زمین لرزه ها و محاسبه مقادیر مولفه‌های b لرزه خیزی، بعد فرکتالی و تهیه نقشه توزیع محلی تنش می‌تواند اطلاعاتی ارزشمند از توزیع تنش در پوسته زمین، ساز‌و‌‌کار گسل‌ها و تغییرات سامانه های گسلی در طول زمان و مکان احتمالی وقوع زلزله های آینده در اختیار قرار دهد. در نواحی فعال نئوتکتونیکی مقدار تغییرات b-value کمتر از 0.6 است و بعد فرکتالی بین مقادیر صفر تا 2 تغییر می کند.

Analysis of correlation of Neotectonic and seismicity in Bakharden-Quchan zone

Introduction Two fundamental goals are followed in this paper: 1 Active neotectonics of the Kopeh Dagh Mountains particularly in its central part that is called the BakhardenQuchan Zone in NE Iran for special features of faulting and role of faults within this zone in the collision between ArabiaEurasia plates. 2 Seismicity hazards of faulting to recognize the relationship between asperities and earthquakes through analyzing the correlation of fractal dimension and bvalue parameters. The Kopeh Dagh Mountain is accommodating a large portion of northward motion of central Iran with respect to Eurasia, involving a major right lateral strikeslip fault system in its central part (the BakhardenQuchan Zone). This fault system corresponds to the northeastern boundary of the ArabiaEurasia collision and can be considered to be a lithospheric scale tectonic feature. The Kopeh Dagh Mountain forms a linear intercontinental foldthrust belt trending NWSE between the stable Turan platform and central Iran (Afshar Harb, 1979; Hollingsworth et al., 2006; Shabanian et al., 2009; Shahidi et al., 2013).   Materials and methods This research uses both historical and instrumental seismicity data along with observations from Landsat 7 satellite imageries, topographic data (SRTM), field observations and mathematical fractal dimension (D) model plus integral mathematical functions to find a logical correlation between tectonic movements, asperities and earthquakes in different active zones.   Results There is an array of active rightlateral strikeslip faults in the central part of the Kopeh Dagh Mountain which obliquely cut the range and produce offsets of several Kilometers in the geological structures. These faults all end in thrusting and link to blind faults, revealed by the uplifts and incision of the Late Quaternary terraces. These faults have rotated around their vertical axes and can account for several Kilometers of the NS shortening. They are responsible for major destructive earthquakes in both 19th and 20th centuries and represent important seismic hazards for populous regions of NE Iran. These faults also require several Kilometers alongstrike extension that is taken up by the westward component of motion between south Caspian sea basin, Shahrood fault system and both Eurasia and central Iran (Hollingsworth et al., 2006; Shabanian et al., 2009; Bretis et al., 2012).   Discussion The BakhardenQuchan faults have identifiable ends, where they turn into thrusting and link to blind faults. The fault changing mechanism to reverse has caused increase of stress, shortening by thrusting in their end bending. Structural relation faults between this zone and the Binaloud Mountain through Meshkan transfer zone which is the major motion engine of this zone to put it constantly under neotectonic stresses for convergence of ArabiaEurasia plates since the last Alpine orogeny phase. Most of the seismic activities of this zone could provide us with precious data on crust tension distribution through microseismic and computing parameters of bvalue, fractal dimension (D) and mapping of local stresses. In neotectonic active zone b  Acknowledgment    We thank the Department of Geology of Shahrood Azad Islamic University and acknowledge support of the respectable editor and reviewers of the Journal of Economic Geology and thank them for their constructive suggestions on alterations to the manuscript.   References Afshar Harb, A., 1979. The stratigraphy, tectonics and petroleum geology of the Kopeh Dagh region, Northern Iran. Ph.D. thesis, Royal school of Mines, London, England, 17 pp. Aki, K., 1981. Source and scatering effects on the spectra of small local earthquakes. Bulletin of the Seismological Society of America, 71(6): 1687–1700. Bretis, B., Grasemann, B. and Conradi, F., 2012. An Active Fault Zone in the Western Kopeh Dagh (Iran). Austrian Journal of Earth Sciences, 105(3): 480–192. Hollingsworth, J., Jackson, J., Walker, R., Gheitanchi, M.‌R. and Bolourchi, M.‌J., 2006. Strikeslip faulting, rotation, and alongstrike elongation in the Kopeh Dagh mountains, NE Iran. Geophysical Journal International, 166(3): 1161–1177. King, G., 1983. The accommodation of large strains in the upper lithosphere of the earth and other solids by selfsimilar fault systems: the geometrical origin of bvalue. Pure and Applied Geophysics, 121(5–6): 761–815. Shabanian, E., Siame, L., Bellier, O., Benedetti, L. and Abbassi, M.‌R. 2009. Quaternary slip rates along the northeastern boundary of the ArabiaEurasia collision zone (Kopeh Dagh Mountains, Northeast Iran): Geophysical Journal International, 178(2): 1055–1077. Shahidi, A., Nazari, H. and Ghaemi, F., 2013. Structure of IranKopeh Dagh. Mining and Geology Organization of Iran, Tehran, 197 pp. Wiemer, S. and Wyss, M., 2002. Mapping spatial variability of the frequencymagnitude distribution of earthquakes. Advances in Geophysics, 45: 259–302.