Fiona Hill

Turkey and Russia: Axis of the excluded?

David Hill, Leendert Combee, and John Bacon, WesternGeco, introduce a new configuration for towed-streamer seismic data acquisition. They argue that the ‘over/under’ technique is a major advance on conventional techniques providing previously unattained signal bandwidth, where the low-frequency content gives deeper penetration, and therefore, improved imaging beneath basalt, salt, and other highly absorptive overburdens. In a conventional towed-streamer marine acquisition configuration, shallow sources and shallow cables increase the high-frequency content of the seismic data needed for resolution. However, shallow sources and shallow cables attenuate the low frequencies, which are necessary for stratigraphic and structural inversion, and for imaging deep objectives. Towing shallow also makes the data more susceptible to environmental noise. In contrast deep sources and deep cables enhance the low frequencies, but attenuate the high frequencies. In addition, the data recorded via a deep tow have a higher signal-to-ambient-noise ratio due to the more benign towing environment. A conventional towed-streamer survey design therefore, attempts to balance these conflicting aspects to arrive at a tow depth for the sources and cables that optimizes the bandwidth and signal-to-noise ratio of the data for a specific target depth or two-way travel time, often at the expense of other shallower or deeper objectives. An over/under, towed-streamer configuration is a method of acquiring seismic data where cables are typically towed in pairs at two different cable depths, with one cable vertically above the other. The depths of these paired cables are typically significantly deeper than would be used for a conventional towed-streamer configuration. In conjunction with these paired cables, it is possible to acquire data with paired sources at two differing source depths. Again, the depths of these paired sources are typically significantly deeper than would be used for a conventional towed-streamer configuration. The seismic data recorded by the over/under towed-streamer configuration are combined in data processing into a single dataset that has the high-frequency characteristics of conventional data recorded at a shallow towing depth and the lowfrequency characteristics of conventional data recorded at a deeper towing depth. This combination process is commonly referred to in the geophysical literature as deghosting. The current benefits of over/under data compared with conventional data can be summarized as: - A significantly broader signal bandwidth, where the lowfrequency content gives deeper penetration, and therefore, improved imaging beneath basalt, salt, and other highly absorptive overburdens. Moreover, the bandwidth extension to lower frequencies makes seismic inversion less dependent upon model-based methods - A simpler signal wavelet with the bandwidth extension to higher frequencies giving enhanced resolving power, allowing for a more detailed stratigraphic interpretation - Higher signal-to-ambient-noise ratio as a consequence of the deeper towed-cable pairs - An extended weather window enabled by the deeper towed-cable pairs.

The Siberian Curse: Does Russia's Geography Doom Its Chances for Market Reform?

This article summarizes Fiona Hill and Clifford Gaddy’s The Siberian Curse: How Communist Planners Left Russia Out in the Cold (Washington, DC: Brookings Institution Press, 2003). A Russian translation appeared in EKO, 2004, no. 6, pp. 72–95. Fiona Hill and Clifford G. Gaddy are senior fellows at the Brookings Institution, Washington, D.C. Problems of Economic Transition, vol. 48, no. 11, March 2006, pp. 7–29.