Efficient Finite Difference Waveform Modeling of Selected Phases Using a Moving Zone

A new technique is presented for efficient finite difference computation and interpretational analysis of seismic wavefields. The basic idea is that the wavefield is only computed in a movingzone embracingthe wave front segment under concern. Two growing challenges in seismic full wavefield modeling are addressed by this technique. Firstly, computational load may be reduced significantly without significant loss in quality. Secondly, the complexity in wavefields may be analyzed by separatinginto phases. Only moderate modifications are required to implement this technique in a given time-space domain finite difference code. The movement of the box which must be given prior to modeling, may be derived more or less accurately from low frequency finite difference modeling or from ray tracing. Tests in 2-D demonstrate significant reduction in memory requirements and computer time at only moderate reduction in accuracy. Extension to 3-D wavefield computation and analysis is straightforward. r 2002 Elsevier Science Ltd. All ri hts reserved

Partial Derivatives And Iterative Inversion Of Seismic Wavefields

Introduction Modelling of seismic waves has been done for as many years as seismics have been considered. Nowadays Full Waveform Modelling of the wave equation is one of the most accurate ways to model the wave equation. Full waveform modelling started in the late 60's, Alterman & Karal (1968). Not until the mid 80's was Wave Form modelling widely used. In 1986 Virieux proposed a staggered grid scheme to solve the elastic wave-equation. Through the 80's Albert Tarantola (1984a, 1984b, 1986) proposed ideas on how to use inversion on the whole wavefield : Full Waveform Inversion. The theory he used was rather complex, but the conclusion he made was easy to use : Full waveform inversion could be seen as 'iterative migration'. The problem at the time was that the amount of computer power needed were tremendous. Thus to perform Full Waveform Inversion on small synthetic models required supercomputers. Still today the demand on computer power is great, but now small models can be inverted

Teleseismic Tomography When Stations Follow Profiles: Pitfalls and Remedies

Online Material: Discussion, figures of resolution matrix analy-sis of alternative cell geometries; alternative station distributions