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Seismic ray tracing and wavefront tracking in laterally heterogeneous media
crop: (152mm, 229mm) cap: 3225 type wd: 11388, ht: 18065, col.wd: 11388(1/100mm)
ADVANCES IN GEOPHYSICS, VOL. 49, CHAPTER 3
SEISMIC RAY TRACING AND WAVEFRONT TRACKING IN LATERALLY HETEROGENEOUS MEDIA N. R AWLINSON† , J. H AUSER AND M. S AMBRIDGE Research School of Earth Sciences, Australian National University, Canberra ACT 0200, Australia
1. I NTRODUCTION 1.1. Motivation One of the most common and challenging problems in seismology is the prediction of source-receiver paths taken by seismic energy in the presence of lateral variations in wavespeed. The solution to this problem is required in many applications that exploit the high frequency component of seismic records, such as body wave tomography, migration of reflection data and earthquake relocation. The process of tracking the kinematic evolution of seismic energy also brings with it the possibility of computing various other wave-related quantities such as traveltime, amplitude, attenuation, or even the high frequency waveform, which can then be compared to observations. The difficulties associated with locating a two point path arise from the nonlinear relationship between velocity and path geometry. Figure 1, which shows a fan of ray paths propagate from a point source in a strongly heterogeneous medium, provides useful insight into this non-linearity. If the medium had been homogeneous, then the paths would simply have been straight lines emitting at uniform angular distance from the source. However, the focusing and defocusing effects of the velocity heterogeneity have imposed strong and varying curvature to the paths. In addition to the extremely non-linear distribution of rays along the boundaries of the medium, the phenomenon of multi-pathing, which equates to wavefront self-intersection, can also be observed. Thus, the already difficult problem of locating a valid path which connects two points has been further complicated by the fact that there may well be more than one path. Over the past few decades, the growing need for fast and accurate prediction of high frequency wave properties (most commonly traveltime) in complex 2-D
† Author thankse-mail: [email protected]; [email protected]; [email protected]
203
© 2008 Elsevier Inc. All rights reserved ISSN: 0065-2687 DOI: 10.1016/S0065-2687(07)49003-3
ADVANCES IN GEOPHYSICS, VOL. 49, CHAPTER 3
SEISMIC RAY TRACING AND WAVEFRONT TRACKING IN LATERALLY HETEROGENEOUS MEDIA N. R AWLINSON† , J. H AUSER AND M. S AMBRIDGE Research School of Earth Sciences, Australian National University, Canberra ACT 0200, Australia
1. I NTRODUCTION 1.1. Motivation One of the most common and challenging problems in seismology is the prediction of source-receiver paths taken by seismic energy in the presence of lateral variations in wavespeed. The solution to this problem is required in many applications that exploit the high frequency component of seismic records, such as body wave tomography, migration of reflection data and earthquake relocation. The process of tracking the kinematic evolution of seismic energy also brings with it the possibility of computing various other wave-related quantities such as traveltime, amplitude, attenuation, or even the high frequency waveform, which can then be compared to observations. The difficulties associated with locating a two point path arise from the nonlinear relationship between velocity and path geometry. Figure 1, which shows a fan of ray paths propagate from a point source in a strongly heterogeneous medium, provides useful insight into this non-linearity. If the medium had been homogeneous, then the paths would simply have been straight lines emitting at uniform angular distance from the source. However, the focusing and defocusing effects of the velocity heterogeneity have imposed strong and varying curvature to the paths. In addition to the extremely non-linear distribution of rays along the boundaries of the medium, the phenomenon of multi-pathing, which equates to wavefront self-intersection, can also be observed. Thus, the already difficult problem of locating a valid path which connects two points has been further complicated by the fact that there may well be more than one path. Over the past few decades, the growing need for fast and accurate prediction of high frequency wave properties (most commonly traveltime) in complex 2-D
† Author thankse-mail: [email protected]; [email protected]; [email protected]
203
© 2008 Elsevier Inc. All rights reserved ISSN: 0065-2687 DOI: 10.1016/S0065-2687(07)49003-3