Lateral variation in Moho depth around the southern Tanlu fault zone and its adjacent area

We estimated Moho depth beneath the southern Tanlu fault zone and its adjacent area using common-conversion-point(CCP)stacking of receiver functions,which were computed from teleseismic records of the CEArray.Our estimated Moho depth matches well with 2-D profiles derived from active-source deep seismic reflection surveys,suggesting that the calculated the Moho depth map is likely accurate beyond the 2-D profiles.Overall,the estimated Moho depth map showed a high spatial correlation with tectonic provinces,i.e.,Moho topographic boundaries are in good agreement with geological boundaries.Beneath the Dabie orogenic belt and the mountainous areas in southern Anhui Province,the Moho lies relatively deep,and there is an obvious difference in Moho depth between the two sides of this segment of the Tanlu fault.We further selected four depth profiles with dense instrumentation to show Moho depth changes across different tectonic blocks in the study area.We saw two step-like changes in Moho depth beneath the Xiangfan-Guangji and Gushi-Feizhong,which run parallel along the WNW-ESE direction and delineate the southern and northern bounds of the northern Dabie orogenic belt,which is likely the suture zone between the North China Block and South China Block.Crust beneath the northeast corner of the study area is significantly thinner than other areas,which is consistent with the crustal detachment model proposed for suturing between the North and South China blocks in the region east to the Tanlu fault.

Active Depths of Main Faults in the Ying-Qiong Basin Investigated by Multi-Scale Wavelet Decomposition of Bouguer Gravity Anomalies and Power Spectral Methods

The Ying-Qiong Basin is located on the northwestern margin of the South China Sea and at the junction of the South China Block and the Indochina Block.It is characterized by complex geological structures.The existing seismic data in the study area is sparse due to the lack of earthquake activities.Because of the limited source energy and poor coverage of seismic data,the knowledge of deep structures in the area,including the spatial distribution of deep faults,is incomplete.Contrarily,satellite gravity data cover the entire study area and can reveal the spatial distribution of faults.Based on the wavelet multi-scale decomposition method,the Bouguer gravity field in the Ying-Qiong Basin was decomposed and reconstructed to obtain the detailed images of the first-to sixth-order gravitational fields.By incorporating the known geological features,the gravitational field responses of the main faults in the Ying-Qiong Basin were identified in the detailed fields,and the power spectrum analysis yielded the depths of 1.4,8,15,26.5,and 39 km for the average burial depths of the bottom surfaces from the first-to fifth-order detailed fields,respectively.The four main faults in the Yinggehai Basin all have a large active depth range:fault A(No.1)is between 5 and 39 km,fault B is between 26.5 and 39 km,and faults C and D are between 15 and 39 km.However,the depth of active faults in the Qiongdongnan Basin is relatively shallow,mainly between 8 and 26.5 km.

Geodetic slip rate and locking depth of east Semangko Fault derived from GPS measurement

65 km Semangko Fault is part of southern segments of Sumatran Fault Zone(SFZ)which is complex corresponds to the transition from the strike-slip regime of the SFZ to the normal faulting tectonics of the Sunda Strait.The recent publication showed branches of Semangko Fault:West Semangko Fault(WSF)and East Semangko Fault(ESF).This study estimated geodetic slip rate and locking depth of ESF using Global Positioning System(GPS)time series data from 2007 to 2019 from all available GPS sites.GPS velocities refer to Sundaland Plate were used to estimate the fault parameters of the WSF and ESF simultaneously.Non-uniformity of velocity direction shows the complexities of Semangko Fault possibly caused by the contribution of all faults around ESF.An ESF geodetic slip rate,which is 12.5±2 mm/yr was lower than WSF,which is 16.5±2 mm/yr.It is consistent with the rigid block nature of the SFZ system as northern segment slip rates have similar value.Small slip rates are possibly leading to lower generated seismic moment than the major segment of SFZ.

Fault depth estimation using support vector classifier and features selection

Depth estimation of subsurface faults is one of the problems in gravity interpretation. We tried using the support vector classifier （SVC） method in the estimation. Using forward and nonlinear inverse techniques, detecting the depth of subsurface faults with related error is possible but it is necessary to have an initial guess for the depth and this initial guess usually comes from non-gravity data. We introduce SVC in this paper as one of the tools for estimating the depth of subsurface faults using gravity data. We can suppose that each subsurface fault depth is a class and that SVC is a classification algorithm. To better use the SVC algorithm, we select proper depth estimation features using a proper features selection （FS） algorithm. In this research, we produce a training set consisting of synthetic gravity profiles created by subsurface faults at different depths to train the SVC code to estimate the depth of real subsurface faults. Then we test our trained SVC code by a testing set consisting of other synthetic gravity profiles created by subsurface faults at different depths. We also tested our trained SVC code using real data.

The 2023 M_(w)6.8 Adassil Earthquake(Chichaoua,Morocco)on a steep reverse fault in the deep crust and its geodynamic implications

The Mw 6.8 Adassil earthquake that occurred in the High Atlas on September 8,2023,was a catastrophic event that provided a rare opportunity to study the mechanics of deep crustal seismicity.This research aimed to decipher the rupture characteristics of the Adassil earthquake by analyzing teleseismic waveform data in conjunction with interferometric synthetic aperture radar(InSAR)observations from both ascending and descending orbits.Our analysis revealed a reverse fault mechanism with a centroid depth of approximately 28 km,exceeding the typical range for crustal earthquakes.This result suggests the presence of cooler temperatures in the lower crust,which facilitates the accumulation of tectonic stress.The earthquake exhibited a steep reverse mechanism,dipping at 70°,accompanied by minor strike-slip motion.Within the geotectonic framework of the High Atlas,known for its volcanic legacy and resulting thermal irregularities,we investigated the potential contributions of these factors to the initiation of the Adassil earthquake.Deep seismicity within the lower crust,away from plate boundaries,calls for extensive research to elucidate its implications for regional seismic hazard assessment.Our findings highlight the critical importance of studying and preparing for significant seismic events in similar geological settings,which would provide valuable insights into regional seismic hazard assessments and geodynamic paradigms.

Improved tilt-depth method for fast estimation of top and bottom depths of magnetic bodies

The tilt-depth method can be used to make fast estimation of the top depth of magnetic bodies. However, it is unable to estimate bottom depths and its every inversion point only has a single solution. In order to resolve such weaknesses, this paper presents an improved tilt-depth method based on the magnetic anomaly expression of vertical contact with a finite depth extent, which can simultaneously estimate top and bottom depths of magnetic bodies. In addition, multiple characteristic points are selected on the tilt angle map for joint computation to improve reliability of inversion solutions. Two- and three- dimensional model tests show that this improved tilt-depth method is effective in inverting buried depths of top and bottom bodies, and has a higher inversion precision for top depths than the conventional method. The improved method is then used to process aeromagnetic data over the Changling Fault Depression in the Songliao Basin, and inversion results of top depths are found to be more accurate for actual top depths of volcanic rocks in two nearby drilled wells than those using the conventional tilt-depth method.

Effect of source parameters on forward-directivity velocity pulse for vertical strike slip fault in half space

It has been found that the large velocity pulse is one of the most important characteristics of near-fault strong ground motions. Some statistical relationships between pulse period and the moment magnitude for near-fault strong ground motions have been established by Somerville （1998）; Alavi and Krawinkler （2000）; and Mavroeidis and Papageorgiou （2003）, where no variety of rupture velocity, fault depth, and fault distance, etc. were considered. Since near-fault ground motions are significantly influenced by the rupture process and source parameters, the effects of some source parameters on the amplitude and the period ofa forward-directivity velocity pulse in a half space are analyzed by the finite difference method combined with the kinematic source model in this paper. The study shows that the rupture velocity, fault depth, position of the initial rupture point and distribution of asperities are the most important parameters to the velocity pulse. Generally, the pulse period decreases and the pulse amplitude increases as the rupture velocity increases for shallow crustal earthquakes. In a definite region besides the fault trace, the pulse period increases as the fault depth increases. For a uniform strike slip fault, rupture initiating from one end of a fault and propagating to the other always generates a higher pulse amplitude and longer pulse period than in other cases.

Study on anti-faulting design process of Urumqi subway line 2 tunnel crossing reverse fault

For the tunnel crossing active fault,the damage induced by fault movement is always serious.To solve such a problem,a detailed anti-faulting tunnel design process for Urumqi subway line 2 was introduced,and seven three-dimensional elastic-plastic finite element models were established.The anti-faulting design process included three steps.First,the damage of tunnel lining from different locations of fault rupture surfaces was analyzed.Then,the analysis of the effect on tunnel buried depth was given.Finally,the effect of the disaster mitigation method on the flexible joint was verified and the location of the flexible joint was discussed.The results show that when the properties of surrounding rock at the tunnel bottom grows soft,the tunnel deformation curve is smoother and tunnel damage induced by fault movement is less serious.The vertical displacement change ratio of secondary linings along the tunnel axis may be the main factor to cause shear damage to the tunnel.The interface between the hanging wall and fracture zone is defined as the most adverse fault rupture surface.The tunnel damage was reduced with the decrease in the tunnel buried depth as more energy was dissipated by overburden soil and the differential uplift zone of soil became more diffuse.The method of the flexible joint can reduce the tunnel damage significantly and the disaster mitigation effect of different locations on the flexible joint is different.The tunnel damage is reduced by the greatest degree when the flexible joint is located on the fault rupture surface.

Study on the distribution characteristics of faults and their control over petroliferous basins in the China seas and its adjacent areas

As one of the main controlling factors of oil and gas accumulation,faults are closely related to the distribution of oil and gas reservoirs.Studying how faults control petroliferous basins is particularly important.In this work,we investigated the plane positions of major faults in the China seas and its adjacent areas using the normalized vertical derivative of the total horizontal derivative(NVDR-THDR)of the Bouguer gravity anomaly,the fusion results of gravity and magnetic anomalies,and the residual Bouguer gravity anomaly.The apparent depths of major faults in the China seas and its adjacent areas were inverted using the Tilt-Euler method based on the Bouguer gravity anomaly.The results show that the strikes of the faults in the China seas and its adjacent areas are mainly NE and NW,followed by EW,and near-SN.Among them,the lengths of most ultra-crustal faults are in the range of 1000–3000 km,and their apparent depths lie between 10 km and 40 km.The lengths of crustal faults lie between 300 km and 1000 km,and their apparent depths are between 0 km and 20 km.According to the plane positions and apparent depths of the faults,we put forward the concept of fault influence factor for the first time.Based on this factor,the key areas for oil and gas exploration were found as follows:the east of South North China Basin in the intracontinental rift basins;the southeast region of East China Sea Shelf Basin,the Taixinan and Qiongdongnan basins in the continental margin rift basins;Zhongjiannan Basin in the strike-slip pull-apart basins;the Liyue,Beikang,and the Nanweixi basins in the rifted continental basins.This work provides valuable insights into oil and gas exploration,mineral resource exploration,and deep geological structure research in the China seas and its adjacent areas.

Research on the fault controlling mechanism of geothermal water in Zhangzhou Basin

Fault has an important influence on the storage and movement of geothermal water. The Zhangzhou Basin is wholly located in a granodiorite rock mass. Due to the low permeability of granodiorite, faulted structure has an evident control action on the hydrothermal activity of geothermal fields. Hot springs in Zhangzhou Basin crack along Pingtan-Dongshan Fault to the northeastern direction and emerge along Fu'an-Nanjing Fault. Through measurement of the temperature of several hot springs in the Basin, we found the temperature along the northwestern direction of Zhangzhou-Tianbao Fault is high and the temperature gap between the two sides of Yangxi-Yuanshan Fault is huge; the estimation of geothermal reservoir temperature of geothermal water through quartz geothermometer indicates that the geothermal reservoir temperature of the northern area of Nanjing-Xiamen Fault is obviously higher than that of southern area. Such result indicates that Fault obviously obstructs underground heat source. Under the condition that the average geothermal gradient of the Zhangzhou Basin is set, the circulation depth of the geothermal water of the Zhangzhou Basin measured by geothermal reservoir temperature is 3 550-5 200 m and the circulation depth of the geothermal water of the north of Nanjing-Xiamen Fault is deeper than that of the South.

A Quantitative Method for Evaluating Fault Vertical Opening and Sealing Properties during Hydrocarbon-Charging Periods

Objective Faults are the main channel of hydrocarbon vertical migration in a faulted basin(Jiang et al.,2018).It is helpful to guide the exploration by accurately evaluating the opening and sealing characteristics of faults at different depths.However,the fault vertical opening and sealing properties cannot at present be evaluated quantitatively.

Geological Guided Tomography Inversion Based on Fault Constraint and Its Application

Fault block reservoirs are one of the main types of hydrocarbon reservoirs found in offshore basins,and they are widely distributed within the Mesozoic and Cenozoic basins of the northern South China Sea.Conventional seismic profiles of complex fault areas often contain obvious fragmentation and distortion of seismic events that is corresponding to geological structure under the fault.This phenomenon is known as a fault shadow;it occurs in relation to rapid changes in velocity near the fault that deviate the ray path of waves,and it seriously affects the ability to determine the geological structure and subsequently evaluate the reserves of fault reservoirs.In the current conventional tomography inversion method,the velocity model is over-smoothed,which results in distortion of the reflection layer under the fault.Based on the velocity tomography inversion of imaging gathers method and the concept of regularization,this paper first introduces the anisotropy Gauss regularization operator.A high-resolution tomography inversion method is then developed,and the fault-controlled geological guidance is constrained.This technology is then applied to a complex fault block reservoir basin in the South China Sea,and the results show that it can significantly solve the problem of fault shadow imaging and determine the geological structures in the target area.The newly developed method thus has very good application prospects.

Spatial-temporal characterization of the San Andreas Fault by fault-zone trapped waves at seismic experiment site,Parkfield,California

In this article,we review our previous research for spatial and temporal characterizations of the San Andreas Fault(SAF)at Parkfield,using the fault-zone trapped wave(FZTW)since the middle 1980s.Parkfield,California has been taken as a scientific seismic experimental site in the USA since the 1970s,and the SAF is the target fault to investigate earthquake physics and forecasting.More than ten types of field experiments(including seismic,geophysical,geochemical,geodetic and so on)have been carried out at this experimental site since then.In the fall of 2003,a pair of scientific wells were drilled at the San Andreas Fault Observatory at Depth(SAFOD)site;the main-hole(MH)passed a~200-m-wide low-velocity zone(LVZ)with highly fractured rocks of the SAF at a depth of~3.2 km below the wellhead on the ground level(Hickman et al.,2005;Zoback,2007;Lockner et al.,2011).Borehole seismographs were installed in the SAFOD MH in 2004,which were located within the LVZ of the fault at~3-km depth to probe the internal structure and physical properties of the SAF.On September 282004,a M6 earthquake occurred~15 km southeast of the town of Parkfield.The data recorded in the field experiments before and after the 2004 M6 earthquake provided a unique opportunity to monitor the co-mainshock damage and post-seismic heal of the SAF associated with this strong earthquake.This retrospective review of the results from a sequence of our previous experiments at the Parkfield SAF,California,will be valuable for other researchers who are carrying out seismic experiments at the active faults to develop the community seismic wave velocity models,the fault models and the earthquake forecasting models in global seismogenic regions.

Study on System of Faults in the Gulf of Mexico and Adjacent Region based on Gravity Data

In the Gulf of Mexico and adjacent landmasses,faults are very complex,and their distribution is closely related to plate tectonics,ocean-land boundary,and former structure.The plane position of the faults can be identified by the maximum characteristic of the vertical derivative of the normalized vertical derivative of the total horizontal derivative(NVDR-THDR)of the Bouguer gravity anomaly.The apparent depth of the faults is inverted by the Bouguer gravity anomaly curvature property.Based on tectonic evolutionary processes and the plane distribution and apparent depth characteristics of the faults,a complete fault system for the Gulf of Mexico and adjacent areas has been established,including 102 faults.The apparent depths of 33 first-class faults are 16-20 km and for 69 second-class faults are 12-16 km.The F_(1-2)and F_(1-3)subduction fault zones are two caused by the subduction of the Cocos Plate into the old Yucatan and Chorti landmasses;F_(1-11)and F_(1-12)fault zones extend westward to the coast of Guatemala and do not extend into the continent;F_(1-17)and F_(1-20)faults,which control the boundary of the oceanic crust,do not extend southward into the continent.The fault system,which radiates in a"fan-shaped"structure as a whole,unfolds to the northeast.Faults of different nature and sizes are distributed in the Cocos Plate subduction zone,Continental,Gulf of Mexico,Yucatan old landmass and Caribbean Plate in NW,NNW,NS,NE and NEE directions.In the Gulf of Mexico region,the fault system is a comprehensive reflection of former tectonic movements,such as plate movement,drift of old landmasses and expansion of oceanic crusts.The first-class faults control the plate and ocean-continental boundaries.The second-class faults are subordinate to the first-class faults or related to the distribution of different sedimentary layers.

Calculating the formation period of fault lateral sealing and its application

The study aims to find out the formation period of fault traps near faults in petroliferous basins,based on an analysis of the formation period of fault lateral sealing and related influential factors.A method to calculate the formation period of fault lateral sealing(i.e.the time when displacement pressure of fault rock is equal to that of reservoir rock in fault wall with hydrocarbon migration)is established by comparing the relationship between displacement pressure and time for fault rock and reservoir rock.This method is then applied to the study on reservoirs in the 1^(st),2^(nd),and 3^(rd) members of Dongying Formation(E_(3)d^(1),E_(3)d^(2) and E_(3)d^(3))in terms of formation period of lateral sealing of F3 fault crossing the three reservoirs in the No.5 structure of Nanpu Sag in Bohai Bay Basin.The results indicate that the formation period of the lateral sealing in the studied reservoirs can date from 7.1 Ma,7.4 Ma and 9.2 Ma respectively,all prior to the hydrocarbon accumulation period(about 2.58 Ma).Hence,it can be concluded that these reservoirs are favorable for the accumulation and preservation of hydrocarbons generated from the underlying source rock E_(3)s^(3),and the method proposed is feasible in calculating the formation period of fault lateral sealing.

宝坻-苗庄凸起新生断裂脆韧性转换深度研究

现今地震是最新构造活动的最直接表现,是认识大陆内部非刚性变形特征的最有力工具。尤其是对晚更新世以来开始活动的新生断裂来说,由于发育成熟度低,几何构造上贯通性差且不同区段走向/不同深度倾向差异明显,地震能够揭示其三维空间的变化,尤其是脆韧性转换深度特征,促进对新生活动断裂孕育、发震过程的认识。渤海湾盆地新生走滑活动断裂曾多次发生强震,如唐山M_(S)7.8、三次宁河M_(S)≥6.2地震,这些地震揭示的地壳脆-韧性转换深度对认识该地区地震发震机理和活动性具有重要的现实意义。本文以渤海湾盆地内宝坻-苗庄凸起新生断裂为目标断裂,以发生于宝坻凸起的2012年宝坻M_(S)4.0、M_(S)3.5地震以及发生于苗庄凸起的1976年宁河M_(S)6.2、M_(S)6.9、1977年宁河M_(S)6.2地震为研究对象,基于首都圈数字地震台网的波形资料,采用CAP方法研究宝坻M_(S)4.0、M_(S)3.5地震震源机制解和震源深度,利用近震转换波Sp精确确定震源深度,采用双差方法定位两个地震序列的震源位置,并结合其他资料探讨该地区地震的发震机理以及新生断裂脆韧性转换深度。结果显示:(1)宝坻M_(S)4.0、M_(S)3.5地震震源性质与宝坻-苗庄凸起出露地表的已知断裂不尽相符,结合宁河三次MS≥6.2地震震源参数的有关研究成果,推测它们均发震于宝坻-宁河深大断裂;(2)结合震源区电性结构以及流变结构等模型,宝坻-苗庄凸起这五次显著地震揭示出宝坻-宁河深大断裂的脆韧性转换深度为15km左右;(3)结合渤海湾盆地动力演化过程以及深部地球物理探测等相关资料,推测该地区地震活动主要是宝坻-宁河深大断裂与深部流体作用的结果。

2023年甘肃积石山M_(S)6.2地震:一次逆冲为主的浅源强震

基于区域数字地震台网波形数据,在三维空间内利用波形拟合反演方法获得2023年12月18日甘肃积石山M_(S)6.2地震最佳震源机制解,结果表明:节面Ⅰ走向305°,倾角56°,滑动角61°;节面Ⅱ为走向169°,倾角43°,滑动角125°;矩震级M_(W)6.02。最佳拟合的空间精细位置为102.377°E,35.968°N,深度9 km。结果显示,地震破裂沿NW方向扩展。初步推断此次地震的发震断层面为节面Ⅱ,发震断层是拉脊山北缘断裂(积石山东缘断裂),是一次逆冲为主,兼少量走滑分量的浅源强震事件。

龙门山断裂带晚三叠世大地震的孕震深度和环境的岩石磁学证据

假玄武玻璃可以形成于深部孕震带到近地表的不同深度,确定其形成深度对揭示断裂带力学性质和大地震孕震环境具有重要意义。本文以龙门山映秀-北川断裂带南段八角庙出露的晚三叠世假玄武玻璃及其围岩(碎裂岩和初碎裂岩)为研究对象,通过岩石磁学、显微结构和地球化学测试,探讨了龙门山断裂带晚三叠世大地震的孕震深度和孕震环境。岩石磁学结果表明,假玄武玻璃和碎裂岩中主要磁性矿物是磁铁矿、单斜磁黄铁矿和顺磁性矿物;初碎裂岩中主要磁性矿物是磁铁矿和顺磁性矿物。假玄武玻璃具有高磁化率值特征,其形成的主要原因是顺磁性矿物在同震摩擦热作用下生成了磁铁矿和单斜磁黄铁矿。磁性矿物的转换过程指示了含有硫化物的弱流体作用的还原性的孕震环境。热磁曲线(χ-T)测试结果揭示了初碎裂岩在自然界中经历的最高温度约为275~300℃,根据地温梯度推算初碎裂岩和假玄武玻璃的形成深度为12.8~14.0km。根据孕震深度、假玄武玻璃构特征和地震机制估算,龙门山断裂带孕震深度的正应力σ≤240.2~264.1MPa,剪应力τ≤144.1~158.5MPa。龙门山断裂带在其漫长的演化过程中发生了多次大地震活动,其中在孕震深度(<14km)固结的碎裂岩带内形成的假玄武玻璃比较容易保存在地震断裂带内,并记录了深部较强的应力特征和弱流体作用的还原性环境。

时序InSAR与GNSS联合约束下的亚东-谷露断裂运动特征

亚东-谷露断裂作为青藏高原东南部自新生代以来规模最大、活动性最强的拉张断裂,在青藏高原的构造变形与物质运移等过程中起着重要的调节与转换作用。但由于以往大地测量资料的不足,导致对亚东-谷露断裂整体运动特征的定量化分析较为匮乏。因此,本文收集并处理了亚东-谷露断裂地区2017年10月至2022年4月的哨兵影像数据,并联合GNSS速度场,解决了不同参考系下的形变场融合问题,获取了覆盖整个亚东-谷露断裂的高精度、高分辨率震间地壳形变场。进一步基于弹性微块体模型,精细厘定了亚东-谷露断裂现今活动特征:断裂整体以东倾为主,最佳倾角为68°,现今以拉张运动为主,速率为2~6 mm/a,并由南到北逐渐递增。另外,该断裂中段和北段的闭锁深度约为14 km;但南段可能受到主喜马拉雅逆冲断裂的影响,导致闭锁区域较浅,深度仅为4 km。最后,基于断裂的滑动亏损率与历史地震分布,分析得到断裂北段的地震危险性更高,为区域的地质灾害评估提供了重要参考。

基于MTF-ResDSCNN二维图像的故障诊断方法

为了有效捕获旋转机械振动信号中蕴含的故障特征,进而高效地完成故障诊断任务,设计了一种将二维特征图像和轻量化神经网络相结合的故障诊断模型。首先,将采集到的一维振动信号以改进的集成经验模态分解(Modified Ensemble Empirical Mode Decomposition,MEEMD)算法进行分解,得到本征模态函数(Intrinsic Mode Function,IMF)分量,并筛选相应的IMF分量进行求和重构,以增强振动信号的幅值波动,进而使得马尔科夫变迁场(Markov Transition Field,MTF)能够更为有效地表征重构信号中的故障特征;然后,将MTF生成的二维特征图像输入到残差深度可分离卷积神经网络(Residual Depth Separable Convolutional Neural Network,ResDSCNN)模型中,进行特征提取与故障诊断。使用行星齿轮箱故障数据集验证了模型性能。结果表明,该模型对于各类齿轮故障的诊断正确率可达98%以上。