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1.
Deformation mechanism of the eastera Tibetan plateau: Insights from numerical models 总被引：1，自引：1，他引：0 
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下载免费PDF全文 青藏高原东缘的地壳结构是两种主流青藏高原隆升模式争辩的焦点之一.中下地壳流曾经被认为是高原东缘隆升的主要构造驱动力,但是中上地壳之间低阻低速层的发现及其与2008 Ms8.0汶川地震良好的对应关系表明,高原东缘具有向东刚性挤出的可能性.然而大部分关于龙门山断裂的数值模拟仍建立在下地壳流的基础上,仅将低阻低速层作为断裂的延续或是弱化地壳物性参数的软弱层,而非能够控制块体滑动的“解耦层”,也没有考虑到刚性块体变形中的断裂相互作用.本文建立了包含相互平行的龙门山断裂与龙日坝断裂的刚性上地壳模型,用极薄的低阻低速层作为块体滑动的解耦带,采用速率相关的非线性摩擦接触有限元方法,基于R最小策略控制时间步长,计算了在仅有侧向挤压力作用下,低阻低速层对青藏高原东缘的刚性块体变形和断裂活动的作用.计算结果显示,低阻低速层控制了刚性块体的垂直变形和水平变形分布特征.在侧向挤压力的持续作用下,在低阻低速层控制下的巴颜喀拉块体能够快速隆升,而缺乏低阻低速层的四川盆地隆升速度和隆升量均极小,隆升差异集中在龙门山断裂附近,使其发生应力积累乃至破裂.龙日坝断裂被两侧的刚性次级块体挟持着一起向南东方向运动,但该断裂的走滑运动分解了绝大部分施加在块体边界上的走滑量,使得相邻的龙门山次级块体的走滑分量遽然减少,也使得龙门山断裂表现出以逆冲为主,兼有少量走滑的运动性质.本文所得的这些计算结果显示了在缺乏中下地壳流,仅在低阻低速层解耦下刚性块体隆升过程及相关断裂活动,提供了青藏高原东缘刚性块体挤出的可行性,为青藏高原东缘隆升机制的研究讨论提供了重要依据. 相似文献
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青藏高原东缘的地壳结构是两种主流青藏高原隆升模式争辩的焦点之一.中下地壳流曾经被认为是高原东缘隆升的主要构造驱动力,但是中上地壳之间低阻低速层的发现及其与2008 MS8.0汶川地震良好的对应关系表明,高原东缘具有向东刚性挤出的可能性.然而大部分关于龙门山断裂的数值模拟仍建立在下地壳流的基础上,仅将低阻低速层作为断裂的延续或是弱化地壳物性参数的软弱层,而非能够控制块体滑动的"解耦层",也没有考虑到刚性块体变形中的断裂相互作用.本文建立了包含相互平行的龙门山断裂与龙日坝断裂的刚性上地壳模型,用极薄的低阻低速层作为块体滑动的解耦带,采用速率相关的非线性摩擦接触有限元方法,基于R最小策略控制时间步长,计算了在仅有侧向挤压力作用下,低阻低速层对青藏高原东缘的刚性块体变形和断裂活动的作用.计算结果显示,低阻低速层控制了刚性块体的垂直变形和水平变形分布特征.在侧向挤压力的持续作用下,在低阻低速层控制下的巴颜喀拉块体能够快速隆升,而缺乏低阻低速层的四川盆地隆升速度和隆升量均极小,隆升差异集中在龙门山断裂附近,使其发生应力积累乃至破裂.龙日坝断裂被两侧的刚性次级块体挟持着一起向南东方向运动,但该断裂的走滑运动分解了绝大部分施加在块体边界上的走滑量,使得相邻的龙门山次级块体的走滑分量遽然减少,也使得龙门山断裂表现出以逆冲为主,兼有少量走滑的运动性质.本文所得的这些计算结果显示了在缺乏中下地壳流,仅在低阻低速层解耦下刚性块体隆升过程及相关断裂活动,提供了青藏高原东缘刚性块体挤出的可行性,为青藏高原东缘隆升机制的研究讨论提供了重要依据. 相似文献
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本文概述了在西藏高原长达450公里左右的南北向测线上取得九次湖中水下爆炸地震记录的处理结果。通过数字处理、拟合和反演等计算,得出了该地区地壳与上地幔的成层结构和速度分布。 结果表明,该区整个沉积岩层厚约3-5公里,雅鲁藏布江以北到当雄地带,地壳巨厚达70-73公里;江南地区为68-45公里,并逐渐向南翘起。在成层地壳介质中发现下地壳中存在低速层,厚约10公里,速度为5.64公里/秒。分析认为,高原地形与巨厚地壳的形成是印度洋板块与欧亚板块碰撞以及长期挤压和内部物质运移的结果。 相似文献
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青藏高原岩石圈多层构造应力场 总被引：3，自引：0，他引：3
青藏高原构造应力场可按岩石圈下层、多震层和浅层地壳区分为三层。除了震源机制解方法和井孔原地测量方法可分别用于推测多震层和浅层的应力状况外,还可根据下层塑性流动网络,采用平分网络共轭角的方法估计下层的应力方向。对比岩石圈下层与上层(多震层)的构造应力场,其结果表明: 由于板块边缘驱动力主要通过下层的网络状流动实现其远程传递,故在总体作用趋势上,上层的应力方向受控于下层;又由于高原靠近喜马拉雅驱动边界,部分驱动力直接沿上层传递,致使局部地区上、下层应力方向相差显著。 相似文献
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本文提出了地壳的构造运动，本质上是地壳与岩层的均衡差运动。它主要由重力作用产生的三种形式的差应力所推动：一是地球整体意义上的真正的重力均衡差应力；二是水平向的均衡差应力；三是垂直向的均衡差应力。本文讨论了这三种差应力产生的机制与规律，三种均衡差运动的规律与地壳实际构造运动普遍存在的对应关系，此外还讨论了地壳构造运动不息的主要原因。 相似文献
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南海北部陆缘地震带的深部结构和孕震机制 总被引：6，自引：2，他引：4
南海北部陆缘地震带的地震震源基本上分布在地壳内６￣１３ｋｍ和１７￣２２ｋｍ两个深度范围内,发震层恰好位于区内中地震低速层和下地壳低速层的顶部附近。地壳深部结构的不稳定性以及侧向应力和垂向应力共同作用下的平移正断层错动,可能是该带地震孕育、发生的一种重要机制。 相似文献
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青藏高原现代构造应力状态及构造运动的三维弹粘性数值模拟 总被引：15，自引：0，他引：15
根据现有的地球物理和地质资料，建立了青藏高原三维弹－粘性有限单元模型，模拟了由地震震源机制解和地质调查资料推断的高原岩石圈的构造应力状态，并模拟岩石圈物质的运动特征，着重考察高原物质向东南方向运动的可能性，并把模拟结果与实际资料结果进行比较。施加载荷时考虑了处于Ａｉｒｙ均衡条件下的高原地壳的重力势能和底面浮力，以及水平边界的挤压作用，根据试错法的试验结果，能够符合观测结果的模型边界条件表明：①印度 相似文献
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重力均衡的现象证明,地壳或上地幔内部必有水平方向的物质流动,它产生重力补偿作用,并且最终达到平衡状态。上地幔的低速层（其顶面在大陆地区约为120公里,在海洋地区约为60公里）可能是产生全球范围内重力补偿作用的一个重要层。地壳内部如有重要的补偿层,莫霍界面的深度将趋一致。莫霍界面深度的变化,说明地壳内部必无较大范围的补偿层。以莫霍界面为顶面的上地幔部分,对于重力补偿是否起作用呢?这个问 相似文献
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本文系统地求解了不连续走时曲线的反演问题.所得到的解答表明,除了在低速层(若存在)内,其余各处的速度分布以及低速层的厚度均可唯一地确定.本文指出Slichter(1932)关于低速层厚度上界的推导和Gerver-Markushevich(1966)的反演公式是不合理的. 相似文献
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《Journal of Geodynamics》1999,27(4-5):567-583
Upper mantle P and S wave velocities in the western South America region are obtained at depths of foci from an analysis of travel time data of deep earthquakes. The inferred velocity models for the Chile–Peru–Ecuador region reveal an increase of P velocity from 8.04 km/s at 40 km to 8.28 km/s at 250 km depth, while the S velocity remains almost constant at 4.62 km/s from 40 to 210 km depth. A velocity discontinuity (probably corresponding to the L discontinuity in the continental upper mantle) at 220–250 km depth for P and 200–220 km depth for S waves, with a 3–4% velocity increase, is inferred from the velocity–depth data. Below this discontinuity, P velocity increases from 8.54 km/s at 250 km to 8.62 km/s at 320 km depth and S velocity increases from 4.81 km/s at 210 km to 4.99 km/s at 290 km depth. Travel time data from deep earthquakes at depths greater than 500 km in the Bolivia–Peru region, reveal P velocities of about 9.65 km/s from 500 to 570 km depth. P velocity–depth data further reveal a velocity discontinuity, either as a sharp boundary at 570 km depth with 8–10% velocity increase or as a broad transition zone with velocity rapidly increasing from 560 to 610 km depth. P velocity increases to 10.75 km/s at 650 km depth. A comparison with the latest global average depth estimates of the 660 km discontinuity reveals that this discontinuity is at a relatively shallow depth in the study region. Further, a velocity discontinuity at about 400 km depth with a 10% velocity increase seems to be consistent with travel time observations from deep earthquakes in this region. 相似文献
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Data are presented from deep seismic sounding along the strike of the Balearic Islands carried out in 1976. The interpretation of the data gives the following results: A sedimentary cover of 4 km around Ibiza to 7 km under Mallorca overlies the crystalline basement. This basement with a P-wave velocity of 6.0 km/s at the top reaches a depth of at least 15 km under Ibiza and 17 km under Mallorca with an increase to 6.1 km/s at these depths. The crust-mantle boundary lies at a depth of 20 km and 25 km, respectively. A well documented upper-mantle velocity of 7.7 km/s is found along the entire profile. The Moho rises to a depth of 20 km about 30 km north of Mallorca and probably continues rising towards the center of the North Balearic Sea. The newly deduced crustal structure together with previously determined velocity-depth sections in the North Balearic Sea as well as heat flow and aeromagnetic data can be interpreted as an extended rift structure caused by large-scale tensional processes in the upper mantle. The available data suggest that the entire zone from the eastern Alboran Sea to the area north of the Balearic Islands represents the southeastern flank of this rift system. In this model the provinces of Spain along the east coast would represent the northwestern rift flank. 相似文献
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利用布设在长白山地区的19个PASSCAL宽频带流动地震台站近一年的远震记录和布设在镜泊湖火山区14个宽频带轻便数字地震仪三个月的远震记录,共得到高质量的423个接收函数,通过对这些接收函数的共转换点叠加得到研究区的间断面的分布及形态.研究结果表明,研究区存在410、520km和660km间断面.410km和660km间断面较为连续且具有正相关性质,410km间断面在长白山天池火山下局部上隆,660km间断面具有复杂的多界面性质.410km和660km之间的过渡带厚约250km,接近全球平均水平.珲春深震区下660km界面下陷,其上还有多组震相,这些震相在珲春深震区东西两侧不连续,推测西太平洋板块至少已经俯冲到欧亚大陆下的上地幔过渡带中.410km间断面在长白山火山区下局部上隆,660km间断面具有的复杂结构和珲春深源地震的发生均与俯冲板块在过渡带中的活动有关. 俯冲板块在受到660km间断面的强大阻力后,在660km间断面之上变为近水平扩张.推测在欧亚大陆下西太平洋板块的最前端可能已经不是一个完整的整体,或许是由几个有一定联系的板块残片组成. 相似文献
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Clouds affect local surface UV irradiance, even if the horizontal distance from the radiation observation site amounts to several kilometers. In order to investigate this effect, which we call remote clouds effect, a 3-dimensional radiative transfer model is applied. Assuming the atmosphere is subdivided into a quadratic based sector and its surrounding, we quantify the influence of changing cloud coverage within this surrounding from 0% to 100% on surface UV irradiance at the sector center. To work out this remote clouds influence as a function of sector base size, we made some calculations for different sizes between 10 km × 10 km and 100 km × 100 km. It appears that in the case of small sectors (base size 20 km × 20 km) the remote clouds effect is highly variable: Depending on cloud structure, solar zenith angle and wavelength, the surface UV irradiance may be enhanced up to 15% as well as reduced by more than 50%. In contrast, for larger sectors it is always the case that enhancements become smaller by 5% if sector base size exceeds 60 km × 60 km. However, these values are upper estimates of the remote cloud effects and they are found only for special cloud structures. Since these structures might occur but cannot be regarded as typical, different satellite observed cloud formations (horizontal resolution about 1 km × 1 km) have also been investigated. For these more common cloud distributions we find remote cloud effects to be distinctly smaller than the corresponding upper estimates, e.g., for a sector with base size of 25 km × 25 km the surface UV irradiance error due to ignoring the actual remote clouds and replacing their influence with periodic horizontal boundary conditions is less than 3%, whereas the upper estimate of remote clouds effect would suggest an error close to 10%. 相似文献
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Previous studies have shown that the Pacific geoid and gravity fields exhibit lineated anomalies, trending approximately in the direction of absolute plate motion over the underlying mantle. Because the undulations obliquely cross fracture zones they have often been attributed a convective origin. Recently, lithospheric boudinage caused by diffuse extension has been proposed as a possible mechanism. We have examined the undulations in the free-air anomalies, geoid and bathymetry over a portion of the Pacific Plate to determine quantitatively how the undulations are related to plate motion. We compare the observed data to an axisymmetric, sinusoidal undulation defined in an arbitrary frame of reference; in particular, we seek the north pole of this reference frame that maximizes the correlation between data and model. Poles that are close to the Pacific hotspot pole represent copolar undulations possibly related to plate motion. The distance between the best-fitting poles and the hotspot pole is determined as a function of undulation wavelength and reveals several minima (with distance < 10°) for discrete geoid wavebands centered on wavelengths of 160 km, 225 km, 287 km, 400 km, 660 km, 850 km, 1000 km and 1400 km. Bathymetry data have copolar bathymetric expressions as well, giving an implied admittance of 2–3 m/km. The most co-polar geoid/bathymetry undulations (with poles within 2–3° of the average Pacific Euler pole) have wavelengths of 280 km and 1050 km, respectively. The latter could have a convective origin or be related to the spacing of hotspot swells. The former may reflect lithospheric boudinage formed in response to diffuse extension, but could also have a dynamic origin since flexural dampening may only have attenuated the bathymetric amplitude by 50% or less. Radiometric dating of volcanic ridges found in the troughs of prominent gravity lineations gives ages that correlate well with documented changes in Pacific and Indo/Australian Plate motion, suggesting the ridges formed in response to intermittent plate boundary stresses and not as a direct consequence of small-scale convection or diffuse extension. 相似文献
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用射线分布分析法对伽师强震群区的高分辨折射地震剖面资料进行了更进一步的分析处理， 得到了伽师强震群区更完整的基底界面结构特征. 结果表明，在伽师强震群区地壳上部存在两个明显的结构界面:第一个界面的结构连续、完整，其埋深变化不大， 在2.6～3.3 km之间，为一向天山方向逐渐抬升、 近平直的倾斜界面；第二个界面的埋深变化较大， 在8.5～11.8 km之间，为古老的塔里木盆地结晶基底. 在约37 km桩号附近结晶基底有近2.5 km的深度突变， 推断可能是伽师强震群区超基底断裂所致. 以该断裂为界，结晶基底分为西南、东北两段. 每段内界面的埋深变化不大， 西南段的埋深约11.5 km， 东北段的埋深约为8.5～9.0 km，该段在从西南向东北整体抬升的背景上略有上隆，反映出在塔里木地块西北缘特殊的构造环境下上部地壳的变形特征. 相似文献
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本文利用中国地震台网及ISC提供的区域地震和远震的P波走时数据,重建了中国大陆及其邻近地区的三维速度图象。 主要结果是:1.本文给出的速度图象揭示了中国大陆及其邻近地区的地壳和上地幔速度存在明显的横向不均匀性,这种不均匀性甚至在下地幔的1100km深度还依然存在。上地幔的速度图象同地表已知的地质构造特征的相关性可以追踪到110km,从220km以下很难找到它们之间的明显关系。2.45-0km和45+0km深度处的速度图象明显地表示出中国大陆的地壳厚度可以102.5°E附近为界分为两部分:其东部地壳薄,厚度都小于45km;西部有一条自若尔盖-松潘（34°N,102.5°E附近）向西北沿38°N往西至塔里木盆地南缘的分界线;其南部除滇西南之外,整个青藏高原的地壳厚度都大于45km;其北部除天山山脉之外,地壳厚度一般不大于45km.3.110km深度处的速度图象表明,速度异常呈块状分布。同中国大地构造分区略图比较之后发现,其中,扬子准地台和塔里木地台对应于高速区,中朝准地台则大都表现为低速异常;华南褶皱系为低速区,青藏地块南缘喜马拉雅和冈底斯念青唐古拉褶皱系则表现为高速异常。4.220km深度处的速度图象表明,中国大陆相当多的地区软流层有明显的显示。5.同450km和45+0km的速度图象一样,400km和600km的速度图 相似文献
18.
1303年在山西洪洞附近发生的8级巨大地震, 是中国根据现存较为详细的文献记载史料所确定的最早的一次8级地震。 这次地震距今已有700多年的历史, 而地震所在区域至今仍有持续不断的小地震活动。 本文根据地震破裂区1981年至2013年的中小地震精定位地震目录, 采用震源断层面拟合方法, 反演得到了1303年山西洪洞地震的震源断层面参数: 走向19.3°、 倾角88.5°、 滑动角-170.0°。 断层面长75.5 km, 宽26.2 km, 深度为地下11.12 ～37.35 km。 将地震破裂区的地震精确定位资料以近东西向的洪洞断裂为界划分为地震北段和地震南段, 分段进行地震震源断层拟合, 反演得到洪洞地震北段震源断层面参数: 走向13.7°、 倾角76.6°、 滑动角-157.6°。 断层面长32.7 km, 宽21.7 km, 深度为地下11.97～32.86 km; 南段震源断层面参数: 走向20.3°、 倾角87.1°、 滑动角-154.6°。 断层面长45.9 km, 宽16.6 km, 深度为地下9.32 km～25.50 km。 无论是分段还是不分段, 反演得到的洪洞地震震源断层均是右倾的近直立断层, 属于右旋走向滑动性质。 分段计算得到的地震北段震源断层深度比南段更深, 将反演得到的震源断层与临汾盆地深部构造最新研究成果进行了分析对比, 北段震源断层深度及倾角大小与深地震剖面推测得到的深大断裂几乎相同。 震源断层在地表的投影与洪洞地震的高烈度区能够较好地对应。 相似文献
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Basement interface structural characteristics beneath Jiashi strong earthquake swarm area in Xinjiang, China 总被引：1，自引：0，他引：1
The seismic data obtained from high resolution seismic refraction profile in Jiashi strong earthquake swarm area in Xinjiang, China were further processed with ray hit analysis method and more complete basement interface struc-tural characteristics beneath Jiashi strong earthquake swarm area were determined. The results show that there are two clear basement interfaces at the upper crust in Jiashi strong earthquake swarm area. The first one with buried depth ranging from 2.6 km to 3.3 km presents integral and continuous structure, and it appears an inclined plane interface and smoothly rises up toward Tianshan Mountain. The second basement interface with buried depth from 8.5 km to 11.8 km, is the antiquated crystalline basement of Tarim basin. Near the post number of 37 km, the bur-ied depth of the crystalline basement changed abruptly by 2.5 km, which maybe result from an ultra crystalline basement fault. If taking this fault as a boundary, the crystalline basement could be divided into two parts, i.e. the southwestern segment with buried depth about 11.5 km, and the northeastern segment with buried depth approxi-mately from 8.5 km to 9.0 km. That is to say, in each segment, the buried depth changes not too much. The north-east segment rises up as a whole and upheaves slightly from southwest to northeast, which reflects the upper crustal deformation characteristics under the special tectonic background at the northwestern edge of Tarim basin. 相似文献