印度洋地震海啸(2004-12-26)及其对中国的警示

2004年12月26日印度尼西亚苏门答腊岛西北近海发生ML9级强烈地震。地震的强度是100a来全球非常罕见的。地震引起了巨大海啸,浪高近10m,波及到东南亚、南亚和东非地区10多个国家,造成近30万人遇难。地震使印度尼西亚、泰国的部分岛屿发生了地形变化。海啸在受灾国留下了大片的盐碱地。苏门答腊板块边缘的一个长距离破裂带通过长时间积累,蓄积了巨大能量。这些能量在2004-12-26集中释放出来。导致了这次地震海啸的发生。地震海啸灾害本身规模巨大,发生异常突然,再加上受灾地区人员密集,缺乏海啸灾害逃生的知识和经验。印度洋沿岸国家没有海啸预警系统,是造成这次灾害巨大伤亡的原因。中国从台湾-海南岛一线的海区,存在地震海啸的可能性。因此应不断完善海啸预警系统,提高沿海地区建设工程的防灾抗灾标准,加强防波堤建设以及采取恢复红树林等生物工程措施,预防潜在的海啸灾害。     

海啸波作用下泥沙运动——Ⅴ.红树林影响下的岸滩变化

近年来频发的海啸灾害造成巨大损失,而红树林具有很好的减小海啸灾害的作用。实验采用PVC圆管来概化模拟红树林,以无黏性沙堆砌而成1/10~1/20组合坡概化岸滩,选取孤立波模拟海啸波。实验结果表明,红树林的存在对岸滩剖面变化产生了较大影响,适当增加植物分布密度,并优化植物的分布方式,可有效减小海啸波对岸滩的冲刷危害。在本次实验条件下,得到了岸滩冲刷坑尺度、淤积沙坝尺度、最大冲刷深度、最大淤积高度与红树林的分布方式和密度、海啸波波高、泥沙比重和岸滩坡度之间的关系式,揭示了沙质岸滩剖面变化与红树林、海啸波水动力特性、泥沙颗粒、岸滩坡度之间的内在联系,为减小海啸灾害提供科学依据。     

国内外海底观测网络的建设进展

海底观测网络是海底技术发展的新领域,它将各种观测仪器放到海底,可对海水层、海底和海底以下的岩石进行长期动态的观测,并实时将数据传回到陆地。简介了国内外主要的海底观测网络,重点跟踪了它们的最新建设进展。     

基于强震动资料的破裂过程快速反演及其自动化的可行性

破裂过程快速反演是目前快速获取地震灾害特征的主要手段之一,是震后应急工作的重要内容.近十年来基于远震资料开展的手动快速反演工作取得了长足进步,但在响应时间方面存在固有的局限,阻碍了反演效率的持续提升.我们根据新近发展的IDS（Iterative Deconvolution and Stacking）自动反演方法,尝试反演近场强震动资料确定破裂过程,探讨破裂过程反演自动化的可行性.对近几年国内发生的强震——包括2013年芦山M_W6.6地震、2016年青海门源M_W5.9地震和2016年新疆阿克陶M_W6.6地震——的应用结果表明,采用IDS方法反演强震数据可以得到稳定可靠的破裂模型,且反演计算时间都控制在几十秒内.此外,以2008年汶川M_W7.9地震为例,测试了不同子断层尺度、截止频率和地壳速度结构模型对反演结果的影响,发现滑动分布主要特征不强烈依赖于反演参数和地壳模型,证实了自动反演的稳定性和很强的适应能力.这一研究表明,基于强震动资料的自动反演可能是破裂过程快速反演的主要发展方向.特别地,在未来强震动台网持续发展、强震动数据的质量和共享速度都得到进一步提高之后,这一工作可望纳入到地震参数的常规自动测定工作中,为震后应急和海域地震的海啸预警提供急需的震源模型.

     

Tsunami bore runup

Nearshore behaviors of tsunamis, specifically those formed as a single uniform bore, are investigated experimentally in a laboratory environment. The transition process from tsunami bore to runup is described by the momentum exchange process between the bore and the small wedge-shaped water body along the shore: the bore front itself does not reach the shoreline directly, but the large bore mass pushes the small, initially quiescent water in front of it. The fluid motions near the runup water line appear to be complex. The complex flow pattern must be caused by irregularities involved in the driving bore and turbulence advected into the runup flow. Those experimental results suggest that the tsunami actions at the shoreline involve significant mean kinetic energy together with violent turbulence. Even though the behaviors of bore motion were found to be different from those predicted by the shallow-water wave theory, the maximum runup height appears to be predictable by the theory if the value of the initial runup velocity is modified (reduced). Besides the friction effect, this reduction of the initial runup velocity must be related to the transition process as well as the highly interacting three-dimensional runup motion.     

A microfaunal and sedimentary record of environmental change within the late Holocene sediments of Boca do Rio (Algarve,Portugal)

The foraminifera and ostracods observed in a late Holocene sedimentary sequence within a fluvial valley at Boca do Rio in the coastal zone of the western Algarve, Portugal, reveal a general, though not smooth transition from marine to fluvial conditions. The relative influence of these two environments appears to depend on the degree of permeability of the barrier system at the coast. Optically stimulated luminescence dates and palaeoecological information obtained from the sequence suggest that barrier formation may be related to changes in climate and/or patterns of ocean current circulation. An unusual deposit rich in sand and gravel found within the otherwise mud-dominated sequence has been dated at AD 1801 ± 76 years. This deposit contains foraminifera and ostracods which indicate marine conditions, and which contrast markedly with the brackish-water, estuarine assemblages found in the mud deposits. The rapid transition in the foraminifera and ostracod assemblages indicates a short-lived coastal flooding, which may represent the tsunami associated with the Lisbon earthquake of AD 1755. The variations in the foraminifera and ostracod assemblages also suggest subsidence during the earthquake, with uplift having occurred in the period since then.     

Real-Time Tsunami Forecasting: Challenges and Solutions

A new method for real-time tsunami forecasting will provide NOAAs Tsunami Warning Centers with forecast guidance tools during an actual tsunami event. PMEL has developed the methodology of combining real-time data from tsunameters with numerical model estimates to provide site- and event-specific forecasts for tsunamis in real time. An overview of the technique and testing of this methodology is presented.     

Planning for Tsunami: Reducing Future Losses Through Mitigation

The National Tsunami Hazard Mitigation Program is a multi-faceted approach that encompasses tsunami identification, alert and warning systems and a comprehensive approach to tsunami risk reduction. This paper describes efforts to promote land use planning and development practices that reduce tsunami risk by local elected government and administrative officials. Seven Principles of Tsunami Risk Reduction are presented that range from risk assessment to site planning criteria.Regional Administrator, California Governors Office of Emergency Services and Manager, California Integrated Seismic Network, Earthquake and Tsunami Program     

Observations of Tsunami Impact on the Coast of Kerala, India

The tsunami generated by the December 2004 Sumatra-Andaman earthquake had a devastating effect on some parts of Kerala coast, which is a coast located in southwest India. Results of post-tsunami field surveys carried out to understand the changes in coastal morphology and sediment characteristics in the worst affected Kayamkulam region of Kerala coast are documented in this study. Analysis of offshore bathymetric data indicates the shifting of depth contours towards shore, indicating erosion of sediments and deepening of innershelf due to the tsunami. Depth measurement along the backwater (T-S canal) in the hinterland region indicates siltation due to the inundation of the canal.     

A smoothing algorithm to enhance finite-element tsunami modelling: An application to the 5 February 1783 Calabrian case,Italy

Numerical simulations are essential tools for studying tsunami generation and evolution and finite-element (FE) methods are widely used, especially because of their capability in modeling water waves in basins with complex bathymetry and irregular coastlines. This paper presents the numerical simulation of an historical Italian tsunami that affected the Tyrrhenian coasts of Calabria and Sicily on 5 February 1783 following a strong destructive earthquake that was the first of a terrible sequence of seismic shocks terrifying the Calabrian population for more than two months. The numerical model is an FE model based on the nonlinear nondispersive shallow-water approximation of the Navier-Stokes equations. Since FE discretization schemes may lead to solutions undesirably affected by noise over coarse grids, in this study numerical noise is controlled by suitably smoothing the FE solution at regular time steps t _s. The performance of our smoothing algorithm is tested for significant linear cases for which an analytical solution is available.