Tectonic deformation and seismic mechanism of the 2021 Aksai MS 5.5 earthquake
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摘要: 2021年8月26日甘肃阿克塞党河南山地区发生了MS 5.5地震，震中位于阿尔金走滑断裂与祁连山西段挤压逆冲断裂的构造转换区。明确此次地震的形变特征及发震机制，有助于认识边界走滑断裂与逆冲断裂系之间应变分配和构造转换的大陆动力学问题，同时对祁连山西段的地震危险性评价也具有重要意义。利用远近场地震波形联合反演（the generalized Cut-and-Paste joint, gCAPjoint）此次地震的震源机制解。通过对地震序列走时信息以及地震前后的合成孔径雷达（Synthetic Aperture Radar, SAR）影像数据进行处理，得到了此次地震序列的精确空间位置和同震形变场。结合震中附近活动构造和构造地貌实地调查，认为此次地震的发震构造为党河南山南缘断裂，断裂活动性质为逆冲型。该断裂走向为315°、倾角为41°、滑动角为81°，震源矩心深度为6.9 km。随着青藏高原向北东向的挤压扩展，柴达木地块北部地震活动显著增强，未来阿尔金断裂东段和祁连山西段的地震危险性应重点关注。
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关键词:
- 甘肃阿克塞MS 5.5地震 /
- 震源机制解 /
- 发震构造 /
- 党河南山南缘断裂
Abstract:Objective On August 26, 2021, an Ms5.5 earthquake occurred in Aksai, Gansu Province. The epicenter is located along the southern piedmont of the Danghe Nan Shan. This event garnered significant attention because of its deformation characteristics and seismogenic mechanisms. Existing studies have mainly focused on emergency response and seismic activity analyses; however, there is a lack of research on tectonic deformation and seismic mechanisms. This study aimed to fill this gap by analyzing the deformation characteristics of the earthquake zone and revealing its seismogenic mechanism. Methods This study employed seismological methods combined with interferometric synthetic aperture radar (InSAR) technology to investigate the tectonic deformation and seismic mechanism of the 2021 Aksai Ms5.5 earthquake. Combining focal mechanism solutions, precise earthquake locations, and InSAR results, the seismogenic fault and its geometric and kinematic parameters were determined and validated through geological field surveys. Results This study applied joint inversion with both local and teleseismic waveforms (the generalized cut-and-paste joint, gCAPjoint) to source parameters. The fault solutions strike 315°, dip 41°, rake 81°, depth 6.9 km. We relocated the Aksai earthquake and its aftershocks using the hypoinverse and double-difference method (HypoDD), and accurate locations of 88 earthquakes were obtained. The 2021 Ms5.5 earthquake sequence in Aksai is distributed near the southern Danghe Nan Shan Fault, with a fault dip toward the NE. The co-seismic deformation field indicated by InSAR matched the macro-epicenter with the precise location results, confirming the reliability of the precise location. Both the ascending and descending orbit surface deformation fields showed uplift near the epicenter with similar magnitudes and signs in the line-of-sight direction, indicating that the earthquake rupture was mainly thrusting. Fault scarps near the epicenter along the southern piedmont of the Danghe Nan Shan were recognized in the field and satellite images. Combined data from focal mechanism solutions, precise earthquake locations, and InSAR coseismic deformation fields, along with field geological survey results, indicate that the seismogenic fault of this event was the southern Danghe Nan Shan Fault, with a strike of 315°, dip of 41°, and rake of 81°. Conclusion This study indicated that the seismogenic fault of this event was the southern Danghe Nan Shan Fault, which is a thrust fault. The fault solutions strike 315°, dip 41°, rake 81°, depth 6.9 km. Because of the northward extrusion thrust of the Qinghai-Xizang Block, the seismic activity in the northern part of the Qaidam Block has significantly increased. The future seismic risk of the eastern section of the Altyn Tagh Fault and western Qilian Shan should be emphasized. [ Significance ] This study provides new insights and methods for researching active tectonics. It holds significant scientific importance and innovation in understanding seismogenic mechanisms and structural transformation, as it helps to understand the mode and magnitude of slip transfer between the strike-slipping of the Altyn Tagh Fault and the shortening of the Qilian Shan and also contributes to a better evaluation of the seismic risk in this region. -
虎头崖多金属矿区位于柴达木盆地西南缘，东昆仑祁漫塔格山北坡，隶属于东昆仑祁漫塔格成矿带。矿区自然环境差，海拔高，地质构造复杂，是该区比较典型的矽卡岩型多金属矿床(李智明等，2007；张爱奎等，2010；高晓峰等，2010；胡杏花等，2011；伍跃中等，2011；马圣钞等，2013；刘渭等，2014；易立文等，2019；张大明等，2020)，矿区侵入岩分布较广，岩体与地层的接触带附近围岩蚀变普遍强烈，其蚀变类型主要有绿帘石化、绿泥石化、黄铁矿化、透闪石化、阳起石化、石榴石化、透辉石化、绢云母化和大理岩化等(张爱奎等，2010；高晓锋等，2010；胡杏花等，2011；刘渭等，2014；杨兴科等，2016)。一些学者已经广泛开展了采用ASTER数据进行遥感蚀变异常信息提取的研究(张玉君等，2006；毛晓长等，2005；耿新霞等，2008；杨长保等，2009；张玉君和姚佛军，2009；高万里等，2010；燕守勋等，2011；姚佛军等，2012；陈菁和周萍，2015；周迪等，2018)，然而对于单个矿区虎头崖矿区遥感找矿方法和手段报道较少。因此现以ASTER遥感影像为数据源，应用成像光谱法和主成分分析法蚀变遥感异常提取技术方法对青海祁漫塔格成矿带虎头崖矿区进行蚀变异常信息提取，并对部分异常点进行了实地查证，以期为扩大找矿规模和发现矿化富集地段提供重要的指导意义。
1. 研究区成矿地质特征
虎头崖多金属矿床位于青海省祁漫塔格地区，大地构造位置上处于东昆仑西段，北昆仑(祁漫塔格)岩浆弧带(李荣社等，2008), 是该区比较典型的矽卡岩型多金属矿床，主要有Fe、Cu、Pb、Zn、Wu和Sn等矿种(张晓飞等2012；刘渭等，2014)。
矿区地层属柴达木地层区的柴达木南缘分区，主要为蓟县系狼牙山组(Jxl)，奥陶系—志留系滩涧山群(OST)，下石炭统大干沟组(C1dg)，上石炭统缔敖苏组(C2d)，中生界上三叠统鄂拉山组(T3e)以及山麓地带及河床等广泛发育的第四系(Q)松散堆积物。矿区内褶皱、断裂等构造非常发育，构造形迹主要表现为东—西向断裂构造(刘渭等，2014)。矿区侵入岩主要出露于矿区中部，以中酸性侵入岩类为主，侵入于狼牙山组(Jxl)、滩涧山群(OST)、大干沟组(C1dg)及缔敖苏组(C2d)等地层中(李侃等，2015)(图 1)。狼牙山组上岩段(碳酸盐段Jxlb)、滩间山群火山岩(OST)、下石炭统大干沟组(C1dg)和上石炭统缔敖苏组(C2d)，大理岩、含铁石英砂岩、灰岩、硅质岩岩性段是主要的含矿岩性段(苏松，2011)。矿区内典型矿床类型为矽卡岩型，褶皱、断裂和岩体与地层接触带是矿体赋存的有利部位。蚀变类型主要有透闪石化、透辉石化、阳起石化、绿泥石化、绿帘石化、石榴子石化、高岭土化、硅化、绢云母化等(杨兴科等，2016)。
图 1 虎头崖矿区地质简图(刘渭等，2014)1—第四系；2—蓟县系狼牙山组；3—奥陶志留系滩间山群；4—下石炭统大干沟组；5—上石炭统缔敖苏组；6—上三叠统鄂拉山组；7—花岗闪长岩；8—二长花岗岩；9—石英斑岩；10—似斑状二长花岗岩；11—闪长岩；12—闪长玢岩脉；13—推断断层；14—逆冲断层；15—褶皱；16—矿带；17—青海祁漫塔格成矿带及虎头崖矿区Figure 1. Simplified geological map of the Hutouya mining area(Liu et al, 2014)2. 遥感数据介绍及预处理
2.1 ASTER数据介绍
ASTER数据有14个波段：可见光、近红外和短波红外到热红外，光谱分辨率较高，特别是在短波红外有6个波段、热红外有5个波段，它们分别对粘土矿物、碳酸盐和硅酸盐类矿物具有较好的识别能力(杨日红等，2012)。
ASTER数据主要有标准HDF格式数据和dat格式地面站数据两种。文中所用ASTER地面站数据采集日期为2003年9月23日，数据级别为L1A，为ASTL1A 0309230444060310050159B，包括了5个文件：prbr0180.brs、prbr0181.jpg、prbr0182. jpg、0183.jpg、prdat018.dat。其中prbr0181.jpg、prbr0182.jpg、prbr0183.jpg 3个文件为多光谱影像的示意图，prbr0180.brs为数据头文件，prdat018.dat为数据源文件。
2.2 数据预处理
2.2.1 串扰校正与辐射定标
因ASTER短波红外通道传感器的相互干扰，B5对B4和B9具有串扰现象，使得B4和B9反射率值升高，因此须对数据进行串扰校正(杨日红等，2012；高慧等，2013)。同时ASTER数据在VNIR波段(1—3)空间分辨率为15 m，在SWIR波段(4—9)空间分辨率为30 m，需对4—9波段进行重采样将分辨率变为15 m，再利用ASTER Radiance模块实现1—9波段图像的辐射定标(刘知和周萍，2017)。
2.2.2 大气校正
将上述生成的1—9波段Radiance图像转换生成BIL格式，之后进行FLAASH大气校正。具体过程包括，一是生成的Radiance图像头文件会丢失中心波长半极值宽度(FWHM)，需要打开头文件依次添加1—9波段头文件相关信息；二是对于ASTER数据FLAASH大气校正来说，其所需的量纲与辐射半径定标后的数据量纲不同，这里辐射亮度值的比例因子应设置为10，完成量纲转换(陈建明等，2009)。三是通过对Radiance图像属性读取功能，设置全部的参数，从而完成FLAASH大气校正。对校正后的影像裁剪，得到稍大于研究区范围的预处理数据。
3. 成像光谱方法提取矿化信息
光谱变换技术对于减少冗余信息十分必要，光谱数据可以通过最小噪音分量(MNF)变换进行降维和压缩。选取预处理后ASTER的6个短波红外波段进行矿物信息提取，基于最小噪音分量MNF变换，像元纯度指数(PPI，Pixel Purity Index)进行波谱端元选择，采用混合谐调匹配滤波(MTMF，mixture tuned matched filtering)等方法进行矿物填图(Pour and Hashim, 2012)。
3.1 最小噪音分量(MNF)变换
最小噪音分量(MNF)变换是一种光谱数据减维技术，可以分离数据中的噪声，减小进一步处理所需的运算量(高慧等，2013)。通过主组分变换。将数据分为两类：一类为噪声图像，另一类为特征图像，与大特征值有关。通过观察最终特征值和MNF图像(特征图像)来确定数据的固有维数，即只利用其中的相关部分将数据中的噪声分离，改善光谱处理的结果。根据预处理后ASTER的6个短波红外波段完成MNF变换，得到特征值(表 1)和较大特征值MNF波段1—3灰度图像(图 2—图 4)。可见MNF波段特征值越大，图像所含有用的信息就越多。
表 1 各波段平均值和特征值Table 1. Average value and eigenvalue of each band波段名称 平均值 特征值 Band 1 21.173028 28.297260 Band 2 7.034879 9.762023 Band 3 6.628618 4.759365 Band 4 6.013828 2.901527 Band 5 4.625094 2.367740 Band 6 3.821772 1.830600 
图 2 MNF变换后波段1灰度图像Figure 2. Grayscale image of the band 1 after the MNF transformation
图 3 MNF变换后波段2灰度图像Figure 3. Grayscale image of the band 2 after the MNF transformation
图 4 MNF变换后波段3灰度图像Figure 4. Grayscale image of the band 3 after the MNF transformation3.2 像元纯度指数(PPI)
像元纯度指数(PPI)是在多光谱或成像光谱图像中寻找“光谱上最纯的”或极端像元的一种工具，它用于从混合像元中提取较纯像元，从而减少确定端元所要分析的像元数目，容易分离和识别端元。基于上述MNF变换后的图像，忽略特征值低的MNF波段，进一步处理高特征值波段(高慧等，2013)。通过多次反复投影N维散点图到随机单元矢量，记录每次投影的极值像元，最后注记每个像元被标定为极值的总次数，最终产生PPI图像(图 5)。
3.3 n维可视化(n-Dimensional Visualization)进行端元识别
n维可视化(n-Dimensional Visualization)，光谱可视为n维散点图中的一个点，n是波段数。对给定的像元，在n维空间中，每个波段对应像元的光谱反射率组成各个点位的坐标，利用点位在n维空间中的位置可以估计分析光谱端元数和它们的纯光谱特征。混合的端元落在纯端元之间，处在纯端元勾画的多面体内，这种混合光谱的凸面几何特征，可用于确定端元光谱数并估算它们的光谱特征，经过PPI选择出的潜在端元光谱输入n维散点图中进行反复多次旋转可识别出纯端元(Pour and Hashim, 2012)。
这里采用了4维可视化散点图，并勾画较好的端元(图 6)。根据前面的分析，较好的端元通常会出现在n维散点图的顶点和拐角处，当一系列的端元点被确定后，就可以将其输入到图像中的感兴趣区(ROI)，从图像中提取每个感兴趣区平均反射率光谱曲线(图 7)作为成像光谱矿物填图的端元。
图 7 n-D Mean绘图窗口获取的平均波谱曲线Figure 7. Average spectral curve obtained by the n-D Mean drawing window3.4 混合谐调匹配滤波(MTMF)
混合谐调匹配滤波(MTMF)是线性混合理论与匹配滤波技术相结合的一种方法，融合了线性光谱分解和匹配滤波的技术优势，能探测微细矿物成分。利用最终确定的端元光谱(它使用端元的MNF光谱而非反射率光谱)进行混合谐调匹配滤波(MTMF)的结果值为0—1范围的灰度图像，可以对矿物的相对丰度进行估计(亮度值高的像素代表较高的矿物含量)(Pour and Hashim, 2012)。最终得到矿区的矿物信息分布图(图 8)。
图 8 虎头崖矿区的矿化信息提取图粉红色—蒙脱石；红色—绿泥石；黄色—方解石Figure 8. Extraction map of mineralization information in the Hutouya mining area4. ASTER主成分分析方法提取矿化蚀变信息
基于研究区围岩蚀变发育情况和主要的蚀变类型(苏松，2011；杨兴科等，2016)，从USGS标准波谱数据库中，有针对性地选择了透闪石、方解石、绿泥石、伊利石、蒙脱石；铁的蚀变矿物代表黄铁矿等的连续光谱，将其重采样到研究区ASTER数据光谱，从而得到研究区主要的蚀变矿物的光谱(图 9)。根据研究区主要蚀变矿物的波谱特征(图 9)显示，伊利石、蒙脱石等在6波段形成一个明显的吸收谷，该吸收谷与Al-OH在2.2 μm处的吸收谷一致；透闪石矿物在5波段有一个微小的吸收谷；绿泥石在3波段有一个微小的吸收谷，方解石也在8波段有一个明显的吸收谷；黄铁矿为代表蚀变矿物在1波段处有吸收谷，在4波段中也存在一个明显的吸收谷。
图 9 研究区ASTER数据主要蚀变矿物的光谱Figure 9. Spectra of major altered minerals in ASTER data of the study area通过对蚀变矿物及所对应的离子或离子团特征分析，基于ASTER数据采用ASTER1、ASTER3、ASTER4、ASTER (N)的波段组合进行主成分分析(耿新霞等，2008；陈晔等，2014；辜平阳等，2016)，分别选择1、2、3、4波段提取铁染信息；1、3、4、5波段提取矽卡岩化蚀变信息；1、3、4、(5+6)/2波段提取蒙脱石、伊利石等Al-OH离子团蚀变矿物的异常信息；利用1、3、4、8波段提取方解石、黑云母、绿泥石等Mg-OH离子团蚀变矿物的异常信息。
4.1 含羟基矿化信息提取
利用ASTER1、ASTER3、ASTER4、ASTER(5+6)/2的波段组合进行主成分分析(张玉君等，2006)，提取包括蒙脱石、伊利石与绢云母等Al-OH离子团蚀变矿物的遥感异常信息。根据Al-OH离子团蚀变矿物主分量的判断标准及对参数值PC1-PC4(表 2)分析可知，ASTER4贡献系数符号为负，ASTER3与ASTER(5+6)/2贡献系数与ASTER4符号相反，PC4为含有蚀变矿物信息的主分向量，聚集了蚀变遥感异常信息。而表 2所示的PC4中ASTER4特征向量的符号为负，故需作PC4×(-1)的处理，使得ASTER4的特征向量符号为正。对虎头崖矿区PC4图像进行低值切割，且进行了异常滤波，即以2倍σ(标准离差)作为主分量输出的动态范围，获得虎头崖地区蚀变遥感异常信息(图 10)。
表 2 虎头崖矿区ASTER1、3、4、(5+6)/2主分量变换统计值Table 2. Statistical values of ASTER1, 3, 4, (5 + 6)/2 principal component transformation in the Hutouya mining areaASTER1 ASTER3 ASTER4 ASTER(5+6)/2 PC1 0.78201 0.61025 0.12076 0.03833 PC2 -0.62199 0.75182 0.21406 0.04560 PC3 -0.03748 0.24894 -0.91790 -0.30674 PC4 -0.01380 0.01967 -0.31155 0.94993 
图 10 虎头崖矿区ASTER遥感图像信息提取总异常图深紫色—Al-OH离子团矿化蚀变信息；黄色—Mg-OH离子团矿化蚀变信息；红色—铁染矿化蚀变信息；蓝色—矽卡岩化蚀变矿物信息Figure 10. Total anomalies of the ASTER remote sensing image extraction in the Hutouya mining area采用ASTER1、ASTER3、ASTER4、ASTER8波段参与主成分分析，提取Mg-OH离子团蚀变矿物的遥感异常信息。根据Mg-OH蚀变矿物主分量的判断标准和信息提取主成分的物理参数可知，ASTER4贡献系数符号为负，ASTER3与ASTER8贡献系数与ASTER4符号相反，PC4为含有蚀变矿物信息的主分向量，聚集了蚀变矿物信息。而表 3所示的PC4中ASTER4特征向量的符号为负，故需作PC4×(-1)的处理，使得ASTER4的特征向量符号为正。对虎头崖矿区第四主分量图像进行低值切割，且进行了异常滤波来获得Mg-OH离子团蚀变矿物的异常信息图像。即以2倍σ(标准离差)作为主分量输出的动态范围，获得虎头崖矿区蚀变遥感异常信息(图 10)。
表 3 虎头崖矿区ASTER1、3、4、8主分量变换统计值Table 3. Statistical values of ASTER1, 3, 4, 8 principal component transformation in the Hutouya mining areaASTER1 ASTER3 ASTER4 ASTER8 PC1 0.78225 0.61043 0.12078 0.02951 PC2 -0.62173 0.75383 0.21140 0.02240 PC3 -0.03460 0.24181 -0.93799 -0.24599 PC4 -0.01824 0.02538 -0.24679 0.96856. 4.2 铁染矿化蚀变矿物的蚀变遥感异常信息提取
采用ASTER1、2、3、4波段做主成分分析，提取与含Fe3+矿物相关的铁染异常主分量，主成分变换的统计结果如表 4所示，在PC4图像中包含了较多的铁染矿化蚀变信息，并且表现为亮色调。
表 4 虎头崖矿区ASTER1、2、3、4主分量变换统计值Table 4. Statistical values of ASTER1, 2, 3, 4 principal component transformation in the Hutouya mining areaASTER1 ASTER2 ASTER3 ASTER4 PC1 0.61068 0.62611 0.47567 0.09382 PC2 0.53342 0.12541 -0.80518 -0.22677 PC3 0.45937 -0.56826 0.02367 0.68227 PC4 0.36264 -0.51898 0.35338 -0.68868 对虎头崖矿区第四主分量图像，进行高值切割获得铁染异常信息图像。以2倍σ(标准离差)作为主分量输出的动态范围，获得虎头崖地区蚀变遥感异常主分量(图 10)。
4.3 矽卡岩化蚀变矿物的蚀变遥感异常信息提取
采用图像ASTER1、3、4、5波段做主成分分析，提取与含矽卡岩化矿物相关的蚀变遥感异常信息，主成分变换的统计结果如表 5所示，在PC4图像中包含了一些的矽卡岩化信息，并且表现为亮色调。
表 5 虎头崖矿区ASTER1、3、4、5主分量变换统计值Table 5. Statistical values of ASTER1, 3, 4, 5 principal component transformation in the Hutouya mining areaASTER1 ASTER3 ASTER4 ASTER5 PC1 0.78211 0.61033 0.12077 0.03498 PC2 -0.62190 0.75288 0.21263 0.03464 PC3 -0.03584 0.24549 -0.92974 -0.27209 PC4 -0.01620 0.02015 -0.27530 0.96101 对虎头崖矿区第四主分量图像，进行高值切割获得矽卡岩化异常信息图像。以2倍σ(标准离差)作为主分量输出的动态范围，获得虎头崖矿区蚀变遥感异常主分量(图 10)。
4.4 异常的中值滤波处理
蚀变提取后图像上会出现比较均匀的某一类图斑上分布孤立异常点的现象，可以去掉图中过于零星孤立的异常像元，或将孤立像元归并到包围它们或与它们相邻的较连续分布的那些异常中去(张玉君等，2006)。这里需要采用滤波的方法，对于每一类异常，给定一个最小连片像元数，去除小于此数的所有连片像元和孤立像元，或者整合到周围的较大的连片异常中。这里采用了3×3像元的窗口对所得异常进行中值滤波，得到总异常图(图 10)。
5. 讨论
为了验证提取的矿化蚀变遥感异常的准确性，特进行野外实地踏勘验证(图 11)。矽卡岩化蚀变验证点多出露透辉石、石榴石、绿泥石、透闪石，多见于褶皱、断裂和岩体与地层接触带中，外带碳酸盐岩裂隙中常见透辉石化、绿帘石化、磁铁矿化、绿泥石化。矽卡岩矿化强烈，一般伴有铜蓝、孔雀石化、磁铁矿化、褐铁矿化；受断层控制明显的矽卡岩化较弱，提取出来的矽卡岩化蚀变信息不明显，大部分还是多见于断裂、褶皱和岩体与地层接触带中。
野外实地踏勘与已有资料表明，多见围岩蚀变有硅化、钠长石化、绿帘石化、绿泥石化、黄铁矿化、角岩化、透闪石化、阳起石化、石榴石化、透辉石化、绢云母化和大理岩化等。Al-OH离子团蚀变矿物蚀变异常多见于绢云母、高岭土、黄铁绢英岩、石英斑岩脉等。蚀变区域里的矿点常有黄铁矿、磁铁矿体产出；Mg-OH离子团蚀变矿物蚀变异常多表现为绿泥石化、绿帘石化、白云母化和碳酸盐化，多见于大理岩和灰岩。
通过野外实地踏勘获得研究区已知矿床、矿(化)点坐标如表 6所示，结合地质图资料(刘渭等，2014)，在ArcGIS10.1软件将已知矿点与蚀变异常信息图进行叠加分析，可以看出提取的蚀变异常与野外验证结果吻合度较高(图 12)。
表 6 虎头崖矿区矿化点坐标(因涉密故总分用*号代替)Table 6. Coordinates of the mineralization points of the Hutouya mining area (The * sign is used instead due to confidentiality reasons)点号 X Y 矿化类型 HT126 E91°38′*″ N37°5′*″ 褐铁矿化、黄铁矿化 HT145 E91°38′*″ N37°4′*″ 铜矿化、磁铁矿化 HT137 E91°37′*″ N37°6′*″ 黄铜矿化 HT25 E91°36′*″ N37°5′*″ 铜铅锌矿化、锡矿化、钨锑矿化 HT27 E91°36′*″ N37°5′*″ 黄铁矿化、黄铜矿化、方铅矿化、铅锌矿化 HT48 E91°36′*″ N37°4′*″ 褐铁矿化、黄铁矿化、磁铁矿化 HT23 E91°37′*″ N37°5′*″ 黄铜矿化、孔雀石化 DY06 E91°36′*″ N37°5′*″ 黄铁矿化、褐铁矿化 DT108 E91°36′*″ N37°4′*″ 矽卡岩化、孔雀石化 HT163 E91°36′*″ N37°4′*″ 闪锌矿化、黄铜矿化 HT189 E91°34′*″ N37°4′*″ 石英斑岩、黄铜矿化、黄铁矿化 HT193 E91°34′*″ N37°4′*″ 黄铁矿化、黄铜矿化 
图 12 虎头崖矿区ASTER遥感图像信息提取总异常与野外验证点叠加图粉红色—成像光谱方法提出的异常信息；深紫色—Al-OH离子团矿化蚀变信息；黄色—Mg-OH离子团矿化蚀变信息；红色—铁染矿化蚀变信息；蓝色—矽卡岩化蚀变矿物信息；黄点—野外验证点坐标Figure 12. Superposition diagram of total anomalies of ASTER remote sensing image extraction and field verification points in the Hutouya mining area6. 结论
(1) 应用成像光谱方法初步得到矿区的矿物分布图，采用ASTER1、ASTER3、ASTER4、ASTER (N)的波段组合进行主成分分析，提取铁染异常信息，矽卡岩化蚀变异常信息，蒙脱石、伊利石与绢云母等矿物的蚀变异常信息，方解石、黑云母、绿泥石等矿物的蚀变异常信息。
(2) 通过野外实地踏勘获得已知矿床、矿(化)点坐标，基于ArcGIS10.1软件将其与基于ASTER数据采用成像光谱法和主成分分析法所提取的蚀变异常信息叠加对比分析，野外验证效果良好。表明提取结果与数据处理方法技术较可靠，对扩大找矿规模和发现富集地段具有重要的指导意义。
(3) 成像光谱方法提取的蚀变异常信息也有不确定性，同时主成分分析法提取出来的矽卡岩化蚀变异常信息不明显，可能是因为USGS标准波谱数据库的矿物波谱没有达到对该区矿物更精细的识别要求，因此应加强野外样品的波谱更加精细地测试工作。
致谢: 长安大学晁会霞博士在论文野外露头照片的矿化类型确认方面给予了悉心指导，同时两位审稿专家的建设性意见对文章的最终定稿帮助很大，在此一并表示感谢。 -
图 1 震中台站分布图和文中使用的地壳速度模型
F1—党河南山南缘断裂；F2—党河南山北缘断裂；F3—阿尔金南缘断裂；F4—阿尔金断裂；F5—野马河−大雪山断裂；F6—疏勒南山断裂；F7—中祁连北缘断裂；F8—昌马断裂；F9—肃南−祁连断裂；F10—红崖子−佛洞庙断裂；F11—柴达木北缘断裂a—近震波形台站分布；b—远震波形台站分布；c—研究区地壳速度模型（Vp 为P波速度，VS为S波速度）
Figure 1. Epicenter and station distribution, and crustal velocity model used in this study
(a) Distribution of local station and active faults; (b) Distribution of teleseismic station; (c) The crustal velocity model for this study (the dashed line represents the S-wave and the solid line represents the P-wave, Vp is the P-wave velocity, and VS is the S-wave velocity) F1— Southern Danghe Nan Shan Fault; F2— Northern Danghe Nan Shan Fault; F3 and F4 are the south and north strands of the Altyn Tagh Fault; F5—Yemahe–Daxue shan Fault; F6—Shule Nan Shan Fault; F7—North Central Qilian Fault; F8— Changma Fault; F9— Sunan–Qilian Fault; F10—Hongyazi–Fodongmiao Fault; F11—North Qaidam Fault
图 2 波速比和地壳速度模型
a—波速比（横坐标为P波走时（Pj）与最小P波走时（Pi）的差，纵坐标为对应S波走时（Sj）与最小S波走时（Si）的差；其中黑色×为波速比拟合数据中的离群点，不参与拟合；红色实心圆为参与波速比拟合的数据点；蓝色虚线为波速比拟合线）；b—文中所使用的地壳速度模型
Figure 2. Wave velocity ratio and velocity model used in this study
(a) Wave velocity ratio (The horizontal axis represents the difference between P-wave travel time (Pj) and the minimum P-wave travel time (Pi), while the vertical axis represents the difference between corresponding S-wave travel time (Sj) and the minimum S-wave travel time (Si). The black "×" marks indicate outliers in the velocity ratio fitting data and are not included in the fitting process. The blue dashed line represents the fitted velocity ratio line.); (b) Velocity model (The dashed line is the initial velocity model and the solid line is the VELEST velocity model; the red line represents the S-wave, and the blue line represents the P-wave.)
图 3 2021年阿克塞地震震源机制反演结果
注：红线和黑线分别代表合成波形和观测波形；波形下方数字代表波形相对时移和互相关系数；波形左侧为台站名称；台站名下方为方位角和震中距；震源球上三角形为P波的离源角投影，正三角为近震Pnl，倒三角为远震P波
Figure 3. The focal mechanism solution of 2021 Aksai mainshock
The red and black lines represent the synthesized and observed waveforms, respectively. The numbers below the waveforms are the time shifts (in seconds) and the maximum cross-correlation coefficients. The station codes are shown on the left, and the azimuth and epicentral distances are shown below the station codes. The triangles on the beach ball are the off-source angle projections of the P-wave, the positive triangles represent the local Pnl, and the inverted triangles represent the teleseismic P-wave.
图 4 反演拟合误差随深度变化图
注：震源球上的数字代表反演所得的矩震级
Figure 4. The inversion residuals vary with depth
Number above the beach ball represents the corresponding moment magnitude.
图 5 地震震中重新定位分布图及剖面两侧各7 km范围内的地震深度分布图
注：深度剖面上的彩色实心圆为剖面两侧7 km范围内地震在剖面上的垂直投影，沙滩球的投影剖面为AA’, 彩色实心圆的颜色表示发震时间, 黑色虚线为拟合断层面a—重新定位地震震中分布；b—AA’剖面上的地震深度分布；c—BB’剖面上的地震深度分布
Figure 5. Map view and depth distribution of the aftershocks along profiles. Earthquakes within 7 km of the line are included
(a) Epicenter distribution of the relocated events; (b) Depth distribution of the aftershocks along AA’ profiles; (c) Depth distribution of the aftershocks along BB’ profiles Note：Colored solid circles on each depth profile represent the vertical projections of earthquakes within a 7 km range on both sides. The beach balls represent the focal mechanisms, and the projection profile is AA’; The colors of the solid circles indicate the occurrence time of the earthquakes; The black dashed line represents the fitted fault plane.
图 6 2021年阿克塞MS 5.5地震InSAR同震形变场特征
a—升轨（A172）视线方向形变场；b—降轨（D77）视线方向形变场
Figure 6. Coseismic deformation fields from InSAR of 2021 Aksai earthquake
(a) and (b) coseismic deformation fields in the ascending (A172) and descending (D77) orbits, respectively
图 7 阿克塞MS5.5 地震发震构造和断层陡坎地貌
a—地震发震构造和破裂模式（δ为断裂倾角）；b—震中卫星影像解译；c—h—党河南山南缘断裂断层陡坎地貌
Figure 7. Seismogenic fault of the Aksai earthquake and fault scarps along the southern Danghe Nan Shan Fault
(a) Seismogenic tectonics and rupture patterns of the Aksai earthquake (δ is the dip of the fault); (b) Geomorphic interpretation from satellite image; (c)—(h) Geomorphology of fault scarps along the southern Danghe Nan Shan Fault
图 8 2008年至今祁连山西段（92°—100°E、37°—41.5°N）MS≥4.0地震震级−时间图
黑竖线为震级，粉红色影区示意地震活跃期，红色虚线为MS 5.0示意线
Figure 8. The Magnitude-time（M-t）diagram of the western Qilian Shan region since 2008
The seismic data used is Ms≥ 4.0 earthquakes in the western Qilian Shan region (longitude 92°–100°; latitude 37°–41.5°), since 2008. Seismic data in the western Qilian Shan region (longitude 92°–100°; latitude 37°–41.5°) with Ms≥ 4.0 magnitude since 2008. The black vertical line represents the magnitude, pink shaded area indicates the active period, and red dashed line represents the symbol line for Ms 5.0.
表 1 阿克塞地震震源机制解
Table 1. The results of focal mechanisms by different organizations
节面I 节面II P轴 T轴 深度/
km数据来源 走向/
（º）倾角/
（º）滑动角/
（º）走向/
（º）倾角/
（º）滑动角/
（º）方位角/
（º）倾伏角/
（º）方位角/
（º）倾伏角/
（º）310 39 71 154 54 105 234 8 111 76 17.4 Globe CMT
（Ekström et al.，2012）331 47 107 127 45 72 49 1 315 78 11.5 美国地质调查局 (USGS) 324.9 40.0 93.6 140.2 50.1 87.0 232.4 5.1 27.9 84.4 万永革，2019 331.3 37.6 66.6 180.0 56.0 107.0 257.9 9.5 134.9 73.0 6.1 薛善余等，2023 315 41 81 146 49 97 231 4 105 83 6.9 文中 
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