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42373-G8
Processes and Implications of Active Tectonism in Petroliferous Basins of Northern Morocco
The second year of the project has involved geomorphic analysis of the DEMs to assess possible signatures of long-term, Quaternary deformation. The aim is to compare these results with present-day deformations constrained by GPS and InSAR. To that end, we are mapping anomalies in the longitudinal profiles of large streams and rivers (stream orders greater than 3) that cross the Rif front. Noteworthy anomalies in these maps of stream length-gradient index suggest Quaternary uplift along the Prerif Ridges. This corresponds with the abrupt gradient in the present-day displacement mapped by GPS.
Coordinating with the Royal Remote Sensing Center of Morocco, we are in the process of analyzing satellite radar data across the southern front of the Rif region. These analyses are challenged by low coherence in many of the interferograms. This is likely a result of the local environment. We are exploring the possibility of using permanent scatterers to reduce the problems of low coherence. However, we have not yet succeeded in using permanent scatterers for an entire radar image footprint (100km by 100km area) – only for small areas (5km by 5km). We are continuing with these efforts.
Working with colleagues from MIT, as well as Moroccan collaborators, another survey of the Morocco GPS network was completed in the Fall of 2006. The resulting velocities have reduced uncertainties, and newer survey sites are now yielding reliable velocities for a more complete picture of the horizontal deformation. The anomalous motion with the Rif Mountains is very well defined, now, and additional survey sites are now constraining the horizontal displacement gradient that seems to stop at the southern front of the Rif region.
Whereas the GPS and radar interferometry are directly measuring crustal strain, we have begun to constrain the regional stress field by analyzing the elongation of boreholes using 3-arm caliper logs (i.e., “borehole breakout analysis”). Data have been provided by the Moroccan national petroleum company, ONHYM. We began with three boreholes in the Rif region. Data were provided in analog form, so they were digitized prior to analysis. Preliminary results show a maximum horizontal compression oriented generally N-S in the eastern part of the Rif. This is considerably different from the NW-SE convergence of Europe and North Africa in the western Mediterranean.
Finally, we are constructing a regional, balanced cross section across the southern Rif. This is going to be synthesized from previously published cross sections and our own structural interpretations of the available seismic reflection data.
