PROCESSING AND MODELLING OF WIDE ANGLE SEISMIC DATA ACQUIRED ALONG THE NORTHERN ANGOLAN CONTINENTAL MARGIN

Wide angle seismic data collected on land on Northern Angola during the March-April 2000 Zaiango seismic experiment provide the first image to date of the whole crust up to the upper mantle on the Northern Angolan passive margin.

A passive, or rifted continental margin comprises the rifted edge of a continent. Understanding the rift-drift evolution requires accurate knowledge of its crustal structure, which contains records of processes such as subsidence, crustal thinning, underplating and volcanism.

Multichannel data were acquired by the R/V le Nadir (IFREMER) using a single bubble air-gun array and a new digital 4.5 km long streamer, and coincident wide angle data were recorded on land by three broad band three component seismic stations. The data collected on land for some selected seismic lines, together with the results of enhanced processing and a first modelling are here presented.

The vertical, radial and transversal components relative to each profile have been processed by a denoising procedure including a coherence filter based on wavelet decomposition of the signal and stacking, with phase correlation, acting in a moving window. A further enhancement of the seismic phases and an aid for their interpretation have been obtained by algorithms for simultaneous analysis of the waves polarization and propagation parameters.

Travel times of P wave refracted arrivals and prominent crustal and mantle reflectors observed to offset of over 200 km were used to model a crust/mantle boundary which beneath the continent rises in an oceanward direction, from 40 km to 25 km. In the center of the line, where the crust thins most rapidly, a high velocity body has been modeled at the base of the crust, reaching some 8 km in thickness. This higher velocity body is thought to represent an area of localized magmatic underplating related to the opening of the South Atlantic and to the Cenomanian volcanism in Angola, as well as the late uplift of the mainland, which may have deep rooted causes.