海啸在冲绳海槽和东海浅水大陆架地形上产生和传播的数值模拟

运用数值模拟的方法对在冲绳海槽产生9.0级地震,并引发海啸的过程和海啸波在东海浅水大陆架地形上的传播过程进行研究.模拟的结果表明,数值模拟产生的波浪符合海啸波的特点,东海浅水大陆架适合海啸波的传播.     

The landslides and tsunamis of the 30th of December 2002 in Stromboli analysed through numerical simulations

On the 30th of December 2002 two tsunamis were generated only 7 min apart in Stromboli, southern Tyrrhenian Sea, Italy. They represented the peak of a volcanic crisis that started 2 days before with a large emission of lava flows from a lateral vent that opened some hundreds of meters below the summit craters. Both tsunamis were produced by landslides that detached from the Sciara del Fuoco. This is a morphological scar and is the result of the last collapse of the northwestern flank of the volcanic edifice, that occurred less than 5 ka b.p. The first tsunami was due to a submarine mass movement that started very close to the coastline and that involved about 20×10⁶ m³ of material. The second tsunami was engendered by a subaerial landslide that detached at about 500 m above sea level and that involved a volume estimated at 4–9×10⁶ m³. The latter landslide can be seen as the retrogressive continuation of the first failure. The tsunamis were not perceived as distinct events by most people. They attacked all the coasts of Stromboli within a few minutes and arrived at the neighbouring island of Panarea, 20 km SSW of Stromboli, in less than 5 min. The tsunamis caused severe damage at Stromboli.In this work, the two tsunamis are studied by means of numerical simulations that use two distinct models, one for the landslides and one for the water waves. The motion of the sliding bodies is computed by means of a Lagrangian approach that partitions the mass into a set of blocks: we use both one-dimensional and two-dimensional schemes. The landslide model calculates the instantaneous rate of the vertical displacement of the sea surface caused by the motion of the underwater slide. This is included in the governing equations of the tsunami, which are solved by means of a finite-element (FE) technique. The tsunami is computed on two different grids formed by triangular elements, one covering the near-field around Stromboli and the other also including the island of Panarea.The simulations show that the main tsunamigenic potential of the slides is restricted to the first tens of seconds of their motion when they interact with the shallow-water coastal area, and that it diminishes drastically in deep water. The simulations explain how the tsunamis that are generated in the Sciara del Fuoco area, are able to attack the entire coastline of Stromboli with larger effects on the northern coast than on the southern. Strong refraction and bending of the tsunami fronts is due to the large near-shore bathymetric gradient, which is also responsible for the trapping of the waves and for the persistence of the oscillations. Further, the first tsunami produces large waves and runup heights comparable with the observations. The simulated second tsunami is only slightly smaller, though it was induced by a mass that is approximately one third of the first. The arrival of the first tsunami is negative, in accordance with most eyewitness reports. Conversely, the leading wave of the second tsunami is positive.     

基于速率-状态摩擦定律的地震二维准动力学数值模拟:浅层正应力变化对断层演化的影响

本文基于结合速率-状态摩擦定律(RSF)的二维准动力学数值模型, 以半空间垂直走滑断层为研究对象, 通过比较两种正应力随深度变化模型的模拟结果, 研究了浅层正应力变化对断层演化参数、地震孕育过程、震后滑移传播等方面的影响.结果显示, 我们的数值模型在给定模型参数和约束条件下, 能够完整模拟出地震周期中震间、震前、同震以及震后多个特征阶段.常数正应力模型下, 动态破裂在浅层速率强化区停止, 而在浅层变化正应力模型下动态破裂可以传播至自由表面, 导致浅层更高的最大滑移速率和同震滑移量.两种模型下的地震矩、地震周期、平均应力降和震后滑移传播等差别不明显.两种滑移模型的傅氏振幅谱与理论K^-2模型傅氏振幅谱均符合较好, 且浅层变化正应力模型下的拐角波数值高于常数正应力模型, 说明两种模型均符合地震同震滑移模型的运动学特征, 并且浅层变化正应力模型下最终应该产生高于常数正应力模型的高频强地面运动水平.我们认为选用不同的模型参数对最终结果存在显著影响, 应当根据具体问题来选择模型参数, 这样才能在保证结果准确前提下有效提高计算效率.

     

日本Mw9.0级地震海啸数值模拟与启示

2011年3月11日13时46分日本东北部海域发生Mw9.0级特大地震,地震诱发了海啸.本文依据USGS的震源机制解,进行了地震海啸的数值模拟,并与美国国家海洋与大气管理局布设的海底压力计记录的水深数据对比分析,结果表明数值模拟结果可信.同时,进一步分析了海啸造成巨大损失的原因,并对未来我国海啸防灾减灾工作给出了几点建...     

基于数值模拟和地震活动性统计的混合地震预测: 在中国地震科学实验场的应用

地震数值预测是近年来最为前沿的科学研究问题之一,但是大部分地震数值预测的探索都受困于数值模拟步长的问题.本文引入混合预测方法,探索了较短预测时长的地震数值预测方法,并在中国地震科学实验场区中进行应用.该混合预测方法主要建立在活动块体理论和构造力学分析的基础上,利用数值模拟推测未来长时间的应力变化量,并引入上一次7级地震之后数十年间,中等强度地震同震应力的影响,最后通过重分类和加权,在应力变化量上叠加年尺度小地震活动异常的统计,从而实现区域地震危险程度的混合评估.基于该方法,我们将地震数值预测的预测时间尺度缩短到年尺度,以年为单位滚动预测了中国地震科学实验场自2021—2030年或更长时间段内可能出现中强地震的区域.2022年芦山6.1级地震、2021年漾濞6.4级地震、2021年泸州6.0级地震和2022年泸定6.8级地震均发生在危险性较高的区域,而2022年马尔康6.0级地震则不在预测区域内.本文展示的混合预测尝试为地震数值预测研究提供了一个可供参考的例证,也为解决数值预测步长控制难的问题提供了一个可能的探索途径.