An assessment of natural and man-made vibrations in Lake Kivu, Rwanda

Robert R. Stewart

ABSTRACT

This report overviews the general level of vibrational disturbance to which Lake Kivu, Rwanda has been subjected (e.g., shak ing of approximately 10cm/s and 0.1g by recent earthquakes in the magnitude 6 range). These levels are compared to man-made sources, especially those of the exploration seismic community (air guns and sub-bottom sounders). The energy released by marine seismic sources is several orders of magnitude smaller than that of recent Rwandan earthquakes. Interest and concern relates to Lake Kivu because of its vast quantities of dissolved carbon dioxide and methane. Due to its thermohaline structure, the Lake is regarded as stable (although potentially vulnerable to extreme events). The sediments bene ath the Lake could be host to hydrocarbons (similar to Lake Albert, Uganda). Thus, there are a number of compelling scientific, hazard reduction, and economic reasons to undertake seismic surveys on the Lake. However, because of the large population around Lake Kivu, potential environmental effects of a seismic survey must be considered. The energy and pressures involved in a seismic survey (using sub-bottom sounders and small airguns) are likely much smaller than those previously experienced in the depths of Lake Kivu. The seismic vibration estimates appear to be safely within West et al.'s ( 2009) factor of safety and stability criteria.

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