CAJ | 학술논문

在磁异常的反演计算中,为了避免由于选错了磁性体的形状而产生很大的误差,前人已研究了多种所谓自动反演的计算方法.与传统的方法不同,用这些方法,可以同时确定磁性体的几何形状和埋藏深度等参数.但是前人研究的方法需要计算磁异常的三阶导数,因此所受高频噪声干扰十分严重,以至于影响到计算结果的可靠性.因此很难用到实际资料处理中.本文提出的场比值法可以同时确定磁性体的形状和埋藏深度.场比值法通过场比值field-ratio来确定磁性体的形状,field-ratio的物理含义与Euler反褶积公式中的形状因子类似.场比值法的优点是在反演计算中只需要计算磁异常的一、二阶导数,因此比前人的方法受高频随机干扰小,可以用于实际资料的处理中.模型实验证明了场比值法的正确性,在河北省宽城地区用场比值法对磁异常反演计算,展示了方法的实用性.
재자이상적반연계산중,위료피면유우선착료자성체적형상이산생흔대적오차,전인이연구료다충소위자동반연적계산방법.여전통적방법불동,용저사방법,가이동시학정자성체적궤하형상화매장심도등삼수.단시전인연구적방법수요계산자이상적삼계도수,인차소수고빈조성간우십분엄중,이지우영향도계산결과적가고성.인차흔난용도실제자료처리중.본문제출적장비치법가이동시학정자성체적형상화매장심도.장비치법통과장비치field-ratio래학정자성체적형상,field-ratio적물리함의여Euler반습적공식중적형상인자유사.장비치법적우점시재반연계산중지수요계산자이상적일、이계도수,인차비전인적방법수고빈수궤간우소,가이용우실제자료적처리중.모형실험증명료장비치법적정학성,재하북성관성지구용장비치법대자이상반연계산,전시료방법적실용성.
The analytic signal method for magnetic anomalies in two dimension (2D) was proposed by Nabighian (1972) and then improved and extended to three dimension (3D) (Roest et al., 1992; Hsu et al., 1996, 1998, 2002; Thurston et al., 1997, 2002; Smith et al., 1998; Salem et al., 2002, 2003, 2005; Keating et al., 2004). The advan-tage of using the absolute value of the analytic signal is that its shape over linear structures is independent of the magnetization direction of the source material. Therefore, the method does not require the knowledge of magneti-zation directions for anomalies caused by 2D sources. It is important to construct an appropriate model through analyzing the properties of a given magnetic anomaly and its analytic signal. Thurston et al. (1997, 2002) and Smith et al. (1998) proposed a method for determining the ap-propriate model type by using the local wavenumber. The method has been used to interpret anomalies arising from contacts, sheets, horizontal cylinders, and thick dikes as well as sloping steps. Hsu et al. (1998) proposed an algorithm recognizing the attributes of the analytic signal maxima, and constructed a criterion that discriminated between maxima from dike-like and step-like structures. Salem and Ravat (2003) presented the AN-EUL method, with which the location coordinates and the geometry of the magnetic source can be determined simultaneously. This paper suggests another method for determining an appropriate model which can obtain an estimate of the depth of the model. The proposed method allows the most appropriate model to be determined according to the field ratio, which is analogous to the structural index in the Euler equations. A disadvantage existent in several commonly-used methods is that the third derivative of the magnetic anomaly has to be calculated. These methods, therefore, are quite sensitive to noise in the data. Especially in the case of complex magnetic anomalies, high-wavenumber noise can distort the higher order analytic signal values to such an extent that the results are unreliable. The present method bases itself only on the first and second derivative fields and is therefore less af-fected by the noise. Synthetic model and real data from Kuancheng area in Hehei Province were used to determine the effectiveness of the method.