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京都大学林爱明教授在港大演讲地震与断裂 精选

已有 5088 次阅读 2017-8-4 19:29 |系统分类:人物纪事

京都大学林爱明教授在港大演讲地震与断裂

岳中琦

应香港大学工程学院邀请,京都大学地球物理学系主任林爱明教授,8月3日下午,在港大做了蒙民伟杰出学人讲座(William Mong Distinguished Lecture)。他的讲座题目是“断裂强度和地震破裂机理”Fault Strength and Seismic Rupture Mechanism)。

教授首先介绍,古代日本人相信,地震是地下鲶鱼(catfish)翻动造成的。在1893年,东京大学小藤文次郎教授(Professor Bunjirou Koto1856-1935)提出了现代断层(断裂)地震理论。在研究了18918级日本濃尾(Nobi)地震的根尾谷断层地表破裂现象之后,小藤文次郎教授1893年在《Journal of the College of Science, Imperial University,Japan》第V卷第IV期发表了题目为“On the Cause of the Great Earthquake in Central Japan, 1891”论文,介绍了地震与断层的关系。之后,这个断层导致地震的观点被Reid教授在研究1906年旧金山大地震中进一步发展,得到世人广泛认可和应用http://blog.sciencenet.cn/blog-240687-971243.html

之后,林教授主要地介绍了他多年来研究断裂带出现的假熔岩(Pseudotachylyes)的成果。The term Pseudotachylyte (Pt) is used to describe a dark aphanitic appearance to a form of glassy basalt rock as tachylyte, showing as simple and network veins within wall rock. 他认为,假熔岩是地震化石。它是地震时断裂两侧岩石快速滑动、摩擦生热造成了围岩熔化和渗流。之后,这些局部熔岩快速冷却形成了假熔岩。他认为,断裂两侧岩石摩擦滑动速度在每秒钟数米(3米)之内。他首次在实验室用单轴压缩-旋转试验制造了岩石熔化。他把两块圆柱状岩石试样紧密挤压放在一条轴线上。一块试样固定,另一块高速旋转。转速高达每秒50转。摩擦生热高温,使得这两块接触带岩石熔化,再降温形成了熔岩。

他根据假熔岩研究,推论出地震断裂可以震源地壳能干层(脆性岩层,温度300 °C以内)向上部地表发展,又可以向下部脆-brittle-ductile转换层发展(温度在300°C到350 °C之间),直到塑性-柔性流动地壳层(温度在350 °C到450 °C之间)。从而,他提出了传统所谓的地震震源与破裂深度存在下限是需要改变的。他进一步地给出了大地震总是在断裂带重复发生的一种解释。他认为,地震断裂带强度是受到断裂角砾岩强度控制的,而不是母岩围岩的强度。这就可以解释,大地震在同一条活动断裂带(例如,昆仑断裂带和鲜水河断裂带)重复发生。产生地震的断裂带是脆弱的。

在演讲结束后,林教授认真回答了不少同学和老师的提问。

林教授港大访问和这场学术报告,让我对日本和世界的地震断裂研究等议题有了详细的了解和认识。我十分感谢他。

2017年8月4日19:13写成于香港大学602办公室

附件1:林爱明教授的个人简历介绍

Professor AimingLIN is a current Professor and Chairman in the Department of Geophysics, Kyoto University, Japan. He received Ph.D. and M.S. degrees from the Graduate Schoolof Science, the University of Tokyo in 1992 and 1989, respectively, and B.S.degree from Nanjing University in 1982. He is experienced in seismotectonics, rupture dynamics and mechanics of large earthquakes, paleoseismology, activefaults and formation mechanisms of fault rocks generated within seismogenic fault zones from brittle to ductile regimes. He has published 18 books and morethan 200 journal papers. He received the 1999 Excellent Researcher Award from the Murao International Foundation.  

附件2:林爱明教授的讲座摘要

Abstract: The strength of seismogenic fault is an important factor in understanding the rupture mechanisms of large earthquakes and the rheological properties ofseismogenic fault. During the past decades, geological and geophysical evidence suggests that some active faults are weak compared with the experimental measurements of frictional strength, but the fault strength is still a subject matter in dispute. In this presentation, I will focus on three related issues:i) the rupture mechanisms of seismogenic fault related with the fault strength,ii) formation processes of seismic fault rocks including Earthquake Fossil (pseudotachylyte)and related earthquake materials that form within natural seismogenic fault zones and in high-speed frictional experiments, and iii) the fault zone model showing the seismic slip resulting from large earthquakes that nucleate in thelower portion of the brittle regime in the upper crust is able to propagate downward through the brittle-ductile transition zone to the plastic flow regime in the lower crust.




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