Análisis morfométrico cuantitativo para la caracterización tectónica del norte de Túnez

Abstract

Northern Tunisia is characterized by low deformation rates and low to moderate seismicity. Although instrumental seismicity reaches maximum magnitudes of Mw 5.5, some historical earthquakes were described with catastrophic consequences in this region. Aiming to improve our knowledge of active tectonics in Tunisia, we carried out a quantitative morphometric analysis in the northwestern region. We applied different morphometric indices, like river profiles, knickpoint analysis, curves and hypsometric integrals and drainage pattern anomalies in order to differentiate between zones with high or low recent tectonic activity. These indices allow identifying uplift and subsidence zones, which we relate to fault activity. A selected sector was studied with a field campaign to test the results obtained with the quantitative analysis. During the field work we identified geological evidence of recent activity and a considerable seismogenic potential along El Alia-Teboursouk (ETF) and Dkhila (DF) faults. Geological evidence include fluvial terraces folded by faults, striated pebbles, wind gaps, clastic dikes, sand volcanoes, coseismic cracks, etc. To estimate the seismic potential of this region and obtain a first seismic hazard estimation, we interpreted fault segmentation affected by a potentially coseismic rupture. Then, we calculated earthquake magnitude expected for each segments using two empirical equations, which relate rupture length and maximum magnitude. Magnitude for each entire fault was also calculated to provide an upper bound. Our study provides evidence of active tectonics in this region, with potential magnitudes ranging from Mw 6 to 7.8. Although not reflected in the instrumental seismicity, our results support an important seismic hazard, evidenced by the several active tectonic structures identified and the two seismogenic faults described. The ETF fault could be responsible of one of the most debastating historical earthquakes in northern Tunisia that destroyed Utique in 412 A.D.