Trench investigations through the trace of the 1980 El Asnam thrust fault: Evidence for paleoseismicity

摘要: During the EI Asnam earthquake of 10 October 1980 ( Ms = 7.3), a clear active thrust fault with left-lateral offset was observed. Three trenches have been excavated across this in order to determine slip rate and recurrence intervals between large earthquakes, thus reconstruct its past activity. Exposure I flood area created by pressure ridge Cheliff Fodda Rivers. Six deposits (silty-sandy muddy horizons) alternating paleosoils appear exposure; they are affected normal faults associated main fault. Assuming that every deposit results from tectonic event magnitude greater than 7, we can correlate previous these events. Exposures II III display displacing different paleosoils. We propose sequence reconstructions based on thickness various dip-slip each event. The Late Holocene is 0.65 mm/yr for 0.46 horizontal vertical movements. Radiocarbon dates coseismic movements indicate rather irregular seismic activity during 7000 yr. Two sequences earthquakes around 4000 yr B.P. modern age separated period quiescence. The average interval 1061 yr; however, faulting episodes, time varies approximately 300 500