洛马普列塔地震的远距离冲击

1989年10月发生的洛马普列塔地震最强烈的地震波到达距震中区约90公里的旧金山和奥克兰足足用了25秒钟。地震引起的振动一般随离开震中的距离而减弱,但是,洛马普列塔地震的地震波最后通过远处的城市时,却以惊人的力量晃动了大地并造成出乎意料的严重生命和财产损失。10月17日地震后,当旧金山湾地区挣扎着恢复过来时,工程师和地球科学家们曾力求找出不寻常的远距离强烈晃动的原因。起初他们把注意力集中于许多被破坏构筑物下面的松软天然沉积和填充物,其中包括奥克兰880号州际公路的崩塌部分和旧金山马里纳地区的一些     

研究结果表明岩层可影响地震波型

加州大学伯克利分校的两位地震学家对旧金山和奥克兰在洛马普列塔地震中尽管离震中相当远却受到强烈震动的原因进行了研究,他们认为洛矶地区下面的岩层可产生这样的影响。这两位研究人员说,在洛马普列塔地震中,来自震中圣克鲁斯县的地震波从地下岩层反射回来,在旧金山的马里纳区产生了比距震源近得多的某些地区更强烈的震动。     

美国举行旧金山地震情况报告会

1989年10月17日在美国旧金山地区发生的7.1级地震(称之为洛马普列塔地震)是1906年以来加州北部地区发生的最大的一次地震,造成了重大的经济损失和社会影响,因而引起了世界地震界、工程界以及与防灾救灾有关各界的广泛关注。1990年2月8—11日在旧金山举行了旧金山地震情况报告会,参加会议的有来自加拿大、日本、英国、中国等18个国家和地区的50多位代表,我国台湾也派人参加了会     

1989年加州洛马普列塔地震前20年的地震活动性

引言洛马普列塔地震前,沿该破裂带至少已出现了20年的地震活动性。洛马普列塔地震前,沿该断层段观测到仅有的异常事件是发生在次级平行的圣安德烈斯和萨金特断层交叉点附近(洛马普列塔主震北北东11公里处)的两次中强地震:1988年6月27日.M=5.0和1989年8月8日 M=5.2的莱克埃尔斯曼(Lake Elsman)地震。本文分析了这一地震活动性的时空分布,试图更多地了解该破裂带的断裂力学和地震孕育过程。洛马普列塔地震前10年期间的地震活动性相对于该震的余震被重新定了位,对此我们提出了下述问题:洛马普列塔地震主震附近有任何前震吗?莱克埃尔斯曼地震与洛马     

近20年来美国旧金山湾地区在地震安全防范方面的行动进展

1989年洛马普列塔(Loma Prieta)地震以来,美国地质调查局(U.S.Geological Survey,USGS)和许多其他组织共同努力,提高了对旧金山湾地区地震的认识,增强了地震灾害意识,并促成了更有效的减灾策略。同时,还广泛定位和分析了最危险的地区,改造和重建了最脆弱的设施。据USGS估计,旧金山湾地区的机构和企业已经投资了超过300亿美元用于改造和修复桥梁、管道、医院、市政建筑和其他基础设施,增强其抗震弹性,减少旧金山湾地区从未来地震灾害中恢复所需的时间。此外,还加强了向公众、企业和政府机构传达地震灾害的相关信息。这些共同努力都有助于降低未来大地震对旧金山湾地区的影响。     

零讯

1989年10月18日世界协调时00时04分的洛马普列塔地震之后,曾有以下一些对大地形变测量感兴趣的单位匆匆采取了行动。喷气推进实验室(JPL)派出了一个小组用全球定位系统(GPS)设置并测量穿过震中区的剖面。美国国家大地测量局(NGS)和国家航空航天局(NASA)向加州的福德奥德(Ford Ord)、普雷西迪奥及其它地方送去了流动甚长基线干涉测量仪(VLBI)天线。UNAVCO 送去了人员和接收机以协助美国地质调查局(USGS)对该区的测量工作。斯坦福大学在旧金山湾地区开     

地震预报已进入成年

1989年10月袭击旧金山湾地区的7.1级地震突出地向人们显示了大自然的破坏力。这次地震(根据震中附近的山名取名为洛马普列塔地震)除造成生命和财产的重大损失外,还是地震预报这个不确定的科学领域取得新进展的标志。在过去的10年里,科学家们已开始估计沿圣安德烈斯断层发生较大地震的长期概率。我工作所在的美国地质调查局,根据对人口稀少的加州中部一条布设有大量仪器的25公里长的断层段的研究,于1985年发布了第一个正式的美国政府地震预报。以附近城镇命名的圣安德烈斯断层的帕克菲尔德地段最近的一次6级大震发生于1966年。据我们的估计,帕克菲尔德在1993年以前发生另一次大地震的概率为     

地震前兆现象的产生机制

本文从力学的角度讨论了地震的发生过程，着重指出震源区内及其周围结构的非均匀性是产生前兆现象最重要的因素之一。前兆现象可分成下列两种类型：其一是由应力增加引起的前兆。长期前兆一般属于此类。作为这一类型的实例，我们讨论了１９８３年日本海地震前群震活动性逐渐增强以及１９８９年洛马普列塔地震的主震前震源周围地震活动性逐渐增强和出现第二类地震空区的现象。另一种类型是主破裂突然发生前因缓慢破裂过程而产生的前兆     

美刊载文论述对美国南加州隆起的重新考察

1980年1月24日旧金山以东的利物莫尔地震是旧金山湾地区5个月之内发生的第二次中强地震。它提出了人们所熟悉的问题:是不是这次地震意     

洛马普列塔地震破坏大部分归因于放大了的地面振动

地震灾害通常是在地球科学家之间单独地讨论,可是,当一次大地震发生时,财产的损失却很少能对每一种地震灾害分别加以概括。横扫北加州的1989年洛马普列塔地震4年之后,对以下的问题仍然没有定量的解答:由地面振动、液化、滑坡、构造地面破裂或者海啸引起的破坏究竟有多大?虽然一次地震的后果并非必定相继发生其它各种灾害,但回答这个问题有助于引导公共政策和建立研究的优先重点。当     

强震观测网、高灵敏度地震观测网、地中强震观测网、宽频带地震观测网

阪神·淡路大震灾后 ,日本着手对原有的地震观测体制作彻底改革 ,多项全国性配置地震计的计划同时开始启动。地震引起的地面晃动的程度不尽相同 ,无感微小地震引发的晃动仅有 0 .0 0 1 μm,频率为1 0 Hz;巨大地震引起的地面晃动的幅度高达 2～ 3 m,周期也有几十秒。虽说都称之为地震计 ,但由于地震动的振幅和频率涉及的范围太大 ,所以应针对观测对象选用不同类型的地震计。下面介绍不同类型的观测网。1　强震观测网 ( K- NET)无论大地有多大的晃动都能将其准确记录下来的地震计称之为强震计。它构造坚实 ,信号明确 ,通常设置在地表 ,对了…     

Age, geology, geophysics, and geochemistry of Mahukona Volcano, Hawai`i

The size, shape, and magmatic history of the most recently discovered shield volcano in the Hawaiian Islands, Mahukona, have been controversial. Mahukona corresponds to what was thought to be a gap in the paired sequence (Loa and Kea trends) of younger Hawaiian volcanoes (<4?Ma). Here, we present the results of marine expeditions to Mahukona where new bathymetry, sidescan sonar, gravity data, and lava samples were collected to address these controversies. Modeling of bathymetric and gravity data indicate that Mahukona is one of the smallest Hawaiian volcanoes (～6,000?km³) and that its magmatic system was not focused in a long-lived central reservoir like most other Hawaiian volcanoes. This lack of a long-lived magmatic reservoir is reflected by the absence of a central residual gravity high and the random distribution of cones on Mahukona Volcano. Our reconstructed subsidence history for Mahukona suggests it grew to at least ～270?m below sea level but probably did not form an island. New ⁴⁰Ar–³⁹Ar plateau ages range from 350 to 654?ka providing temporal constraints for Mahukona’s post-shield and shield stages of volcanism, which ended prematurely. Mahukona post-shield lavas have high ³He/⁴He ratios (16–21?Ra), which have not been observed in post-shield lavas from other Hawaiian volcanoes. Lava compositions range widely at Mahukona, including Pb isotopic values that straddle the boundary between Kea and Loa sequences of volcanoes. The compositional diversity of Mahukona lavas may be related to its relatively small size (less extensive melting) and the absence of a central magma reservoir where magmas would have been homogenized.     

The Yecheng,Xinjiang, China,earthquake of February 14, 1980

In this study, we have checked the location and focal depth of the Yecheng earthquake (m _b = 6.0, maximum intensity VII) of February 14, 1980. The result shows that this is an intermediate event with a focal depth of 90 km. The microepicenter is located at 36. 4°N, 76, 9°E, while the macroepicenter is at 37.3°N, 76.9°E, 90 km to the north of the microepicenter. This is the first destructive intermediate event in China which led to a damage as severe as of intensity VII. The focal mechanism of the event is determined to be of thrust type. Combined with the analysis of seismological and geological data in surrounding area, the possible relation between the event and plate movement has been discussed. The result in this paper indicates that in some particular place, the destructive effect of intermediate event should be considered in seismic hazard assessment.     

Sun, climate, hunger, and mass migration

Paleoclimatic studies indicate four epochs of global cooling during the last 4 000 years, i. e. during the few centuries before and after 2000 BC, 800 BC, 400 AD, and 1 600 AD; the quasiperiodicity corresponds to cyclic variation of solar activity. Global temperature changes influenced regional precipitation patterns: Northern Europe was wetter while the middle- and low-latitude lands were more arid during colder epochs. Both sets of cold climatical conditions were unfavorable for agricultural production. Historical records show that large demographic movements in history took place because of crop failures and mass starvation, rather than escaping from war zones. The “wandering” of the Germanic tribes during the first two or three centuries of the Christian Era is one example. Whereas the accelerated release of carbon dioxide from the burning of fossil fuels is ultimately to cause global warming, historical evidence indicates, however, that global warming has been on the whole a blessing to mankind. Global cooling, on the other hand, has curtailed agricultural production and has led to famines and mass migrations of people. Perhaps the most important task at the present is not so much computer-modelling of greenhouse effect on global climate, but water-management and agricultural researches to insure food-supply for an everincreasing world population.     

Physical properties,vitrinite reflectance,and microstructure of coal,Taiyuan Formation,Qinshui Basin,China

In this study, we experimentally established the relationship between physical properties, vitrinite reflectance, and microstructure of coal, Taiyuan Formation, Qinshui Basin, China using representative coal samples collected from three different mines via the rock mechanics testing system (MTS). We analyzed the organic macerals, vitrinite reflectance, and microstructure of 11 coal samples using petrography and scanning electron microscopy (SEM). The experimental results suggest that (1) the elastic parameters can be described by linear equations, (2) both P-and S-wave velocities display anisotropy, (3) the anisotropy negatively correlates with vitrinite reflectance, and (4) the acoustic velocities and Young’s modulus are negatively correlated with the volume of micropores. The derived empirical equations can be used in the forward modeling and seismic inversion of physical properties of coal for improving the coal-bed methane (CBM) reservoir characterization.     

山西高平地震

阐述了发生在山西高平的地震和对高平有影响的地震，分析了高平市的地震灾害，通过分析得出高平地震与晋获断裂带活动有关的结论。