Mahboob (Mac) Al-Chalabi is being cited for Special Commendation for providing the industry with a clear understanding of velocity and its inter-relationships in terms of such qualities as velocity heterogeneity and rms-velocity bias. Through his highly acclaimed course and publications, Mac has educated multitudes of geophysicists about the nature of velocities derived from seismic data and their applications from interpretation to depth imaging. Mac is deeply revered as a teacher by geophysicists around the world.
Biography Citation for SEG Special Commendation
Contributed by R. E. White
If one had to single out the most important parameter in reflection seismology, it would be seismic velocity. Mahboub (Mac) Al-Chalabi is a renowned authority on seismic velocities and time-to-depth conversion. His research on seismic velocity analysis introduced concepts that now underpin our understanding of the difficult relationships between seismic propagation velocities and velocities extracted from seismic reflection data. As a teacher, he has pioneered the transfer of that understanding into industry practice.
Mahboub gained a BSc in geology and MSc in geophysics from the University of Birmingham. There followed a fouryear spell with the Iraq National Oil Company, a Diplôme d’Ingenieur from the French Petroleum Institute, and a PhD from the University of Durham. His dissertation dealt with methods of inversion of gravity, magnetic, seismic, and electrical data. At that time geophysical inversion was a young subject and the publications derived from his thesis were among the first to expound the inherent nonuniqueness of these methods. He also ventured into global tectonics and produced an incisive critique of the methods used in fitting continental boundaries.
Mahboub’s work on seismic velocities and time-to-depth conversion began when he joined BP’s Geophysical Research Branch in 1970. Starting from careful definitions and distinctions, Mahboub analyzed the various velocities associated with seismic data and developed concepts, such as velocity heterogeneity and rms velocity bias, that unraveled the relationships between them. The key results, published in 1974, included an analysis of the fourth-order term of the normal moveout equation and its relationship to layering heterogeneity and long wavelength anisotropy. This analysis and its application to moveouts at long offsets in the 1970s foreshadowed more recent interest in the fourth-order term. Moreover, although the fourth-order term is often related directly to intrinsic anisotropy in rocks, layering is always likely to play a major role on moveout at seismic frequencies. For a comprehensive review of all aspects of seismic velocity analysis, Mahboub’s 1979 paper (Developments in Geophysical Exploration Methods, Volume 1) remains the standard reference.
In 1974 Mahboub transferred to BP’s geophysical exploration operations. He worked in a wide variety of exploration and development settings, mainly in seismic interpretation, but with opportunity to apply his background in potential field methods in developing integrated geophysical models. On leaving BP in 1990, Mahboub became an independent consultant concentrating, though not exclusively, on velocity and depth conversion studies and on conducting courses in these subjects to industry. The change has allowed him to return to research and to champion a proper understanding of velocity analysis to a wider audience: even long-standing techniques like velocity analysis need champions, especially in the prevailing oil industry climate, since technology—or rather the ability to use it correctly—is not just a commodity that can be bought off the shelf when a company lacks or loses knowhow. Mahboub’s introduction of the term “provelocity” was a much needed reminder of the pitfalls on the route from velocity analysis to propagation velocity estimates. His distinction between depth imaging and true depthing and revelations of the differing requirements of focusing, lateral positioning, and depthing has had major impact on how depth conversion is performed. His most recent work has exposed the nonuniqueness of instantaneous velocity parameters, such as V0 and k, and shown how, nonetheless, the V0 – k “solution trough” is not only an important step in accurate depth conversion but can also reveal uplift and lithological variation.
From the clarity of language in Mahboub’s publications it is not surprising to find he is an accomplished linguist. From their depth of thought, it is not surprising to find he is a formidable chess player.