Summary Between the 1783 February 5 and 1783 March 28, five earthquakes struck the southern part of Calabria. The main shock (February 5) and the first aftershock (February 6) devastated the region ENE of the Messina Strait. The greatest damage occurred along the foot of the Aspromonte Mountains south of San Giorgio Morgeto, and along the Tyrrhenian coast south of Palmi. A surface break about 18 km long, with several feet of downthrow to the west, formed along the Cittanova (Santa Cristina) Fault as a result of the main shock. On February 7, a third large shock ruined villages at the foot of the Serre Mountains north of San Giorgio Morgeto. Morphological and structural evidence, combined with a reassessment of observations made at the time of the earthquakes, suggest that these three shocks were shallow (≤ 20 km) and related to slip on the west‐dipping, NE‐striking Cittanova–Sant'Eufemia, Palmi–Scilla and Serre normal faults, respectively, which juxtapose the basement of the Aspromonte and Serre mountains with the Pleistocene deposits of the Gioia Tauro and Mesima basins, and border the Palmi coastal high. The three faults belong to an active rift that stretches from northern Calabria to offshore the Ionian coast of Sicily. The spatial coupling between the 1783 events is investigated by resolving changes of Coulomb failure stress. The main shock (1783 February 5, M ∼ 7), on the Cittanova and Sant'Eufemia faults, increased that stress by several bars on the Scilla Fault, triggering the 1783 February 6 earthquake (M ∼ 6.5). The cumulative effect of these two shocks was to raise the Coulomb stress by more than 1 bar on the SW part of the Serre Fault, which was subsequently the site of the 1783 February 7 shock (M ∼ 6.5). In turn, the first three events increased the stress by about 1 bar on the NE part of this latter fault, leading to the 1783 March 1 shock (M ∼ 5.7). The gap between the 1783 February 7 and 1783 March 1 events may be related to the previous occurrence of an earthquake 124 yr before (1659 November 5, M ∼ 6), which had already released stress locally. The occurrence of the last 1783 event (28 March) is not as simply accounted for by Coulomb modelling, in part because it remains unclear which fault slipped and how deep this event was. Overall, the 1783 sequence increased the Coulomb failure stress by several bars south of the Messina Strait and north of the epicentral region of the 1693 SE Sicily (Catania–Noto) earthquakes. 125 yr later, this same region was the site of the 1908 Messina earthquake, also a normal faulting event. Our study thus provides one convincing example in which Coulomb stress modelling brings insight into the spatial dynamics of seismic sequences.

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Laboraroire de GPodynamique er ModPlisation des Bassins Sidimenraires, U P P A , auenue dr I'UnivrrsiiP, 64 000 Pau, France .'Laborntoire de Tectonique. MCcanique cie la Lirhosphe're, IPGP, 4 place Jussieu, 75 252 Paris cedex 05, France 'Depurtarnento de Geologiu, EPN, A p . 2759, Olrito, Ecuador S U M M A R Y T h e segment of the Interandean Depression of Ecuador between Ambato and Quito is characterized by an uppermost Pliocene-Quaternary basin, which is located between two N-S trending reverse basement faults: the Victoria Fault t o the west, and the Pisayambo Fault to the east. T h e clear evidence of E-W shortening for the early Pleistocene (between 1.85 and 1.21 Ma) favours a compressional basin interpretation. The morphology (river deviations, landslides, folded and flexure structures) demonstrates continuous shortening during the late Quaternary. T h e late Pliocene-Quaternary shortening reached 3400 f 600 m with a rate of 1.4 f 0.3 m m yr-'. T h e E-W shortening is kinematically consistent with the current right-lateral reverse motion along the NE-SW trending Pallatanga Fault. T h e Quito-Ambato zone appears t o act as a N-S restraining bend in a system of large right-lateral strike-slip faults. T h e compressive deformation. which affects the Interandean Depression during the Pliocene is apparently coeval t o the beginning subduction of very young oceanic lithosphere north of the Gulf of Guayaquil. The relatively buoyant new crust may have significantly increased the mechanical coupling in the subduction zone from Pliocene t o Present.

Review of seismological and structural data coupled with new data on topographical, geomorphology, and Quaternary geology allows delineating the major active faults of the High Atlas. These are the North and South border faults of which fault segmentations correspond to Mw max ranging between 6.1 and 6.4. Detail active tectonics analyses were performed on the South Atlas Fault Zone in the Souss and Ouarzazate basins, where deformed Quaternary levels permit to estimate slip rates on individual faults in the order of 0.1 mm yr −1 . Such low slip rates imply that large observational time-window is needed to analyze active deformation in low-seismicity regions. However, the complex 3D geometry of reverse or thrust faults may cause difficulty to relate surface observations with the deeper faults that have the potential to nucleate big earthquakes. Further studies are necessary to interpret the Anti Atlas seismicity. To cite this article: M.