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[转载]汶川地震成因的龙门山断裂带异常高压天然气体力源简述

已有 2207 次阅读 2016-3-1 20:20 |系统分类:论文交流|文章来源:转载

汶川地震成因的

龙门山断裂带异常高压天然气体力源简述

岳中琦

编者按:遵照倡导自由探索,鼓励学术争鸣的方针,为科学家萌芽时期的学术思想、观点提供交流平台,本刊特此发表了香港大学岳中琦教授就汶川地震成因的论文,希望大家就此问题进一步加以讨论

《岩石力学与工程动态》——2009年第2期(总第86期)第45-50页

 

 

在大量资料和证据的基础上,在众多不同学科专家的指导和帮助下,笔者认为传统断层带长期地形变力源而突然断裂弹性回跳的地震成因理论无法解释汶川地震的众多地震地质现象。因而,在进一步研究龙门山地质构造演变历史基础上,笔者在2008年9月15日向香港四家报社提出了汶川地震的异常高压天然气体破裂、膨胀、气化、岩爆与喷发的成因机制。这一天然气成因机制假设基本上可以很好解释我和我朋友、同事们迄今所调查到的、在震前、震时和震后发生的各种地震地质现象。它可以简洁地表述如下:

众所周知,四川盆地是中国三大天然气生产区之一,已探明有1.2万亿立方米天然气。龙门山前川西坳陷存在大量圈闭构造,3千米以下的巨厚地层含大量异常高压天然气体。在侏罗纪以前,龙门山地区和四川盆地一样处于海洋和海岸环境,有巨厚产油气沉积。龙门山经历了各种板块构造运动,这个前陆逆掩断层带压了大量海相岩层,如巨厚煤层、碳质岩、页岩等生气油地层体系,有生成大气田的物源和环境。自侏罗纪以来,龙门山进一步经历了2亿年的早期陆相沉积、构造断裂、和抬升侵蚀运动。总体呈东北-西南走向全长约500km宽约50 km的龙门山断裂-不整合带也可划分为前山、中央和后山叠瓦状推覆断裂不整合带。

现今龙门山叠瓦状推覆逆掩断裂带由不少坚硬岩石块体组成,在整体上形成了刚性岩体构造和构架。数百公里长的叠瓦状推覆断裂不整合接触使得龙门山断裂带或不整合接触带深处(特别是山涧盆地和大沟谷深部10-20千米上下)存在串珠状分布的、局部封密的大型缝洞空隙闭圈构造。天然气的不断输入使得它们成了高压气囊。

龙门山断裂带长期受到区域性西北-东南方向挤压形成高压岩体,这使得地下深部中温(摄氏200-300度)高压地层不断生成天然气体,且被运移到、挤逸入压强相对较低的大型气囊中储存。随着时间,被挤逸入气囊内的天然气体也就越来越多,气体压强也就逐渐增大。高压气体对气囊围岩作用也逐渐增大,使得围岩弹性变形能增多。区域应力场和刚性块体构造限制了气囊外围岩体产生的大应变并发生体变,同时使得中温高压地层中天然气不断增生和不断灌入这些气囊中。囊内天然气体得到不断地增多和增强,成异常高压气体(估计压强达200-300MPa),同时,也缓慢挤推围岩。

终于,在2008年5月12日下午2时28分,位于映秀山涧盆地深部的大型缝洞空隙闭圈构造内的异常高压气体打破整体力学平衡。囊内异常高压气体沿断裂或不整合面岩体强度低的周边方向突然将岩体致裂、剪胀开上覆岩层(P波初动)。异常高压气体在地下快速(估计速度可达1-3千米每秒)向上方四周致裂剪胀、飞移、流动和扩散。它逐个使得位于彭州九峰山-绵竹红白、安县高川-晓坝、擂鼓-北川城、陈家坝、青川南坝-东河口等地下深部高压气囊打破力学平衡。这些囊内异常高压天然气体也对上覆岩层的致裂和胀开,在地下地下裂隙和断层等面状通道快速剪胀开地层、飞移、流动和扩散。高压气体通过后,岩层再弹性反弹、错动,释放弹性变形能。高压气体在地下裂隙和断层面状通道的飞速破裂剪胀开地层和运移流动形成了近场巨大的轰隆隆的地声和远场的弹性体波。

深部异常高压气体破裂开抗垃抗剪低的地层(如煤层)或沿断层、裂隙和不整合面通道而快速上升、扩散,它们的体积因地层压力的降低而快速膨胀、弥漫或集中。数秒钟之内,高压气体流达近地表地层5-2千米深度内,高压气体因通道变小或堵塞而受阻,速度减慢聚集,进而四处冲填、气化、顶起、抬升、晃动、摆动和扭动上覆地层,同时,与向下作用的岩体重力一道,造成了瞬间广大且局部孤立集中的近场地面波动和破毁,以及时间长且复杂的远场弹性地震波(或许是远场面波)。这一高压气体膨胀(体积可瞬间增大数十、数百至数千倍)、顶起和气化引起的巨大地面震荡波动过程是在十到数十秒钟内瞬间完成的,是随着地下气体逸出、喷出地面、进入空气(压强0.1MPa)的增多和完成而结束的。

同时,局部集中高压气体将上方的岩体致裂挤喷突出地表,发生地面张开、闭合和开花,岩爆和岩体的抛射,造成山体崩塌、滑坡、滚石,河床阶地谷地的地鼓、抬升、裂开和逆冲,孤立建筑物竖向破坏或瞬间摧毁、顿时巨大尘土腾空而起,以及大面积的河沟、山坡和河水面上白色气体溢出或白色粉尘飞扬。在小部分山地,地下溢出、喷出到空气中的天然气体高度地弥漫、混合于空气中,形成气体瞬间爆炸和燃烧。这种混合气体的瞬间燃烧形成了地光。在有些地方,高压气体带着煤等矿物岩石粉尘冲天而黑暗天空,黄烟弥漫,尘土遮天蔽日。进入空气的气体和粉尘又慢慢地向高空运移和聚集成厚厚的云团。在地震当天晚上,龙门山极震区和周边广大范围有中到大雨,局部地方有暴雨。一直到第三天晚(2008年5月14日晚),降雨才停止。

特别地,龙门山区和山前的都江堰、彭州、什邡、绵竹、安县、北川、青川等地区近地表浅层存在有不少零星孤立垂向分布的可释放瓦斯薄煤层(或煤线)和低抗张剪强度的矿物(如生石灰、磷矿等)。它们可作为异常高压天然气高速流动、喷出和溢出的地表通道,同时很容易地被高压天然气体致裂和致爆,造成强烈地震动和煤层和矿物破坏、瓦斯突出爆炸和粉尘,进一步造成大面积局部小场地的毁灭性破坏和灾难。

在部分异常高压天然气体挤破推开岩层飞逃出气囊后,气囊内的气体压强迅速降低、挤推力速减。从而,开口两侧地层在原有水平挤压地应力的作用下而弹性闭合,又关闭了囊内大量天然气体。囊内和地下关闭留存的高压气体又可在岩体中聚集,生气地层因力学破碎和变形以及应力场的变化而又更大量快速地产生气体,从而气体再聚集而产生余震和为未来大地震作准备。随着时间的推移,龙门山断裂带地下囊内天然气体又逐渐增多、压强也逐渐增大,或许在若干年后又可发生大地震。

笔者进一步总结出如下的构造地震孕震形成的必要和充分条件:断层和盆地等深部地质构造是地震的必要条件,提供了高压天然气形成深部地下缝洞空间、岩层爆破和气体瞬间上升的地质和空间环境。天然气体在深部构造带聚集、积累、增生和高压是充分条件,提供了地震发震的长期力源和巨大岩体弹性变形能和高压气体内能的能源。构造地震是断陷沉积盆地深部缝洞高压天然气体沿低强度面致上升破裂爆破岩土体的瞬间变化过程。

再进一步地,笔者总结出如下的强地震极震区人们的体验:先听到一阵由远而近的轰隆隆地声,见到地光闪烁。之后,才感到地面的震动、晃动,且加剧,从上下起伏晃动到变成左右摇摆,坚硬的大地就像被狂风激怒的大海翻滚着、咆哮着,同时,飞砂走石、山崩地裂,天昏地暗。过了十多秒,剧烈的震动逐渐趋缓,似乎又从海上回到了陆地,能稳当地坐在地上了。笔者再在上述构造地震孕震形成的必要和充分条件的基础上,提炼出如下与极震区体验过程相对应的强地震形成过程机理:地震发震过程是在重力和构造应力场配合作用下的上升异常高压气体和岩土体间的瞬态相互作用变化完成过程。它包括深部异常高压气体破裂、胀开和错断岩体,地下深部高速运移、迅速聚集、扩散和膨胀上覆地层,顶起、抬起上覆地层,冲填、气化和液化上覆地层,晃动、摆动和扭动上覆地层,错断、推断、撕裂和抛出地表地层,和逸出、喷发和混合到大气层中,混合气体或再有瞬间燃烧闪光。这个极震区瞬时完成的岩土体变化运动过程也以弹性地震波形式向外快速传播。

The Source of Energy Power directly Causing the May 12 Wenchuan Earthquake: Huge Extremely Pressurized Natural Gases Trapped in Deep Longmen Shan Faults

Abstract

The Wenchuan Earthquake in Longmen Shan or Dragon’s Gate Mountains on May 12, 2008 in Sichuan, China is a great earthquake of a magnitude 7.9 by the U.S. Geological Survey or 8.0 by the China Earthquake Administration.  The following question must be asked and answered: what caused the devastating Wenchuan Earthquake? !

To many people, it may not be a question or has been definitely answered. Many people believe that the earthquake occurred due to the elastic rebounding of the Longmen Shanfaults (i.e., tectonically related northeast striking thrust faults on the northwestern margin of the Sichuan Basin), as a result of the convergence of crustal material slowly moving from the high Tibetan Plateau against the strong crust underlying the Sichuan Basin and Southeastern China in association with the northward convergence of the Indian Plate against the Eurasian Plate.

But, many observed natural phenomena cannot be explained consistently and reasonably using the classical elastic rebound theory of earthquake in association with the Longmen Shan fault.  These phenomena happened before, during and after the Earthquake.  One of the extremely unusual and rare phenomena is the occurrence of many catastrophic deep-seated landslides during quaking. The catastrophic landslides were huge and happened only at some localized and isolated sites on both sides of the 300 km long fault line. Their surrounding and adjacent mountain slopes, however, had only some comparably small landslides or even remained green and untouched.

Based on many evidences and facts, the author has found an unexpected, unbelievableand absolutely new answer to the question. The Earthquake was caused by instantaneous fracturing, expanding, lifting, bursting and exploding of huge extremely pressurized natural gases trapped in deep Longmen Shan fault zones from Wenchuan to Beichuan and further to Qingchuan. Consequently, all of the observed natural phenomena so far can be explained consistently and logically. Details will be published in the near future.  It is also noted that this finding would have a significant implication to the correct understanding of the mainshock and aftershocks and their prediction and prevention of many other strong earthquakes in China and aboard either in the past or in the future.


1:地震瞬间形成的唐家山堰塞坝

Fig.1 Tangjia Shan quake dam site

  (注:原坡度仅33º的岩石山体发生巨大垮塌,体积2千万立方米。但是,四周附近山体没有或仅有较小破坏。表明地震时巨大瞬态动能集中打击到这个破坏山体。Note: A huge portion of the mountain with slope angle 33º collapsed of a volume 2×107m3. However, its adjacent mountains had small failures or remained untouched. A huge dynamic energy application was instantly focused to the isolated mountain area.

 

2:陈家坝地震瞬间形成的喷出爆破炕和地下喷出的5000年前古树杆

 Fig.2 Gas eruption site and erupted ancient tree trunks at Chan Jia Ba Site

 (注:2a:地震一周内古树仍埋在破碎岩体中; 2b:近处堆在一起的古树和远处喷出爆破炕全景。共有17根长度8米、直径1米古树杆同破碎的岩土体一道被喷出地面。由中国科学院广州地球化学研究所AMS-14C制样实验室和北京大学核物理与核技术国家重点实验室联合完成的一树干样品14C数据测试年龄为5217±25a B.P.Note: 2a:  Ancient tree trunk still buried partially in the erupted rock debris one week after the Earthquake2b: A far distance view of the erupted slope site behind the erupted ancient tree trunks piled together by rescue engineering. A total of 17 ancient tree trunks of length 8 m and diameter 1 m erupted out of the ground.  The 14C age of a tree trunk specimen is 5217±25 a B.P., tested by the joint effort of Guangzhou Institute of Geochemistry, Chinese Academy of Sciences and State Key Laboratoryof Nuclear Physics & Technology, Peking University) 

 

3:地震瞬时拍录的龙门山断裂带某山地气体爆炸喷出和空中燃烧

Fig.3: Video recorded natural gas erupting and exploding and firing at a site in Longmen Shan fault zone

(注:3b图片比3a图片仅晚1.55; 参见网上录像;The image in 3b is 1.55 second later than that in 3amade from the video at http://v.ku6.com/show/kb-lNwWaXCXxw8JX.html) 

 

4:地震瞬时拍录的龙门山断裂带一块气体正在喷出的植被山坡岩土体

Fig.4: Video recorded the moment of a vegetated hill slope site being erupted by natural gas in Longmen Shan fault zone

(注:4b图片比4a图片仅晚2.12;参见网上录像;The image in 4bis 2.12 second later than that in 4amade from the video at http://js.pp.sohu.com/ppp/mv/swf200811281417/Main.swf?id=1111353&type=Singleton&domain=out&skin=4&hostname=http%3A%2F%2Fvideo.baidu.com%2Fv%3Fct%3D301989888%26rn%3D20%26pn%3D0%26db%3D0%26s%3D0%26fbl%3D1024%26word%3D%25B5%25D8%25D5%25F0%2B%25CA%25B5%25C5%25C4)

5:笔者在安县高川乡大光包地震瞬间形成的最巨大喷出爆破破碎体考察

Fig.5  The author at the Da Guang Bao huge strock debris site of instant gas eruption and explosion during Wenchuan Earthquake

   (瞬间形成纵向长4.2km,宽3.2 km,面积6.2 km2的滑坡堆积区,堆积体最大厚度达690 m,滑坡体体积7.42×109m3。估计需要1百万吨TNT炸药的能量,相当6级地震。The huge strock debris site was formed instantly, occupied an area of 6.2 km2 of long 4.2 km and wide 3.2 km, had the thickness up to 690 m and the rock debris volume is of 7.42×109m3. It is estimated to need a million tons of TNT energy, equivalent to an earthquake of magnitude 6.2.)

   2008512日地震发生以来,众多老师、朋友和同事给与笔者非常多的极其有价值的指导、帮助、支持、关心、批评和讨论。他们分别工作在中科院地質与地球物理研究所,中科院遥感应用研究所,中石化-西南分公司勘探开发研究院,中国地震应急搜救中心,中国地震台网中心,四川省地震局,成都理工大学,中科院和水利部成都山地災害与环境研究所,北京大学地球物理学系、地质学系,中国地震局地质研究所,清华大学土木水利学院,中国地质大学(北京)水资源与环境学院,中国地质调查局,大连理工大学,西南交通大学,四川大学,长江水利委员会长江科学院,中国水利水电科学研究院,山东大学,山东科技大学,等等。笔者在此衷心感谢他们!笔者也感谢傅冰骏教授和方祖烈教授邀请在《中国岩石力学与工程学会动态》发表本篇短文。

Acknowledgements

The author thanks many friends and colleagues who gave him invaluable advices, helps, assistances, discussions and information and supports during the investigation.They work respectively at Institute of Geology and Geophysics, Chinese Academy of Sciences; Institute of Remote Sensing Applications, Chinese Academy of Sciences; Exploration and Development Institute, SINOEPC’s Southwest Division Company; Earthquake Administration Bureau of Sichuan Province; China Earthquake Response Support Service; Chengdu University of Technology; China Earthquake Networks Center; Institute of Mountain Hazard and Environment, Chinese Academy of Sciences; Departments of Geophysics and Geology, Peking University; Schoolof Water Resources and Hydropower, Tsinghua University; Geological Institute, China Earthquake Administration Bureau; Dalian University of Technology; School of Water Resources and Environment, China University of Geosciences; China Institute of Water Resources and Hydropower Research; Shandong University; Shandong University of Science and Technology, etc..

参考文献(略)

200962610:35写成于香港大学黄克楼办公室

应邀于20097月发表在《中国岩石力学与工程学会动态》

20163119:40再登上科学网博文




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