برآورد عمق و نوع توده‌‌هاي مولد بي‌هنجاري مغناطيسي با استفاده از تلفيق تابع‌هاي ويژه سيگنال تحليلي و اويلر واهماميخت

Depth and body type estimation of the magnetic anomalies using analytic signal and Euler deconvolution

تابع‌هاي ويژه اويلر و سيگنال تحليلي نقش اساسي در تفسير خودكار داده هاي ميدان پتانسيل به‌‌ويژه داده‌‌هاي مغناطيس‌‌سنجي ايفا مي‌‌كنند. در اين مقاله با تركيب اين دو تابع روشي خودكار براي تفسير داده‌‌هاي مغناطيس‌سنجي دو و سه‌بُعدي عرضه شده است. با اين روش هر دو عمق و شاخص ساختاري (نوع توده) مربوط به توده هاي زيرسطحي برآورد مي شود. معادله نهايي از جاي‌گذاي مشتقات معادله اويلر در تابع سيگنال تحليلي حاصل مي شود. اين روش روي داده هاي مغناطيسي مصنوعي مدل هاي گوناگون و در اعماق متفاوت به كار برده شده است و در همه موارد، نتايج قابل‌‌قبولي را به‌دست داده است. همچنين اين روش روي داده هاي مغناطيس هوايي فلات ييلگارن استرالياي غربي به كار رفته كه منجر به بارزسازي دايك‌‌هاي موجود شده است. ضمناً اين روش با موفقيت روي داه هاي مغناطيس‌سنجي زميني نيم‌رخي در معدن سنگ آهن مركزي ايران (بافق) به كار رفته و نتايج آن با استفاده از مدل‌سازي معكوس صحت‌سنجي شده است.

A variety of semiautomatic methods, based on the use of derivatives of the magnetic anomalies, have been developed for the determination of both of the causative source parameters such as locations of boundaries and depths. One of these techniques is the method of the analytic signal for magnetic anomalies, which was initially used in its complex function form and makes use of the properties of the Hilbert transform. Initially, it was successfully applied on profile data to locate dike like bodies. The method was further developed by Roest et al. (1992) for the interpretation of aeromagnetic maps. Moreover, Bastani and Pedersen (2001) employed the method to estimate many parameters of dike like bodies, including depth, strike, dip, width, and magnetization. Also, Salem et al. (2002) demonstrated the feasibility of the method to locate compact magnetic objects often encountered in environmental applications. The success of the analytic signal method results from the fact that source locations of magnetic anomalies are obtained using only a few assumptions .For example, horizontal positions are estimated by the maxima of the amplitude of the analytic signal (AAS). In addition, depths can be obtained from the shape of the AAS or based on the ratio of the AAS to its higher derivatives. However, a correct estimate of the depth is obtained only when the source corresponds to the chosen model. Several attempts have been made to enable the analytic signal method to estimate both the depth and model type of magnetic sources. Furthermore, a number of automated methods only for source location from 2D (profile) magnetic data have been developed, based on either the local wavenumber. The main advantage of using derived quantities such as the local wavenumber (LW) and amplitude of the analytic signal (AS) is that they are generally independent of source magnetization and dip effects, therefore allowing positional parameters such as depth and horizontal location to be determined more directly than from the magnetic field. Special function such as Euler deconvolution and analytic signal play an important role in potential field data interpretation particularly in the case of magnetic data. In this paper, a new method is proposed based on the combination of these two functions that can lead to automatic interpretation of 2D and 3D magnetic data. In this method both the depth and type of subsurface body will be estimated simultaneously. The final equation is produced with substitution of the Euler deconvolution derivatives in the analytic signal equation. The proposed method has been applied on synthetic and real magnetic data successfully. Also this method is applied on high-resolution aeromagnetic data from Yigarn plateau in Western Australia in which it enhaned the dykes. This method is applied on a ground magnetic profile in Central Iranian Iron ore in Bafgh and the results was tested using inverse modeling.