Methods for Evaluation of Geodetic Data and Seismicity Developed with Numerical Simulations: Review and Applications

In this work we review the development of both established and innovative analytical techniques using numerical simulations of the southern California fault system and demonstrate the viability of these methods with examples using actual data. The ultimate goal of these methods is to better understand how the surface of the Earth is changing on both long-and short-term time scales, and to use the resulting information to learn about the internal processes in the underlying crust and to predict future changes in the deformation and stress field. Three examples of the analysis and visualization techniques are discussed in this paper and include the Karhunen-Loeve (KL) decomposition technique, local Ginsberg criteria (LGC) analysis, and phase dynamical probability change (PDPC). Examples of the potential results from these methods are provided through their application to data from the Southern California Integrated GPS Network (SCIGN), historic seismicity data, and simulated InSAR data, respectively. These analyses, coupled with advances in modeling and simulation, will provide the capability to track changes in deformation and stress through time, and to relate these to the development of space-time correlations and patterns.     

Virtual California: Fault Model, Frictional Parameters, Applications

Virtual California is a topologically realistic simulation of the interacting earthquake faults in California. Inputs to the model arise from field data, and typically include realistic fault system topologies, realistic long-term slip rates, and realistic frictional parameters. Outputs from the simulations include synthetic earthquake sequences and space-time patterns together with associated surface deformation and strain patterns that are similar to those seen in nature. Here we describe details of the data assimilation procedure we use to construct the fault model and to assign frictional properties. In addition, by analyzing the statistical physics of the simulations, we can show that that the frictional failure physics, which includes a simple representation of a dynamic stress intensity factor, leads to self-organization of the statistical dynamics, and produces empirical statistical distributions (probability density functions: PDFs) that characterize the activity. One type of distribution that can be constructed from empirical measurements of simulation data are PDFs for recurrence intervals on selected faults. Inputs to simulation dynamics are based on the use of time-averaged event-frequency data, and outputs include PDFs representing measurements of dynamical variability arising from fault interactions and space-time correlations. As a first step for productively using model-based methods for earthquake forecasting, we propose that simulations be used to generate the PDFs for recurrence intervals instead of the usual practice of basing the PDFs on standard forms (Gaussian, Log-Normal, Pareto, Brownian Passage Time, and so forth). Subsequent development of simulation-based methods should include model enhancement, data assimilation and data mining methods, and analysis techniques based on statistical physics.     

Representing the bed roughness of coarse‐grained streams in computational fluid dynamics

Computational fluid dynamics (CFD) applications are increasingly utilized for modelling complex flow patterns in natural streams and rivers. Although CFD has been successfully implemented to model many complex flow situations in natural stream settings, adequately characterizing the effects of gravel and cobble beds on flow hydraulics in CFD is a difficult challenge due to the scale of roughness lengths and the inadequacy of traditional roughness representations to characterize flow profiles in situations with large roughness elements. An alternative method of representing gravel and cobble beds is presented. Appropriate drag forces associated with different grain sizes are computed and included in the momentum equations to account for the influence of a hydraulically rough bed. Comparisons with field measurements reveal reasonable agreement between measured and modelled profiles of spatially averaged velocity and turbulent kinetic energy, and model fidelity to the non‐logarithmic behaviour of the velocity profiles. The novel method of representing coarse beds expands the utility of CFD for investigating physical processes in natural channels with large bed roughness. Copyright © 2005 John Wiley & Sons, Ltd.     

On the nature of turbulent kinetic energy in a steep and narrow Alpine valley

This contribution investigates the nature of turbulent kinetic energy (TKE) in a steep and narrow Alpine valley under fair-weather summertime conditions. The Riviera Valley in southern Switzerland was chosen for a detailed case study, in which the evaluation of aircraft data (obtained from the MAP-Riviera field campaign) is combined with the application of high-resolution (350-m horizontal grid spacing) large-eddy simulations using the numerical model ARPS. The simulations verify what has already been observed on the basis of measurements: TKE profiles scale surprisingly well if the convective velocity scale w _* is obtained from the sun-exposed eastern slope rather than from the surface directly beneath the profiles considered. ARPS is then used to evaluate the TKE-budget equation, showing that, despite sunny conditions, wind shear is the dominant production mechanism. Therefore, the surface heat flux (and thus w _*) on the eastern slope does not determine the TKE evolution directly but rather, as we believe, indirectly via the interaction of thermally-driven cross-valley and along-valley flows. Excellent correlation between w _* and the up-valley wind speed solidifies this hypothesis.     

EFFECTS OF PACIFIC SSTA ON SUMMER PRECIPITATION OVER EASTERN CHINA, PART Ⅱ: NUMERICAL SIMULATIONS

Based on an observational analysis, seven numerical experiments are designed to study the impacts of Pacific SSTA on summer precipitation over eastem China and relevant physical mechanism by NCAR CCM3. The numerical simulation results show that preceding winter SSTA in the Kuroshio region leads to summer precipitation anomaly over the Yangtze River valleys by modifying atmospheric general circulation over eastern Asia and middle-high latitude. West Pacific subtropical high is notably affected by preceding spring SSTA over the middle and east of Equator Pacific; SSTA of the central region of middle latitude in the corresponding period causes the summer rainfall anomaly over eastern China so as to trigger the atmospheric Eurasia-Pacific teleconnection pattern.     

Numerical studies of shear banding in interface shear tests using a new strain calculation method

Strain localization is closely associated with the stress–strain behaviour of an interphase system subject to quasi‐static direct interface shear, especially after peak stress state is reached. This behaviour is important because it is closely related to deformations experienced by geotechnical composite structures. This paper presents a study using two‐dimensional discrete element method (DEM) simulations on the strain localization of an idealized interphase system composed of densely packed spherical particles in contact with rough manufactured surfaces. The manufactured surface is made up of regular or irregular triangular asperities with varying slopes. A new simple method of strain calculation is used in this study to generate strain field inside a simulated direct interface shear box. This method accounts for particle rotation and captures strain localization features at high resolution. Results show that strain localization begins with the onset of non‐linear stress–strain behaviour. A distinct but discontinuous shear band emerges above the rough surface just before the peak stress state, which becomes more expansive and coherent with post‐peak strain softening. It is found that the shear bands developed by surfaces with smaller roughness are much thinner than those developed by surfaces with greater roughness. The maximum thickness of the intense shear zone is observed to be about 8–10 median particle diameters. The shear band orientations, which are mainly dominated by the rough boundary surface, are parallel with the zero extension direction, which are horizontally oriented. Published in 2007 by John Wiley & Sons, Ltd.     

Discharge and transport processes along the German Baltic Sea Coast

The western Baltic Sea infront of the German coast is a highly variable dynamical system, dominated by a complex and small-scale morphometry, the water exchange between the Baltic and North Seas, and driven by local wind. Neither data collection, nor satellite images or model simulations alone were able to explain the observed spatial patterns and transport processes. Therefore, all these methods were combined to explain the dynamical features and to systematise them according to the typical local wind pattern and time series. The aim was to develop an instrument for regional authorities which supports the interpretation of coastal water monitoring data and forms a basis for an improved monitoring strategy. Satellite data of sea surface temperature and ocean colour from the sensors NOAA-AVHRR and SeaWiFS were applied for synoptic investigations in the entire region and Landsat-7-ETM+ for regional studies. Model simulations were performed for the western Baltic using a 3D model MOM-3 and for the Szczecin Lagoon using 2D model FEMFLOW. For the first time, regional particularities in the coastal dynamical features and processes are derived for the main wind directions and for transitions between dominant wind situations west and east as derived from wind statistics. The simulated transport of particles released from different coastal and open sea sources indicate the affected areas during changing forcing conditions. The results support the interpretation of acquired coastal monitoring data as well as the assessment and optimisation of the monitoring programme.     

NUMERICAL SIMULATIONS OF β-GYRES IN TROPICAL CYCLONES

1INTRODUCTIONEversincethe1940抯,thetropicalcyclone(TC)hasbeenviewedasapointvortexorrigidvortex.Thepredictionissummedupasoneforairflowintheambientfield.Themethodusuallysucceeds.Thesteeringtheoryfortheairflowbecomesitstheoreticalfoundation.Thoughwithsomesuccess,theactualtrackofTCmovementcanbemuchdeviatedfromthesteeringcurrent,asseeninroutineforecastpractice.Withoutmuchchangesintheambientsteeringcurrent,theTCcanhaveunexpectedchangesinthedirection,speedofmotionorintensity.Atypicalexamplewo…     

A new approach for calculating strain for particulate media

Discrete element modelling is a viable alternative to conventional continuum‐based analysis for analysing problems involving localized deformations of particulate media. However, to aid in the interpretation of the results, it is useful to express the results of discrete element analyses in terms of the continuum parameters of stress and strain. A number of homogenization methods have been proposed to calculate strain in discrete systems; however, two significant limitations of these methods remain. First, none of these methods incorporate particle rotation effects satisfactorily, although significant particle rotation occurs in shear bands in both physical tests and numerical simulations of granular materials. Additionally, observations of the particle displacement fields in shear bands in granular materials indicate that the displacements within the localizations are erratic. Consequently, existing linear, local interpolation approaches produce substantial variations in the strain values calculated in adjacent elements in the region of localization, hindering clear visualization of the strain localization as it evolves. A new method of domain discretization for calculating strain is proposed. This method is capable of capturing particle rotation and employs a non‐local meshfree interpolation procedure capable of smoothing the erratic displacements in strain localizations, which better defines their evolution. The proposed method is validated for problems involving both two and three dimensions. A number of methods are compared with the proposed method and pertinent insights are made. Copyright © 2003 John Wiley & Sons, Ltd.     

Amplification of earthquake ground motion by steep topographic irregularities

The problem of amplification of seismic waves by surface topographic irregularities is addressed through analytical and numerical investigations. First, a closed‐form expression for estimating the fundamental vibration frequency of homogeneous triangular mountains is obtained, using Rayleigh's method. Subsequently, numerical modelling based on the spectral element approximation is used to study the 3D seismic response of several real steep topographic irregularities excited by vertically propagating plane S‐waves. A topographic amplification factor is obtained for each case, by a suitable average of the ratio of acceleration response spectra of output vs input motion. The 3D amplification factors are then compared with those derived by 2D analyses as well as with the topographic factors recommended in Eurocode 8 for seismic design. Copyright © 2002 John Wiley & Sons, Ltd.