Banca de DEFESA: RENATO RAMOS DA SILVA DANTAS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : RENATO RAMOS DA SILVA DANTAS
DATA : 17/05/2019
HORA: 09:00
LOCAL: Auditório do DGEF
TÍTULO:

Full-waveform inversion based on analytic trace functionals

PALAVRAS-CHAVES:

Seismic inversion; Full waveform inversion; Hilbert transform

PÁGINAS: 149
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

Currently, the greatest challenge to overcome in order to apply FWI is avoiding cycle-skipping. Accomplishing this goal requires an initial velocity model that has a significant amount of longwavelength information from the subsurface velocity distribution. In order to produce a suitable initial model, this thesis proposes an inversion approach composed of three stages. The output of each stage is the input of the next one. In the first stage, Dix-Stage, we build a model derived from a coarse Dix velocity analysis. In the second stage, K-Stage, we derive velocity models that honor the first-arrival traveltimes using a transmission inversion approach. In the third stage, FWI-Stage, a concluding waveform inversion process is carried out. The focus here is on the second stage, where we compare first-arrival traveltime tomography with the inversion of a misfit functional based on the windowed early arrivals of the envelope in producing starting models for the FWI-Stage, and on third stage. We use the Marmousi and Overthrust models to show that, in the K-Stage, the early-arrival envelope functional produces solutions with at least the same quality as those derived from first-arrival traveltime tomography. As a result, in the FWI-Stage, final velocity models with similar quality are obtained not mattering whether this stage was initialized with early-arrival envelope or with first-arrival traveltime tomography models. However, unlike the first-arrival traveltime tomography, the early-arrival envelope inversion does not require time picking, which could save an expressive amount of time. In addition, the early-arrival envelope functional is robust to noise. We conclude then that the early-arrival envelope functional has good potential to substitute first-arrival traveltime tomography in the K-Stage. However, neither earlyarrival envelope or traveltime functionals are free from problems and, as a result, the interpreter ultimately must judge the resulting velocity models to decide whether they are valid to initialize an FWI process. For the FWI Stage, we propose a sequence of different misfit functions in time domain. The employed misfit functions are sensitive to different wavelengths but use the same modeling algorithm and the same model grid. In the first and third inversion steps the transmitted (early arrivals) and reflected (late arrivals) components of the wavefield envelopes are respectively fitted. The second step promotes a smooth transition between the first and third steps, by using the envelope of the complete waveform. The phases of the reflected waves are mostly fitted in the fourth step, which is based on the waveform misfit function preserving only the late arrivals. The third and fourth steps are of crucial importance to fit the reflected events. We test this approach with the Marmousi model using datasets with different frequencies, obtaining better estimates of the velocity field than those obtained with the classic FWI. The solutions obtained with both classic FWI and sequential inversion approach degrade with a progressively higher peak frequency dataset, but the classic FWI solution degrades more rapidly.

MEMBROS DA BANCA:
Interno - 1451214 - ADERSON FARIAS DO NASCIMENTO
Externo à Instituição - JOERG SCHLEICHER - UNICAMP
Interno - 1863578 - JORDI JULIA CASAS
Externo à Instituição - MILTON JOSE PORSANI - UFBA
Presidente - 349684 - WALTER EUGENIO DE MEDEIROS