مدل‌‌سازی تغییر مختصات مسطحاتی نقاط سطحی زمین در چارچوب‌‌های مرجع ITRF در محدودة فلات ایران

نوع مقاله : مقاله پژوهشی‌

نویسندگان

دانشکده مهندسی نقشه‌برداری، دانشگاه صنعتی خواجه نصیرالدین طوسی، تهران، ایران

چکیده

آشنایی با نحوه حرکت و تغییر مختصات نقاط سطح زمین با زمان برای انواع کاربردهای ژئودتیک امری بسیار مهم و ضروری است. هدف از این تحقیق مدل‌سازی وابسته به زمان جابه‌جایی و تغییر مختصات نقاط سطحی زمین در اثر حرکت صفحه‌های زمین‌ساختی و زمین‌لرزه‌ها در محدوده فلات ایران است. از مدل عرضه شده می‌توان برای پیش‌بینی تغییر مختصات نقاط سطحی زمین و یا پیش‌بینی مشاهدات ژئودتیک (طول و زاویه) از یک اپوک زمانی دلخواه به اپوک دلخواه دیگر نیز بهره جست. این مدل مختصات نقاط ورودی را در انواع چارچوب‌های مرجع ITRF و یا WGS84 دریافت می‌کند و بعد از اجرای محاسبات، خروجی را در چارچوب مرجع دلخواه عرضه می‌دارد. به‌منظور مدل‌سازی حرکت دائمی صفحه‌ها و حرکت‌های بین‌لرزه‌ای و همچنین حرکت‌های هم‌لرزه از روابط تحلیلی اکادا (1985) استفاده شده است. جذر میانگین مربعات (rms) خطای مدل‌سازی حرکت‌های دائم و بین‌لرزه‌ای برای مدلی که بهترین انطباق را با مشاهدات GPS داشت برابر mm/yr 35/0 محاسبه شد. نتایج مدل‌سازی نشان می‌دهد که سهم گسلش‌های اطراف صفحه عربستان در تولید میدان سرعت GPS شبکه غیردائم ژئودینامیک سراسری ایران بیشتر از سهم گسلش‌های فلات آناتولی و حتی گسلش‌های داخلی ایران است. استفاده از پارامترهای هندسی دقیق گسلش ناشی از زمین‌لرزه‌ها که با بهره‌گیری از مشاهدات InSAR و با حل مسئله معکوس به‌دست آمده باشند و مدل‌سازی حرکت‌های بعدلرزه‌ای با استفاده از مدل وانگ (2006) برای تکمیل و بالا بردن دقت خروجی‌های مدل پیشنهاد می‌شود.
 

کلیدواژه‌ها


عنوان مقاله [English]

Horizontal coordinates change modeling of Earth surface points in ITRF reference frames in the region of Iranian plateau

نویسندگان [English]

  • Asghar Rastbood
  • Behzad Voosoghi
چکیده [English]

Being familiar with the modes of motion and coordinate changes of the Earth surface points as a function of time is very important and essential in different types of geodetic applications. The puepose of this research is the time-dependent modeling of displacement and coordinate changes of the Earth’s crust surface points due to the plate tectonic motions and earthquakes in the region of Iranian plateau. The provided model could be used to predict the coordinate changes of surface crust points or to predict the geodetic observations (distance and angle) from one arbitrary epoch to another. This model receives the coordinates in various ITRFs or WGS84 reference frames and after the computations are made, the results could be provided in any reference frame.
The Bursa-Wolf seven-parameter conformal model was used to transform three dimensional Cartesian co-ordinates between WGS84 and ITRF2000. In the absence of a crustal motion, the equations for transforming positional coordinates from one ITRF to another are rather familiar to the surveying community, i.e. it is a seven-parameter transformation. In the presence of a crustal motion, the transformation equations can be generalized to allow one frame to move relative to the other. Thus, each of the seven defining parameters becomes a function of time. Therefore, in modeling, fourteen transformation parameters were used for ITRF2000 reference frame transformation to the previous and later reference frames.
Okada (1985) analytical model was used to model sudden coseismic and interseismic motions due to earthquakes. In previous works (Pearson, 2010 and Meade, 2005) the block model was used for secular and interseismic deformation modeling, but in this research, we used Okada (1985) analytical modeling for this purpose since (1) Modeling the present-day velocity field determined with GPS networks incorporates geological constraints on the geometry of the main structures and on the long-term deformations; (2) Regions between the major faults are not rigid and so the modeling allows for internal deformations. Finally, we have a tectonic model for Arabia-Eurasia oblique collision zone in Iran that is more realistic than the rigid block model. This model shows that about 30% of GPS velocity field components are produced by faults inside Iran, 60% by Arabian plate and 10% by Anatolian plate.
Continuous use of GPS data and local network observations is recommended to get a more precise model for secular and interseimic motions. Also using more precise geometric faulting parameters due to earthquakes obtained by inverse problem solution based on GPS or InSAR observations is recommended to get more precise outputs. Postseimic motions were not modeled in this research since this effect is a function of time and its amplitude is just considerable for large earthquakes, beside that the amount of this effect is reduced with time. Anyway, the postseismic deformation modeling due to intense earthquakes with a large focal depth using Wang (2006) model is recommended. In this research, just the effects of secular, interseismic and coseismic motions were included in the model. To complete the model, it is recommended to consider the effects of the crustal motions associated with land subsidence, volcanic activity, postglacial rebound etc.
 
 

کلیدواژه‌ها [English]

  • GPS velocity field
  • Dislocation theory
  • Tectonics
  • reference frame
  • ITRF
  • WGS84
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