辽东地区和海城地震区的地热观测

1980年至1984年间,在辽东地区和海城地震区,我们利用地质、冶金和化工部门的一批勘探钻孔,观测了这些井孔不同深度的温度,由此获得它们沿深度方向的温度梯度.同时,从这些观测孔取得岩样,在实验室中测定它们的热导率,从而得到每个钻孔的热流值.我们一共得到23口钻孔的热流数据,其中包括海城地震区的两个热流观测孔.这些热流值可粗略地给出海城地震区和辽东地区的热结构.结果表明,平行郯庐断裂的辽阳——熊岳北东条带具有相对高的热流值,平均热流为8.2910-2J/m2s(2.0cal/cm2s).这个条带恰好是下辽河盆地和辽东山地的交界,它与重力异常梯度带显示的北东向上地幔隆起带一致.海城地震区的平均热流值达9.2210-2J/m2s(2.2 cal/cm2s),又是高热流值条带上热流最高的区域.比较海城地震区已知的其它地球物理资料后,给出了该地区地球物理资料的综合解释剖面.我们推测,海城地震区下,地壳中的低速层是由于上地幔物质的大规模侵入产生的.高温和低速意味着该层具有塑性力学性质.海城地震震源区恰好位于这样一个塑性状态的介质层上部.这个结果对于研究海城地震和其它板内地震的形成过程无疑是有意义的.我们试图强调,对于地震研究而言,热流观测是地球物理观测中不可缺少的组成部分.地热资料      

中国辽南地区地壳与上地幔介质的横向不均匀性与海城7.3级地震s

近几年来,在辽南地区开展深部地球物理探测的基础上,通过对深地震测深、大地电磁测深、重力、航磁、大地热流等综合地球物理资料对辽南地区地壳与上地幔介质进行不同物性的正、反演计算与研究,获得了辽南地区地壳与上地幔介质的速度结构、电性结构、密度结构和温度结构,揭示了该区介质的横向不均匀性及其重要特征.发现在海城地震区一带,存在壳内低速、高导、低密度、高热流等一系列重大地球物理异常,在空间上与震源区存在相当好的一致关系,对分析大震的震源物理过程提供了重要实际依据.      

海城地震孕育的地球物理环境的讨论

根据海城地震余震的空间分布特征，震后地震裂缝分布和形变测量结果，结合震区的地球物理探测资料，对海城地震孕育的地球物理环境做了讨论。     

四川泸定地区三维速度结构与精定位研究

基于四川数字地震台网记录到的该研究区域(27.5°～31.5°N,100°～104°E)103 990个地震的震相数据,运用双差层析成像方法对泸定M_S6.8地震震源区及周边地区执行地震层析成像和精定位。结果表明：(1)余震序列主要分布于鲜水河断裂西南侧,长度约60 km,整体沿鲜水河断裂呈北西向展布,震源深度多集中在5～15 km,呈现出由北向南逐渐加深的迹象。根据余震序列空间分布特征及主震位置,提出鲜水河断裂东南段为发震断层,并且发现余震序列南北两端或许存在分支断层。根据背景地震的空间分布特征,推断其或许为泸定主震的前震。(2)主震的西北侧存在高速异常体,其或许阻挡了泸定地震向西北向破裂,结合鲜水河断裂东南段力学性质较弱,其滑动方向为首选的传播方向,推断泸定地震为单侧破裂,方向为东南。(3)泸定地震震源区下方30 km深度处存在弱S波低速层和高波速比,已有结果得知研究区中下地壳存在明显的高导层和低阻层,泸定主震位于热流值为65 mW·m²的大地热流等值线附近,综合推断震源区下方30 km或许存在地壳流体。同时,泸定地震发生在应力易积累,同时...     

Seismic imaging of the middle and upper crust by double-difference tomography: the Haicheng earthquake (Ms 7.3) in Liaoning Province

The Haicheng earthquake (Ms 7.3) occurred in Liaoning Province (39°N–43°N, 120°E–126°E ), China on February 4, 1975. The mortality rate was only 0.02% owing to the first timely and accurate prediction, although the area affected by the earthquake was 9200 km² and covered cities with a population density of 1000 p/km². In this study, the doubledifference (DD) tomography method was used to obtain high-resolution three-dimensional (3D) P- and S-wave velocity (Vp and Vs) structures and Vp/Vs as well as the earthquake locations. Tomography results suggest that velocity structure at shallow depth coincides well with topography and sediment thickness. The earthquake locations form a northwest-striking zone associated with the Jinzhou(JZ) Fault and a northeast-striking zone associated with the Haichenghe-Dayanghe (HD) Fault, and suggest that the JZ Fault consists of three faults and the Ms 7.3 Haicheng earthquake originated at the intersection of the JZ and the Faults. Lowvelocity zones (LVZs) with low Vp/Vs are observed at 15–20 km depth beneath the Haicheng (HC) region. We interpret the LVZs in the middle crust as regions of fluids, suggesting rock dehydration at high temperatures. The LVZs and low Vp/Vs in the upper crust are attributed to groundwater-filled cracks and pores. We believe that large crustal earthquakes in this area are caused by the combination of faulting and fluid movement in the middle crust.     

Heat flow,radioactive heat generation,and theoretical tectonics for northwestern Mexico

Nine heat flow values from Baja California and Sonora represent the first determinations of heat flux from Mexico and, in general, justify southerly extensions of the Basin and Range and Southern California thermal provinces of the southwestern United States. Heat flow in northern Baja California is low (0.84 hfu), consistent with known values from the Sierra Nevada Batholith, but a value of 1.23 hfu was recorded in the central area of the peninsula. Seven measurements from Sonora, averaging 2.5 hfu, are similar to Basin and Range values.Reduced heat flow values (q*) have been calculated for Sonora and are interpreted as indicative of a separate Basin and Range thermal subprovince in Mexico. A tectonic model developed for northwestern Mexico attributes the high heat flow of the Basin and Range to behind arc extension associated with the termination of Cenozoic subduction. Opening of the Gulf of California and sea-floor spreading therein has provided a vent for the release of heat accumulated under northwestern Mexico. Thus, the southern portion of the Basin and Range province (in Mexico) appears to be cooling and narrowing and a subprovince of high reduced heat flow is defined east and perhaps southwest of the Gulf of California.     

Research on geomagnetic tectonic characteristics of the crust in Haicheng seismic area

In this paper, the two metnods, rectangular spectrum (RS) and maximum entropy power spectrum (MES), have been used in calculating the geomagnetic structures of the crust in Haicheng and its adjacent areas and carrying out the geomagnetic stratification of the crust. The result of the research indicates that the crust can be devided into such three layers as nonmagnetic layer, magnetic layer and regressive magnetic layer from the top to the bottom. It is also found the distribution of the geomagnetic bottom interface (Curie surface) is consistent with the lower interface of the upper crust and the top interface of the middle crust of the velocity structure of the crust. It is very interesting that the Haicheng earthquake of Feb. 4, 1975,M 7.3 occurred at the depth gradient belt of the Curie isotherm surface. So, to research on the geomagnetic layers and the distribution characteristics of the Curie isotherm surface is meaningful in judging potential seismic foci. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 448–454, 1993. The data of velocity and electricity materials used in this paper are as reference from the related materials of the maps and directions etc. of Donggou-Haicheng-Dong Ujimqin Qi Geoscience Transect by Prof. Zao-Xun LU, Huai-Kuan XIA and others.     

On the geothermal regime of some tectonic units in Romania

Heat flow values of 33–58 mW m^–2 were found for the Transylvanian Depression, 45–57 mW m^–2 for the crystalline nucleus of the Eastern Carpathians, and 70–120 mW m^–2 for the Neogene volcanic area. Temperature-depth profile and some geophysical implications of the low values for the Transylvanian Depression are discussed, rendering evident clear-cut differences between this tectonic unit and other Noegene depressions. The heat flow values for the other two investigated tectonic units are usual ones for areas of their age.A preliminary map of the heat flow distribution over the Romanian territory is presented and its relation to other geophysical fields is discussed. A positive correlation was found between gravity and heat flow, and a negative one between crustal thickness and heat flow. A general conclusion could be drawn that the heat flow distribution over the Romanian territory seems to be governed by processes taking place in the upper mantle, rather than by the radioactive decay within the crust.     

唐山地震区地壳结构和构造:深地震反射剖面结果

1976年7月28日,在唐山地区发生了7.8级大地震.为了研究该区的地壳结构和断裂的深浅构造关系,2009年,我们在唐山市南部的丰南地区,跨唐山断裂带完成了1条道间距40m、炮间距200m、50次覆盖的深地震反射探测剖面.结果表明:研究区的地壳厚度为32 ～ 34km,莫霍面自东向西逐渐加深,在丰南县和宣庄镇之间,中-...     

河北邢束地区地壳上地幔的热作用

通过研究邢束地区的地温场、大地热流和其它地球物理资料,对该区的地温场分布、深部结构及其相互关系有了较深入的认识。研究证实:该区地温场具有明显的横向不均匀性,并与地壳上地幔结构有较清楚的对应关系。地温场的分布与构造的关系表明,凸起区与凹陷区相比,前者具有较高的热流值和较大的地温梯度。对该区地震分布与地温场的关系分析以及热应力的数学模拟结果说明,热应力在地震发生过程中具有重要作用。     

青藏高原东南缘热流估算及与地震活动相关性分析

青藏高原东南缘地区内部构造运动强烈,是地热资源发育与地震事件频发的活动地区.大地热流记录了发生在地球深部各种作用过程的热学信息,可以作为地质构造活动和地震活动研究的有效约束,但是大范围的热流数据测量很难实现,因此,本文根据居里面深度结合放射性元素分布等计算了青藏高原东南缘的大地热流分布.首先,通过地表放射性元素的分布计算出地表产热量的分布,然后,利用相关地热参数之间的关系迭代计算出该地区地壳上下层的热导率分布,最终估算出地表热流及地下不同深度处热流值的分布.本文结果表明:(1)青藏高原东南缘的大地热流位于44～108mW·m~(-2)之间,平均75mW·m~(-2),符合研究地区西南高、东北低的背景趋势,地壳内部热流值随深度的增加而降低.大部分地区地表热流异常与实际地热带分布相吻合,如川西、藏东南与滇西地区等地为地热高值区,川东和楚雄等地为热流低值区.(2)结合其他地球物理探测结果,总结了地壳内部热流与地震事件的联系:在地热梯度带地区,当两侧地层在一定深度范围内存在明显物性差异时,地震事件高发.     

郯庐断裂带是热异常带吗:来自断裂带南段热流的约束

郯庐断裂带是东亚最重要的断裂之一,在构造地质、岩石矿物、地震分布等领域得到了广泛的关注,然而少有针对郯庐断裂带地热学的研究.本文作者对郯庐断裂带南段7口钻井进行了系统测温,采用光学扫描法测试了6口钻井的142块岩心和13块露头样品的热导率,获得了6个高质量的热流数据.结合已发表的热流和地震剖面资料,我们获得了郯庐断裂带南段的岩石圈结构.研究表明,郯庐断裂带南段现今地温梯度从南到北有增大的趋势,介于21.8~30.3℃·km^-1.大地热流值介于44.0~81.7 mW·m^-2,平均61.4±10.8 mW·m^-2,表现为正常大地热流的特征,并非热异常带.最大热流值出现在庐枞盆地的大陆科学钻探井ZK03处,上地壳浅部极高的生热层很可能是高热流的主要因素.沿郯庐断裂南段地震带浅源地震发震带的底界和350℃等温面耦合较好,指示了深部结构的差异.     

共和盆地恰卜恰地热区现今地热特征

恰卜恰地热区位于青海共和盆地的东北部,是我国重要的具有干热岩地热资源勘探开发潜力的地区之一.自2013年起,不同的研究者针对该区开展了大量地球物理探测工作,然而现今地热场的研究相对较少.本文基于4口干热岩钻孔的稳态测温资料和81块岩芯样品的热导率测试数据,计算了研究区4个大地热流值.研究结果表明：研究区基底花岗岩层现今地温梯度为39.0~45.2℃·km^-1,平均值为41.3℃·km^-1,大地热流值介于93.3~111.0 mW·m^-2之间,平均值为102.2 mW·m^-2,与我国主要的克拉通型盆地（如柴达木盆地、四川盆地和鄂尔多斯盆地）和新生代裂谷型盆地（如渤海湾盆地）相比,该区属于青藏高原高热流背景下的局部异常高地温梯度和高大地热流区.分析认为,研究区高地热异常可能暗示共和盆地浅部（20 km以浅）存在局部异常热源体（岩浆囊）.     

One-Dimensional Thermal Modeling of the Eastern Pontides Orogenic Belt (NE Turkey)

The eastern Pontides orogenic belt is one of the most complex geodynamic settings in the Alpine–Himalayan belt due to the lack of systematical geological and geophysical data. In this study, 1D crustal structure and P-wave velocity distribution obtained from gravity modeling and seismological data in the area has been used for the development of the thermal model of the eastern Pontides orogenic belt. The computed temperature-depth profiles suggest a temperature of 590?±?60°C at a Moho depth of 35?km indicates the presence of a brittle-ductile transition zone. This temperature value might be related to water in the subducted crust of the Tethys oceanic lithosphere. The Curie temperature depth value of 29?km, which may correspond to the crustal magma chambers, is found 5–7?km below the Moho depth. Surface heat flow density values vary from 66.5 and 104.7?mW?m^?2. High mantle heat flow density value of 48?mW?m^?2 is obtained for the area should be related to melting of the lithospheric mantle caused by upwelling of asthenosphere.     

中朝地台东北缘地区的地震层析成像

根据中朝地台东北缘地区 (东经 1 1 7°0 0′— 1 2 6°0 0′ ,北纬 36°0 0′— 44°0 0′) 1 980— 1 997年的 380 0 0余条P波走时数据 ,利用正交投影法重建了该区地壳和上地幔的三维速度结构 .通过分析及同人工地震测深剖面的详细对比 ,证明了成像结果的可靠性 .结果表明 :中朝地台东北缘地区地壳上地幔介质存在显著的横向不均匀性 ,直至 1 2 0km深度处依然明显 ;地壳上部的速度图像清楚地反映了不同岩石单元的分布与该区不同性质的基岩分布基本吻合 ;从上、中地壳的速度图像中发现了研究区存在海城、朝阳、义县、丹东南、唐山等几个低速异常区(即速度逆反层区 ) ,其中海城、唐山、朝阳等地区的壳内低速层已由深地震测深资料所证实 ;研究区陆地发生的几次强震均发生于壳内低速层上方的高速脆性介质内 ,而渤海发生的强震 ,此现象不明显 ,但都发生于横向介质速度显著突变的位置 ;在地壳不同深度上发现了普兰店至山海关横跨渤海的北西向低速异常带 ;地震层析二维速度图像与深地震测深资料的对比表明 ,研究区利用地震层析成像技术 ,在一定条件下可以获得与人工地震测深相似的效果     

大陆下地壳层流作用及其大陆动力学意义

大量的地质和地球物理资料表明 ,年轻的大陆构造活动区的下地壳可能因热软化而出现透入性非地震式顺层韧性流动 ,这种下地壳层流作用驱动大陆上地壳发生地震式脆性断块运动 ,形成盆山格局 ,发生圈层耦合。大陆下地壳低粘度物质顺层流动可能是在地幔岩浆底侵作用为下地壳提供热能和添加幔源物质的基础上 ,并在地幔上升派生的重力和剪切力作用下 ,造成大陆下地壳热软化物质从盆地下部的幔隆区顺层流向相邻造山带之下的幔拗区。在下地壳层流过程中 ,地温场和速度场发生变     

The Lemnos 8 January 2013 (M w = 5.7) earthquake: fault slip,aftershock properties and static stress transfer modeling in the north Aegean Sea

We investigate mainshock slip distribution and aftershock activity of the 8 January 2013 M _w?=?5.7 Lemnos earthquake, north Aegean Sea. We analyse the seismic waveforms to better understand the spatio-temporal characteristics of earthquake rupture within the seismogenic layer of the crust. Peak slip values range from 50 to 64 cm and mean slip values range from 10 to 12 cm. The slip patches of the event extend over an area of dimensions 16?×?16 km². We also relocate aftershock catalog locations to image seismic fault dimensions and test earthquake transfer models. The relocated events allowed us to identify the active faults in this area of the north Aegean Sea by locating two, NE–SW linear patterns of aftershocks. The aftershock distribution of the mainshock event clearly reveals a NE–SW striking fault about 40 km offshore Lemnos Island that extends from 2 km up to a depth of 14 km. After the mainshock most of the seismic activity migrated to the east and to the north of the hypocenter due to (a) rupture directivity towards the NE and (b) Coulomb stress transfer. A stress inversion analysis based on 14 focal mechanisms of aftershocks showed that the maximum horizontal stress is compressional at N84°E. The static stress transfer analysis for all post-1943 major events in the North Aegean shows no evidence for triggering of the 2013 event. We suggest that the 2013 event occurred due to tectonic loading of the North Aegean crust.     

Tectonic modelling in the Bjørnøya West Basin of the Western Barents Sea1

The Bjøirnøya West Basin lies between latitudes 73° and 74°, longitudes 16°E and 18°E, contains at least 8 km of sediments deposited from the Late Jurassic, and is of considerable interest for hydrocarbon exploration. The Cenozoic extensional tectonics in the basin can be clearly seen from seismic data with normal faulting and from subsidence curves with rapid subsidence. The extension occurred during the Late Palaeocene with active extension lasting about 6 million years (m.y.) followed by thermal cooling. The tectonic subsidence within the study area shows a three-phase development: phase 1, synrift (58–52 Ma (million years before the present day)), is characterized by rapid subsidence; phase 2, postrift (52–5 Ma), by slow subsidence with occasional uplift; and phase 3 (5–0 Ma), by rapid subsidence. An adaptive finite-element model, with consideration of the radiogenic heat production in the lithosphere, has been used to model the subsidence and heat flow. The modelling of subsidence shows the β-factor distribution varying from 1.9 to 3.5 with an average of 2.4 for the uniform lithospheric extension. The heat-flow modelling predicts a rapid increase of heat flow during the Early Palaeocene. The maximum heat flow at about 52 Ma, which could be as much as 3.0 hfu (10^?6 cal/cm²/s), was followed by a decrease in heat flow. A plate-weakening model has been proposed to explain the rapid subsidence for the last 5 m.y. by flexure of the elastic lithosphere which is weakened by a decrease in elastic thickness caused by an increase of the temperature gradient in the lithosphere. The plate-weakening model predicts a heat-flow increase at 5 Ma of up to 2.0 hfu. Our study, using quantitative modelling of the tectonic subsidence, provides a partial (if not a full) understanding of the tectonic development and thermal evolution of the Bjønøya West Basin.     

初论华北地区的地壳低速层

本文根据华北地区人工地震测深的地震记录特征及得到的地壳速度结构和介质Q值结构,并结合其它地球物理资料,论述了华北地区壳内低速层的存在。通过分析对比,研究了与壳内低速层有关的一些现象,如构造运动、地震震源分布和地热异常等。在此基础上,对地壳内低速层的成因机制作了初步的探讨     

A possible mechanism of stimulation of seismic activity by ionizing radiation of solar flares

A possible mechanism of earthquake triggering by ionizing radiation of solar flares is considered. A theoretical model and results of numerical calculations of disturbance of electric field, electric current, and heat release in lithosphere associated with variation of ionosphere conductivity caused by absorption of ionizing radiation of solar flares are presented. A generation of geomagnetic field disturbances in a range of seconds/tens of seconds is possible as a result of large-scale perturbation of a conductivity of the bottom part of ionosphere in horizontal direction in the presence of external electric field. Amplitude-time characteristics of the geomagnetic disturbance depend upon a perturbation of integral conductivity of ionosphere. Depending on relation between integral Hall and Pedersen conductivities of disturbed ionosphere the oscillating and aperiodic modes of magnetic disturbances may be observed. For strong perturbations of the ionosphere conductivities amplitude of pulsations may obtain ~10² nT. In this case the amplitude of horizontal component of electric field on the Earth surface obtains 0.01 mV/m, electric current density in lithosphere –10^–6 A/m², and the power density of heat release produced by the generated current is 10^–7 W/m³. It is shown that the absorption of ionizing radiation of solar flares can result in variations of a density of telluric currents in seismogenic faults comparable with a current density generated in the Earth crust by artificial pulsed power systems (geophysical MHD generator " Pamir-2” and electric pulsed facility " ERGU-600”), which provide regional earthquake triggering and spatiotemporal variation of seismic activity. Therefore, triggering of seismic events is possible not only by man-made pulsed power sources but also by the solar flares. The obtained results may be a physical basis for a novel approach to solve the problem of short-term earthquake prediction based on electromagnetic triggering phenomena.