Fault slip in the 1997 Manyi, Tibet earthquake from linear elastic modelling of InSAR displacements

The M _w 7.6 1997 Manyi earthquake occurred in an area of central northern Tibet where sparse vegetation coverage and a lack of human habitation provide excellent conditions for Interferometric Synthetic Aperture Radar (InSAR) studies. We use coseismic pairs of radar images acquired by the ESA ERS-2 satellite to construct interferograms of the surface displacement field due to the earthquake. The location and extent of the coseismic fault rupture are mapped using a combination of optical satellite imagery, high-resolution digital topography, interferometric correlation and azimuth offset measurements; in so doing, we are able to relate prominent geomorphic features in the fault zone to bends in the fault.
Using elastic dislocation models consistent with this mapped fault trace, we then test a range of fault geometries and slip conditions to find the combination which best explains the InSAR displacements. Our favoured model contains a reversal in fault dip, approximately halfway along its length, occurring at the location of a restraining bend. Slip on this model fault is heterogeneous, with two areas of peak slip of 7 m or greater, and components of dip-slip displacement which vary significantly along-strike. The success of this model in fitting the data implies that an observed asymmetry in the coseismic interferograms can be explained in terms of the local fault geometry, rather than by using non-linear elastic rheologies as suggested by earlier authors.     

The great British earthquake of 1984 seen from afar

Summary. The Lleyn Peninsular earthquake which occurred at 0656 on 1984 July 19 was recorded at three medium aperture seismological array stations located at teleseismic distances. From these recordings an estimate is made of the hypocentre, origin time, magnitude and fault-plane solution of the earthquake. The fault-plane solution was determined using the Pearce algorithm and indicates that the focal mechanism is predominantly strike-slip. The fault-plane solution was used to generate synthetic seismograms for comparison with the observed to confirm the nature of the source and in particular the depth of focus which was estimated to be 20.5 km. It is concluded that the determination of the earthquake parameters using only three teleseismic seismograms is in good agreement with the results obtained from an analysis of 45 local and regional seismological stations.     

Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering

10 M ≥ 6.7 earthquakes ruptured 1000 km of the North Anatolian fault (Turkey) during 1939–1992, providing an unsurpassed opportunity to study how one large shock sets up the next. We use the mapped surface slip and fault geometry to infer the transfer of stress throughout the sequence. Calculations of the change in Coulomb failure stress reveal that nine out of 10 ruptures were brought closer to failure by the preceding shocks, typically by 1–10 bar, equivalent to 3–30 years of secular stressing. We translate the calculated stress changes into earthquake probability gains using an earthquake-nucleation constitutive relation, which includes both permanent and transient effects of the sudden stress changes. The transient effects of the stress changes dominate during the mean 10 yr period between triggering and subsequent rupturing shocks in the Anatolia sequence. The stress changes result in an average three-fold gain in the net earthquake probability during the decade after each event. Stress is calculated to be high today at several isolated sites along the fault. During the next 30 years, we estimate a 15 per cent probability of a M ≥ 6.7 earthquake east of the major eastern centre of Ercinzan, and a 12 per cent probability for a large event south of the major western port city of Izmit. Such stress-based probability calculations may thus be useful to assess and update earthquake hazards elsewhere.     

基于元胞模型的河道纵剖面调整动态模拟

纵剖面的调整是河道演化的重要内容,其对于河道整治及水沙灾害机理研究都具有重要意义。利用多年观测资料可以较为精确地分析和推断河道纵剖面的调整过程。但是,这种方法不能从过程机理上对纵剖面的调整进行模拟分析。而自然条件下河道边界条件的复杂性使得对河道纵剖面演化的物理过程模拟有很大困难。元胞自动机是一个时间、空间和状态都离散的动力模型,是研究复杂系统动态演化过程的有力工具。本文以黄河尾闾河道为例,利用一维元胞模型对河道纵剖面的调整进行动态模拟。模拟揭示了河道纵剖面在初始形态、不同水沙组合以及河道延伸等情况下的演化规律与趋势。     

GIS-based dynamic modelling and analysis of flash floods considering land-use planning

Flood inundation is a common natural disaster and a growing development challenge for many cities and thousands of small towns around the world. Soil features have frequently altered with the rapid development of urbanised regions, which has led to more frequent and longer duration of flooding in urban flood-prone regions. Thus, this paper presents a geographic information system (GIS)-based methodology for measuring and visualising the effects on urban flash floods generated by land-use changes over time. The measurement is formulated with a time series in order to perform a dynamic analysis. A catchment mesh is introduced into a hydrological model for reflecting the spatial layouts of infrastructure and structures over different construction periods. The Geelong Waurn Ponds campus of Deakin University is then selected as a case study. Based on GIS simulation and mapping technologies, this research illustrates the evolutionary process of flash floods. The paper then describes flood inundation for different built environments and presents a comparison by quantifying the flooding extents for infrastructure and structures. The results reveal that the GIS-based estimation model can examine urban flash floods in different development phases and identify the change of flooding extents in terms of land-use planning. This study will bring benefits to urban planners in raising awareness of flood impact and the approach proposed here could be used for flood mitigation through future urban planning.     

高地震烈度区堆积体边坡动力响应时程特征分析

考虑到在地震过程中,工程边坡的动安全系数最小值出现在某一瞬间,而用这个值评价边坡在地震荷载作用下的抗滑稳定性不合适宜。在简单分析地震荷载作用下边坡稳定性评价的主要方法及差异基础上,介绍了地震动力响应时程分析法的基本原理和计算过程,明确指出了边坡动力稳定分析时应注意的边界条件、材料参数等问题,建立了评价动力稳定性的有限元应力法表达式。基于地震动力时程反应,结合金安桥水电站库岸堆积体边坡工程,用动力有限元计算获得了边坡的动力响应在空间的变化规律(包括动应力和加速度等)和整体稳定性,计算成果合理地评价了其稳定性。     

Neural network modelling of planform geometry of headland-bay beaches

The shoreline of beaches in the lee of coastal salients or man-made structures, usually known as headland-bay beaches, has a distinctive curvature; wave fronts curve as a result of wave diffraction at the headland and in turn cause the shoreline to bend. The ensuing curved planform is of great interest both as a peculiar landform and in the context of engineering projects in which it is necessary to predict how a coastal structure will affect the sandy shoreline in its lee. A number of empirical models have been put forward, each based on a specific equation. A novel approach, based on the application of artificial neural networks, is presented in this work. Unlike the conventional method, no particular equation of the planform is embedded in the model. Instead, it is the model itself that learns about the problem from a series of examples of headland-bay beaches (the training set) and thereafter applies this self-acquired knowledge to other cases (the test set) for validation. Twenty-three headland-bay beaches from around the world were selected, of which sixteen and seven make up the training and test sets, respectively. As there is no well-developed theory for deciding upon the most convenient neural network architecture to deal with a particular data set, an experimental study was conducted in which ten different architectures with one and two hidden neuron layers and five training algorithms – 50 different options combining network architecture and training algorithm – were compared. Each of these options was implemented, trained and tested in order to find the best-performing approach for modelling the planform of headland-bay beaches. Finally, the selected neural network model was compared with a state-of-the-art planform model and was shown to outperform it.     

Decision-theoretic limits on earthquake prediction

I apply Decision Theory to the question of how accurate earthquake predictions must be to serve as a reliable basis for action. Even with optimistic estimates of the parameters involved, the lower bound on the required accuracy is extraordinarily demanding, being over 10 times higher than that of current meteorological forecasts. Given the abruptly self-organizing nature of earthquakes, it is extremely unlikely that precursors can attain such levels of accuracy. I therefore conclude that prediction of major earthquakes is, in any practical sense, impossible.