Along the Ecuadorian margin, oblique subduction induces deformation of the overriding continental... more Along the Ecuadorian margin, oblique subduction induces deformation of the overriding continental plate. For the last 15 Ma, both exhumation and tectonic history of Ecuador suggest that the northeastward motion of the North Andean Sliver (NAS) was accompanied by an eastward migration of its eastern boundary and successive progressively narrowing restraining bends. Here we present geologic data, earthquake epicenters, focal mechanisms, GPS results, and a revised active fault map consistent with this new kinematic model. All data sets concur to demonstrate that active continental deformation is presently localized along a single major fault system, connecting fault segments from the Gulf of Guayaquil to the eastern Andean Cordillera. Although secondary faults are recognized within the Cordillera, they accommodate a negligible fraction of relative motion compared to the main fault system. The eastern limit is then concentrated rather than distributed as first proposed, marking a sharp boundary between the NAS, the Inca sliver, and the Subandean domain overthrusting the South American craton. The NAS limit follows a northeast striking right-lateral transpressional strike-slip system from the Gulf of Guayaquil (Isla Puná) to the Andean Cordillera and with the north-south striking transpressive faults along the eastern Andes. Eastward migration of the restraining belt since the Pliocene, abandonment of the sutures and reactivation of north-south striking ancient fault zones lead to the final development of a major tectonic boundary south and east of the NAS, favoring its extrusion as a continental sliver, accommodating the oblique convergence of the Nazca oceanic plate toward South America.
Along the western margin of South America, plate convergence is accommodated by slip on the subdu... more Along the western margin of South America, plate convergence is accommodated by slip on the subduction interface and deformation of the overriding continent 1-6. In Chile 1-4 , Bolivia 6 , Ecuador and Colombia 5,7 , continental deformation occurs mostly through the motion of discrete domains, hundreds to thousands of kilometres in scale. These continental slivers are wedged between the Nazca and stable South American plates. Here we use geodetic data to identify another large continental sliver in Peru that is about 300-400 km wide and 1,500 km long, which we call the Inca Sliver. We show that movement of the slivers parallel to the subduction trench is controlled by the obliquity of plate convergence and is linked to prominent features of the Andes Mountains. For example, the Altiplano is located at the boundary of converging slivers at the concave bend of the central Andes, and the extending Gulf of Guayaquil is located at the boundary of diverging slivers at the convex bend of the northern Andes. Motion of a few large continental slivers therefore controls the present-day deformation of nearly the entire Andes mountain range. We also show that a 1,000-km-long section of the plate interface in northern Peru and southern Ecuador slips predominantly aseismically, a behaviour that contrasts with the highly seismic neighbouring segments. The primary characteristics of this low-coupled segment are shared by ∼20% of the subduction zones in the eastern Pacific Rim. Along the western margin of South America, rapid convergence (∼60-70 mm yr −1) of the oceanic Nazca Plate towards South America has produced three of the ten largest subduction earthquakes since 1900. Almost its entire length has been ruptured by M > 8 megathrust earthquakes since the 1500s (ref. 8). Contrasting with this observation, north of the 1746 M w ∼ 8.6 Lima earthquake 9 and south of the 1906 M w 8.8 Ecuador-Colombia event 10 , no M > 8 megathrust earthquake has occurred at least since the Spanish conquest of the Inca Empire in 1532 (Fig. 1a). The only noteworthy historical events occurred in 1619, when the city of Trujillo was destroyed, and in 1912 in the Piura area, but their attribution to subduction events remains uncertain 9. Among the four events with magnitude larger than 7 recorded by seismometers in this region, the 1960 M w 7.6 and 1996 M w 7.5 earthquakes
Rapid subduction of the Nazca plate beneath the northen Andes margin (~6 cm/yr) results in two di... more Rapid subduction of the Nazca plate beneath the northen Andes margin (~6 cm/yr) results in two different processes: (1) elastic stress is accumulating along the Nazca/South American plate interface which is responsible for one of the largest megathrust earthquake sequences during the last century. The 500-km-long rupture zone of the 1906 (Mw= 8.8) event was partially reactivated by three events
ABSTRACT Subduction of the Nazca plate along the northern Ecuadorian coast has produced an except... more ABSTRACT Subduction of the Nazca plate along the northern Ecuadorian coast has produced an exceptional sequence of large thrust events during the 20th century (1906, 1942, 1958, and 1979). The sequence has evidenced a particular spatial organization of the rupture along the margin. However the segmentation along this margin has not been yet precisely established due to aftershocks sequences poorly registered and located and to rupture zones roughly estimated. We present a new seismic data set of the north-western region of Ecuador registered by a local broad band seismic network set up since late 2008. A new velocity model was derived for the zone inside the network. A nonlinear optimization for simultaneous determination of hypocenters and 1D velocity gradient model was achieved by systematic exploration over thickness and gradient parameters. The set of relocated events allows us to finely characterize the shape and geometry of the seismogenic structures, so far unknown. Three linear seismic structures roughly perpendicular to the subduction trench, segment the upper plate above the rupture zone of the 1942 event. To the north, the Esmeraldas canyon, previously interpreted as the off shore prolongation of the Esmeraldas fault, is also very active. These west northwest trending structures are connected inland to a very active north south trending seismic structure. This structure is parallel to the costal cordillera and located along its western flank. Its seismicity is distributed vertically from 5 to 22 km in depth, all in the upper plate as the interplate contact is estimated at 35 km depth beneath the coastal cordillera. New focal mechanisms indicate that this structure, as well as the canyon of Esmeraldas, has a left-lateral strike slip movement, consistent with the northward escape of the central part of the Northern Andean block. A strong compressive component due to the convergence is also observed. This north south trending active structure is interpreted as a consequence in the upper plate of a slip regime change along the subduction interplate from locked zone to slip free zone.
The North Andean Sliver (hereinafter NAS) lies at the northwestern end of the South American plat... more The North Andean Sliver (hereinafter NAS) lies at the northwestern end of the South American plate (hereinafter SOAM). This extensive area exhibits a complex deformation process controlled by the interactions of Nazca, Caribbean, South America plates, and Panama block, producing crustal seismicity, arc-continental collision, and subduction processes. Previous models based on partial GPS data sets have estimated the NAS kinematics as a single rigid block moving towards northeast at 8-10 mm/yr (Nocquet et al. 2014, Mora-Paez et al 2019). By contrary, geologic interpretations as well as seismotectonic data propose more complex kinematic models based on the interaction of several blocks (Audemard et al 2014, Alvarado et al 2016). Here, we present an updated and most extensive interseismic horizontal velocity field derived from continuous and episodic GPS data between 1994 and 2019 that encompasses the whole North Andean Sliver. We then interpret it, developing a kinematic elastic block ...
Along the Ecuadorian margin, oblique subduction induces deformation of the overriding continental... more Along the Ecuadorian margin, oblique subduction induces deformation of the overriding continental plate. For the last 15 Ma, both exhumation and tectonic history of Ecuador suggest that the northeastward motion of the North Andean Sliver (NAS) was accompanied by an eastward migration of its eastern boundary and successive progressively narrowing restraining bends. Here we present geologic data, earthquake epicenters, focal mechanisms, GPS results, and a revised active fault map consistent with this new kinematic model. All data sets concur to demonstrate that active continental deformation is presently localized along a single major fault system, connecting fault segments from the Gulf of Guayaquil to the eastern Andean Cordillera. Although secondary faults are recognized within the Cordillera, they accommodate a negligible fraction of relative motion compared to the main fault system. The eastern limit is then concentrated rather than distributed as first proposed, marking a sharp boundary between the NAS, the Inca sliver, and the Subandean domain overthrusting the South American craton. The NAS limit follows a northeast striking right-lateral transpressional strike-slip system from the Gulf of Guayaquil (Isla Puná) to the Andean Cordillera and with the north-south striking transpressive faults along the eastern Andes. Eastward migration of the restraining belt since the Pliocene, abandonment of the sutures and reactivation of north-south striking ancient fault zones lead to the final development of a major tectonic boundary south and east of the NAS, favoring its extrusion as a continental sliver, accommodating the oblique convergence of the Nazca oceanic plate toward South America.
Along the western margin of South America, plate convergence is accommodated by slip on the subdu... more Along the western margin of South America, plate convergence is accommodated by slip on the subduction interface and deformation of the overriding continent 1-6. In Chile 1-4 , Bolivia 6 , Ecuador and Colombia 5,7 , continental deformation occurs mostly through the motion of discrete domains, hundreds to thousands of kilometres in scale. These continental slivers are wedged between the Nazca and stable South American plates. Here we use geodetic data to identify another large continental sliver in Peru that is about 300-400 km wide and 1,500 km long, which we call the Inca Sliver. We show that movement of the slivers parallel to the subduction trench is controlled by the obliquity of plate convergence and is linked to prominent features of the Andes Mountains. For example, the Altiplano is located at the boundary of converging slivers at the concave bend of the central Andes, and the extending Gulf of Guayaquil is located at the boundary of diverging slivers at the convex bend of the northern Andes. Motion of a few large continental slivers therefore controls the present-day deformation of nearly the entire Andes mountain range. We also show that a 1,000-km-long section of the plate interface in northern Peru and southern Ecuador slips predominantly aseismically, a behaviour that contrasts with the highly seismic neighbouring segments. The primary characteristics of this low-coupled segment are shared by ∼20% of the subduction zones in the eastern Pacific Rim. Along the western margin of South America, rapid convergence (∼60-70 mm yr −1) of the oceanic Nazca Plate towards South America has produced three of the ten largest subduction earthquakes since 1900. Almost its entire length has been ruptured by M > 8 megathrust earthquakes since the 1500s (ref. 8). Contrasting with this observation, north of the 1746 M w ∼ 8.6 Lima earthquake 9 and south of the 1906 M w 8.8 Ecuador-Colombia event 10 , no M > 8 megathrust earthquake has occurred at least since the Spanish conquest of the Inca Empire in 1532 (Fig. 1a). The only noteworthy historical events occurred in 1619, when the city of Trujillo was destroyed, and in 1912 in the Piura area, but their attribution to subduction events remains uncertain 9. Among the four events with magnitude larger than 7 recorded by seismometers in this region, the 1960 M w 7.6 and 1996 M w 7.5 earthquakes
Rapid subduction of the Nazca plate beneath the northen Andes margin (~6 cm/yr) results in two di... more Rapid subduction of the Nazca plate beneath the northen Andes margin (~6 cm/yr) results in two different processes: (1) elastic stress is accumulating along the Nazca/South American plate interface which is responsible for one of the largest megathrust earthquake sequences during the last century. The 500-km-long rupture zone of the 1906 (Mw= 8.8) event was partially reactivated by three events
ABSTRACT Subduction of the Nazca plate along the northern Ecuadorian coast has produced an except... more ABSTRACT Subduction of the Nazca plate along the northern Ecuadorian coast has produced an exceptional sequence of large thrust events during the 20th century (1906, 1942, 1958, and 1979). The sequence has evidenced a particular spatial organization of the rupture along the margin. However the segmentation along this margin has not been yet precisely established due to aftershocks sequences poorly registered and located and to rupture zones roughly estimated. We present a new seismic data set of the north-western region of Ecuador registered by a local broad band seismic network set up since late 2008. A new velocity model was derived for the zone inside the network. A nonlinear optimization for simultaneous determination of hypocenters and 1D velocity gradient model was achieved by systematic exploration over thickness and gradient parameters. The set of relocated events allows us to finely characterize the shape and geometry of the seismogenic structures, so far unknown. Three linear seismic structures roughly perpendicular to the subduction trench, segment the upper plate above the rupture zone of the 1942 event. To the north, the Esmeraldas canyon, previously interpreted as the off shore prolongation of the Esmeraldas fault, is also very active. These west northwest trending structures are connected inland to a very active north south trending seismic structure. This structure is parallel to the costal cordillera and located along its western flank. Its seismicity is distributed vertically from 5 to 22 km in depth, all in the upper plate as the interplate contact is estimated at 35 km depth beneath the coastal cordillera. New focal mechanisms indicate that this structure, as well as the canyon of Esmeraldas, has a left-lateral strike slip movement, consistent with the northward escape of the central part of the Northern Andean block. A strong compressive component due to the convergence is also observed. This north south trending active structure is interpreted as a consequence in the upper plate of a slip regime change along the subduction interplate from locked zone to slip free zone.
The North Andean Sliver (hereinafter NAS) lies at the northwestern end of the South American plat... more The North Andean Sliver (hereinafter NAS) lies at the northwestern end of the South American plate (hereinafter SOAM). This extensive area exhibits a complex deformation process controlled by the interactions of Nazca, Caribbean, South America plates, and Panama block, producing crustal seismicity, arc-continental collision, and subduction processes. Previous models based on partial GPS data sets have estimated the NAS kinematics as a single rigid block moving towards northeast at 8-10 mm/yr (Nocquet et al. 2014, Mora-Paez et al 2019). By contrary, geologic interpretations as well as seismotectonic data propose more complex kinematic models based on the interaction of several blocks (Audemard et al 2014, Alvarado et al 2016). Here, we present an updated and most extensive interseismic horizontal velocity field derived from continuous and episodic GPS data between 1994 and 2019 that encompasses the whole North Andean Sliver. We then interpret it, developing a kinematic elastic block ...
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Papers by Paul Jarrin