{"title":"了解地震学中的邻接法:时域理论与实施","authors":"Rafael Abreu","doi":"arxiv-2408.15060","DOIUrl":null,"url":null,"abstract":"The adjoint method is a popular method used for seismic (full-waveform)\ninversion today. The method is considered to give more realistic and detailed\nimages of the interior of the Earth by the use of more realistic physics. It\nrelies on the definition of an adjoint wavefield (hence its name) that is the\ntime reversed synthetics that satisfy the original equations of motion. The\nphysical justification of the nature of the adjoint wavefield is, however,\ncommonly done by brute force with ad hoc assumptions and/or relying on the\nexistence of Green's functions, the representation theorem and/or the Born\napproximation. Using variational principles only, and without these mentioned\nassumptions and/or additional mathematical tools, we show that the time\nreversed adjoint wavefield should be defined as a premise that leads to the\ncorrect adjoint equations. This allows us to clarify mathematical\ninconsistencies found in previous seminal works when dealing with visco-elastic\nattenuation and/or odd-order derivative terms in the equation of motion. We\nthen discuss some methodologies for the numerical implementation of the method\nin the time domain and to present a variational formulation for the\nconstruction of different misfit functions. We here define a new misfit\ntravel-time function that allows us to find consensus for the long-standing\ndebate on the zero sensitivity along the ray path that cross-correlation\ntravel-time measurements show. In fact, we prove that the zero sensitivity\nalong the ray-path appears as a consequence of the assumption on the similarity\nbetween data and synthetics required to perform cross-correlation travel-time\nmeasurements. When no assumption between data and synthetics is preconceived,\ntravel-time Frechet kernels show an extremum along the ray path as one\nintuitively would expect.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"20 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Understanding the Adjoint Method in Seismology: Theory and Implementation in the Time Domain\",\"authors\":\"Rafael Abreu\",\"doi\":\"arxiv-2408.15060\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"The adjoint method is a popular method used for seismic (full-waveform)\\ninversion today. The method is considered to give more realistic and detailed\\nimages of the interior of the Earth by the use of more realistic physics. It\\nrelies on the definition of an adjoint wavefield (hence its name) that is the\\ntime reversed synthetics that satisfy the original equations of motion. The\\nphysical justification of the nature of the adjoint wavefield is, however,\\ncommonly done by brute force with ad hoc assumptions and/or relying on the\\nexistence of Green's functions, the representation theorem and/or the Born\\napproximation. Using variational principles only, and without these mentioned\\nassumptions and/or additional mathematical tools, we show that the time\\nreversed adjoint wavefield should be defined as a premise that leads to the\\ncorrect adjoint equations. This allows us to clarify mathematical\\ninconsistencies found in previous seminal works when dealing with visco-elastic\\nattenuation and/or odd-order derivative terms in the equation of motion. We\\nthen discuss some methodologies for the numerical implementation of the method\\nin the time domain and to present a variational formulation for the\\nconstruction of different misfit functions. We here define a new misfit\\ntravel-time function that allows us to find consensus for the long-standing\\ndebate on the zero sensitivity along the ray path that cross-correlation\\ntravel-time measurements show. In fact, we prove that the zero sensitivity\\nalong the ray-path appears as a consequence of the assumption on the similarity\\nbetween data and synthetics required to perform cross-correlation travel-time\\nmeasurements. When no assumption between data and synthetics is preconceived,\\ntravel-time Frechet kernels show an extremum along the ray path as one\\nintuitively would expect.\",\"PeriodicalId\":501270,\"journal\":{\"name\":\"arXiv - PHYS - Geophysics\",\"volume\":\"20 1\",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2024-08-27\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"arXiv - PHYS - Geophysics\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/arxiv-2408.15060\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - PHYS - Geophysics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2408.15060","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
Understanding the Adjoint Method in Seismology: Theory and Implementation in the Time Domain
The adjoint method is a popular method used for seismic (full-waveform)
inversion today. The method is considered to give more realistic and detailed
images of the interior of the Earth by the use of more realistic physics. It
relies on the definition of an adjoint wavefield (hence its name) that is the
time reversed synthetics that satisfy the original equations of motion. The
physical justification of the nature of the adjoint wavefield is, however,
commonly done by brute force with ad hoc assumptions and/or relying on the
existence of Green's functions, the representation theorem and/or the Born
approximation. Using variational principles only, and without these mentioned
assumptions and/or additional mathematical tools, we show that the time
reversed adjoint wavefield should be defined as a premise that leads to the
correct adjoint equations. This allows us to clarify mathematical
inconsistencies found in previous seminal works when dealing with visco-elastic
attenuation and/or odd-order derivative terms in the equation of motion. We
then discuss some methodologies for the numerical implementation of the method
in the time domain and to present a variational formulation for the
construction of different misfit functions. We here define a new misfit
travel-time function that allows us to find consensus for the long-standing
debate on the zero sensitivity along the ray path that cross-correlation
travel-time measurements show. In fact, we prove that the zero sensitivity
along the ray-path appears as a consequence of the assumption on the similarity
between data and synthetics required to perform cross-correlation travel-time
measurements. When no assumption between data and synthetics is preconceived,
travel-time Frechet kernels show an extremum along the ray path as one
intuitively would expect.