COMBINED TRAVELTIME AND FREQUENCY-DOMAIN SEISMIC WAVEFORM INVERSION: A CASE STUDY ON MULTI-OFFSET ULTRASONIC DATA

Abstract

We present the acquisition and processing of a multi-offset ultrasonic tomography experiment in which we aim to precisely reconstruct the image and kinematic properties of two scatterers that contrast strongly with the water background. The resultant non-linearity causes the failure of a frequency-domain waveform fitting strategy for retrieving the whole range of experimentally covered wavenumbers. A mixed tomographic approach is instead adopted in which traveltime and waveform inversion are combined iteratively. This strategy helps in overcoming the waveform inverse problem non-linearity and the data computed in our final tomographic model match most of the observed features in the experimental seismograms. This model is in good agreement with what is known concerning the properties of the scatterers and it is characterized by both the high focusing of waveform tomography and the accurate kinematics of traveltime tomography. These achievements are reached in spite of a limited, but nevertheless uniform, geometric coverage. Our strategy of using two different tomographic tools sequentially therefore appears to be a possible solution to addressing the issue of highly non-linear seismic inverse problems.