地震海啸在东海大陆架上传播过程的数值模拟研究

在东海潜在震源区冲绳海槽假定了五个震源点,根据Steven地震海啸地震参数经验值作为初始条件,分别考虑6.5、7.0、7.5、8.0、8.5、9.0级地震条件下的30个震例,采用数值模拟的方法,对海啸在东海传播过程进行情境分析,特别是对上海沿岸地区可能会遭受的海啸灾害做了较为精细的研究.结果发现:小于8.0级的震例对上海地区几乎不会造成影响;8.0级震例只有最北端震源点震例会对上海地区有明显影响;8.5级以及9.0级震级基本上均会对上海沿岸地区造成较大的影响.特别是冲绳海槽北段9.0级震例可能会对上海沿岸局部地区造成危害,最大波高可达3.9m.     

Tsunami–tide interactions: A Cook Inlet case study

First, we investigated some aspects of tsunami–tide interactions based on idealized numerical experiments. Theoretically, by changing total ocean depth, tidal elevations influence the speed and magnitude of tsunami waves in shallow regions with dominating tidal signals. We tested this assumption by employing a simple 1-D model that describes propagation of tidal waves in a channel with gradually increasing depth and the interaction of the tidal waves with tsunamis generated at the channel's open boundary. Important conclusions from these studies are that computed elevations by simulating the tsunami and the tide together differ significantly from linear superposing of the sea surface heights obtained when simulating the tide and the tsunami separately, and that maximum tsunami–tide interaction depends on tidal amplitude and phase. The major cause of this tsunami–tide interaction is tidally induced ocean depth that changes the conditions of tsunami propagation, amplification, and dissipation. Interactions occur by means of momentum advection, bottom friction, and variable water flux due to changing total depth and velocity. We found the major cause of tsunami–tide interactions to be changing depth. Secondly, we investigate tsunami–tide interactions in Cook Inlet, Alaska, employing a high-resolution 2-D numerical model. Cook Inlet has high tides and a history of strong tsunamis and is a potential candidate for tsunami impacts in the future. In agreement with previous findings, we find that the impacts of tsunamis depend on basin bathymetries and coastline configurations, and they can, in particular, depend on tsunami–tide interactions. In regions with strong tides and tsunamis, these interactions can result in either intensification or damping of cumulative tsunami and tide impacts, depending on mean basin depth, which is regulated by tides. Thus, it is not possible to predict the effect of tsunami–tide interaction in regions with strong tides without making preliminary investigations of the area. One approach to reduce uncertainties in tsunami impact in regions with high tides is to simulate tsunamis together with tidal forcing.     

试论地震海啸的成因

经统计与研究,多数地震是不引发海啸的,故地震与海啸不存在直接的因果关系。这是因为引发地震海啸(特别是大的地震海啸)的直接原因,主要是海底地震所造成的次生的巨大体积的海底滑坡和崩塌,而不是海底地震时海底地面的同震错断与变形。因此,若未来震中附近存在不稳定海底滑坡和崩塌体,只要发生地震,不论震级大小与震源深浅,也不论震源类型(即倾滑或走滑)都可引起海底滑坡和崩塌,进而引发海啸。若未来震中附近不存在不稳定海底滑坡和崩塌体,再大震级的地震,即使是倾滑型地震也不能引发海啸     

Inundation flow velocity of tsunami on land

An estimation of tsunami inundation flow velocity is one of the most challenging issues among tsunami research. Based on field data of inundation depth and inundation flow velocity u estimated using Bernoulli's theorem and inundation depth, fundamental characteristics of the relationship between inundation flow velocity and inundation depth are examined. Fundamental characteristics of the velocity coefficient where g is gravitational acceleration, h_f and h_r are inundation depths at the front and the back of structures such as a rectangular building with vertical walls, respectively) implicitly included in the relationship are examined through hydraulic experiments. As a result, C_v = 0.6 is recommended as its simple and practical value. It is confirmed through these examinations that the Froude number, defined by where , ranges 0.7–2.0, and when C_v = 0.6 is adopted this Froude number ranges 0.42–1.2. By using the relationship and C_v = 0.6, two simple and practical relationships are presented for two cases where inundation flow velocity exerts the largest or the smallest fluid force on structures. These relationships can be used to roughly grasp the practical side of tsunami damage, and estimate fluid force acting on individual structures, moving velocity and collision force of floating objects and sediment transport such as boulder and sand. Fundamental characteristics of the waterline (tsunami trace) distribution around/on the typical object model (square pillar, corn and column) are also examined through steady flow experiments, and it is confirmed that the maximum and the minimum values of h_f/h₀ in the full type model of the square pillar are almost the same as those of h_f/h_r obtained by field surveys where h₀ is uniform flow depth. It is also confirmed that h_r ? h₀ when the Froude number, defined by where u₀ is uniform flow velocity, is much less than 1.0. Using a newly defined velocity coefficient, tsunami inundation flow velocity on land can be estimated practically and would be useful for checking proposed sediment transport models that are now being developed by tsunami geologists.     

Putting a spin on palaeotsunami deposits

Palaeotsunami research is a relatively young discipline and while considerable progress has been made in identifying the evidence of past events there are still difficulties on occasion in differentiating between palaeotsunami and palaeostorm deposits. This has tended to focus debate on the similarities and differences between deposits laid down by the two differing processes at the expense of alternative hypotheses. Although coastal research in New Zealand a decade ago drew attention to high elevation coarse sediment deposits laid down by waterspouts, it was largely ignored by the research community. Re‐analysis of a possible palaeotsunami deposit on a nearshore island in New Zealand, however, highlights the likelihood that this deposit, and perhaps many similar coastal ones, may have been laid down by waterspouts. In essence, the palaeotsunami–palaeostorm debate can no longer ignore waterspouts as an alternative hypothesis, but only time will tell how significant a contribution waterspouts have made to catastrophic coastal sedimentation. Copyright © 2016 John Wiley & Sons, Ltd.     

Continuous estimates on the earthquake early warning magnitude by use of the near-field acceleration records

In this article, the seismic records of Japan’s Kik-net are selected to measure the acceleration, displacement, and effective peak acceleration of each seismic record within a certain time after P wave, then a continuous estimation is given on earthquake early warning magnitude through statistical analysis method, and Wenchuan earthquake record is utilized to check the method. The results show that the reliability of earthquake early warning magnitude continuously increases with the increase of the seismic information, the biggest residual happens if the acceleration is adopted to fit earthquake magnitude, which may be caused by rich high-frequency components and large dispersion of peak value in acceleration record, the influence caused by the high-frequency components can be effectively reduced if the effective peak acceleration and peak displacement is adopted, it is estimated that the dispersion of earthquake magnitude obviously reduces, but it is easy for peak displacement to be affected by long-period drifting. In various components, the residual enlargement phenomenon at vertical direction is almost unobvious, thus it is recommended in this article that the effective peak acceleration at vertical direction is preferred to estimate earthquake early warning magnitude. Through adopting Wenchuan strong earthquake record to check the method mentioned in this article, it is found that this method can be used to quickly, stably, and accurately estimate the early warning magnitude of this earthquake, which shows that this method is completely applicable for earthquake early warning.     

深圳海域潮汐海啸波耦合数值研究

以COMCOT海啸模式和TPXO7.1全球潮汐模式为基础,采用三层嵌套网格,建立了南海海啸与潮汐耦合计算模型,分析深圳海域海啸和潮汐相互作用。潮汐计算结果与实测数据吻合较好,高、低潮位平均误差小于15 cm,20 cm;在潮汐验证的基础上,以马尼拉海沟潜在地震海啸源为案例,进行8.0,9.0级地震海啸与潮汐耦合情景模拟计算,计算结果表明,9级地震海啸在深圳海域外海波高为140~150 cm,如先行波为正波发生在高潮时将产生异常高潮位,负波发生在低潮时将产生异常低潮位,线性叠加计算结果偏大,在25.0 cm之内,到达时间差异小于6 min。     

Roles of financial innovation and information technology: Lessons from US sub-prime mortgage crisis and its implications for China

The mortgage loan has evolved from a local lending instrument into a major global security and its role is unparallel to other financial instruments in the process of financial globalization.This paper explains how technology and financial innovation transformed the mortgage loan from a local security into a premier global security traded worldwide.It examines the fundamental flaws of this process and why it does not work in regards to mortgage lending and the re-securitization products that were created through financial innovation.The findings show that regulation was unable to keep pace with financial innovation,which created an environment where actors in the financial service sector were able to behave geographically irresponsibly by using information asymmetries to their advantage by participating in moral hazard activities and engaging in other immoral and unethical business practices that were centered around localized geography,which ultimately contributed to the global financial crisis.It also examines the roll of financial innovation in regard to the Lehman Brothers Mini-Bond in Hong and its role as a driving force behind China’s newly emerging shadow banking sector.It concludes with a policy recommendation and its implication for China’s continued economic development.     

从2011 海啸演习看中国海啸危害

2011 年11 月, 联合国教科文组织政府间海洋学委员会(IOC/UNESCO)发起了代号为“Exercise Pacific Wave 11”的跨国海啸演习, 演习区域为整个太平洋海区。中国应邀参加了本次演习, 演习在我国海域地震带上假设了两个震源, 分别位于琉球海沟和马尼拉海沟。为了评估这两个潜在海啸对我国的影响, 本文采用数值模拟的方式, 对其进行了计算。计算结果表明: 这两处震源所引发的海啸均能对我国造成灾害性影响, 受影响严重的省市有江苏、上海、浙江、福建、广东和海南等; 从传播时间图上看, 若发生大海啸, 海啸波将在5 h 内, 陆续影响沿海各省市; 相比琉球海沟, 马尼拉海沟震源产生的海啸会更快到达我国沿岸。     

全球海啸灾害事件统计及预警系统简述

统计分析了全球历史海啸灾害数据,结合相关海啸研究成果,给出了全球海啸的分布特点及历史重大事件,并介绍了全球海啸预警系统、数值技术以及海啸监测等防灾情况。