关于2011年3月东日本M_W9.0地震与M_W7.3地震关系的讨论

2011年3月日本MW7.3地震51h之后,发生了东日本MW9.0地震并引发巨大灾难。地震学家多角度、多方法探讨了两次地震之间的关系,结果判断日本MW7.3地震是东日本9.0级地震的前震。本文计算了MW7.3前震和2005~2011年沿日本海沟一系列7级左右地震对MW9.0地震的静态库仑应力,结果显示其并未直接触发MW9.0主震,但对主震震中位置及周边区域的应力加载效应是明确的。利用Suito等(2011)基于GPS数据计算的板间地震滑移速率,分析了一般地震与有广义前震的地震在震后和同震释放能量的不同来分析2005年以来日本海沟发生的5次7级左右地震与MW9.0地震的关系。总的来说,日本MW7.3地震是东日本MW9.0地震的前震,从长时间尺度的GPS时间序列分析来看,2005~2011年日本海沟一系列7级左右地震可能是东日本MW9.0地震的广义前震。     

2011年3月11日日本地震海啸越洋传播及对中国影响的数值分析

北京时间2011年3月11日13时46分(05:46 UTC)日本东北部近海(38.3°N,142.4°E)发生Mw9.0级特大地震,此次地震的强度为日本近1200a来最强.随后环太平洋的数十个国家和地区的验潮站和海啸监测浮标均监测到了强震引发的越洋海啸,海啸奔袭23 h到达南美洲的智利沿岸;此次海啸除了对近场的日本东北部沿岸地区造成了巨大灾害,还对太平洋东岸的部分国家和地区造成了一定程度的影响.地震发生4 h后海啸波到达我国台湾东部沿海,6~8 h海啸波到达我国大陆东南沿海,受此影响我国发布了第一份海啸蓝色警报.本文利用海啸数值模型对此次地震海啸的产生、越洋传播过程进行了数值模拟,给出了海啸波能量在我国近海及泛太平洋区域分布特征;同时重点模拟分析了海啸波在日本及中国近海传播的波动特征,模拟结果与观测数据吻合良好.最后通过对数值模拟结果的分析,阐述了此次海啸对中国的影响,给出了潜在的日本地震海啸对中国的风险估计.     

2011年3月11日日本地震海啸越洋传播及对中国影响的数值分析

北京时间2011年3月11日13时46分(05:46 UTC)日本东北部近海(38.3°N,142.4°E)发生M_w9.0级特大地震,此次地震的强度为日本近1200a来最强.随后环太平洋的数十个国家和地区的验潮站和海啸监测浮标均监测到了强震引发的越洋海啸,海啸奔袭23 h到达南美洲的智利沿岸;此次海啸除了对近场的日本东北部沿岸地区造成了巨大灾害,还对太平洋东岸的部分国家和地区造成了一定程度的影响.地震发生4 h后海啸波到达我国台湾东部沿海,6~8 h海啸波到达我国大陆东南沿海,受此影响我国发布了第一份海啸蓝色警报.本文利用海啸数值模型对此次地震海啸的产生、越洋传播过程进行了数值模拟,给出了海啸波能量在我国近海及泛太平洋区域分布特征;同时重点模拟分析了海啸波在日本及中国近海传播的波动特征,模拟结果与观测数据吻合良好.最后通过对数值模拟结果的分析,阐述了此次海啸对中国的影响,给出了潜在的日本地震海啸对中国的风险估计.     

从同震和震后形变分析日本东北Mw9.0级大地震对近场地震活动性的影响

2011年日本东北大地震后,不断有报道认为日本南海海槽可能会发生强震,日本东北大地震对南海海槽断层活动有何影响?本文采用粘弹性半无限空间模型,利用反演得到的日本东北大地震的断层模型,计算了岛内部分断层的同震和震后形变以及库仑应力变化.结果表明:2011年日本东北大地震,使得平行于日本海沟的岛内逆冲断层应力释放明显,5km深度,库仑应力降低值都在50 kPa以上,按照该地区每年应力积累1～10 kPa计算,相当于释放了5～50年的应力积累;平行于南海海槽的岛内逆冲断层,同震库仑应力增加了1 kPa左右,相当于0.1～1年的正常构造运动应力积累;对于岛内的走滑断层,若其滑动方向与同震或震后形变方向一致,则库仑应力增加,反之则降低,如1948年福井地震发震断层库仑应力增加10 kPa左右,相当于1～10年的正常构造运动应力积累,地震危险性明显增加.同时,分析了不同软流圈粘滞性对震后形变和库仑应力的影响,发现对于不同的软流圈粘滞性系数,震后的形变和库仑应力相比同震都会有所增加.因此,对于平行南海海槽的岛内逆冲断层和岛内部分滑动方向与同震形变一致的走滑断层,震后地震危险性相比同震会进一步增强.     

2011年3月11日日本9.0级强震上海地区同震效应分析

2011年3月11日日本发生了MW9.0级地震,在这次地震中,上海地区的两个形变台站的7套观测仪器都记录到了不同程度的异常现象,应变及地倾斜出现幅度不同的震荡波,佘山台垂直摆东西分量在初动时就记录到最大波动,而佘山重力仪记录到的最大波值出现在震级更小的余震发生后。此外查山台钻孔倾斜北南分量以及佘山台垂直摆东西分量均在震后一段时间出现了与GPS记录相一致的加速倾斜。通过将上述现象进行简述分析,以期进一步深入了解上海地区的地形变响应特征。     

2011年日本MW9.0地震引发的海啸对地震背景噪声的影响

基于北美沿岸和内陆地震台站的连续地震波形记录,并结合沿岸台站附近布设的DART系统记录的海底压力数据以及预测潮汐数据,利用时频分析和极化分析方法对2011年3月11日日本东北部海域MW9.0大地震所激发的海啸对地震背景噪声所产生的影响予以深入分析.结果显示:海啸对高频噪声(1.3—1.5 Hz)以及短周期双频微地动噪声...     

2011年M_W9.0东日本大地震动力学破裂过程的数值模拟

力学上,地震可以看作在应力场作用下由于断层带介质的突然损伤或软化导致的断层带失稳事件.本文基于这个地震动力学模型,利用一种可以模拟断层大位错的有限元方法,研究了2011年MW9.0东日本大地震(Tohoku-Oki)的动力学破裂过程.比较了无障碍体和具有不同刚度障碍体的断层带模型产生的断层位移、位错和应力降.主要结果表明,障碍体的存在并不明显地改变障碍体区域的初始构造应力场.对有障碍体情形,准静态结果显示断层上盘最大逆冲位移和最大剪切位错分别为51m和58m,均发生在海底表面海沟处,与无障碍体的结果(最大剪切位错约55m)相比差别不大;下盘最大倾向位移(-10m)并不与上盘最大值出现在同一位置,而是在障碍体处.障碍体处剪应力降(约11 MPa)大于周围非障碍体区域.障碍体处正应力降的最大值约为3 MPa.模拟结果似乎不支持海山是导致本次地震异乎寻常大位错的原因,而倾向于断层带剪切刚度在地震过程中极度损伤或软化.     

2011年4月11日日本东北福岛县浜通Mw6．6地震的地表断层破裂和滑动分布

2011年4月11日日本东北福岛县浜通地震于2011年3月11日东北地方太平洋海岸近海地震之后1个月发生在一地震活动区。这次浜通地震在北北西一南南东走向的系浞断层上造成14km长向西的正滑破裂,同时在西北西～东南东走向的汤野岳断层造成16kin长向南的正滑破裂。沿系浞断层的滑动从南端到中部突然增加,其中测量的最大位移近2m;该断层的中段到北西端的滑动逐渐降低。汤野岳断层也有不对称的滑动分布,在其北西段附近峰值约为0．9m。从破裂沿这两条断层扩展的方向来考虑,显然测量到的地表断错在走向上不对称,在更靠近破裂起始的断层末端观测到最大断错,而在破裂终止的方向显现出逐渐减小。滑动分布和震中位置的地表观测结果与滑动反演模型得出的地震破裂的总体特征一致。浜通地震断层超过60％的破裂长度以及其他历史正断层地震,滑动位移量小于或等于最大滑动的30％。根据破裂长度、最大和平均位移估计的该地震的矩震级（Mw）在6．5～6．8之间,与地震学确定值6．6相一致。     

日本2011年3月11日灾难性地震前地磁场长期变化的异常扰动

2011年3月11日,在日本东北以东的近海发生了M9地震,这是日本地震监测史上最大的一次,其震中位于海底下约24km处,距离海岸约130km。根据位于日本领土上距离此次震中约180~200km的两个地磁监测站——江差町和水泽的数据研究了地球主磁场的长期变化。地球主磁场的分量在过去的上百年间变化都非常平稳,然而在2000~2011年期间,在日本领土发生大地震的区域内监测到了4次主磁场长期变化的异常情况,其持续时间从半年到3年不等。这些异常出现的同时,在地磁台站周边100km的区域内有地震活跃带发展,且之后发生了6级强震。从两个地磁台站监测的相关磁场分量差可发现一些最显著的异常。最近的一次异常情况最为强烈,其出现在大地震发生的约3年前。地震前地球磁场异常的原因可能是由构造运动过程引起的地壳局部区域的导电性变动造成。在初始阶段,这个过程会导致未来震源区域温度和导电性的升高,从而导致地表地电流的重新分配以及磁场的改变。之后,构造运动过程的发展导致未来震源区域裂缝的加剧,并降低了地震来临前的电导率。     

2011年3月11日日本本州东海岸附近海域发生8.6级地震

中国地震台网中心和美国地质调查局(USGS)公布的该地震的参数如下:1中国地震台网中心发震时间:北京时间2011年3月11日13时46分;震中位置:日本本州东海岸附近海域     

利用海啸数值模拟结果进行海底地震有限断层模型验证

基于地震有限断层模型进行海啸的数值模拟通常被用来估计海啸的到时、 波高等, 另一方面, 海啸数值模拟的结果也可以作为限定条件用来考察同一地震的不同断层模型之间的相对合理性。 采用国际上各地震研究机构在震后各自得出的不同的有限断层模型作为海啸源, 使用基于二维浅水波方程的海啸传播模型对2011年日本东北地震海啸的传播过程进行模拟, 以海啸模拟所得到的沿岸浪高分布、 平均波高、 最大波高等与实际观测值相比较, 进而判断由各有限断层模型所计算得到的海啸中哪个结果与实际的海啸情况更为符合, 由此推断断层模型的相对合理性。     

The response of the electromagnetic field to the catastrophic earthquake of March 11, 2011

The electric and magnetic variations observed during the earthquake of March 11, 2011 that occurred in the Pacific close to the northeastern coast of Honshu Island in Japan are analyzed. The variations in the electric voltage were measured at the decommissioned submarine telecommunication cable laid on the bed of the Sea of Japan. The neighboring observatories recorded the anomalous geomagnetic variations during the studied time interval; the sources and spatial location of these anomalies are studied. The seismic signals were identified from the seismograms recorded by the broadband seismometer STS-2 at the nearest seismic station.

     

The response of the electromagnetic field to the catastrophic earthquake of March 11, 2011

The electric and magnetic variations observed during the earthquake of March 11, 2011 that occurred in the Pacific close to the northeastern coast of Honshu Island in Japan are analyzed. The variations in the electric voltage were measured at the decommissioned submarine telecommunication cable laid on the bed of the Sea of Japan. The neighboring observatories recorded the anomalous geomagnetic variations during the studied time interval; the sources and spatial location of these anomalies are studied. The seismic signals were identified from the seismograms recorded by the broadband seismometer STS-2 at the nearest seismic station.     

Geotechnical engineering aspects of the catastrophic Tohoku (Japan) earthquake of March 11, 2011: the review of first results

Geotechnical engineering aspects of the catastrophic earthquake, which occurred in Japan on March, 11, 2011 and called Tohoku earthquake are discussed. A review is presented of the first results obtained mainly by Japanese scientists based on records of seismic networks of Japan K-NET, Kik-net and on GPS data. The basic concepts of seismic zoning in Japan and the location of the Tohoku-oki earthquake on the seismic zoning maps are described, as well as models of the source process obtained by various authors based on teleseismic data, strong motion data, GPS data, and tsunami observations. The recorded peak accelerations and velocities and their correspondence to the current empirical attenuation curves are discussed. The records of the Tohoku earthquake made by Japanese seismic networks K-NET, Kik-net and some others represent unique seismological material and the most complete seismic database (including vertical array records) in the near-source zone of a strongest earthquake with magnitude M _w = 9. These data will be studied by seismologists all over the world for many years and, probably, they will answer many questions of geotechnical seismic engineering.     

东日本地震在北京GNSS连续观测站E分量的反应

Several new demands have been put forward for the application of the Beijing continuous GNSS observations due to some particular reasons,such as the limited coverage of the observation network,the different construction and management criterion executed by different units and the intense interference resulting from human activity. In this paper,necessary processing of data is carried out, including more accurate calculation,corrections to the replacement,outliers and relocation of equipment,and elimination of linear trends in the E-component for every station. The E-components of the 16 available stations showed a lower sawtooth wave anomaly( s lowly westward propagating) b efore the2011 Tohoku M W9. 0 earthquake,a coseismic step rebound( rapid eastward propagating)and a post-seismic Ω-shaped recovery. These steps constituted a complete earthquake process which was rarely seen before in the GNSS observations and provides a good example for further study. Moreover, t he rapid eastward propagating during the earthquake is not influenced by the size of the given normal values,which may play a significant role in earthquake forecasting and early warning.     

The 11 March 2011 East Japan Earthquake and Tsunami: Tsunami Effects on Coastal Infrastructure and Buildings

The 11 March 2011 East Japan Earthquake and Tsunami caused unprecedented damage to well-engineered buildings and coastal structures. This report presents some notable field observations of structural damage based on our surveys conducted along the Sanriku coast in April and June 2011. Engineered reinforced concrete buildings failed by rotation due to the high-velocity and deep tsunami inundation: entrapped air in the buildings and soil liquefaction by ground shaking could have contributed to the failure. The spatial distribution pattern of destroyed and survived buildings indicates that the strength of tsunami was affected significantly by the locations of well-engineered sturdy buildings: weaker buildings in the shadow zone tended to survive while jet and wake formations behind the sturdy buildings enhanced the tsunami forces. We also found that buildings with breakaway walls or breakaway windows/doors remained standing even if the surrounding buildings were washed away or destroyed. Several failure patterns of coastal structures (seawalls) were observed. Flow-induced suction pressure near the seawall crown could have caused the failure of concrete panels that covered the infill. Remarkable destruction of upright solid-concrete type seawalls was closely related with the tsunami induced scour and soil instability. The rapid decrease in inundation depth during the return-flow phase caused soil fluidization down to a substantial depth. This mechanism explains severely undermined roads and foundations observed in the area of low flow velocities.     

From 3-Hz P Waves to 0 S 2: No Evidence of A Slow Component to the Source of the 2011 Tohoku Earthquake

In the hours following the 2011 Honshu event, and as part of tsunami warning procedures at the Laboratoire de Géophysique in Papeete, Tahiti, the seismic source of the event was analyzed using a number of real-time procedures. The ultra-long period mantle magnitude algorithm suggests a static moment of 4.1 × 10²⁹ dyn cm, not significantly different from the National Earthquake Information Center (NEIC) value obtained by W-phase inversion. The slowness parameter, $\Uptheta = -5.65, $ is slightly deficient, but characteristic of other large subduction events such as Nias (2005) or Peru (2001); it remains significantly larger than for slow earthquakes such as Sumatra (2004) or Mentawai (2010). Similarly, the duration of high-frequency (2–4 Hz) P waves in relation to seismic moment or estimated energy, fails to document any slowness in the seismic source. These results were confirmed in the ensuing weeks by the analysis of the lowest-frequency spheroidal modes of the Earth. A dataset of 117 fits for eight modes (including the gravest one, ₀ S ₂, and the breathing mode, ₀ S ₀) yields a remarkably flat spectrum, with an average moment of 3.5 × 10²⁹ dyn cm (*/1.07). This behavior of the Tohoku earthquake explains the generally successful real-time modeling of its teleseismic tsunami, based on available seismic source scaling laws. On the other hand, it confirms the dichotomy, among mega-quakes (M ₀ > 10²⁹ dyn cm) between regular events (Nias, 2005; Chile, 2010; Sendai, 2011) and slow ones (Chile, 1960; Alaska, 1964; Sumatra, 2004; and probably Rat Island, 1965), whose origin remains unexplained.     

Time variations of the stresses in the source region of the Tohoku earthquake of March 11, 2011 (<Emphasis Type="Italic">M</Emphasis> = 9) from tidal response data

The idea of forecasting the earthquakes by continuous monitoring the time variations of tidal responses was suggested by E. Nishimura in 1950. However, the implementation of this idea has only become possible with the deployment of the GSN and F-net global seismic networks. Below, we present the new method for identifying the time variations of tidal response of the medium in seismically active regions using the data from these networks. We show that our approach significantly increases the sensitivity and time resolution of the standard methods of moving spectral analysis. The analysis of the data from the horizontal pendulums which record the northward tilts demonstrates the slow growth of the tidal tilts during six years before the earthquake, which is followed by the instantaneous drop of the amplitudes at the moment of the earthquake. During four years after this drop, the tidal amplitudes remained at a noticeably lower level than their average preearthquake values. These changes in the tidal amplitudes indicate the nonlinear response of the medium in the presence of large tectonic