Tensile Fractures and in situ Stress Measurement Data Constraints on Cretaceous-Present Tectonic Stress Field Evolution of the Tanlu Fault Zone in Shandong Province,North China Craton

Tectonic stress fields are the key drivers of tectonic events and the evolution of regional structures.The tectonic stress field evolution of the Tanlu fault zone in Shandong Province,located in the east of the North China Craton(NCC),may have preserved records of the NCC’s tectonic history.Borehole television survey and hydraulic fracturing were conducted to analyze the paleo and present tectonic stress fields.Three groups of tensile fractures were identified via borehole television,their azimuths being NNW-SSE,NW-SE and NE-SW,representing multiple stages of tectonic events.Hydraulic fracturing data indicates that the study region is experiencing NEE-SWW-oriented compression and nearly-N-Soriented extension,in accordance with strike-slip and compression.Since the Cretaceous,the orientation of the extensional stress has evolved counterclockwise and sequentially from nearly-NW-SE-oriented to NE-SW-oriented and even nearly N-S-oriented,the stress state having transitioned from strike-slip-extension to strike-slip-compression,in association with the rotating and oblique subduction of the Pacific Plate beneath the NCC,with the participation of the Indian Plate.

Thermal Evolution of the Tanlu Fault Zone on the Eastern Margin of the Dabie Mountains and Its Tectonic Implications

Five samples of muscovite from mylonites of the earlier Tanlu ductile shear zone on the eastern margin of the Dabie Mountains yield 40Ar/39Ar ages ranging from 178 Ma to 196 Ma. Three of them have reliable plateau ages of 188.7±0.7 Ma, 189.7±0.6 Ma and 192.5±0.7 Ma respectively, which indicates a syn-orogenic, sinistral strike-slip thermal event. This displacement movement derived from the continent-continent collision of the North and South China blocks took place in the Early Jurassic and after uplifting of high-pressure to ultrahigh-pressure slabs to the mid-crust. It is suggested that during the collision the Tanlu fault zone was an intracontinental transform fault caused by differential subduction speeds. The 40Ar/39Ar ages of mylonite whole-rock and muscovite from the later Tanlu ductile shear zone suggest another sinistral strike-slip cooling event at 128 Ma. During this strike-slip faulting, large-scale intrusion and doming uplift occurred in the eastern part of the Dabie orogenic belt. Data of K-feldspar 40Ar/39Ar MDD and apatite fission-track analysis from metamorphic rocks indicate two high-speed cooling events experienced by the Tanlu fault zone, which took place at 90 Ma and 45-58 Ma respectively. They correspond respectively to two phases of extensional activities in the Late Cretaceous and Eogene as well as development of the Qianshan fault-controlled basin to the east of the Tanlu fault zone. The cooling times recorded by K-feldspar and apatite show that the uplifting in the Dabie orogenic belt occured earlier than that on the eastern margin occupied by the Tanlu fault zone. The above phenomena suggest that the uplifting of the Dabie orogenic belt during the Late Cretaceous to Eogene was not controlled by the Tanlu normal faulting, but as a result of the lithospheric delamination.

Crustal thickness beneath the Tanlu fault zone and its tectonic significance based on two-layer H-κstacking

Tanlu fault zone(TLFZ)is the largest active fault zone in eastern China.It is characterized by complex tectonic evolution and multiple faults and marks the boundary between the North and South China blocks.An indepth understanding of the distinct crustal structures of both parts of the TLFZ will provide valuable insights into the lithospheric and crustal thinning in eastern China,extensive magmatism since the Mesozoic,and formation mechanisms of metallogenic belts along the Yangtze River.In this study,a two-layer H-κstacking approach was adopted to estimate the thicknesses of the sediment and crystalline crust as well as the corresponding vP/vS ratios based on high-quality teleseismic P-wave receiver functions recorded by permanent and temporary stations in and around the TLFZ.The geological units in the study region were delineated,especially the crustal structures beneath extensive sedimentary basins on both sides of the TLFZ.The following conclusions can be drawn:(1)The crustal thickness in and around the TLFZ greatly varies depending on the segment.In the northern segment,the crust is relatively thin beneath the eastern part of the Songliao Basin,a broad uplift of the Moho can be observed,and the Moho descends from south to north.The crust below the central and southern segments becomes thinner from west to east.The thickness of the crust is less than 30 km toward the eastern side of the boundary between the Jiangsu and Anhui provinces,that is,significantly thinner than in other areas.In terms of the vP/vS ratios,high anomalies were detected in the central-southern segments of the TLFZ,indicating the upwelling of deep mantle magma via deep faults.(2)Positive isostatic gravity anomalies were observed in the eastern part of the northern segment of the TLFZ and in the eastern part of the Suwan segment.The crustal thickness is smaller than that obtained from the Airy model of isostasy.This suggests that the lower crust in this area may have experienced intensive transformation processes,which may be related to crustal thinning(caused by crustal extension)and the strong uplift of the mantle in eastern China.The isostatic gravity anomalies between the eastern and western parts of the TLFZ indicate that the fault zone plays a dominant role in controlling the development of the deep crustal structure.(3)Significant crustal thinning was observed beneath the eastern part of the boundary between the Jiangsu and Anhui provinces in the southern segment of the TLFZ,suggesting that this area is prone to lithospheric thinning of the North China Craton.Due to the subduction,compression,and retreat of the Paleo-Pacific Plate during the Yanshanian Period as well as the dehydration of subducting oceanic crust(within subduction zones),the asthenosphere and oceanic crust in eastern China partially melted,resulting in mantle enrichment.The basic magma from the mantle is accumulated at the base of the crust,leading to magmatic underplating.In areas with weak topography toward the east of the TLFZ,magma rises to the upper crust and surface,resulting in the enrichment of multiple metal deposits in this area.

High resolution tomography of the Tanlu fault zone near Hefei with passive seismic and magnetotelluric linear array data

As the largest fault trending NNE-SSW to NE-SW in the eastern Eurasia Continent,the Tanlu fault zone(TLFZ)extends over 2,400 km within China,roughly from Wuxue,Hubei Province,to Russia.Since the Quaternary period,the TLFZ has been an earthquake-prone area in eastern China where several major earthquakes resulted by tectonic compression occurred,causing tremendous casualties and significant economic losses.Many studies on different segments of the TLFZ have been carried out in the past few decades.However,numerous key questions regarding the fault zone remain unanswered due to a lack of clear subsurface characterization and fault delineation.In this study,we present high-resolution tomographic results across the TLFZ to the east of Hefei,where one 22-km-long passive seismic array with densely spaced short-period nodes,and a 24-km-long magnetotelluric array were deployed adjacent to each other.We find the velocity and resistivity variations are highly consistent with known surface geology.Sharp property contrasts in both the seismic shear wave velocity and electrical resistivity profiles clearly delineate the Tanlu F1 fault(TLF-1)near Hefei.More interestingly,an upwelling with distinct high velocity is imaged within the Hefei Basin to the west of the TLF-1,whereas a slanted block with lowvelocity and low-resistivity seems to cut into or thrust upon the high-grade to low-grade middle-pressure rocks in the Zhangbaling uplift right below the Tanlu F2 ductile shear fault(TLF-2).The presented results show a new approach to characterize deep subsurface structure of the TLFZ beyond 2-km depths using passive data,which it is often difficult for active seismic surveys with refracted and reflected waves to image.

Dispersion attenuation structure of the crust around the Weifang-Jiashan segment of the Tanlu fault zone in North China

On the condition that the velocity ratio of compressive wave to shear wave is stable during the propagating process of seismic wave, this paper develops an estimation method for medium quality factor based on single station＇s travel time difference between direct S and P waves and the first period signal of direct P wave. 8 774 high SNR wave data altogether recorded by 75 stations are analyzed. The results show that： （1） under the normal regional stress field, the quality factors QmsP in the stable tectonic area are higher than that in the active tectonic area around the Weifang-Jiashan section and its surrounding area in the Tanlu fault zone; （2） in the Juxian-Tancheng section the seismic wave attenuation is relatively quick, and the media is relatively broken, suggesting no tectonic stress accumulation; （3） the Xinyi-Sihong section is currently locking and in accumulating elastic strain energy stage, which has the deep environment and conditions of strong earthquake generation similar to those of the 1668 M8.5 Tancheng strong earthquake.

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.

Recent activity of Chihe segment of Tanlu fault zone

By means of differentiation of remote sensing image, field seismo-geological survey, analysis on drilling explora- tion materials, sampling and dating of rock samples, combined with seismicity and microscopic tectonic analysis, this paper studies the recent activity of Chihe segment of the Tanlu fault zone. The result indicates that the Chihe fault segment undergoes the deformation alternately in the mode of stick slip and creep during Late Quaternary, and its recent activity is mainly creep.

A multi-scale 3-D crust velocity model in the Hefei-Chao Lake area around the southern segment of Tanlu Fault Zone

Regional high-precision velocity models of the crust are an important foundation for examining seismic activity,seismogenic environments,and disaster distribution characteristics.The Hefei-Chao Lake area contains the main geological units of Hefei Basin,with thick sediments and the Chao Lake depression.Several major concealed faults of the southern NNE-trending Tanlu Fault Zone cross this area.To further explore the underground distribution characteristics of the faults and their tectonic evolutionary relationship with adjacent tectonic units,this study used ambient noise data recorded by a seismic array deployed in Hefei City and Chao Lake,constructing a 3-D velocity model at the depth of 1–8 km.Then a multi-scale high-resolution 3-D velocity model of this area was constructed by this new upper crustal velocity model with the previous middle and lower crustal model.The new model reveals that a high-velocity belt is highly consistent with the strike of the Tanlu Fault Zone,and a low-velocity sedimentary characteristic is consistent with the Hefei Basin and Chao Lake depression.The distribution morphology of high and low velocity bodies shows that the sedimentary pattern of Hefei-Chao Lake area is closely related to the tectonic evolution of the Tanlu Fault Zone since the Mesozoic.This study also identifies multiple low-velocity anomalies in the southeastern Hefei City.We speculate that strong ground motion during the 2009 Feidong earthquake(magnitude of 3.5)was related to amplification by the thick sediments in the Hefei Basin.We also discuss further applications of multi-scale high-resolution models of the shallow layer to strong ground motion simulations in cities and for earthquake disaster assessments.

Co-seismic Coulomb stress changes on the northern Tanlu fault zone caused by the Tohoku-Oki M_(W)9.0 earthquake

Based on the spherical earth dislocation theory and a fault slip model of the Tohoku-Oki M_(W)9.0 earthquake,the co-seismic Coulomb failure stress changes(ΔCFS)on the northern Tanlu fault zone at depths of 0–40 km are calculated.By comparing two sets of results from the spherical earth dislocation theory and the semi-infinite space one,the effect of earth curvature on the calculation results is analyzed quantitatively.First,we systematically summarize previous researches related to the northern Tanlu fault zone,divide the fault zone as detailed as possible,give the geometric parameters of each segment,and establish a segmented structural model of the northern Tanlu fault zone.Second,we calculate the Coulomb stress changes on the northern Tanlu fault zone by using the spherical earth dislocation theory.The result shows the Coulomb stress changes are no more than 0.003 MPa,which proves the great earthquake did not significantly change the stress state of the fault zone.Finally,we quantitatively analyze the disparities between the results of semi-infinite space dislocation theory and the spherical earth one.The average disparity between them is about 7.7%on the northern Tanlu fault zone and is 16.8%on the Fangzheng graben,the maximum disparity on this graben reaches up to 25.5%.It indicates that the effect of earth curvature can not be ignored.So it’s necessary to use the spherical earth dislocation theory instead of the semi-infinite space one to study the Coulomb stress change in the far field.

A recent paleoearthquake on Qingfengling seismic fault of Tanlu fault zone

Introduction The Tanlu fault zone lies in the eastern China, which is an important huge active fault with a long history. It has experienced a complex generation and evolution process and affects significantly the regional structure, paleogeography, magma activity, minerogenesis and earthquake activity in the area. With a length of 2 400 km, the fault zone consists of 2-4 or more parallel faults of 10-40 km in width, cutting through different geotectonic elements in the eastern China （FANG et al, 1986）. On July 25 in 1668, an extraordinarily large earthquake of M=8.5 occurred on the Changyi-Dadian fault （F1） that is an embranchment of Tanlu fault zone, resulting in a surface rupture with a total length of 130 km （LI et al, 1994; CHAO et al, 1995）. The paleoseismic study reveals that 3 events with a magnitude equal to 8 occurred on the Changyi-Dadian fault. The recent event occurred 3 500 a ago and the reoccurrence interval is about 3 500 a （LIN and GAO, 1987）. During the Tancheng earthquake （on July 25, 1668）, the Anqiu-Juxian fault was not ruptured, which was a Late Pleistocene active fault （ZHENG et al, 1988; GAO et al, 1988; CHAO et al, 1994） and was doubted as the seismogenic fault of the M=7.0 Anqiu earthquake occurred in 70 BC by certain geologists （CHAO et al, 1994）.

Active fault survey on the Tanlu fault zone in Laizhou Bay

Shallow-depth acoustic reflection profiling survey has been conducted on the Tanlu fault zone in Laizhou Bay. It is found that the Tanlu fault zone is obviously active during the late Quaternary and it is still the dominating structure in this region. The Tanlu fault zone consists of two branches. The KL3 fault of the western branch is composed of several high angle normal faults which had been active during the period from the latest Pleistocene to early Holo- cene, dissected by a series of northeast or approximate east-west trending fault which leaped sediment of the late Pleistocene. The Longkou fault of the eastern branch consists of two right-laterally stepped segments. Late Quaternary offsets and growth strata developed along the Tanlu fault zone verify that the fault zone retained active in the latest Pleistocene to the early Holocene. The Anqiu-Juxian fault that passes through the middle of Shandong and corresponds to the Longkou fault is composed of a series of right-laterally stepped segments. The active faults along the eastern branch of the Tanlu fault zone from the Laizhou bay to the north of Anqiu make up a dextral simple shear deformation zone which is characterized by right-lateral strike-slip movement with dip-slip component during the late Quaternary.

New Activity of the Tanlu Fault Zone in the South of Huaihe to the Nvshanhu Segment since the Late Quaternary

Taking the Huaihe to the Nvshanhu segment of the Tanlu( Tancheng-Lujiang) fault zone as the main research target to explore whether there has been new activity since the late Quaternary,and based on the interpretation of remote sensing images and repeated surface investigations,we excavated trenches at the sections where the tectonic landform is significant,identified and recorded the deformation patterns of the fault and analyzed the activity behavior. Samples of new activity and deformation were collected and oriented slices were ground based on the samples ' original state to make the micro structural analysis and demonstration. All of the above research shows very clear linear tectonic geomorphology along the fault,three trenches across the fault zone all revealed new deformation traces since late Quaternary. The latest stratum dislocated by the fault is the late Quaternary and Holocene. The main slip mode is stick slip,as represented typically by fault scarps,wedge accumulation,the faults and the filled cracks and so on. In general,it shows the characteristics of brittle high-speed deformation and belongs to the prehistoric earthquake ruins. The above understanding was confirmed partially by microscopic analysis. In addition,the similarities and differences and the possible reasons for the characteristics of the latest activities of the Tancheng-Lujiang fault zone in the north and south of the Huaihe River regions are also discussed in this paper.

Tanlu Fault Zone and Gold Ore Metallogenesis

Tanlu Fault Zone (TFZ) is a large NE trending deep fracture system in East China and is about 2500 km long. It extends from the south of Lujiang to Tancheng, and passes through the Bohai Sea and continues to the north, where it branches into Yilan - Shulan Fault and Dunhua - Mishan Fault. TFZ is a long lasting huge deep - rooted lithospherical fault system with different characteristics in different parts and at different periods of its evolution. TFZ also controls the distribution and occurrences of many superlarge, large, middle and small sized gold ore deposits, e.g. Jiapigou, Haigou, Xiaoxinancha and Ciweigou gold deposits in Noaheast China; Linglong, Jiaojia, Sanshandao, Taishang, Xincheng, Rushan, and Pengjiakuang gold deposits in Jiaodong Peninsula of Shandong Province; and Guilaizhuang and Yinan in Western Shandong Province.

Sedimentary and tectonic evolution of the Banquan pull-apart basin and implications for late Cenozoic dextral strike-slip movement of the Tanlu Fault Zone

The Banquan Basin is a pull-apart basin with the largest scale and the most prominent structure due to dextral slip of the Tanlu Fault Zone(TLFZ) in late Cenozoic. The depositional history of the basin records the start time and evolution of the right-lateral strike-slip movement of the TLFZ. This paper studies the sedimentary and tectonic evolution of the Banquan Basin by seismic reflection exploration, borehole detection and cosmogenic nuclide chronology. We analyze the coupling relationship between the pull-apart basin and the strike-slip fault and discuss the start time and tectonic significance of the right-lateral strikeslip of the TLFZ. Our study indicates that the Banquan Basin has undergone three evolutionary stages: weak rifting during the pre-pull-apart period, strong extension during the syn-pull-apart period and subsidence during the post-pull-apart period. This implies that the TLFZ, which controls the evolution of the basin, experienced an evolutionary process of weak activity,intensified activity and migration of activity toward the central basin. The sedimentary filling of the basin has strong response to the episodic pull-apart and extension of the basin. Lying upon the basement of the basin, a thin layer of Miocene mudstone slowly accumulated due to local rifting before the strong pull-apart event. Along with the dextral slipping and pull-apart process, the basin was filled with alluvial fan facies, fluvial facies and floodplain facies strata from bottom to top. The latest tectonic movement of the TLFZ in the North China Block in late Cenozoic was dominated by episodic dextral strike-slip motion, and this deformation pattern started at 4.01±1.27 Ma. The latest tectonic deformation in North China since late Cenozoic was governed by eastward extrusion and tectonic orogenesis of the eastern margin of the Qinghai-Xizang Plateau since late Miocene. The eastward thrusting of the Liupanshan fault zone and sinistral shearing of the Qinling fault zone led to the anticlockwise rotation and pushing of secondary blocks in North China, resulting in a planar bookshelf faulting and rotation pattern. This unique deformation pattern transferred eastwards to the North China Plain at ~4.01 Ma and the process continues to the present time.This planar bookshelf rotation, accompanied with regional sinistral strike-slip movement of the ~EW-trending boundary fault zones to the north and south of the North China Block and dextral strike-slip motion of the NNE-trending boundary faults between secondary blocks, is likely to be the long-range effect of the strong extrusion of the eastern margin of the QinghaiXizang Plateau.

Seismites in the Dasheng Group： New evidence of strong tectonic and earthquake activities of the Tanlu Fault Zone

More than 80 layers of seismites were recognized from the Early Cretaceous Dasheng Group in the Mazhan and Tancheng graben basins in the Tanlu Fault Zone, eastern China. The responsible seismic events took place about 110–100 Ma in the Early Cretaceous. The fault zone was affected at the time by strong tectonics, due to tension-related stretching and scattered squeezing by strike-slip faults. These tectonic activities induced a series of strong earthquakes with Richter magnitudes(M) of 5–8.5. The earthquakes affected saturated or semi-consolidated flood and lake sediments, and produced intra-layer deformations by several processes, including liquefaction, thixotropy, drop, faulting, cracking, filling and folding, which resulted in the formation of various soft-sediment deformation structures, such as dikes and veins of liquefied sand, liquefied breccias, liquefied homogeneous layers, load structures, flame structures, ball-and-pillow structures, boudinage, diapirs, fissure infillings, a giant conglomerate wedge, and syn-sedimentary faults. The seismites are new evidence of tectonic and seismic activities in the Tanlu Fault Zone during the Early Cretaceous; the series of strong seismic events that can be deduced from them must be considered as a response to the destruction of the North China Craton.

Seismic event, sequence and tectonic significance in Canglangpu Stage in Paleo-Tanlu Fault Zone

The Canglangpu Stage of Lower Cambrian Series is widely distributed along both sides of the Tanlu (Tancheng-Lujiang) Fault Zone in the Jiao-Liao-Xu-Huai regions. In the Liaodong Peninsula, the Canglangpu Stage consists of three formations, i.e. Gejiatun, Dalinzi and Jianchang formations in ascending order (lying on the eastern side of the Tanlu Fault Zone). The Dalinzi Formation, developing in a littoral Sabkha environment, is full of catastrophic event records of violent seism, such as liquefied muddy-sandy veins, hydroplastic folds, hydroplastic micro-faults (three forming an organic whole), liquefied crinkled deformations, liquefied breccia and sandy dikes. Based on such records, the seismic liquified sequence of argillaceous rocks in Sabkha is built up. In northern Jiangsu and Anhui provinces, however, there hardly observe seismic records in the Canglangpu Stage, which consists of Jinshanzhai and lower Gouhou and upper Gouhou formations (lying on the western side of the Tanlu Fault Zone). Even if the Gouhou Formation, developing in a lagoon-dry environment, is in the same climate zone as the Dalinzi Formation, and 4 depositional sequences have been identified in the Canglangpu Stage in Northern Jiangsu and Anhui provinces, however, in the same stage in the Liaodong Peninsula, there exist only 3 ones. Therefore, it is not supported by the above mentioned evidence (such as catastrophic events, sequences stratigraphy and lithologic correlation of formations) that the Canglangpu Stage in the Liaodong Peninsula came from northern Jiangsu and Anhui provinces through a long-distance, about hundreds kilometers, left-hand displacement of the Tanlu Fault in the Mesozoic era.

滁州地区铜金矿控矿构造特征及资源潜力浅析

滁州地区横跨桐柏—大别—苏鲁和长江中下游2个成矿带,是重要的铜、金成矿区。通过野外调研和典型矿床控矿分析,明确了郯庐深大断裂带、黄破断裂和管马断裂等主要断裂构造特征及区内控岩控矿构造特征。郯庐深大断裂带和黄破断裂是区内一级控岩控矿断裂,分别控制了北北东向和北东向构造-岩浆-成矿作用,一级断裂的次级构造、层间破碎带、褶皱伸展部位和断裂交汇部位等是重要的容矿构造。生产矿山实践表明,在已有矿山深边部,斑岩-矽卡岩型铜金矿和石英脉-构造蚀变岩型金矿的找矿潜力较大,是本区下一步地质找矿工作重点勘查和开发利用目标。

“泰山震”的震中在郯庐断裂带安丘地区的证据

“泰山震”发生于公元前1831年,是中国史料记载的最早的历史地震。据《竹书纪年》记载:夏帝发七年(公元前1831年),当名为“发”的皇帝正在登泰山时,发生了一次强地震。因这次地震使皇帝受到了惊吓,因此,被名之为“泰山震”而首次记载下来。显然,名为“发”的皇帝受地震恐吓的地理位置是泰山坡麓。由于在泰山及其附近,地震地质学家一直未找到“泰山震”的地震地质记录。因此,“泰山震”的震中和震级一直是个谜。重新观察已发现的地震地质遗迹,结合一系列的测试、实验与剖析,本研究为“泰山震”是震中处在郯庐断裂带内安丘地区的强烈的历史地震提供了证据。首先,在距泰山以东约200 km远的郯庐断裂带安丘—夏庄盆地内的全新世湖沼相软土层中,存有震陷向斜与同震微断层等宏观的地震事件遗迹,它们记录的震中烈度Ⅸ度、震级达M7.0;二是借助于^(14)C同位素年龄测定结果,结合计算相关土层的沉积时间,而获得了极为接近公元前1831年的发震时间(公元前1827年);三是依据华北地震烈度衰减模型,计算出该地震在泰山的衰减烈度为Ⅵ度。中国地震烈度表显示,Ⅵ度烈度完全使人站立不稳或惊逃户外,这符合当年登山皇帝受地震惊恐的史料记录。

基于改进的多分量频率-贝塞尔变换法研究郯庐断裂带潍坊段上地壳径向各向异性结构

郯庐断裂带潍坊段位于郯庐断裂带中部,具有复杂的地质结构,总体呈现“两堑夹一垒”的构造格局.相比于郯庐断裂带其他区域,潍坊段地震活动性较弱,属于地震空区,未来发生大地震的可能性尚不明确.前人对该地区的研究目前仅局限于速度结构和方位各向异性结构,对于上地壳径向各向异性结构特征鲜有报道.因此,研究该区域上地壳速度模型和径向各向异性结构,有助于更好地认识郯庐断裂带潍坊段浅地壳(<10 km)变形特征,评估该区域发生地震的可能性.我们利用2017年在潍坊段所布设的302个短周期地震仪采集的背景噪声数据,基于改进的多分量频率-贝塞尔变换(MMFJ)法,同时提取到潍坊段东南侧四个区域子阵列的Rayleigh波和Love波的基阶及高阶频散数据,并且进一步反演这些频散数据得到了SV波和SH波速度以及径向各向异性结构.数值实验结果表明,高阶模式频散数据的加入能够降低反演的非唯一性,更好地约束浅地壳径向各向异性结构.实例中的径向各向异性结果表明,郯庐断裂带潍坊段四个区域都有近似相同的变形特征:在约2 km以浅,径向各向异性为负(V_(SH)<V_(SV)),这可能主要源于潍坊段垂向断裂结构的控制作用;5~7.5 km,径向各向异性为正(V_(SH)>V_(SV)),这可能与早期地壳伸展沉积导致的水平变形结构有关.2~5 km,四个区域径向各向异性结构各有不同,但总体处于由负到正的转折状态.这可能因为2~5 km不仅受到断裂结构的控制作用,也受到水平沉积结构的影响,导致径向各向异性结构较为复杂.

Fault detection by reflected surface waves based on ambient noise interferometry

Detecting subsurface fault structure is important for evaluating potential earthquake risks associated with active faults.In this study,we propose a new method to detect faults using reflected surface waves observed in ambient noise cross correlation functions.Ambient noise tomography using direct surface waves obtained from ambient noise interferometry has been widely used to characterize active fault zones.In cases where a strong velocity contrast exists across the fault interface,fault-reflected surface waves are expected.We test this idea using a linear array deployed in the Suqian segment of Tanlu fault zone in Eastern China.The fault-reflected surface waves can be clearly seen in the cross-correlation functions of the ambient noise data,and the spatial position of the fault on the surface is close to the stations where the reflected signals first appear.Potentially reflected surface waves could also be used to infer the dip angle,fault zone thickness and the degree of velocity contrast across the fault by comparing synthetic and observed waveforms.