The 17 July 2013 Hammam Melouane earthquake: observations and analysis of geological and seismological data

On July 17th, 2013, a moderate-sized earthquake of Mw 4.9 hits the locality of Hammam Melouane, North-Central Algeria. The event was followed by an intense aftershock activity that lasted about two years. For a better constraint of the main shock and the causative fault, we present and discuss new geological and accelerometric data, in addition to an updated macroseismic study. A maximum macroseismic intensity of VII (EMS-98) was attributed to this event. The right-lateral strike-slip fault zone outcropping north of Hammam Melouane locality is the only structure that shows characteristics coherent with the seismological results. This fault system consists of several main branches about 1 km distant from each other, with a ~ N120° overall trending. The fault zone structure is clearly materialized by a Riedel shear structures imprinted on Miocene post-thrust tectonic formations and cross cutting all the previous structures. Moreover, reading the P-wave polarity at two additional broadband seismic stations, allowed better constraining the strike of the focal mechanism nodal planes. The GRY strong-motion station, west of the epicenter, which has not been triggered by the mainshock first arrival, means that possibly this station is located close to the ~ E‒W nodal plane.