Spatio-temporal characteristics of aftershocks and seismogenic structure of the 2011 Mw9.0 Tohoku earthquake,Japan

The Tohoku megathrust earthquake, which occurred on March 11, 2011 and had an epicenter that was 70 km east of Tohoku, Japan, resulted in an estimated ten′s of billions of dollars in damage and a death toll of more than 15 thousand lives, yet few studies have documented key spatio-temporal seismogenic characteristics. Specifically, the temporal decay of aftershock activity, the number of strong aftershocks (with magnitudes greater than or equal to 7.0), the magnitude of the greatest aftershock, and area of possible aftershocks. Forecasted results from this study are based on Gutenberg-Richter’s relation, Bath’s law, Omori’s law, and Well’s relation of rupture scale utilizing the magnitude and statistical parameters of earthquakes in USA and China (Landers, Northridge, Hector Mine, San Simeon and Wenchuan earthquakes). The number of strong aftershocks, the parameters of Gutenberg-Richter’s relation, and the modified form of Omori’s law are confirmed based on the aftershock sequence data from the Mw9.0 Tohoku earthquake. Moreover, for a large earthquake, the seismogenic structure could be a fault, a fault system, or an intersection of several faults. The seismogenic structure of the earthquake suggests that the event occurred on a thrust fault near the Japan trench within the overriding plate that subsequently triggered three or more active faults producing large aftershocks.

Review of the Research of the 2011 Mw9.0 Tohoku-Oki Earthquake

On March 11,2011, a M_W9.0 earthquake occurred in the Japan Trench, causing tremendous casualties,and attracting extensive concern. Based on the results of related research,this paper analyzes the observations,phenomena and understandings of the earthquake from varied aspects,and obtains four main conclusions.(1) The earthquake,occurring in the subduction zone in the Japan Trench located in the northwest boundary of the pacific plate has two zones of concentrated coseismic slip at different depths,and the slip in the deep zone is relatively small. Though there have been many M7. 0 historical earthquakes,slips in the shallow zone are large,but there have been few historical strong earthquakes.(2) Constrained by GPS data,the study of fault movement shows that fault movement in the Japan Trench has a background of widely distributed stability and locking( the locking zone is equivalent that of coseismic rupture zone). Perturbation occurred after the 2008 M8. 0 Hokkaido earthquake,several M7. 0 events had after slips larger than the coseismic slip,and two obvious slow slip events were recorded in 2008 and2011. Eventually,the March 9,2011 M7. 0 foreshock and the March 11,2011 M_W9.0 mainshock occurred. The pre-earthquake changing of the fault movement in the Japan Trench is quite clear.(3) Traditional precursory observation show no obvious anomaly,possibly due to monitoring reason. Anomaly before earthquake consists of high stress state in focal zone reflected by some seismic activity parameters,short period anomaly in regional ground motion,etc.(4) The analysis of physical property in focal zone aroused more scientific issues,for example,is there obvious difference between physical property in focal zone and its vicinity? Does frictional property of fault determine seismogenic ability and rupture process? Whether pre-earthquake fault movement include pre-slips? Could deep fluid affect fault movement in focal zone? Experience is the best teacher,and authors hope this paper could be a modest spur to induce others in basic research in earthquake forecast and prediction.

Co-seismic displacements of 2011 Japan Mw9.0 earthquake recorded by far-field GPS stations

Co-seismic displacements of the 2011 Mw9.0 Japan earthquake recorded by GPS stations in China and surrounding areas showed a movement toward the epicenter. The horizontal displacements were up to 1 - 3 cm in northeastern China, 3 -8 mm in the North China, and 2 cm in the Korean peninsula. The vertical movements in China were small uplifts.

Co-seismic deformation of 2011 Mw9.0 Japan earthquake observed by InSAR technique

Co-seismic line-of-sight displacements of the 2011 Mw9.0 Japan earthquake derived from InSAR data of Envisat ASAR, ALOS PALSAR and TerraSAR-X show a maximum value of about - 245cm to -221cm near the epicenter. This result is in good agreement with the result of GPS measurement. The ob- served displacement pattern suggests an earthquake-rupture zone over 500km long, with a ground-motion pat- tern in the vicinity of the northern segment more complex than that of the southern segment, possibly due to immediate aftershocks that occurred between satellite passes.

Analysis of the co-seismic responses of the fluid well pattern system in Jiangsu Province to the Wenchuan and Tohoku earthquakes

This thesis discusses the earthquake reflecting ability of the observation well pattern system of Jiangsu Province, China, which has been digitally renovated, and probes into the cause of the major differences in the earthquake reflecting abilities of well holes at different measurement points. This is achieved through the analysis of the co-seismic responses to the Wenchuan (2008; Ms8.0, China) and Tohoku (2011; Ms9.0, Japan) earthquakes. We found that the co-seismic response of water level from regional well holes in Jiangsu Province was stronger than that of water temperature. The water-level co-seismic response follows a consistent law and is closely related to the earthquake magnitude. The co-seismic response of water temperature strongly varied among well points, and was more often manifested as a slow restorative change. The co-seismic responses also varied based on tectonic elements. The response in central and northern Jiangsu was weaker than that of southern Jiangsu, possibly due to the thicker loess cover layer in central Jiangsu which makes it less effective at capturing the micro-changes of stress-strain states relative to the hilly land in the south. The more complicated geological structure in southern Jiangsu makes it contribute to greater changes in the state of underground water after a minor disturbance.

Coseismic gravity and displacement changes of Japan Tohoku earthquake(Mw 9.0)

The greatest earthquake in the modern history of Japan and probably the fourth greatest in the last 100 years in the world occurred on March 11, 2011 off the Pacific coast of Tohoku.Large tsunami and ground motions caused severe damage in wide areas, particularly many towns along the Pacific coast. So far, gravity change caused by such a great earthquake has been reported for the 1964 Alaska and the 2010 Maule events. However, the spatial-temporal resolution of the gravity data for these cases is insufficient to depict a co-seismic gravity field variation in a spatial scale of a plate subduction zone. Here, we report an unequivocal co-seismic gravity change over the Japanese Island, obtained from a hybrid gravity observation（combined absolute and relative gravity measurements）. The time interval of the observation before and after the earthquake is within 1 year at almost all the observed sites, including 13 absolute and 16 relative measurement sites, which deduced tectonic and environmental contributions to the gravity change. The observed gravity agrees well with the result calculated by a dislocation theory based on a self-gravitating and layered spherical earth model. In this computation, a co-seismic slip distribution is determined by an inversion of Global Positioning System（GPS） data. Of particular interest is that the observed gravity change in some area is negative where a remarkable subsidence is observed by GPS, which can not be explained by simple vertical movement of the crust. This indicated that the mass redistribution in the underground affects the gravity change. This result supports the result that Gravity Recovery and Climate Experiment（GRACE） satellites detected a crustal dilatation due to the 2004 Sumatra earthquake by the terrestrial observation with a higher spatial and temporal resolution.

WFSD地应力台应变特征及其同震效应分析——以日本MW9.0级特大地震为例

2011年3月11日在日本东北部海域发生MW 9.0级强烈地震,汶川地震断裂带科学钻探(WFSD)项目设在陕西汉中地区的体应变仪记录到了完整的应变数据。通过采集数据的分析,探讨了日本MW 9.0级特大地震发生时的同震变化以及地震前后固体潮异常变化过程,分析了地震孕育、发生过程中应变固体潮的趋势性异常及畸变等各种异常现象,并针对这些应变异常进行分析,以期成果能为中国未来地震趋势的预测研究有所帮助。

Response of tilt and strain meters in Hubei province to the 2011 Mw9. 0 Japan earthquake

Tih and strain meters of the deformation-observation network in Hubei Province all responded to the Mw9.0 Japan earthquake on March 11,2011. By analyzing the co-seismic responses,we found that firstly there was essentially a linear correlation between response time and epicentral distance. Secondly, there was some correlation between maximum response amplitude and earthquake magnitude as well as between the duration and earthquake magnitude. Thirdly, the response amplitudes and decay rates were different for different types of instruments. Due to less data-sampling frequency, the deformation instruments, could not display the first motion of P and S waves, but responded mainly to far-field surface waves. Before the earthquake, the NS earthtide component recorded by the cave stainmeter at Yichang was distorted for nearly eight hours. While digital deformation observation did not show complete information about the earthquake source, it still reflected some key features of seismic-wave propagation.

The December 26, 2004, off the west coast of northern Sumatra, Indonesia, M_W=9.0, earthquake and the critical-point-like model of earthquake preparation

Long-term seismic activity prior to the December 26, 2004, off the west coast of northern Sumatra, Indonesia, MW=9.0 earthquake was investigated using the Harvard CMT catalogue. It is observed that before this great earth-quake, there exists an accelerating moment release (AMR) process with the temporal scale of a quarter century and the spatial scale of 1 500 km. Within this spatial range, the MW=9.0 event falls into the piece-wise power-law-like frequency-magnitude distribution. Therefore, in the perspective of the critical-point-like model of earthquake preparation, the failure to forecast/predict the approaching and/or the size of this earthquake is not due to the physically intrinsic unpredictability of earthquakes.

Co-seismic groundwater-level and temperature changes of the 2011 Mw9. 0 Japan earthquake in Chinese mainland

Co-seismic groundwater-level and temperature changes caused by the Mw9. 0 Japan earthquake in Chinese mainland are described. The recorded water-level changes were mostly oscillations, with some step decreases mostly in the coastal area of Southeast China and step increases mostly in Northeast China and the North-South Seismic Belt. The water-temperature changes were mainly decrease with slow recovery in Sichuan- Yunnan, South China, and lower reaches of Jiangzhong, and sharp increase followed by sharp decrease, or vice versa, in North China and Northeast China. For wells that showed step changes in both water level and temperature, more showed them in the same direction than in the opposite direction.

从同震和震后形变分析日本东北M_W 9.0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50kPa以上,按照该地区每年应力积累1～10kPa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1kPa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10kPa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.

利用GRACE观测资料分析日本M_W9.0地震前区域重力变化特征

利用GRACE重力卫星观测资料,获得了日本MW9.0地震前的区域重力变化;获取了TSKB、DAEJ、SUIY和HLAR站GPS连续观测垂直位移。地震前区域重力变化主要经历2个过程:1)2002年8月至2007或2008年底的先上升后下降的小幅变化过程,该过程可用二次多项式拟合;2)第1个过程后的重力快速上升后下降的较大幅度变化。2008年黑龙江至乌苏里区域重力下降明显,2009年和2010年在太平洋俯冲带的广大区域重力呈显著上升,并且正、负重力变化区域都向SW方向迁移。2010年与2009年相比,重力变化沿板块边界带呈东、西部分的正、负分布特征;东部区域点位2010年初开始重力快速下降至地震发生;而西部点位在此期间仍然为重力正变化高值,地震发生后开始下降变化。远场GPS垂直位移具有2006年中开始的隆升变化,2009年初开始转向。经过与GLDAS陆地水储量改变引起的重力变化比较,认为区域重力变化主要由地表水储量改变引起。但位于海洋侧的P01和P03位置类似下降变化也非常明显,这表明区域重力的异常变化很可能与地下深部的地幔物质运移和热引起的区域气候改变有关。这种异常变化特征与地震孕育的关系有待今后深入研究。

Comparative analysis of the characteristics of global seismic wave propagation excited by the M_w 9.0 Tohoku earthquake using numerical simulation

Giant earthquakes generate rich signals that can be used to explore the characteristics of the hierarchical structure of the Earth’s interior associated with the eigenfrequencies of the Earth.We employ the spectral element method,incorporated with large-scale parallel computing technology,to investigate the characteristics of global seismic wave propagation excited by the2011 Mw9.0 Tohoku earthquake.The transversely isotropic PREM model is employed as a prototype of our numerical global Earth model.Topographic data and the effect of the oceans are taken into consideration.Wave propagation processes are simulated by solving three-dimensional elastic wave governing equations with the seismic moment tensor obtained from the Global Centroid Moment Tensor Catalog.Three-dimensional visualization of our computing results displays the nature of the global seismic wave propagation.Comparative analysis of our calculations with observations obtained from the Incorporated Research Institutions for Seismology demonstrates the reliability and feasibility of our numerical results.We compare synthetic seismograms with incorporated and unincorporated ocean models.First results show that the oceans have obvious effects on the characteristics of seismic wave propagation.The peak displacement and peak velocity of P waves become relatively small under the effect of the ocean.However,the effect of the ocean on S-waves is complex.The displacement and velocity of S waves decrease rapidly over time using an unincorporated ocean model.Therefore,the effects of the ocean should be incorporated when undertaking quantitative earthquake hazard assessments on coastal areas.In addition,we undertake comparative analysis on the characteristics of the Earth’s oscillation excited by the 2004 Sumatra-Andaman,2008 Wenchuan,and 2011Tohoku earthquakes that incorporate the effect of the Earth’s gravitational potential.A comparison of the amplitude spectra of the numerical records indicates that energy released by the three big earthquakes is different.Our comparative analysis realizes that the computing results can accurately reproduce some eigenfrequencies of the Earth,such as toroidal modes 0T2 to 0T13and spheroidal modes 0S7 to 0S31.These results demonstrate that numerical simulations can be successfully used to investigate the Earth’s oscillations.We propose that numerical simulations can be used as one of the major tools to further reveal how the Earth’s lateral heterogeneities affect the Earth’s oscillations.

日本M_(W)9.0地震前后郯庐断裂带中南段构造应力场动态变化特征

本文以郯庐断裂带中南段及周缘为研究区,计算和收集了1970—2016年1148次地震震源机制解,采用阻尼应力张量方法反演了构造应力场,通过分析应力场时空动态变化过程和地震活动性特征,探讨了2011年3月11日日本9.0级地震对郯庐断裂带中南段及周缘的影响.结果显示:9.0级地震对郯庐断裂带中南段及周缘造成了显著影响,表现为应力场出现扰动变化和地震活动显著增强.以挤压为主的背景应力场呈现出一定的拉张作用,应力结构及应力方向发生变化,最大主应力σ_(1)轴倾伏角增大,中等主应力σ_(2)轴倾伏角减小,最大主应力σ_(1)轴方向发生小幅逆时针偏转.包括研究区在内的中国陆地东部地区地震活动显著增强,中强地震丛集活动.应力场扰动变化和地震起伏活动存在较好的相关性,并先后呈现出3个不同阶段,扰动导致的构造应力作用方式的阶段性改变是地震活动增强的动力机制.结果还显示,应力场扰动变化和地震活动增强开始于9.0级地震前1~2年,揭示了9.0级地震的影响不仅限于同震和震后,在其孕震后期已经对远场的中国陆地东部产生了影响.本文结果可以为日本俯冲带大震对中国陆地构造活动影响的相关研究提供参考依据.

利用粘弹性球体位错理论研究2011年日本M_W9.0地震引起的震后位移时空变化

基于2011年3月~2015年9月的GPS观测数据,研究了2011年日本M_W9.0地震引起的震后位移时空变化,分析震后4.5a内震后断层余滑和粘滞性松弛对震后位移场的贡献。基于子断层叠加的思想,对Tanaka的粘弹性球体位错理论配套计算程序(环型解部分)加以改进,克服其近场计算精度不足(甚至错误)的缺陷,提高了近场震后位移的计算精度。利用弹性球体位错理论配套计算程序和改进后的粘弹性球体位错理论配套计算程序,分别计算2011年日本M_W9.0地震产生的同震位移,两组结果的差异仅占信号的1%左右,验证了对粘弹性球体位错理论配套计算程序改造的正确性。最后,结合震后3~4.5aGPS观测数据,利用Tanaka的粘弹性球体位错理论确定了2011年日本M_W9.0地震震中周边区域地幔粘滞性系数,其最佳拟合值为6×10^(18)Pa·s。

基于粘弹性球体地球模型的震后位移与重力变化计算软件

在考虑地球曲率、成层结构、可压缩性与自重的前提下,Tanaka等[1-2]提出一套较为完备的粘弹性球体位错理论,可计算全球任意位置由地震产生的同震与震后形变(含位移、重力变化、大地水准面变化)。Gao等[3]给出了与上述理论相匹配、界面友好的计算软件,能计算30个震后时间点对应的震后形变。本研究针对Gao等的软件进行改进,可计算震后任意时间点对应的震后形变。新软件由3个部分组成:1)与32个震后时间点相对应的32套离散格林函数数值框架;2)格林函数插值计算程序,可针对上述32套格林函数数值框架进行插值运算,输出任意震后时间点对应的格林函数数值结果;3)积分计算程序,调用上述格林函数数值结果,计算任意类型地震在地表任意位置产生的同震与震后形变。一般情况下,使用者只需按要求准备辅助文件,提供发震断层模型和观测站位置信息,以及震中周围地区地幔粘滞性因子,先后运行格林函数插值计算程序和积分计算程序,即可计算出目标地震在地表任意位置产生的同震与震后形变。本文基于粘弹球体位错理论与弹性球体位错理论,分别计算2011年日本MW9.0地震引起的远场同震位移,2套结果的高度一致性证明了新程序的正确性。最后,介绍需要注意的若干事项,便于使用者掌握该软件。

印尼9.0级地震前后远场水平地壳微动态变形

利用中国大陆GPS基准站及震中附近IGS站数据,研究了2004年12月26日印尼苏门答腊9.0级地震前后GPS观测到的远场水平位移微动态变形过程。震前E分量位移序列出现"分群"现象,震中东北侧大陆板块上的GPS站点表现出受挤压向东的运动,而位于断裂带西北侧大陆板块上的站点则表现出受引张向西运动的趋势,具有大尺度空间的协调一致性,与理论孕震模型符合较好。远至3 000km的站点也观测到了地震的同震位移,同震位移矢量有整体向震中汇聚的特点,反映了震时俯冲板块和上覆板块会聚作用对远场的影响。而震后由于地震断层的强烈运动,使得一些点位位移态势发生了较震前异常更明显、持久的改变。

对日本9级地震的中期预测及其依据

对2011年3月11日发生在日本的9级大地震所做出的中期预测进行小结,并对所提出预测意见及其依据做了简要论述。预测地区在日本南部、台湾以及菲律宾一带;预测震级为8～8.3级;预测时间是今后几年;预测依据是青藏滇缅印尼歹字型构造体系。预测地震三要素与日本9级大地震三要素的对比结果表明,这一中期预测是基本正确的。

利用GPS和InSAR数据反演2011年日本东北M_W9.0地震断层的同震滑动分布

本文首先对Envisat/ASAR数据进行干涉处理,获取2011年日本东北MW9.0地震的地表InSAR同震形变场;然后通过对InSAR同震形变数据重采样方法的深入分析,选择条纹率法结合干涉图的空间相干性对InSAR同震形变数据进行重采样;最后基于弹性半空间位错模型,联合InSAR与GPS形变数据,采用最小二乘法反演发震断层的滑动分布.研究结果表明:考虑相干性的条纹率重采样方法,更适用于形变场中存在除断层外的有限边界、且形变场范围较大的InSAR数据重采样处理;断层滑动主要发生在地表以下50km范围内,最大滑动量为49.9m,矩张量为4.89×1022 N·m,所对应的矩震级为MW9.1,与地震学反演的结果比较吻合.

2011年日本东北Mw 9.0级地震的岩石圈三维建模分析

2011年3月11日日本东北地区太平洋海域发生Mw 9.0级地震。日本海沟板块俯冲速率高,地震活动性强,因此研究程度高,到目前为止已获得了覆盖日本海沟弧前区域的地震波剖面数据。本文利用8条岩石圈结构剖面建立了日本海沟的三维岩石圈结构模型。日本海沟岛弧地壳由上到下包含5层:古近系—新近系—第四系海相沉积岩、白垩系海相沉积岩、岛弧上地壳俯冲杂岩、岛弧下地壳和地幔楔;日本海沟北部还存在中地壳;洋壳是一个双层构造,上层为熔岩和席状岩墙群,下层为堆晶辉长岩;陆壳和洋壳之间存在一个低速的板间层。本文在三维模型基础上讨论了俯冲板块的弯曲点和弯曲轴等几何学特征,分析了日本海沟俯冲带的历史地震和日本东北Mw 9.0级地震主震和余震的震源分布,日本东北地区的地震活动与太平洋板块向日本岛弧下方的俯冲活动关系密切。