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基于东北地区已有的宽频带流动台阵远震数据,利用波场延拓和分解的H-β网格搜索法,对松辽盆地的沉积层及地壳结构进行了深入分析。结果显示:松辽盆地的沉积层厚度为0.2—2.5 km,整体呈现中央坳陷区厚、边缘薄且西南地区最薄的分布特征;研究区地壳较薄,厚度介于24—34 km之间,其横向变化特征与沉积层厚度分布具有一定的对应性。依据沉积层和地壳的厚度计算了地壳伸展系数,其平均值接近于以往接收函数研究估测的岩石圈伸展因子。因此,本文推测松辽盆地在伸展构造过程中,其地壳和岩石圈的减薄以纯剪切模式为主。此外,松辽盆地具有较高的地壳平均波速比vP/vS,暗示盆地下方岩石圈地幔的减薄过程中可能存在岩浆的底侵作用。 相似文献
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沉积盆地形成的张性模式 总被引：7，自引：0，他引：7
在过去的十余年中，对沉积盆地的成因已取得了很大进展，并提出了许多定性和定量的模型。本文旨在对张性盆地进行讨论，并简要分析影响盆地发展的主要因素和导致岩石圈内部张应力的力源。本文对三种主要模型进行了详细讨论，即纯剪切模型，简单剪切模型和纯剪切－简单剪切联合模型。所有模型虽都建立在对不同盆地的研究基础之上，但它们都揭示出盆地的发展主要受岩石圈内部热动力学过程和沉积物负载作用的控制。其它因素，如拆离面的 相似文献
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长江中下游成矿带位于大别造山带、长江中下游凹陷、江南隆起带等大地构造单元结合部位,通过在研究区内布设两条首尾相接共计150km长的大地电磁剖面,获得了50km以浅岩石圈尺度的电性分布.长江中下游地区中段地下电性结构显示出在地下10km和30km处分别存在明显的圈层结构,以此认为现今横向稳定的"电莫霍"反映了研究区经历燕山期陆内构造-岩浆活动后已基本上完成壳幔重新平衡;而分隔大地构造单元的郯庐断裂带、长江断裂带以及江南断裂带在电性上具有特征的梯度显现,在印支造山期后的引张背景下,断裂带成为强伸展活动带与控制了燕山期大范围的陆内岩浆活动;高导地幔的局域性存在以及从北向南地幔导电性的变化反映了在经受深部动力学过程中处于不同大地构造部位的地幔所遭受的不同类型的改造以及地幔深部的构造极性. 相似文献
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通过对南北地震带北段区域所布设的676个流动地震台站观测资料进行处理,联合反演面波频散与接收函数数据,获得了研究区内地壳厚度、沉积层厚度的分布情况以及地壳上地幔高分辨率S波速度结构成像结果.反演结果显示研究区地壳厚度从青藏高原东北缘向外总体逐渐变薄,秦岭造山带地壳厚度较同属青藏高原东北缘的北祁连块体明显减薄;鄂尔多斯盆地及河套盆地分布有非常厚的沉积层,阿拉善块体部分区域也有一定沉积层分布,沉积层与研究区内盆地位置较为一致;松潘—甘孜块体、北祁连造山带等青藏高原东北缘总体表现为S波低速异常;在中下地壳,松潘—甘孜块体下方的低速体比北祁连造山带下方的低速体S波速度值更小、分布深度更浅,更有可能对应于部分熔融的地壳;鄂尔多斯盆地在中下地壳以及上地幔内有着较大范围的高速异常一直延伸到120 km以下,而河套盆地地幔只在80 km以上部分有着高速异常的分布,此深度可能代表了河套盆地的岩石圈厚度,来自深部地幔的热物质上涌造成了该区域的岩石圈减薄;阿拉善块体在地壳和上地幔都表现出高低速共存的分布特征,暗示阿拉善块体西部岩石圈可能受青藏高原东北缘的挤压作用发生改造. 相似文献
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The North China Craton (NCC) witnessed Mesozoic vigorous tectono-thermal activities and transition in the nature of deep lithosphere. These processes took place in three periods: (1) Late Paleozoic to Early Jurassic (～170 Ma); (2) Middle Jurassic to Early Cretaceous (160–140 Ma); (3) Early Cretaceous to Cenozoic (140 Ma to present). The last two stages saw the lithospheric mantle replacement and coupled basin-mountain response within the North China Craton due to subduction and retreating of the Paleo-Pacific plate, and is the emphasis in this paper. In the first period, the subduction and closure of the Paleo- Asian Ocean triggered the back-arc extension, syn-collisional compression and then post-collisional extension accompanied by ubiquitous magmatism along the northern margin of the NCC. Similar processes happened in the southern margin of the craton as the subduction of the Paleo-Tethys ocean and collision with the South China Block. These processes had caused the chemical modification and mechanical destruction of the cratonic margins. The margins could serve as conduits for the asthenosphere upwelling and had the priority for magmatism and deformation. The second period saw the closure of the Mongol-Okhotsk ocean and the shear deformation and magmatism induced by the drifting of the Paleo-Pacific slab. The former led to two pulse of N-S trending compression (Episodes A and B of the Yanshan Movement) and thus the pre-existing continental marginal basins were disintegrated into sporadically basin and range province by the Mesozoic magmatic plutons and NE-SW trending faults. With the anticlockwise rotation of the Paleo-Pacific moving direction, the subduction-related magmatism migrated into the inner part of the craton and the Tanlu fault became normal fault from a sinistral one. The NCC thus turned into a back-arc extension setting at the end of this period. In the third period, the refractory subcontinental lithospheric mantle (SCLM) was firstly remarkably eroded and thinned by the subduction-induced asthenospheric upwelling, especially those beneath the weak zones (i.e., cratonic margins and the lithospheric Tanlu fault zone). Then a slightly lithospheric thickening occurred when the upwelled asthenosphere got cool and transformed to be lithospheric mantle accreted (～125 Ma) beneath the thinned SCLM. Besides, the magmatism continuously moved southeastward and the extensional deformations preferentially developed in weak zones, which include the Early Cenozoic normal fault transformed from the Jurassic thrust in the Trans-North Orogenic Belt, the crustal detachment and the subsidence of Bohai basin caused by the continuous normal strike slip of the Tanlu fault, the Cenozoic graben basins originated from the fault depression in the Trans-North Orogenic Belt, the Bohai Basin and the Sulu Orogenic belt. With small block size, inner lithospheric weak zones and the surrounding subductions/collisions, the Mesozoic NCC was characterized by (1) lithospheric thinning and crustal detachment triggered by the subduction-induced asthenospheric upwelling. Local crustal contraction and orogenesis appeared in the Trans-North Orogenic Belt coupled with the crustal detachment; (2) then upwelled asthenosphere got cool to be newly-accreted lithospheric mantle and crustal grabens and basin subsidence happened, as a result of the subduction zone retreating. Therefore, the subduction and retreating of the western Pacific plate is the outside dynamics which resulted in mantle replacement and coupled basin-mountain respond within the North China Craton. We consider that the Mesozoic decratonization of the North China Craton, or the Yanshan Movement, is a comprehensive consequence of complex geological processes proceeding surrounding and within craton, involving both the deep lithospheric mantle and shallow continental crust. 相似文献
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依据地震波速得到的上地幔温度和气象台站记录的地表温度为约束,结合地表热流和热导率观测数据,利用有限元方法计算了中国大陆及邻区岩石圈三维热结构.基于此温度结果和GPS观测得到的应变率数据,以滑动摩擦、脆性破裂和蠕变三种强度机制为约束,计算得到了中国大陆及邻区岩石圈三维流变结构.结果显示:弱强度和低等效黏滞性系数的下地壳在中国大陆及邻区普遍存在,并且下地壳的流变强度和等效黏滞性系数比上地壳和岩石圈地幔一般要低1~2个数量级;中国大陆范围内青藏高原存在着厚度最大、强度最低的下地壳;青藏高原的岩石圈强度和等效黏滞性系数比华北、华南和印度板块的都要低;岩石圈流变结构的横向分布特征与重力梯度带和地形过渡带比较一致. 相似文献
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基于ChinArray三期项目布设于华北克拉通中部的流动台阵观测数据,利用背景噪声互相关和地震面波层析成像获取了研究区内6—140 s周期的瑞雷面波频散,使用蒙特卡罗非线性反演方法获得了华北克拉通中部岩石圈的高分辨率三维S波速度结构。结果显示华北克拉通不同地块的岩石圈速度结构存在显著的横向差异：其中鄂尔多斯盆地腹地整体表现为高速特征,延伸至200 km以下,但其东南缘存在小范围的低速异常;东部的华北盆地整体表现为低速特征,具有较薄的地壳和岩石圈厚度;中部造山带南北两端以及南北重力梯度线下方存在相连接的低速区域,在深处延伸至华北盆地下方;在下地壳和上地幔顶部,大同火山群区域的低速体逐渐向西偏移至鄂尔多斯盆地东北角下方;而在上地幔中,该区域的低速异常随深度增加而逐渐减弱,低速体延伸至东南方向的华北盆地下方。基于本研究获得的S波速度模型,我们认为：鄂尔多斯盆地腹地保持了克拉通特性,但其东南缘存在局部的岩石圈改造作用;华北盆地发生了强烈的岩石圈破坏减薄和地壳伸展变形;中部造山带南北端以及南北重力梯度线下方的岩石圈发生了局部的改造减薄,其机制可能都来源于华北盆地下方地幔热物质的上涌;大同火山群下... 相似文献
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LIU Shaowen WANG Liangshu GONG Yuling LI Cheng LI Hua & HAN Yongbing . Department of Urban Resources Nanjing University Nanjing China . Department of Earth Sciences Nanjing University Nanjing China 《中国科学D辑(英文版)》2005,48(10)
Thermal regime of the lithosphere is the scenario of the lithospheric thermal evolution, and the thermo-mechanical state of lithosphere definitively controls its deformation style and mechanism. Better understanding of the lithospheric deep thermal-rheo- logical structure of sedimentary basin will shed light on the formation and evolution dynamic process of the basin. Surface tectonics is the response of the deep structure, and is controlled by the lithospheric ther-mal-rheological properties.… 相似文献
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用深地震反射方法研究邢台地震区地壳细结构 总被引：59，自引：23，他引：59
为了取得邢台地震区的地壳细结构,1990年冬,国家地震局地球物理研究所等实施了一条穿过华北平原中部束鹿断陷盆地的深地震反射剖面.经过叠加和偏移后的剖面显示出清晰的地壳细结构图像.剖面图上1-4s之间的强反射对应于由一组正断层产生的沉积层变形,其中新河断裂为束鹿盆地和新河凸起之间的边界主断裂,它伸展到8km以下深处.在5s左右显示出一组较强的反射界面,它可能对应于脆性上地壳的下界面.10-11s之间的壳-幔过渡带包含一组振幅大、连续性好的强反射,在震源下方的Moho界面上似乎被间断.岩浆从上地幔顶部侵入到地壳中,使得地壳可能出现部分熔融,这一过程是产生扩张盆地和发生邢台地震的主要原因. 相似文献
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依据大地电磁测深所发现的上地幔高导层顶面深度可以给出大陆岩石圈-软流圈界面(LAB)的空间发育特征,为认识岩石圈结构及壳幔相互作用等提供重要信息.本文在1996年编制的中国大陆上地幔高导层顶面深度图的基础上,补充了1995—2010年大地电磁测深结果和大地热流数据,以1°×1°网度编制了新的中国大陆上地幔高导层顶面深度图.我国上地幔高导层顶面深度变化很大,具有南北分带,东西分块的特征,呈东浅、西深、北浅、南深的格局,从最浅的50~60km到最深的230km,平均深度为100~120km.据上地幔高导层顶面分布形态,全国共可划分出27个隆起区.通过与中国已知内生金属矿产和油气田的分布对比,发现我国大陆80%以上中生代内生金属矿床分布在上地幔高导层隆起带或其梯度带上方.中国大陆东部含油气盆地主体对应上地幔隆起区,油气田多位于隆起区上方或其边部的过渡带上;西部主体位于幔坳区,主要油气田对应盆地中心的幔坳向周边幔隆过渡的梯度带上;中部表现为仅盆地腹地对应幔坳,盆地周边对应规模较大的上地幔隆起带,主要油气田位于隆起带.总的来看内生金属矿床一般分布在上地幔隆起区靠近造山带一侧,而油气田一般分布在上地幔隆起区靠近盆地一侧.软流圈的不断上隆,造成岩石圈减薄、拉张,张性断裂的出现成为地球深部物质和热量向地壳上部运移的有利通道,为内生金属矿产的形成提供了成矿物质和能量保障,也为含油气盆地带来了生烃催化剂、热能和无机成因的石油与天然气.地球深部超临界流体的存在对上地幔高导层的形成、成矿物质运移可能发挥了重要作用. 相似文献
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青藏高原东南缘处于印度板块与欧亚板块碰撞的侧翼,揭示该地区的岩石圈结构有助于完整理解青藏高原碰撞造山的动力学过程,对构建大陆碰撞成矿理论框架至为关键.本研究对横过青藏高原侧向碰撞带的一条深反射地震剖面的15个大炮资料,进行了针对性静校正、去噪等处理和单次叠加成像,结果剖面显示了侧向碰撞带岩石圈结构的骨架特征:(1)双程走时(TWT)8～10s的强反射(Tc)将地壳分为上、下两层;Tc可能是大型滑脱构造的拆离面,其存在使上地壳的变形与下地壳解耦;(2)Moho间断面反射(Tm)为3～4个同相轴的窄带反射波组,横向不连续,与深大断裂交汇处被错断,但断距不大;(3)在兰坪—思茅地块下方TWT21s和扬子克拉通西缘下方TWT22～24s存在相向倾斜的反射波组(TL);以Tc、Tm和TL构成的骨架结构,定性地描绘出剖面下方岩石圈地幔以汇聚为主、地壳块体以侧向滑移为主和上地壳为薄皮逆冲或滑脱的分层动力学模式.该岩石圈变形样式明显不同于以正向碰撞挤压、地壳缩短垂向增厚为主的"冈底斯模式". 相似文献
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Zhen Guo Yuliang Cao Xianguang Wang Y. John Chen Jieyuan Ning Weiguang He Youcai Tang Yongge Feng 《地震科学（英文版）》2014,27(3):265-275
P-wave and S-wave receiver function analyses have been performed along a profile consisted of 27 broadband seismic stations to image the crustal and upper mantle discontinuities across Northeast China. The results show that the average Moho depth varies from about 37 km beneath the Daxing’anling orogenic belt in the west to about 33 km beneath the Songliao Basin, and to about 35 km beneath the Changbai mountain region in the east. Our results reveal that the Moho is generally flat beneath the Daxing’anling region and a remarkable Moho offset (about 4 km) exists beneath the basin-mountain boundary, the Daxing’anling-Taihang Gravity Line. Beneath the Tanlu faults zone, which seperates the Songliao Basin and Changbai region, the Moho is uplift and the crustal thickness changes rapidly. We interpret this feature as that the Tanlu faults might deeply penetrate into the upper mantle, and facilitate the mantle upwelling along the faults during the Cenozoic era. The average depth of the lithosphere-asthenosphere boundary (LAB) is ~80 km along the profile which is thinner than an average thickness of a continental lithosphere. The LAB shows an arc-like shape in the basin, with the shallowest part approximately beneath the center of the basin. The uplift LAB beneath the basin might be related to the extensive lithospheric stretching in the Mesozoic. In the mantle transition zone, a structurally complicated 660 km discontinuity with a maximum 35 km depression beneath the Changbai region is observed. The 35 km depression is roughly coincident with the location of the stagnant western pacific slab on top of the 660 km discontinuity revealed by the recent P wave tomography. 相似文献
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Mireille Laigle Anne Becel Batrice de Voogd Alfred Hirn Tuncay Taymaz Serdar Ozalaybey Members of SEISMARMARA Leg Team 《Earth and Planetary Science Letters》2008,270(3-4):168-179
Increased source strength, streamer length and dense spatial coverage of seismic reflection profiles of the SEISMARMARA Leg 1 allow to image the deep structure of the marine North Marmara Trough (NMT) on the strike-slip North Anatolian Fault (NAF) west of the destructive Izmit 1999 earthquake. A reflective lower crust and the Moho boundary are detected. They appear upwarped on an E-W profile from the southern Central Basin eastwards, towards more internal parts of the deformed region. Thinning of the upper crust could use a detachment suggested from an imaged dipping intracrustal reflector that would allow upper crustal material to be dragged from beneath it and above the lower crust, accounting for the extensional component but also southwest motion of the southern margin of the NMT. Sections across the eastern half of the NMT, crossing the Cinarcik and Imrali basins, reveal several faults that are active reaching into the basement and have varying strike and proportions of normal and strike-slip displacement. They might be viewed as petals of a large scale negative flower-structure that spreads over a width of 30 km at surface and is rooted deeper in the lithosphere. Under the Central Basin a very thick sediment infill is revealed and its extensional bounding faults are active and imaged as much as 8 km apart down to 6 km depth. We interpret them as two deep-rooted faults encompassing a foundering basement block, rather than being merely pulled-apart from a jog in a strike-slip above a décollement. The deep-basin lengthening would account for only a modest part of the proposed 60 km finite motion since 4 Myr along the same direction oblique to the NMT that sidesteps the shear motion from its two ends. Thus differential motion occurred much beyond the deep basins, like subsidence involving the NMT bounding faults and the intracrustal detachments. The complex partitioned motion localized on active faults with diverse natures and orientations is suggested to represent the overburden deformation induced from horizontal plane simple shear occurring in depth at lithospheric scale, and in front of the North Anatolian Fault when it propagated through the region. 相似文献
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Formation of deep basins in continental crust is usually explained by stretching. Intense stretching produces typical deformations in sedimentary cover. These deformations are observed in rift valleys. Deformations produced by stretching can in principle be revealed in presentsedimentary basins. There are also simple ways to reveal such deformations in fold belts, where the remmants of numerous deep basins in the continental crust were found. The sedimentary cover structure was analyzed in the Urals, Appalachians, Scandinavian Caledonides, North-American Cordilleras and in the Alpine, Verkhoyansk and Franklinian fold belts, but no deformations that are typical for significant stretching of continental lithosphere have been found there in most of the deep basins in the continental crust. These basins were commonly formed in cool cratonic areas by very rapid subsidence of the duration of a few million years. Such subsidence cannot be explained by thermal relaxation. Thrust loading as a cause of subsidence can also be excluded in most cases. The authors suggest a gabbro to eclogite transformation with the destruction of the basaltic layer as a possible cause of rapid subsidence. This occurs under upwelling of wet asthenosphere of not too high temperature to the base of the crust. Crustal attenuation from destruction of the basaltic layer permits an intense subsequent crustal shortening. This may explain why continental crust was intensely compressed only in those regions, where rapid subsidence of large magnitude took place. 相似文献
16.
参考青藏高原东缘松潘-甘孜地块至四川盆地陡变地形起伏和地壳密度结构的横向差异,本文建立了二维牛顿黏性流体有限元模型,计算分析构造加载、陡变地形和重力效应控制下青藏高原东缘岩石圈变形特征,探讨横向不均匀的地壳密度结构、陡变地形和岩石圈流变性质对区域现今垂向运动的影响.计算结果显示：在构造加载作用下,松潘-甘孜地块至四川盆地地表抬升微弱.区域横向不均匀的地壳密度结构驱使松潘-甘孜地块地壳整体抬升,速率高达2 mm·a-1,四川盆地整体下沉,速率约1 mm·a-1,与龙门山两侧现今观测到的地表垂向变形模式相近.龙门山地区陡变地形驱使柔性地壳流动,调整区域地壳局部变形;岩石圈流变结构影响重力驱动作用下的模型变形量值和岩石圈变形耦合程度,松潘-甘孜地块较低的中地壳黏滞系数引起上、下地壳的变形解耦;模型较高的岩石圈地幔黏滞系数使重力驱动作用下区域垂向变形量降低.因此,青藏高原东缘地壳密度结构差异、地形起伏和岩石圈流变性质是现今区域垂向变形的重要动力学控制因素. 相似文献
17.
华北地区地壳上地幔S波三维速度结构 总被引：3，自引：0，他引：3
利用华北地区大型流动地震台阵的记录资料,采用近震和远震联合成像方法,得到了水平分辨率0.5°×0.5°、深至600km的S波速度结构.研究结果表明,上地壳S波速度结构与地表地质构造基本一致,燕山—太行山山脉均呈现高速异常,延庆—怀来盆地、大同盆地表现为低速异常,华北盆地内部的拗陷和隆起分别呈现低速和高速.唐山地区中地壳、山西裂陷盆地中下地壳存在明显的低速异常,可能分别与流体和热物质作用有关,有利于形成孕育强震的地质构造环境.90km的速度结构图像依然与地表的构造特征有较大的相关性,可能说明深部结构对地表构造有一定的控制作用.燕山隆起区岩石圈的厚度可达120～150km左右,华北盆地的岩石圈厚度可能在80km左右,太行山地区的岩石圈厚度介于两者之间.山西裂陷盆地上地幔低速层较厚,反映了该区不稳定的构造环境造成了地幔热物质的上涌.华北盆地下方220～320km出现的高速异常体,可能揭示了华北盆地上地幔仍然存在拆沉后残留的难熔、高密度的古老岩石圈地幔.研究区东部地幔转换带呈低速异常,推测可能与太平洋板块俯冲至该区下方地幔转换带前缘120°E左右的俯冲板块相变脱水有关. 相似文献
18.
Enrico Bonatti 《Earth and Planetary Science Letters》1978,37(3):369-379
Anomalous topographic highs are found along many large oceanic fracture zones, frequently in the form of transverse ridges elongated parallel to the fractures both within and outside of the transform zone. These crustal highs are one or more kilometers shallower than the adjacent “normal” crust of equivalent age. Their elevation is frequently higher than the axial zone of lithospheric accretion. Geophysical and petrological data from the Vema, St. Paul, Romanche (Atlantic Ocean), Owen (Indian Ocean), Alula (Gulf of Aden), and other fracture zones suggest that the anomalous transverse ridges are not the result of excess volcanism, but rather of tectonic uplift of upper mantle and crustal blocks.Factors which may determine vertical tectonism along fracture zones include: (1) horizontal thermal conduction across a fracture zone from a lithospheric accreting segment; (2) viscodynamic forces operating in a fracture zone close to its intersection with an accreting segment; and (3) compressional and tensional horizontal stresses operating along a fracture zone, and created by several causes, the major one being small changes in the direction of spreading. Among these various factors, compressional and tensional horizontal stresses are probably the main cause of vertical tectonism in fracture zones. During the vertical motion of upper mantle/crustal blocks, ultramafic rocks, due to their physical properties, are uplifted preferentially.One of the implications of fracture zone vertical tectonism is that the age/depth of the crust relationship may not apply in regions with large fracture zones. In one well-documented case, a transverse crustal block at the Romanche fracture zone subsided during the last 5 m.y. at an average rate more than one order of magnitude faster than crust of equivalent age. 相似文献
19.
拉分盆地是走滑断层系中受拉伸作用形成的断陷盆地.一般在两条平行断层控制下发育.盆地形似菱形,几何形态主要受两条主控走滑断层错距和叠接长度影响.本文以青藏高原东北缘海原断裂带老龙湾拉分盆地第四纪所处的构造环境为基础,参考盆地周围断层几何分布,建立了三维有限元数值模型,模拟该拉分盆地的演化过程;进一步分析了断层力学性质、地壳分层结构等各因素对盆地形成和演化的影响.模拟结果显示,盆地地表沉降伴随有下地壳物质的上涌,此上涌对盆地地表沉降存在阻碍作用.各因素的影响具体表现为:(1)断层力学性质(弹性模量和黏滞系数)越弱,其对构造应力较低的传递效率导致盆地两端差异性运动越明显,从而形成较大的盆地地表沉降和明显的上地壳减薄.(2)平行主控断层的叠接长度反映盆地形成的拉伸作用范围,叠接长度越大,相同的差异性运动在单位面积形成的拉伸应力越小,盆地地表沉降较小.(3)下地壳流变性影响其物质的上涌量,下地壳黏滞系数越小,其对上部拉伸作用的响应越明显,上涌量越大,此上涌对上地壳沉降形成的阻碍作用也越明显.根据老龙湾拉分盆地所处的构造格局,将平行断层的叠接长度取20km,当断层黏滞系数取值为周围基岩的1/10,参考该盆地第四纪构造演化历史,模拟得到的盆地第四纪下沉量与盆地内第四系沉积层厚度在规模上近似,下地壳黏滞系数取值在(2.5~5.0)×1021 Pa·s范围内时,盆地下沉量模拟结果与老龙湾拉分盆地第四系地层厚度吻合较好. 相似文献
20.
Bertalan Bodri 《Journal of Geodynamics》1996,21(4):309-328
On the basis of data on crustal structure and terrestrial heat flow, a 3-D geothermal model for the lithosphere in the Pannonian basin, Hungary, has been calculated. This model, together with information on crustal composition, laboratory data on rock friction, and certain assumptions about fluid conditions and strain-rate levels within the lithosphere, has been used to construct a rheological model of the area.The results obtained show a layered rheological structure where an aseismic part of the crust is “sandwiched” between an upper and a lower seismogenic crustal layers. According to the proposed rheological model, seismic activity in the upper crust may be expected down to depths of 10–12 km, which is confirmed well by the observed depth distribution of seismicity. The model also predicts a lower crustal seismogenic layer down to 20–22 km. Because of infrequent occurrences of deep earthquakes and/or a generally small number of reliable hypocenter depth determinations in the study area, this seismogenic zone is less constrained by observations.The depth of the different rheologic horizons within the crust is governed mainly by thermal conditions. The lower boundary of both seismogenic layers appears isothermal. Brittle-ductile transition in the upper crust coincides with the ˜200 °C isotherm, while in the lower crust it coincides with the ˜ 375 °C isotherm. The lowermost crust and the upper mantle beneath Hungary show ductile behavior, thus the possibility of siesmic activity at these horizons can be excluded. 相似文献