| 芦山—康定地区布格重力异常及其归一化梯度图像的构造物理涵义 |
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| 引用本文： | 玄松柏,申重阳,谈洪波.芦山—康定地区布格重力异常及其归一化梯度图像的构造物理涵义[J].地球物理学报,2015,58(11):4007-4017. |
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| 作者姓名： | 玄松柏 申重阳 谈洪波 |
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| 作者单位： | 中国地震局地震研究所(大地测量重点实验室), 武汉 430071 |
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| 基金项目： | 中国地震局地震研究所所长基金(IS201326122),国家自然科学基金(41304060),国家重点基础研究发展计划(2013CB733305)和四川省芦山"4·20"7.0级地震科学考察项目联合资助. |
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| 摘 要： | 芦山—康定地区是川滇块体、松潘—甘孜块体和华南块体三个块体过渡的"Y"型交汇区,构造变形十分强烈.本文对EGM2008计算的布格重力异常进行1~5阶离散小波变换,得到三方向分量平方和的平方根(HVDM)图像;利用实测剖面布格重力异常数据,得到剖面的布格重力异常归一化总梯度(NFG)图像.结果分析表明:(1)垂直于龙门山断裂带南段剖面的NFG图像显示推覆构造体前端切割较浅、后端逐步变深至中地壳,说明松潘—甘孜块体在深约10~30km之间存在滑脱构造,在青藏高原东向挤出和四川盆地的阻挡作用下,造成深、浅部构造差异性运动,形成逆冲推覆的龙门山构造带;(2)HVDM图像和剖面的NFG图像均显示龙门山断裂带西南段与中段和东北段不同,松潘—甘孜块体对四川盆地的逆冲推覆作用沿北东方向具有分段性;(3)雅江—洪雅剖面NFG图像显示鲜水河断裂带和龙门山断裂之间存在高梯度变化带,在鲜水河断裂带下方强变形带不仅在20km左右东倾至龙门山断裂带前缘,且逐渐近垂直向下伸入至少到下地壳,反映了两大断裂带交汇区域变形作用较强.川滇块体内部和四川盆地内部则显示低值,说明其变形作用较弱.强烈左旋剪切的鲜水河断裂带对芦山—康定地区构造活动具有主要的控制作用.
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| 关 键 词： | 重力异常 HVDM 归一化总梯度 地壳结构 芦山-康定地区 |
| 收稿时间： | 2015-01-12 |
Tectonic implications of images of Bouguer gravity anomaliy and its normalized full gradient in Lushan-Kangding area |
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| XUAN Song-Bai,SHEN Chong-Yang,TAN Hong-Bo.Tectonic implications of images of Bouguer gravity anomaliy and its normalized full gradient in Lushan-Kangding area[J].Chinese Journal of Geophysics,2015,58(11):4007-4017. |
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| Authors: | XUAN Song-Bai SHEN Chong-Yang TAN Hong-Bo |
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| Institution: | Key Laboratory of Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan 430071, China |
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| Abstract: | The Lushan-Kangding area, which containing the complicated tectonic deformation, is the Y-shaped transitional zone of the Chuan-Dian block, the Songpan-Garzê block and the South China block. The crustal structure and tectonic deformation of this region are quite complicated, which aroused our great interest.We focus on determining the deep mass anomaly in this region, and the HVDM (the square root of the sum of the squares of wavelet detail components in horizontal, vertical and diagonal direction produced by the discrete wavelet transform) and the NFG (the normalized full gradient of Bouguer gravity anomaly) by provided valid approach. In this study, we present the HVDM and the NFG maps, which were inferred from Bouguer gravity anomaly (BGA) data, to investigate the characteristics of crustal structure and tectonic deformationin the Lushan-Kangding area.#br#We collected the regional BGA derived from EGM2008 in the eastern Tibetan Plateau. The BGA of two measured profiles (Jinchuan-Ya'an-Qianwei profile and Yajiang-Hongya profile) are obtained from the scientific investigation of the 2013 Lushan earthquake. Therefore, the regional BGA and the BGA of the measured profiles had been used to calculate the 1st-5th level HVDM and the 2-D NFG along the two profiles, respectively.#br#From the HVDM and the NFG maps in this study, we confirmed that: (1) The NFG map of the profile perpendicular to the Longmenshan fault zone showed that the greater NFG extended downward from surface in the Longmenshan fault zone into about 30 km depth in Songpan-Garzê block; (2) The distribution of the HVDM and the NFG all showed that the southwest segment of the Longmenshan fault zone was different from the middle and northeast segments. The greater HVDM located in the middle and northeast segments but not in the southwest segment. Beneath the Longmenshan fault zone,the NFG distribution presented an obvious gradient belt from northwest to southeast as well as from upper crust to middle crust along the Jinchuan-Ya'an-Qianwei profile, and changed not obviously along the Yajiang-Hongya profile; (3) The NFG map of the Yajiang-Hongya profile showed that the high-gradient belts existed in the regions between the Xianshuihe fault zone and the Longmenshan fault zone, and the low NFG value located in the Chuan-Dian block and the Sichuan basin.#br#According to the characteristics of the HVDM and the NFG images, we concluded that: (1)The front of the nappe structure cut the shallow crust relatively, and extended to the middle crust. Detachment structures presented at about 10~30 km depth beneath the Songpan-Garzê block. For restriction by the Sichuan basin, the eastward extrusion of the Tibetan Plateau was the driving force for the formation of the Longmenshan Thrust Nappe. The crustal activities presented the nappe structure in the shallow crust and the rigid block in the deeper crust beneath the Longmenshan fault zone. (2) The NE trending Longmenshan fault zone appeared segmentation from northeast to southwest. (3) The strong deformation belt beneath the Xianshuihe fault zone not only dipped eastward to the Longmenshan fault zone, but also stretched from surface into lower crust (about 40 km) almost in vertical direction. The above two faults contained the strong deformationin transitional zone. Contrarily, the Chuan-Dian block and the Sichuan basin had weak deformation. The tectonic activities were mainly controlled by the sinistral shearing of the Xianshuihe fault in the Lushan-Kangding area. |
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| Keywords: | Bouguer gravity anomaly HVDM Normalized full gradient Crustal structure Lushan-Kangding area |
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