Yuri Roslov
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Yuri Victorovich Roslov (1963 – 2015) died at the age which is thought of as a peak of life, time of personal self-fulfillment and complete mastery of professional skills. Foundation and guidance of XGeo was only one and far from the main episode in his multifaceted activity. However, it was his leadership that made XGeo successful and presented a unique opportunity of collaboration with the remarkable personality and first-rate specialist.
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Beginning of career
Yuri Roslov was a graduate of the Chair of Physics of the Earth of St Petersburg University, Department of Physics. The university was also the place where he began his career: first postgraduate course and getting his Ph.D., then work at the university Institute of Physics. His thesis adviser was Tatiana Yanovskaya, an outstanding mathematical geophysicist, a pupil of Georgy Petrashen'. These names and Yuri's first works [1-3] indicate that Yuri Roslov as a scientist was formed in the walls of the famous St Peterburg school of dynamic theory of elastic wave propagation, which combined the highest level of theoretic investigations with vivid interest in practice of seismic experiments. It is enough to mention that mathematical justification of ray method – the main instrument of any specialist in seismology and seismics – was performed by mathematicians of this school. The theoretic works [2-3] were recognized by the professional community. In 80-th and early 90-th Yuri was a regular participant of the famous Petrashen's seminars in the Mathematical Institute. The first experience as a field engineer influenced Yuri's outlook as much as mathematical problems of seismic wave propagation.
"The first blows on my mentality of a mathematician of homogeneous media were struck in 1986 when I worked for some time in Kola Institute of Geology after graduation from the university… The world of horizontal homogeneous spaces began collapsing from the first step – setting a measuring tool… If you want to be successful even in theoretical geophysics, you must work with field engineers and geologists in order to understand you place in the technology of geophysical prospecting and have enough knowledge in adjacent fields… Symptomatically, that terms geophysicist, geologist are now being replaced with geoscientist which underlines the critical importance of integral knowledge of the Earth in addition to specialization… It was my field experience that defined my evolution as a researcher from the simplest to more and more complex models aimed at more precise description of real media. Seismic tomography was the most important stage in this evolution."
This is a citation from a paper found in Yuri's archive. His whole career followed this program.
Firstomo
In 1993 Yuri Roslov, together with Pavel Ditmar, also a pupil of Tatiana Yanovskaya, published his first work on seismic tomography [4]. At the same time, the authors developed a program package for 3D first arrival tomography for a PC under DOS. It was tried as a means of interpretation in several seismic surveys in 1992 – 1996 [5,6]. This experience allowed perfecting it up to the state of a commercial product. The subtitle "The best of Russian tomography" on the user guide cover was not exaggeration in the least. Mathematical part of the product was excellent. Additionally to its scientific and practical value, Firstomo helped the authors survive in the hardships of transitional period of the 90-th.
Sevmorgeo
The year 1998 opened a new stage in Yuri Roslov's career: he joined the stuff of the state geophysical company Sevmorgeo as the senior researcher. The servicing company was created in the beginning of the 90-th from the geophysical department of the Research Institute for Geology and Mineral Resources of the Ocean, which had had a long history of investigations of the Russian Arctic. Yuri worked in the company till 2010 taking up different positions up to deputy director, but the most important for his career was leadership of Department of Geophysical Data Analysis.
In the period 1995 to 2010 Sevmorgeo implemented huge volume of marine exploration works, mostly in the northern and eastern seas of Russian Federation. The first to mention is a megaproject of marine base profiles across the Barentz see, the Kara see, the East-Siberian sea and the Sea of Okhotsk. Sevmorgeo was the general contractor in this project. The complex of geophysical investigations (seismic wide-angle reflection/refraction profiling – WARRP, multichannel seismic, gravity/magnetic measurements and geochemical study of bottom sediments) was carried out along the profiles. The surveys resulted in fundamental contribution to the study of the Russian Arctic shelf. Seismic surveys in transition zones (Pechora sea, Varandei area and others) were also of great importance.
The spectrum of works to be carried in the Department headed by Yuri Roslov was very wide: working out the ocean bottom stations (OBS) specifications and OBS testing; participation in fieldwork; seismic data processing; complex geophysical interpretation; developing of seismic/gravity/magnetic models; geological interpretation. The base profile project required mobilization of scientific and technical stuff, careful planning and coordination. In the first place, Yuri Roslov managed to consolidate the scientific potential of the Department and to encourage innovational approaches to technological and interpretation problems. That was very important as the Department's strategy, and as stimulus to professional growth, and for creating the team. As a result, the stuff of the Department was able to face the challenge and perform all tasks required by the project adhering to high professional standards [9-28]. It was the time of quite stressful work with hot discussion and brainstorms around puzzling tasks inherent in geophysical data interpretation. Yuri was able to create the specific atmosphere of friendly co-operation and joint creative search. That was his gift.
Works [9-28], in which Yuri Roslov was a co-author, often the main one, is just a small sample. They are devoted to problems of geological structure of the Arctic shelf, prospects of oil-and-gas deposits, methods and technology of geophysical surveys, problems of data interpretation. Among the latter there were some concerning applications of seismic tomography, which had been an object of Yuri's special interest.
Tomography and WARRP data interpretation
Enormous volume of WARRP data acquired on the base lines was not met with proper interpretation tools. The Firstomo package was applied for building velocity sections but it could not be an adequate instrument for interpretation of deep seismic sounding data on the following reasons.
1. An adequate seismic model for deep seismic sounding is the layered model. WARRP wave field contains waves of different nature. First arrival tomography is based on the gradient model; the "first arrivals" approach ignored wave differentiation and excluded reflections from tomography inversion. The package had no infrastructure for wave differentiation.
2. Rectangular grid, usually used for model representation is not good for description of non-horizontal boundaries: precision of ray-tracing in domains with non-horizontal boundaries drops dramatically.
3. Input data (source and receiver positions and traveltimes) are delivered in an ASCII file. The question of how to make it up, if not manually was simply put aside. Meanwhile, one bottom seismograph on a base line stored useful record at offsets of 250 km while an air-gun went off every 250 m. Thus, the problem of preparing the observed data for input became urgent.
Problem 2 was Yuri's concern as can be seen from two Ph.D. theses prepared under his guidance by Michail Gurevich [8] and Еkaterina Vsemirnova [20]. In [8] a triangular mesh was used instead of the rectangular, while in [20] the grid was formed by a set verticals crossed by a family of simple curves without common points. In both theses ray-tracing schemes were developed with estimations of accuracy. Both approaches turned out to be fruitful. The curvilinear grid was used later in 2D tomography system ХТомо-LM, while triangle mesh proved to be more appropriate for 3D generalization [30-31].
XGeo
In 2003 Yuri Roslov and Andrea Zerilli from Schlumberge Ltd. founded a new company – XGeo Ltd. Both geophysicists faced the same obstacle in their research work: problems they worked on required development of specific software. Yuri Roslov was engaged in seismic tomography applications, while Andrea Zerilli was interested in joint inversion problems.
Foundation of the company with the proper investments allowed implementing the founders' intentions, at least, in part. The priority was given to seismic tomography because it had a good backlog (Firstomo) and immense application field. A year later, in 2004, XGeo released the first version of 2D seismic tomography system XTomo, which included the entire 2D functionality of Firstomo and allowed to trace rays of diving, reflected and head waves on a curvilinear grid. Now each observation in input file was supposed to have reference to the wave it belonged to. Versions 2.0.1 – 2.1.2 (7 releases total) were published in the period of 2006 – 2012. The late releases of version 2 had already quite satisfactory environment for processing, a powerful model editor, allowed implanting seismic horizons in the grid, contained its own means of building horizons, let still imperfect [29]. It was possible to do tomography inversion using traveltimes of reflections and refractions. The system, in some degree, became a tool for work with layered model, and to mark that, acronym LM (Layered Model) was added to its title. In 2006 the first version of Data Preparation Unit (DPU) was published. It solved the problem 3 from the previous section, accepting the field data in the form of common source point seismograms and ASCII files with positional data, if they were absent in seismogram trace headers. Arrival times of different waves were to be picked from the seismograms by an interactive program and then exported in the form of an input file for XTomo-LM.
Joint Inversion Problem
This problem, initially included in XGeo plans, had been put aside because it needed serious theoretical study. Here joint inversion means an algorithm and its program implementation. The objective function of the problem includes deviations of observed traveltimes and magnetotelluric impedances from their values computed for initial model by solving forward problems of seismics and magnetotellurics. To solve the forward problems, one needs model description in terms of P-wave velocity and impedance. And here the main problem lies. The parameters are not independent, and their dependence is far from being direct; it is defined by a set of petrophysical characteristics. One has to describe the velocity-impedance dependence in such way that it should agree with known geophysical facts and secure the minimization problem to be a well-posed problem under a proper regularization.
Yuri Roslov returned to the problem in 2007. Then his collaboration with Dmitry Molodtsov began. It turned out to be very productive. In [30-31] ray-tracing on a triangular mesh was generalized to 3D media, while the works [32-33] treated the joint inversion problem. Two variants of velocity-impedance dependence and, respectively, two problem statements were offered and studied. Returning to joint inversion problem was Juri's next step in his life-long search of more complex models for description of real geological media.
Seismo-Shelf
Change of the Sevmorgeo administration in 2008 and new trends in inner policy resulted in that some leading specialist left the company in the next years, Yuri Roslov among them. Some time before he left, Yuri had been involved in setting up a new servicing company Seismo-Shelf Ltd. Its scope of activity was declared as dense seismics on the seafloor. The stress was made on using domestic equipment and software. Since 2010 to the end of his life Yuri worked as deputy director of Seismo-Shelf. In the first two years he was engaged in working out the company's strategy, setting up OBS production and data processing team. During 3-4 years the company managed to implement its technology and test it in several surveys. The first commercial contracts were concluded and accomplished: the Barents Sea (2011, 2012), the Norwegian Sea (2012), the Pechora see (2013)…
…Yuri Roslov had very sharp, fast, combinatory mind. Chess was his life-long hobby: he was an excellent chess composer. His creativity took different forms and manifested itself in any task he worked on. And he seemed to be an unyielding optimist. His confidence in final success and his unfading sense of humor never left him. He was very sociable, lively and full of new plans and ideas until his last days.
Selected Works
The full list consists of more than 90 publications. Below only those important for the above life story are cited.
1. Roslov Yu.V. Estimation for contribution of second member of ray expansion in seismic wave field. Abstarct of Ph.D. thesis. (04.00.22). Leningrad, 1989.
2.Yanovskaya T.B. & Roslov Yu.V. 1989. Peculiarities of surface wave fields in laterally inhomogeneous media in the framework of ray theory. Geophys J.Int. 99, 297-303.
3.Kiselev A. P., & Roslov Yu. V. Use of additional components for numerical modeling of polarization anomalies of elastic body waves, Sov. Geology & Geophysics 32(4), 105-114, 1991.
4.Ditmar P.G. & Roslov Yu.V. Non-linear tomographic inversion of seismic data. International Geophysical Conference SEG-93. Moscow August 16-19, 1993.
5.Isanina E.V. & Roslov Yu.V. 1996 Tomographic reconstruction of the medium around cola superdeep well International Workshop "Geodynamics of lithosphere and Earth's mantle". Praha/Trest. 8-13, July, 1996.
6.Sharov N.V., Isanina E.V., Roslov Yu. V. Seismo-tomograpic study of the crust. InSeismo-geological model of Northern Europe lithosphere: Lapland-Pechenga region. Russian Academy of Science, Apatity, 1997
7.Yanovskaya T.B., Roslov Yu.V., Lyskova E.L. Earthquake quantification based on P-wave spectra. Physics of the Solid Earth, 1996, 1, стр. 3-15.
8.Gurevich M.V. & Roslov Yu.V. Two-point raytracing with wavefront method in anisotropic inhomogeneous media, Geofizika, 1997, 5. p. 23-31.
9. Sakoulina T.S., Vinnik A.A., Kopylova A.V., Roslov Yu.V. Processing and interpretation of deep seismic sounding data acquired on the base profile 1-AR in the Barents Sea. In International conference “50-th anniversary of DSS”, May 19-22 1999. Moscow, The Schmidt Institute of Physics of the Earth. Abstracts, p. 45.
10.Matveev Yu.I., Nikitin B.A., Rovnin L.I., Roslov Yu.V., Sapozhnikov B.G. 3D survey in the transition zone of Pechora Sea. Russian Offshore 1999, St.Petersburg
11.Sakoulina T., Roslov Yu., Vinnik A., Kopylova A. On technique for Ocean – Bottom Seismic data processing: Investigations on Barents Sea Shelf. 9th International Symposium on Deep Seismic Profiling of the Continents, 18-23 June, 2000, Brakanes Hotel Conference Centre, Ulvik, Norway, s.114.
12.Roslov Yu.V., Telegin A.N., Sakoulina T.S., Tikhonova I.M. Time image derived from refracted wave Kirchhoff migration EAGE 64th Conference & Exhibition — Florence, Italy, 27 - 30 May 2002.
13.Matveev Yu.I., Yu.V.RoslovRussian arctic offshore transect program; The 10th International Symposium of "Deep Seismic Profiling of the Continents and Their Margins", Taupo, New Zealand. 2003.
14.Roslov Yu.V., Sakoulina T.S. Integrated multidisciplinary processing and interpretation of geophysical data acquired on transects in Barents and Kara seas The 10th International Symposium of "Deep Seismic Profiling of the Continents and Their Margins", Taupo, New Zealand. 2003.
15.Roslov Yu.V, Sakoulina T.S., Belyaev I.V., Ivanova N.M., Telegin A.N., Panteleeva L.A. Integrated processing and interpretation of geophysical data acquired on base profiles 1-AR and 2-AR in the Barents and Kara Seas. Fifth Fedynsky geophysical conference, Febr. 27 – March 1 2003, Moscow. Geon. p. 36.
16.Roslov Yu.V., Sakoulina T.S. Traveltime tomography in WARRP. International conference “Acad. G.A. Gamburtsev's Scientific Legacy and contemporary geophysics”. Moscow, The Schmidt Institute of Physics of the Earth. April 21-23 2003. Abstracts.
17.Sakoulina T.S., Roslov Yu.V., Telegin A.N., Tikhonova I.M., Panteleeva L.A. Integrated processing of reflection and refraction data acquired on base lines in the Barents and Kara seas. “Acad. G.A. Gamburtsev's Scientific Legacy and contemporary geophysics”. Moscow, The Schmidt Institute of Physics of the Earth. April 21-23 2003. Abstracts.
18.Belyaev I.V., Verba M.L., Ivanova N.M., Roslov Yu.V., Sakoulina T.S. Prediction aspect of integrated geophysical investigations on bases lines across the Barents sea oil-and-gas province. In: International geophysical conference and Exhibition. Moscow, Sept 1-4 2003. Abstarcts.
19.Ivanova, N.M., Sakoulina T.S., Roslov Yu.V., 2006. Deep seismic investigation across the Barents-Kara region and Novozemelskiy Fold Belt (Arctic Shelf). Tectonophysics, vol. 420, issues 1-2, p. 123-140.
20. Vsemirnova Е.A., Roslov Yu.V. Raytracing on irregular mesh. V Int. Conf. "Problems of Geocosmos". Book of abstracts. St. Petersburg. 2004.
21.Pavlenkin A.D., Roslov Yu.V. Application of seismic tomography for velocity section study in different geological problems. In: International conference "Information technology and Inverse problems of rational nature management". Khanty-Mansiysk, April 12-14 2005.
22.Verba M.L, Matveev Yu.I., Roslov Yu.V. Geophysical investigations on the base profiles in the Barents Sea as a means of refinement of oil and geological prediction. In: 5th International Forum “Russian Oil, Gas and Energy Forum”, St Petersburg, April 4–7 2005. p. 31 – 34.
23.Verba M.L., Roslov Yu.V. On possibility of finding shoestring oil deposits on the Barents sea shelf (according to results of investigations on the base profiles). In Non-structural complex oil traps".VNIIGRI, St Petersburg 2005, p. 33 – 36.
24.Roslov Yu.V, Dergunov N.T., Efimova N.N., Sakoulina T.S., Nechkhaev S.A. Prediction of gas deposits in the transition zone with the help of using seismic tomography. International conference "Oil And Gas of the Arctic", Moscow, June 27-29 2006, p. 108-111.
25.Sakoulina T.S., Verba M.L., Ivanova N.M., Roslov Yu.V., Belyaev I.V. Deep structure of the northern region of the Barents-Kara region along profile 4-АР. In 7-th International conference “Russian Oil, Gas and Energy Forum”, St Petersburg, April 10-12 2007. p. 371-374.
26.Verba M.L., Ivanov G.I, Roslov Yu.V., Sakoulina T.S., Belyaev I.V. Structures of crust stretching in the north of the Barets sea oil-and-gas province. In: RAO/CIS Offshore 2007. 8th International Conference and Exhibition for Oil and Gas Resources Development of the Russian Arctic and CIS Continental Shelf. Sept 11-13, St Petersburg, 2007, p. 75.
27.Roslov Yu. V., Matveev Yu. I., Belyaev I.V., Ivanova N.M., Sakulina T.S. Deep model of the Barents-Kara Region by results of geophysical investigations along regional lines 1-4 AR. 33rd International Geological Congress, Oslo, 4-15 August, 2008.
28.Sakoulina T.S., Matveev Yu. I., Roslov Yu.V., Kashubin S.N., Lukachin Yu.P., Pavlenkova N.I. Offshore multi component deep seismic investigations. 13-th Int. symp. on Deep Structure of the Continents and their Margins, 2008, Finland.
29. Roslov Yu.V., Vinnik A.A., Kopylova A.V. Building complex velocity models using seismic tomography and kinematic migration. In: Models of the crust and upper mantle. International theoretic and practical seminar, Sept. 18-20 2007. VSEGEI, St Petersburg 2007, p. 177-180.
30.Molodtsov D.M., Roslov Yu.V. Modeling of eikonal in 3D inhomogeneous medium using irregular triangular mesh. Problems of Geophysics, 2009, v. 42, p. 48-55.
31.Molodtsov, D.M., Yu.V. Roslov. Shortest-path seismic ray tracing with interpolation on irregular tetrahedral grid. 2010 SEG Annual Meeting, Expanded Abstracts.
32.Molodtsov D., Kashtan B. and Roslov Yu. Joint inversion of seismic and magnetotelluric data with structural constraint based on dot product of image gradients. 2011 SEG Annual Meeting, Expanded Abstracts.
33.Molodtsov D. M., Troyan V.N. and Roslov Yu.V. Joint inversion of seismic and magnetotelluric data with a differential structural constraint. 2012 SEG Annual Meeting, Expanded Abstracts.