Coseismic and postseismic displacements related with the 1997 earthquake sequence in Umbria-Marche (central Italy)

We study the coseismic and postseismic displacements related with the 1997 Umbria-Marche earthquake sequence by means of leveling lines along a deformed aqueduct located in the epicentral area. Comparing the 1960 and 10/1997 measurements we obtain 0.49 0.10 m of coseismic displacement distributed along 3 km across the normal fault zone. Modeling of the coseismic surface dislocation is obtained from a combination of low angle (38°) faults at depth and high angle (80°) upper fault branches. The best fit model indicates that the upper branches stop at 0.4 km below the ground surface and have 60% of slip with respect to the lower faults. The postseismic displacement measured during 1998 is 0.18 m and represents 36% of the apparent coseismic deformation. Moderate earthquakes in the Apennines and related surface deformation may thus result from curved faults that reflect the brittle-elastic properties of the uppermost crustal structures

Paleoseismology of the North Anatolian Fault at Güzelköy (Ganos segment, Turkey): Size and recurrence time of earthquake ruptures west of the Sea of Marmara

International audienceThe Ganos fault is the westernmost segment of the North Anatolian Fault that experienced the Mw = 7.4 earthquake of 9 August 1912. The earthquake revealed 45-km-long of surface ruptures inland, trending N70 E, and 5.5 m of maximum right lateral offset near Güzelköy. The long-term deformation of the fault is clearly expressed by several pull-apart basins and sag ponds, pressure and shutter ridges and offset streams. In parallel with detailed geomorphologic investigations, we measured co-seismic and cumulative displacements along the fault, and selected the Güzelköy site for paleoseismology. A microtopographic survey at the site yields 10.5 AE 0.5 m and 35.4 AE 1.5 m cumulative lateral offsets of stream channels and geomorphologic features. Seven paleoseismic parallel and cross-fault trenches document successive faulting events and provide the timing of past earthquakes on the Ganos fault segment. Radiocarbon dating of successive colluvial wedges in trench T1, and the fresh scarplet above (probably 1912 surface rupture) indicate the occurrence of three faulting events since the 14th century. Parallel trenches (3, 5, 6 and 7) expose paleo-channels and show a cumulative right-lateral offset of 16.5 AE 1.5 m next to the fault, and 21.3 AE 1.5 m total channel deflection. Radiocarbon dating of past channel units and fault scarp-related colluvial deposits imply an average 17 +/À 5 mm/year slip rate and 323 AE 142 years recurrence interval of large earthquakes during the last 1000 years on the Ganos fault. The succession of past faulting events and inferred slip rate west of the Marmara Sea provide more constraint on the long-term faulting behavior in the seismic gap of the North Anatolian Fault and may contribute to a better seismic hazard assessment in the Istanbul region

Paleoseismic History of the Dead Sea Fault Zone

International audienceThe aim of this entry is to describe the DSF as a transform plate boundary pointing out the rate of activedeformation, fault segmentation, and geometrical complexities as a control of earthquake ruptures. Thedistribution of large historical earthquakes from a revisited seismicity catalogue using detailedmacroseismic maps allows the correlation between the location of past earthquakes and fault segments.The recent results of paleoearthquake investigations (paleoseismic and archeoseismic) with a recurrenceinterval of large events and long-term slip rate are presented and discussed along with the identification ofseismic gaps along the fault. Finally, the implications for the seismic hazard assessment are also discussed

Africa alive corridors : transdisciplinary research based on African footprints

This paper results from the AAC workshop, held 17-19th May 2022, which was dedicated to memory of Maarten de Wit. It is AEON contribution No. 208 and Iphakade publication 281.DATA AVAILABILITY : The data that support the maps and findings are available on request from the corresponding author.The idea of Africa Alive Corridors (AAC) evolved from Gondwana geological mapping to a comprehensive, more inclusive and dynamic approach to transdisciplinary research known as Earth Stewardship Science. Twenty designated corridors explore the geo-biological and cultural heritage of different regions of Africa over various periods, from deep time to the Anthropocene. Each corridor reveals a specific lens through which to investigate some of the rich scientific narratives embedded within it. The concept also facilitates learning and knowledge exchange across numerous disciplines: archeology, geology, geophysics, oceanography, glaciology, biology, botany, ecology, agriculture, engineering, spatial statistics, social sciences, and the humanities. This contribution analyses ten selected corridors in southern and western Africa, the Congo Basin, East Africa, and Madagascar. The various research themes explored include Earth impact hazard, origins of humankind, Snowball Earth, coastal food systems and conservation, the biogeography of lemurs, human settlement dynamics in Cameroon, tectonically linked earthquake occurrences in Algeria and Morocco, modelling land-use changes in the Western Rift Valley, trades and civilizations of the Mali Empire, Mbira music, and contemporary art. The ongoing work on these—and ten other—corridors has considerable potential to host new international collaborations to develop the links between society and natural sciences in Africa. Ultimately, AAC will benefit all stakeholders, especially the youth, in understanding and responding to societal needs and current global challenges.Open access funding provided by Nelson Mandela University.http://link.springer.com/journal/12371hj2024Centre for the Advancement of ScholarshipSDG-06:Clean water and sanitationSDG-07:Affordable and clean energySDG-11:Sustainable cities and communitie

Neotectonics of the SW Iberia margin, Gulf of Cadiz and Alboran Sea: a reassessment including recent structural, seismic and geodetic data

We use a thin-shell approximation for the lithosphere to model the neotectonics of the Gulf of Cadiz, SW Iberia margin and the westernmost Mediterranean, in the eastern segment of the Azores-Gibraltar plate boundary. In relation to previous neotectonic models in the region, we utilize a better constrained structural map offshore, and the recent GPS measurements over NW Africa and Iberia have been taken into account, together with the seismic strain rate and stress data, to evaluate alternative geodynamic settings proposed for the region. We show that by assuming a relatively simple, two-plate tectonic framework, where Nubia and Eurasia converge NW-SE to WNW-ESE at a rate of 4.5-6 mm yr-1, the models correctly predict the amount of shortening and wrenching between northern Algeria-Morocco and southern Spain and between NW Morocco and SW Iberia, as estimated from both GPS data and geological constraints. The consistency between modelled and observed velocities in the vicinity of Gibraltar and NW Morocco indicates that forcing by slab sinking beneath Gibraltar is not required to reproduce current horizontal deformation in these areas. In the Gulf of Cadiz and SW Iberia, the modelling results support a diffuse Nubia-Eurasia Plate boundary, where the convergence is accommodated along NNE-SSW to NE-SW and ENE-WSW thrust faults and WNW-ESE right-lateral strike-slip faults, over an area >200 km wide, in good general agreement with the distribution of the seismic strain rate and associated faulting mechanisms. The modelling results are robust to regional uncertainties in the structure of the lithosphere and have important implications for the earthquake and tsunami hazard of Portugal, SW Spain and Morocco. We predict maximum, long-term average fault slip rates between 1-2 mm yr-1, that is, less than 50 per cent the average plate relative movement, suggesting very long return periods for high-magnitude (Mw > 8) earthquakes on individual structures.publishe

Strain partitioning of active transpression within the Lebanese restraining bend of the Dead Sea fault (Lebanon and SW Syria)

This material has been published in The Journal of the Geological Society of London, the only definitive repository of the content that has been certified and accepted after peer review. Copyright and all rights therein are retained by The Geological Society of London. Copyright 2001, The Geological Society of London. See also: http://atlas.geo.cornell.edu/deadsea/publications/Gomez2007_GSL.htmRecent neotectonic, palaeoseismic, and GPS results along the central Dead Sea fault system elucidate the spatial distribution of crustal deformation within a large (~180 km long) restraining bend along this major continental transform. Within the "Lebanese" restraining bend, the Dead Sea fault system splays into several key branches, and we suggest herein that active deformation is partitioned between NNE-SSW strike-slip faults and WNW-ESE crustal shortening. When plate motion is decomposed into strike-slip parallel to the two prominent NNE-SSW strike-slip faults (the Yammouneh and Serghaya faults) and orthogonal motion, their slip rates are sufficient to account for all expected strike-slip motion. Shortening of the Mount Lebanon range is inferred from the geometry and kinematics of the Roum fault, as well as preliminary quantification of coastal uplift. The results do not account for all expected crustal shortening, suggesting that some contraction is likely accommodated in the Anti Lebanon range. It also seems unlikely that the present kinematic configuration characterizes the entire Cenozoic history of the restraining bend. Present-day strain partitioning contrasts with published observations on finite deformation in Lebanon demonstrating distributed shear and vertical-axis block rotations. Furthermore, the present-day proportions of strike-slip displacement and crustal shortening are inconsistent with the total strike-slip offset and the lack of a significantly thickened crust. This suggests that the present rate of crustal shortening has not persisted for the longer life of the transform. Hence, we suggest that the Lebanese restraining bend evolved in a polyphase manner: An earlier episode of wrench-faulting and block rotation, followed by the later period of strain partitioning

Active faulting and transpression tectonics along the plate boundary in North Africa

We present a synthesis of the active tectonics of the northern Atlas Mountains and suggest a kinematic model of transpression and block rotation that illustrates the mechanics of this section of the Africa - Eurasia plate boundary. Neotectonic structures and significant shallow seismicity (with Mw > 5.0) indicate that coeval east-west trending right-lateral faulting and NE-SW thrust-related folding, result from the oblique convergence at the plate boundary, and form a transpressional system. The strain distribution obtained from fault - fold structures and P axes of focal mechanism solutions, and the geodetic (NUVEL1 and GPS) convergence shows that shortening and convergence directions are not coaxial. The transpressional strain is partitioned along strike and the quantitative description of displacement field yields a compression to transcurrence ratio varying from 33% near Gibraltar, to 50% along the Tunisian Atlas. Shortening directions oriented NNE to NNW for the Pliocene and Quaternary, respectively, and the S shape of Quaternary anticline axes are in agreement with the 2.24° - 3.9 °/Myr modeled clockwise rotation of small tectonic blocks and paleomagnetic results. The convergence between Africa and Eurasia is absorbed along the Atlas Mountains, at the upper crustal level, by means of thrusting above decollement systems, controlled by subdued transcurrent faults. The Tell Atlas of NW Algeria that experienced numerous large earthquakes with respect to other regions is interpreted as a restraining bend that localizes strain distribution along the plate boundary