文中推导并给出了基于非格网分布的起伏面扰动重力或重力异常解算区域扰动重力梯度场模型的数值计算公式.基于澳大利亚 West Arnhem Land 地区的格网重力数据,以频谱域(二维快速傅里叶变换)解算的扰动重力梯度全张量作为"基准值",然后利用基于推导公式的最小二乘配置方法(LSC)对相同区域非规则范围的重力数据进行扰动重力梯度模型解算,将结果作为"评估值".对比"基准值"与"评估值"之差,研究发现:1)基于推导公式的最小二乘配置方法解算得到的扰动重力梯度值与频谱域方法得到扰动梯度"基准值"各分量在空间形变变化上是一致的;2)统计扰动重力梯度各分量的差值 ΔδΓfft-lscxx、ΔδΓfft-lscxy、ΔδΓfft-lscxz、ΔδΓfft-lscyy、ΔδΓfft-lscyz 和 ΔΓfft-lsczz,"基准值"与"评估值"差值的标准差分别为 5.54E、5.30E、1.85E、6.55E、2.09E 和 9.67E(1 E=1×10-9s-2),远低于国际上实测重力梯度与解算模型差值的研究结果.最后,基于云南地区实测地表差分重力值,文中首次给出了该区域半波长约 20km的重力梯度场年际变化模型.文中的思路和方法提高了广泛分布的重力数据(主要为重力异常和扰动重力)的使用效率,可为地球物理学、地质学研究更好地理解和解释重力数据、重力梯度数据及其与场源的关系提供数据基础.
第四纪碎屑沉积物是新构造运动和第四纪地质环境变化的重要信息载体.对第四纪碎屑沉积物,尤其是对距今 200ka以上不含火山灰的粗颗粒样品(如砾石堆积)进行测年,一直是第四纪年代学研究中的重点和难点问题,石英 ESR 测年法是能够直接测定这类样品的测年方法之一.但是,将石英 ESR法测年应用于早更新世沉积物(特别是粗颗粒沉积)结果的可靠性国内外至今鲜有报道,是目前亟待解决的年代学问题之一.文中基于石英 ESR法测年原理和前人的研究成果,以已知年龄的下更新统靖远砾石层为研究对象,探讨了早更新世砾石堆积石英 ESR法测年的可靠性.结果显示:1)靖远砾石层石英 Ti-Li心在 11 000Gy附加剂量范围内 ESR信号未饱和,Al心在 13 000Gy附加剂量范围内 ESR信号未饱和;2)单饱和指数函数和"指数+线性"函数可分别为 Ti-Li心和 Al心提供更优的等效剂量拟合结果,且拟合效果均优于 0.98;3)靖远砾石层石英 Ti-Li心和 Al心的平均ESR测年结果分别为(1.67±0.15)Ma和(1.65±0.69)Ma,与已知的宇生核素测年结果(约为(1.73±0.13)Ma)和岩石地层结果在误差范围内是一致的.综上所述,石英 Ti-Li 心和 Al 心 ESR法测年均可为早更新世含砂质透镜体的砾石层堆积提供可靠的年代学数据.
目前中国有60余处四分量钻孔应变测点,这些测点的观测数据在地球动力学和地震前兆等研究中均发挥着重要作用.但在实际观测中,不少四分量钻孔应变仪会受到不同周期气压波的干扰.截至目前,还鲜有关于该类仪器对气压频响效应研究的报道.文中以江宁台为例,尝试采用传递函数对其进行系统诊断;在此基础上,进一步利用双衬套力学模型反演其钻孔围岩的力学参数.结果表明:1)在 0.1～30cpd频带内,气压和钻孔应变的相干性较好;2)低频带(0.1～0.5cpd)的气压响应最好,高频带(＞8cpd)次之,中频带(0.5～8cpd)则略差;3)若不考虑日波和半日波频段的影响,在整个频带内,4 个分量的应变和面应变气压系数谱近线性平稳;4)在高频带,钻孔应变对气压响应的相位谱呈指数形式上升,平均滞后约 24.2°,频率依赖性明显;5)利用面应变低频气压系数均值反演的钻孔围岩弹性模量和泊松比分别为 33.9GPa 和 0.27.以上结果将不仅有助于气压效应的分频改正,同时还能为钻孔围岩力学参数的定量反演提供新方法.
在破坏性地震中,快速估算震级对于早期预警和应急响应具有重要意义.然而,利用强震动地面峰值速度(Peak Ground Velocity,PGV)快速准确地估算震级仍是一项挑战.文中开展了基于强震动 PGV 的震级快速估算方法研究.首先,基于全球范围内 23 次 MW6.0～9.0 地震事件的5 596 条强震动 PGV,构建了可用于震级快速估算的强震动 PGV 震级模型.其次,采用未参与建模的 4 次地震事件进行模型验证,并开展了震级快速估算研究.结果表明:23 次地震事件的强震动PGV 预测值与观测值基本一致,残差的均方根误差为 0.296.4 次地震事件的强震动 PGV 估算震级与美国地质调查局报告的矩震级基本相符,其绝对偏差分别为 0.15 个、0.14 个、0.05 个、0.13 个震级单位,震级快速估算的收敛时间分别为 76s、50s、84s、70s.
作为中国大陆最为活跃的断裂带之一,鲜水河断裂现今的滑动模式,尤其是北西段的浅部蠕滑特征长期以来备受关注.文中首先利用 Sentinel-1 卫星降轨数据,基于小基线集时序分析(SBAS)方法获取鲜水河断裂带北西段 2014-2021 年的地表视线向(LOS 向)平均速度场;再采用弹性螺旋位错模型拟合 InSAR跨断层剖面速度,估计断层的长期滑动速率和浅部蠕滑速率;最后结合黏弹性地震周期模型分析炉霍段地震的复发周期、下地壳和上地幔流变对滑动速率估计的影响.In-SAR处理结果显示,断层两侧 LOS 向速度场呈现出明显的速度差异.使用弹性螺旋位错模型估计得到的鲜水河断裂北西段的断层滑动速率为 7.2～11.0mm/a,自西向东逐渐减小.断裂带浅部蠕滑速率为 0.3～3.1mm/a,蠕滑主要集中在虾拉沱和道孚—松林口之间.基于历史地震的复发周期及青藏高原东缘下地壳和上地幔黏滞系数的研究,文中采用黏弹性地震周期模型反演得到炉霍段的滑动速率为(7.91±0.3)～(9.85±0.4)mm/a,略低于纯弹性螺旋位错模型的结果((10.14±0.5)mm/a).
在地震重力区域监测网数据处理过程中,相对重力仪的格值标定和基准控制通常采用本网内的绝对重力基准值,由于仪器格值和控制基准的影响相互耦合,难以定量分析格值、基准控制对测网数据平差处理的影响.文中基于大别山金寨重力基线场的混合重力测量数据,解耦了格值、基准控制的影响,获得了金寨重力基线场的初值.结果表明:金寨重力基线场可以满足安徽地震重力测网仪器标定的需求,对提升监测效率、节约经济成本具有重要意义,也可为其他基线场、地震重力区域监测网数据处理提供参考.
不同型号地震计的自噪声水平直接影响了地震观测数据的质量,并进一步限制了利用地震数据解决地球科学问题的能力.长久以来,由于受到观测条件的限制,准确地测量和比较不同型号地震计的自噪声水平颇具挑战.文中利用马陵山地震台 4 个月的连续地震波形,基于概率密度函数的表示方法计算了 7 个型号地震计的自噪声功率谱密度曲线.对于超宽频带地震计 CMG-3T-360,在微震频带(0.1～1 Hz),水平方向的自噪声明显高于垂直方向,这可能是地震计水平方向相对方位未对齐导致的计算偏差;在低频段(＜0.03Hz),水平方向显著偏高的自噪声可能源于大气压的变化.短周期地震计 JS-S02 的自噪声水平在频率为 0.15～7Hz 时低于全球新低噪声模型(NLNM).宽频带地震计 TDV-60B和甚宽频带地震计 TDV-120VB 在垂直方向的自噪声水平基本一致.宽频带地震计 JS-60 和甚宽频带地震计 JS-120 的自噪声水平在微震频段接近或低于 CMG-3T-360.当频率为 0.008～0.08Hz时,JS-120 水平向 NS 通道的自噪声水平高于 CMG-3T-360 功率谱密度 68%的置信区间.
强震发生时,震源断层错动引发上覆土体变形破裂是地面建(构)筑物破坏的重要原因.为研究和分析上覆土层地表变形与破裂特征及其影响因素,文中通过有限元数值模拟方法,综合分析断层倾角、断层错动位移量、上覆土层厚度对上覆土层地表变形与破裂的影响及其规律.结果表明:1)断层垂直位错量为上覆土层厚度的 3.3%、倾角仅为 30°时,发生地表破裂;断层垂直位错量为上覆土层厚度的 5%、倾角为 30°、45°时,发生地表破裂;断层垂直位错量为上覆土层厚度的6.6%、倾角为 30°、45°、70°时,发生地表破裂;断层垂直位错量为上覆土层厚度的 10%、倾角为30°、45°、70°与逼近 90°时,均发生地表破裂.2)随垂直位错量的增加或上覆土层厚度与断层倾角的减小,地表等效应变逐渐变大,越容易发生地表破裂.3)随着断层倾角由 30°、45°增加至 70°,上、下盘地表破裂宽度比值从约 3∶1 增加至 3∶2～1∶1.4)上覆土层的变形与破裂,首先始于断层基岩与土体交界面的土体破裂,随着位错量的增加,当断层倾角为 30°、45°、70°时,地表均出现了 1个初始破裂点;当断层倾角逼近 90°时,地表出现了 2 个初始破裂点,最后上覆土层出现贯通破裂.
地电场是重要的地球物理场,长周期地电场是地球电磁场的重要组成部分.文中针对2015-2022 年青海省都兰地震台较长时间尺度的地电场观测数据资料,采用小波分析、中值滤波、卷积滤波及线性拟合等多种方法和途径,对长周期地电场及其变化特征进行提取和分析.研究结果显示:1)都兰地震台地电场观测数据具有比较强的长期平稳性和变化可靠性,同测向日相关系数的算术平均值≥0.98,日变化差值的算术平均值≤0.2mV/km;2)FFT频谱分析结果表明,数据除包含24h、12h、8h和 6h等中短周期变化外,同时也包含年周期、半年周期及 3 月周期等长周期变化成分;3)地电场观测值的日变化幅度呈现夏高冬低的季节性变化,显著性变化包括年周期、半年周期、4 月周期、27 日周期及半月周期等;4)观测值的趋势性变化呈现比较典型的周期性年变化特征,变化形态近似正弦波,且每年的极值点和变化幅度基本相当;5)玛多 MS7.4 地震前后地电场观测值出现了较为明显的破年变化异常畸变现象.机理分析显示,在地球围绕太阳公转及自转过程中,太阳直射点的往复改变是长周期地电场变化的重要激发机制.综合分析认为,都兰地震台较长时间尺度的地电场观测数据变化具有比较优良的客观性、可靠性及长期变化平稳性,能够充分反映长周期地电场的基本变化特性,具有较高的研究和应用价值.
文中对2013年4月—2022年7月发生在芦山震区的地震进行重定位,并反演了芦山2022 年 6 月 1 日 MS6.1 地震的震源机制解.芦山 MS6.1 地震序列的震源深度北浅南深,断层长约10km,自深向浅破裂.通过分析芦山震区的发震构造和地震活动特征,认为震源断层为一条走向NE、倾向 SE 的盲逆冲断层,其与 2013 年 MS7.0 地震走向 NE、倾向 NW的主逆冲断层及其上盘走向 NE、倾向 SE 的反向逆冲断层共同组成双层"Y"字形结构.进一步综合分析库仑应力变化,认为2013 年芦山 MS7.0 地震对 2022 年芦山 MS6.1 地震具有抑制作用.
同震地表破裂是地震在地表最直观的地貌表现,其几何形态和展布特征记录了丰富的断层活动信息.近年来,高分辨率遥感影像的日益丰富和摄影测量方法等的快速发展,能帮助我们快速获取研究区高分辨率地形地貌数据,以便更好地识别地震地表破裂带的精细几何结构,并测量沿线断错位移分布等信息.文中选取川西理塘断裂 1890 年地震的同震地表破裂为研究对象,利用WorldView遥感卫星影像立体像对和摄影测量方法生成了研究区 0.5m分辨率的正射影像和 1m 分辨率的数字高程模型(DEM).基于此数据解译获取了 1890 年地震地表破裂带的空间展布范围和精细几何结构,沿破裂带测量了 90 组冲沟、田埂等线性地貌标志的左旋位移,并统计了其累积概率密度分布(COPD).结果表明,理塘断裂全新世中期以来至少经历过 4 次规模相当的强震事件,其中最近一次的 1890 年地震事件的破裂长度约为 27km,同震左旋位移约为 1.3m,估算震级为 MW6.8～7.1,其他 3 次由老到新的地震事件的同震位移约为 1.8m、1.9m、1.1m.研究结果充分展示出高分辨率遥感影像数据在同震地表破裂研究中的应用潜力.
地震作为最严重的地质灾害之一,具有突发性和巨大的破坏性,开展地震监测预警工作具有十分重要的意义.地表热红外辐射增强的现象是普遍存在的中强地震前兆,目前已被作为地震监测预警与短临预报的重要参考信息.学者们对其产生的内在机理给出了多种解释.其中,应力致热假说已被广泛接受,并已在实验室的岩石力学加载实验中得到证实,即岩石受力挤压时升温、拉张时降温,但这种地壳的挤压拉张运动和热辐射异常间的对应关系能否在野外条件下被观测到,一直以来尚未有相关研究报道.为此,文中采用GRACE 重力和MODIS热红外 2 种卫星遥感数据,以构造应力变化明显的大地震——汶川地震为时间节点开展应力致热假说的野外遥感验证研究.首先,借助 GRACE 卫星反演得到的地壳质量密度进行与热红外辐射增温的比对分析;然后,分别采用基于最大切应变的重力异常提取方法和原地温度法获得重力异常和热异常,并分别从时间尺度和空间尺度上检测震前重力异常和热异常的关联性,对二者与构造断裂带的空间展布进行一致性分析,得到以下结论:1)应力致热假说在野外条件下能够被遥感手段验证.地壳的升温区(热偏移指数为正)与挤压区(地壳质量密度增加)、降温区(热偏移指数为负)与拉张区(地壳质量密度减少)皆高度对应,二者正、负变化的一致性高达 88.9%,这为应力致热假说提供了野外观测证据.2)震前重力异常和热异常的时空变化具有较强的关联性.在时间域上,重力异常和热异常具有较强的相关性,主要表现为在震前 3 个月,2 种异常的强度同步出现了突增现象,并同时达到最大值.在空间域上,重力异常多出现在热偏移指数值的正、负值交界处,这表明重力异常和热异常的空间分布亦具有一定的关联性.此外,2 种异常多次呈现出沿断裂带分布的现象,由此可知,二者与构造活动皆密切相关.
精细地壳应力场在地球动力学研究中具有至关重要的作用.2021 年云南漾濞地震序列发生在地震观测台站密集分布的地区,丰富的漾濞地震序列资料为该地区的精细应力场分析提供了大量地震震源机制解数据.为分析漾濞地震震源区的应力状态、断层构造和地震动力学关系,首先选择震源机制中心解算法对搜集到的漾濞地震序列震源机制解进行中心解求解,以保证震源机制数据的准确性;其次基于地震序列发生的位置,采用移动窗方法将震源机制解划分为 6 个区域,分别求解了 6 个区域的应力张量数据;最后分析了非均匀应力场所揭示的动力学问题.研究结果表明:漾濞地震震源区西北部和东南部的压应力轴方向由 NNW-SSE 向转换为 NNE-SSW向,偏转角度达23°,且西北部的应力形因子大于东南部.推测西北部和东南部明显的应力场变化是由破裂区北部物质南移受阻和印缅弧深部 NNE 向低角度俯冲导致研究区浅部出现 NNE 向拉张联合作用所致.漾濞地震序列破裂东南区呈现马尾状散开的断层分布及山脉和水系走向在周围的分布均与本研究推测的应力偏转和应力形因子改变相符.这些研究对认识该地区的断裂活动特性和地震动力学具有一定意义.
由于震中附近强震台分布不均,文中联合使用近场 2 个国家强震动观测台网的强震台和7 个云南地震预警台网烈度台的强震记录,采用经验格林函数法构建了特性化震源模型,并利用此模型对近场强震动进行了模拟.结果表明:烈度台的记录可与强震台的记录联合,共同作为强震动模拟的对象,但应注意区分二者的有效频带;在 0.20～30.0Hz 频带,在 53YBX 台处的 NS 分量上,模拟结果的伪加速度反应谱较好地再现了 0.1s处的峰值,在 EW分量上,合成的速度波形虽然幅值较低,但较好地再现了速度脉冲波段;在 53DLY 台处的合成波形较好地再现了约 2s 的长周期地震动;在 0.50～30.0Hz频带,合成波形和反应谱与信噪比较高的烈度台的记录较为一致.文中确定的用于模拟强震动的特性化震源模型由一个强震动生成域构成,其面积和相应的短周期范围内加速度震源谱的水平段幅值与地震矩的关系均遵循经验标度律.
青藏高原东缘是高原物质向 E 及 SE 扩展的重要通道,掌握青藏高原东缘的地壳密度结构对研究青藏高原的隆升、变形机制具有重要意义.文中在前人研究成果的基础上,选取了地面实测的 9 条交叉的重力测线数据,以深地震反射剖面为约束,采用人机交互模式反演得到了青藏高原东缘地下的二维密度结构,并通过克里金插值法获取了三维密度结果.反演结果表明,青藏高原东缘地区具有巨厚的地壳,莫霍面埋深最深约为 61 km,而四川盆地的莫霍面埋深约为 42km,以龙门山-安宁河-小金河断裂为界,两侧形成了莫霍面深度变化梯度带;从反演得到的沉积层厚度来看,沉积层在青藏高原东缘几个块体内呈现中心普遍厚度较大、边缘厚度较薄的特点.结合该地区的地震空间分布特征分析,青藏高原东缘的莫霍面和沉积层厚度分布与该地区的地震分布均具有很强的相关性,这对未来地震预测也具有重要的参考价值.
In order to study the deep electrical structure and its formation mechanism of different tectonic units in the central and southern part of the North China Depression,especially the southern North China Depression with NW-NNW trending tectonic lines and the northern North China Depression with NE-NNE trending tectonic lines,as well as the deep tectonic background of three destructive earthquakes in the study area,a 110km long magnetotelluric（ MT） sounding profile across the main structural units in the study area was deployed to study the deep fine electrical structure in the central and southern part of the North China Depression by using high-density and broadband MT method with the support of the active fault exploration project in Kaifeng City. The profile is NS-trending as a whole,starting from Tongxu County of Kaifeng City in the south,passing through Xiangfu District of Kaifeng City,Fengqiu County and Changyuan County of Xinxiang City,and terminating at Banpodian Township of Huaxian County of Anyang City in the north,with a total length of 110km and an average point distance of about 3km. The observation points in the survey area of Kaifeng City are dense,with a point distance of 2km. From south to north,the whole profile crosses two first-order tectonic units of the southern North China Block and the northern North China Block and four second-order tectonic units of the Taikang Uplift,the Kaifeng Depression,the Dongpu Depression and the Neihuang Uplift.In MT data processing,in addition to the remote reference and robust techniques,the multi-point and multi-frequency tensor decomposition was employed to determine the regional electric strike,and the NLCG 2D inversion was performed on TE and TM data. And finally,the deep electrical structure is obtained.The result shows that,with Xinxiang-Shangqiu Fault as the boundary,the deep electrical structure on its north is relatively simple than that on the south. The electrical structure of Neihuang Uplift and Dongpu Depression in the northern North China Depression is relatively simple,and its resistivity structure is characterized by vertical segmentation and divided into low resistivity and high resistivity zones corresponding to the crust of the area consisting of sedimentary cover and crystalline basement of hard block with good basement integrity. At the same time,the high resistivity zone is very thick,which could represent the unified crystallization basement in the North China Block region. The deep electrical structure of the tectonic units in the southern North China Depression on the south of Xinxiang-Shangqiu Fault is relatively complex,showing a three-layer structure of lowhigh-low resistivity in the vertical direction and alternating high and low resistivity in the horizontal direction. For example,the resistivity of the crust below the Taikang Uplift shows a low-high-low three-layer structure,that is,a low resistivity zone above the depth of 2km,a high resistivity zone at the depth between 2km and 15km,and a low resistivity zone below 15km. This may be related to the mutual subduction and collision between the Yangtze plate and the southern margin of the North China plate,while the northern North China Depression is less affected by the Yangtze plate and QinlingDabie orogeny due to the control of the boundary Xinxiang-Shangqiu Fault.The two destructive earthquakes of 1342 and 1918 in Tongxu,Henan Province are located in the intersection area of high and low resistivity zones beneath the Taikang Uplift,and the Fengqiu earthquake of 1737 in Henan Province is located near the gradient zone of high and low resistivity in the crust.
The Haiyuan-Liupanshan tectonic belt is one of the most significant tectonic deformation areas in the northeastern Qinghai-Tibetan plateau with frequent strong earthquakes. It is an important opportunity to study the northeast extension of the Qinghai-Tibetan plateau and an ideal place to study the earthquake breeding process.The published GPS observations show that the southwest side of the Haiyuan fault may still be undergoing deformation caused by the crustal viscoelastic relaxation effect of the 1920 Haiyuan M8. 5earthquake. And the publicly published leveling data results show local vertical deformation of the crust in the area west of the Liupanshan fault is significant. According to the seismic geological data,there exist historical earthquake rupture gaps in the middle and south sections of the Liupanshan fault and the southeast section of the Xiangshan-Tianjingshan fault in the Haiyuan-Liupanshan structural area,which have the background of strong earthquakes above M7. 0. In view of the low spatial resolution of GPS and leveling observations,we need to use high-resolution crustal deformation fields to further study the crustal deformation characteristics of the above regions. Therefore,we further discuss the above issues in combination with In SAR observations.The Sentinel-1A/B SAR data of two orbits covering the Haiyuan-Liupanshan fault from 2014 to2020 were processed to obtain the current crustal deformation field in the line-of-sight direction.Furthermore,the high-density regional crustal deformation field was obtained by integrating In SAR and published GPS observations of the horizontal crustal movement velocity field on a time scale of 20years. By comparing the observations of GPS, leveling and In SAR and high-resolution threedimensional deformation integrated GPS-In SAR field,the characteristics of crustal deformation and strain field in the region are analyzed and discussed. The main conclusions are as follows:（ 1） GPS and In SAR observations show that the post-seismic viscoelastic relaxation effect of the1920 Haiyuan M8. 5 earthquake may still be pronounced on the south side of the Haiyuan fault,but this conclusion is still speculative and needs to be confirmed by further observations;（2） The high-resolution horizontal deformation field from GPS-In SAR shows that the decrease of the sinistral slip rate of the Haiyuan fault along the fault strike mainly occurs in the Middle East section. In contrast,the decrease of the middle and west sections is not significant,which may be related to the transformation of the left-lateral strike-slip to thrust nappe structure between the Haiyuan fault and the Liupanshan fault.（ 3） GPS vertical and leveling observations both show that the vertical crustal deformation characteristics in the middle and south sections of the Liupanshan fault are similar to the vertical deformation of the Longmenshan fault before the Wenchuan earthquake. Considering the similar structural characteristics of the Liupanshan fault and the Longmenshan fault,and combining with the seismic and geological data,we believe that the Liupanshan fault may be in the relatively late stage of the earthquake breeding process. It can also be recognized by the high-resolution horizontal deformation and strain field derived from GPS-In SAR data. According to the fault motion parameters obtained in our study and the existing seismic and geological data,it is estimated that the maximum moment magnitude of an earthquake in the middle-south section of Liupanshan Mountain is approximately 7. 5.（ 4） The areas with rapid maximum strain accumulation in the study region are mainly concentrated in the vicinity of the Haiyuan fault and the left lateral shear zone between the Haiyuan fault and the Xiangshan-Tianjingshan fault. The dilatation strain rate west of the Liupanshan fault shows prominent compressive deformation characteristics corresponding to the nappe deformation in the Liupanshan tectonic area. The strain rate field in the southeast section of the Xiangshan-Tianjingshan fault is smaller than that of the surrounding area. There is a strain mismatch phenomenon,which may be related to the preparation for strong earthquakes. From the perspective of rotational deformation,the study area presents multiple deformation units,among which counterclockwise rotation corresponds to left-lateral strike-slip deformation（ the left-lateral shear belt from the Haiyuan fault to the Xiangshan-Tianjingshan fault）. In contrast,clockwise rotation corresponds to right-lateral strike-slip deformation（ the right-lateral shear belt in the western margin of Ordos and Longxi block）.
With the recent development of geodetic observation theory,the increasing satellite platforms and the progress of related technology,InSAR is emerging as a new data source and useful tool for remotely-based geodetic observations.More importantly,In SAR observations play an increasingly irreplaceable role in the field of coseismic deformation observations,earthquake emergency responses,earthquake hazard evaluation and seismogenic structure research.Particularly,In SAR is the most commonly used tool in coseismic deformation measurements on the Qinghai-Tibetan plateau or other global seismic zones,where GPS data are sparse or inaccessible in some cases.Specifically,InSAR measurements help us to respond in time after disastrous earthquakes and provide valuable information associated with how the surface of the crust deforms due to large earthquakes.In the area of scientific research,InSAR provides products of surface deformation observations and serves as model constraints kinematically or dynamically in identifying the buried faults,studying the characteristics of seismogenic faults,obtaining three-dimensional displacements,and investigating the relationship between earthquakes and tectonic structures.InSAR observations and its deformation products have the technical advantages of large spatial scale,high precision and in-time,compared to other geodetic measurements.Consequently,InSAR has the ability to provide scientific and technological support for earthquake emergency observations,and meeting the practical needs of earthquake disaster reduction on the Qinghai-Tibetan plateau.In this review,we mostly limit our focus to the application of In SAR technology in earthquake cycle deformation monitoring in different structural settings on the Qinghai-Tibetan plateau.We also summarize the In SAR-based studies on fault kinematics and seismogenic structures related to some noted earthquakes on the Qinghai-Tibetan plateau.We highlight how the applications of InSAR data can greatly promote earthquake science and can be used as routine observations in some important areas.Then proceed to discuss the cutting-edge development trend and some new challenges of InSAR technology,which are frequently discussed and investigated,but not well resolved,in recen applications.The endeavors in increasing the precision of small-magnitude deformation measurements and expanding the InSAR data volumes can make the scientific objectives of earthquake disaster reduction on the Qinghai-Tibetan plateau and its surrounding areas feasible and reliable.To better understand how InSAR observations have changed the way we study earthquakes,we summarize the development,commercialization,insights,and existing challenges associated with InSAR coseismic deformation measurements and application in recent two decades.
The southern Alashan block is located at the crustal front of the northern Tibetan plateau. It was initially considered as a relatively stable area with weak tectonic activity. In recent years,an increasing number of studies have shown that the Alashan block has undergone significant tectonic deformation since the Cenozoic. Multiple active faults with a horse-tail distribution are developed in the southern margin of the Alashan block. However,there is still controversy over the tectonic deformation patterns of these active faults. One view is that the fault system in the southern margin of Alashan is the result of the eastward extension of the Altyn Tagh Fault and belongs to the tail structure of the strike-slip fault. Another view is that the fault system in the southern Alashan block is the result of the revival of the pre-existing fault caused by the northward compression and thrust of the Tibetan plateau. Therefore,deciphering fault’s kinematics and slip rates since the late Quaternary in the southern Alashan block is crucial to understand the tectonic deformation pattern of the block and its response to Tibet’s northward growth. In this paper,combined with interpretations of remote sensing images and field investigations,we documented the Quaternary activity of the Beida Shan Fault,one of the major faults in the southern Alashan block,along the segment developed in Quaternary alluvium.The Beida Shan Fault is a sinistral strike-slip fault with paralleled north and south branches that displaced the late Quaternary alluvial fans and terraces,forming offset gullies and fault scarps.According to the geometric distribution characteristics,activity and the landforms along the fault,we divided the fault into three segments: the Langwa Shan segment,the northern branch of the Jiapiquan Shan segment,and the southern branch of the Jiapiquan Shan segment. The fault is east-west trending,and the offset geomorphic features along the fault reveal that there are differences in the activity of different segments. The Langwa Shan segment is 10km long and developed at the junction of bedrock and alluvial fan. The fault trace is straight,and a series of gullies and ridges offset by the fault indicate that it is a sinistral strike-slip fault. The Jiapiquan Shan segment is 35km long and divided into two parallel north and south branches with a spacing of about 1. 5km. The north branch fault strikes NE on the east side of Langwa Shan and has an angle of about 30° with the south branch fault. After extending about 2km to the northeast direction and entering the north side of Dahong Shan,the fault turns to the EW direction and is parallel to the south branch fault. It is distributed along the boundary between the bedrock and the alluvial fan with the south or north fault scarps and the secondary branch faults. To the east,the north branch fault is developed in bedrock,which is mainly characterized by offset gullies and ridges. The southern branch fault offset multi-stage alluvial fan,forming fault scarps of different heights and left-lateral offset gullies of different scales,and the exposed fault profiles show high angle reverse faults,which dip south or north,indicating that this segment is sinistral strike-slip.Based on the 1. 5m resolution DEM data obtained from UAV-Sf M,we measured the horizontal displacement of fault landforms using the La Di Cao Z software developed by Zielke et al.（ 2012） on the MATLAB platform. Combined with field survey data, we obtained the left-lateral horizontal displacements of 70 sites along the Beida Shan Fault. The sinistral offset of ～ 1m is not included in slip distribution statistics due to limitations of the quantity and data accuracy. Statistical analysis of the displacements reveals that the left-lateral displacements along the fault are concentrated between 3m to20m,with the majority in two pronounced peaks at 5. 3m and 10. 1m. The 5. 3m peak contains the most data points,with 17 displacements data,accounting for 24% of the total,while the 10. 1m peak contains 6 data points,accounting for 9% of the total. This indicates that the Beida Shan Fault has experienced multiple seismic events involving the displacement and rupture of stratigraphic layers on the surface.An ～ 8km-long surface rupture is discovered on the south fault branch,and it is represented by of fault scarps and of tens of centimeters 1 ～ 2m left-lateral displacement of small gullies. Fresh surface rupture and left-lateral offset gullies indicate the latest fault activity. Using the previously dated alluvial fan ages in Taohuala Shan, ～ 30km south of the Beida Shan, we calculated the late Pleistocene sinistral slip rate of 0. 3 ～ 0. 6mm/a along the Beida Shan Fault,which is consistent with the slip rate of the Taohuala Shan Fault estimated by Yu et al.（ 2017）. Compared with the fault slip rate accommodated in the Hexi Corridor area and regional GPS rates,the southern Alashan block plays a significant role in absorbing deformation in response to the northern Tibetan growth.
Dongpu depression is located at the junction of Henan and Shandong in the south of Bohai Bay Basin in eastern China.It is an early Tertiary faulted basin with NNE strike,with thick sedimentation.It is adjacent to Luxi uplift in the East and Luxi uplift in the West.There are mainly three major faults in the area:Lanliao fault,Changyuan fault,and Yellow River fault.Lanliao fault is a major fault that controls the boundary between the Dongpu depression and the Luxi uplift.Changyuan fault is the boundary between the Dongpu depression and the Neihuang uplift.Yellow River fault is a secondary fault in the Dongpu depression.Dongpu depression controlled by these three fault zones has formed a structural form of“two depressions and one uplift”.To understand better the distribution of faults and velocity structure in the Middle-North Section of the Dongpu depression,from March 26 to April 22,2018,the Geophysical Exploration Center,China Earthquake Administration set up a short-period dense seismic array consisting of 412 short-period seismometers in the middle-north section of the Dongpu depression,the Luxi Uplift the Neihuang Uplift.The array range is about 50km×45km,the station spacing is 1.3～2.5km,and the station spacing around the array is 4.5km.In the array,there is also a linear array with a length of about 50km,with a station spacing is about 500m,and 98stations,which are distributed near vertical fractures.Based on noise cross-correlation technology,cross-correlations of vertical component ambient noise data of different station pairs are computed in1-day segments and stacked.Clear fundamental-mode Rayleigh waves are observed from 0.5s to 5s period.Then we use the direct surface wave tomographic method with period-dependent ray tracing and a wavelet-based sparsity constrained to invert phase dispersion travel-time data simultaneously for3-D shear-wave velocity structure.The shear-wave velocity model results from 0.5km to 3.5km depths are consistent with the known geologic features and reveal strong shallow crustal heterogeneity.The results follows:1) the velocity of the Middle-North Section of Dongpu depression in the study area is low,the velocity of the Neihuang uplift and Luxi uplift on both sides are high,and the shear velocity variation between uplift and depression continues to about 3.5km.2) The boundary between high and low velocity coincides with the boundary of depression and uplift,and is also consistent with Lanliao Fault and Changyuan Fault,indicating that the caprock deposition in the Dongpu depression is controlled by the Lanliao fault and Changyuan fault.3) The Cenozoic sedimentary structure of the Dongpu depression is mainly controlled by Lanliao fault.The 1～3.5km depression shows obvious low velocity characteristics,indicating that the Paleogene Lanliao fault activity has a strong impact on the sedimentary characteristics of the middle-north section of the Dongpu depression;the velocity difference between the depression and uplift of 0～1km decreases,the Neogene and quaternary Lanliao fault activities become weaker,and the sedimentary structures in this period are less affected by the Lanliao fault.Although the velocity of the Dongpu depression is generally low,the depression also shows some heterogeneity:the sedimentary structure of the northern section is not only controlled by the Lanliao fault,At the same time,it also received that the control of the secondary fault in the depression presents“W”shape,which disappears in the middle section,indicating that the Cenozoic sedimentary structure of Dongpu depression is mainly controlled by the Lanliao fault,and the Paleogene Lanliao fault activity has a strong impact,with obvious segmentation characteristics,resulting in the existence of multiple sedimentary centers in Dongpu depression,thus making the velocity structure in the Dongpu depression present non-uniformity.4) The characteristics of the Lanliao fault in the middle-north section of the Dongpu depression are shown as an SEE trend,and the dip angle of the Lanliao fault in the north section is significantly steeper,indicating that there are differences in the activity characteristics of Lanliao fault in the study area.The Shijiazhuang-MazhaiLiuta fault is a branch fault of the Changyuan fault extending northward,with a strike of NNE and a dip of E or SEE.From the velocity distribution feature image,it can be seen that it is significantly different in the north-central section of the Dongpu depression.From the velocity distribution image,it can be seen that it is significantly different in the north-central section of the Dongpu depression,with a gradual steep dip from south to north,and then gradually slowing down.This feature is consistent with the different structural characteristics of each branch fault of the Changyuan fault at a different section.
