Paleoseismology and tectonic geomorphology of the Pallatanga fault (Central Ecuador), a major structure of the South-American crust

Baize, Stéphane; Audin, Laurence; Winter, Thierry; Alvarado, Alexandra; Moreno, Luis Pilatasig; Taipe, Mercedes; Reyes, Pedro; Kauffmann, Paul; Yépes, Hugo

doi:10.1016/j.geomorph.2014.02.030

Cited by 38 publications

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“…Beauval et al [] have located a second historical M w ~7 earthquake that occurred in 1645, about 50 km SSW of the 1797 event on the same structure (Figure ). The occurrence of two M w >7 within a short time span is in conflict with paleoseismological studies [ Baize et al ., ], because the recurrence time is too short for the segment. Therefore, it is plausible that a neighboring active structure could have failed during the 1645 earthquake, since the Pallatanga fault is moving at ~50% of the overall velocity established for NAB [ Winter et al ., ; Baize et al ., ].…”

Section: Discussionmentioning

confidence: 94%

“…The occurrence of two M w >7 within a short time span is in conflict with paleoseismological studies [ Baize et al ., ], because the recurrence time is too short for the segment. Therefore, it is plausible that a neighboring active structure could have failed during the 1645 earthquake, since the Pallatanga fault is moving at ~50% of the overall velocity established for NAB [ Winter et al ., ; Baize et al ., ]. This is an important aspect to take into consideration when modeling fault sources in the region.…”

Section: Discussionmentioning

confidence: 99%

“…The sharper picture of the country's seismicity provided by the new catalog depicts the downgoing slab geometry and confirms the relationship of the involved plates at depth where inherited oceanic plate structures have an influential role. For the continental domain, convergence obliquity, and tectonic stress partitioning, focal mechanisms and seismic energy release patterns are analyzed along with new knowledge obtained from recent geologic investigations on active continental faults [Baize et al, 2014;Alvarado et al, 2016]. We merge all that information with the seismic catalog and active deformation data to better define geometries and boundaries of continental source zones corresponding to the seismotectonic model.…”

Section: Yepes Et Almentioning

confidence: 99%

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A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment

et al. 2016

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A new view of Ecuador's complex geodynamics has been developed in the course of modeling seismic source zones for probabilistic seismic hazard analysis. This study focuses on two aspects of the plates' interaction at a continental scale: (a) age‐related differences in rheology between Farallon and Nazca plates—marked by the Grijalva rifted margin and its inland projection—as they subduct underneath central Ecuador, and (b) the rapidly changing convergence obliquity resulting from the convex shape of the South American northwestern continental margin. Both conditions satisfactorily explain several characteristics of the observed seismicity and of the interseismic coupling. Intermediate‐depth seismicity reveals a severe flexure in the Farallon slab as it dips and contorts at depth, originating the El Puyo seismic cluster. The two slabs position and geometry below continental Ecuador also correlate with surface expressions observable in the local and regional geology and tectonics. The interseismic coupling is weak and shallow south of the Grijalva rifted margin and increases northward, with a heterogeneous pattern locally associated to the Carnegie ridge subduction. High convergence obliquity is responsible for the North Andean Block northeastward movement along localized fault systems. The Cosanga and Pallatanga fault segments of the North Andean Block‐South American boundary concentrate most of the seismic moment release in continental Ecuador. Other inner block faults located along the western border of the inter‐Andean Depression also show a high rate of moderate‐size earthquake production. Finally, a total of 19 seismic source zones were modeled in accordance with the proposed geodynamic and neotectonic scheme.

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Section: Discussionmentioning

confidence: 94%

Section: Discussionmentioning

confidence: 99%

Section: Yepes Et Almentioning

confidence: 99%

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A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment

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“…Note the systematic right lateral NE offset, dated as late Miocene and the systematic offset of older (late Oligocene to Miocene) NS sutures and terranes north of Juan de Velasco village. These NE faults do not affect the Quaternary to recent volcanic outcrops in the Interandean Valley, contrasting with the Pallatanga Fault system that does offset Quaternary formations [ Baize et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Partitioning of oblique convergence in the Northern Andes subduction zone: Migration history and the present‐day boundary of the North Andean Sliver in Ecuador

et al. 2016

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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.

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“…A large‐scale mapping of the potential active segments of the CCPP has been recently proposed (Alvarado, ) and a first paleoseismological study has been carried out along the Pallatanga segment, pointing out evidences of several large ( M 7+) paleoearthquakes (Baize et al, ). Besides classical field mapping of fault segments based on geomorphological analyses, we performed a systematic interferometric synthetic aperture radar (InSAR) analysis of the Riobamba‐Ambato‐Latacunga region (Figure b).…”

Section: Introductionmentioning

confidence: 99%

Evidences of Surface Rupture Associated With a Low‐Magnitude (M_w5.0) Shallow Earthquake in the Ecuadorian Andes

et al. 2017

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This study analyzes surface displacements generated by a low‐magnitude crustal earthquake in the Ecuadorian Andes by combining analysis of synthetic aperture radar (SAR) interferometry, geological field investigations, and seismological data. In March 2010, a significant surface faulting event occurred in the Pisayambo area (Eastern Cordillera), along the major dextral fault zone bounding the North Andean Sliver and the South America Plate. Interferograms were inverted to determine fault plane geometry and slip displacement distribution. The event affected a 9 km long previously unknown fault, referred as the Laguna Pisayambo Fault, with purely dextral movement reaching 45 cm and concentrated in the top 3 km of the crust. Geological investigations confirm both the fault mechanism and the amplitude of displacements. While these large displacements would be related to an event with a magnitude of 5.44 if using a standard crustal rigidity, we show that they can be convincingly associated with an Mw5.0 earthquake, that occurred on 26 March 2010. Reconciling the apparent differences in magnitude requires the existence of a low‐rigidity medium at shallow depths and/or postseismic activity of the fault. However, considering only the latter hypothesis would imply an unusually active postseismic process, in which 400–500% of the coseismic moment is released in the 6 days following the earthquake. Our observations highlight that the scaling laws relating surface observations to earthquake magnitude, classically used for seismic hazard assessment, should be carefully used. This study also illustrates how systematic InSAR analysis, even in places where no clues of ground deformation are present, can reveal tectonic processes.

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Paleoseismology and tectonic geomorphology of the Pallatanga fault (Central Ecuador), a major structure of the South-American crust

Cited by 38 publications

References 31 publications

A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment

A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment

Partitioning of oblique convergence in the Northern Andes subduction zone: Migration history and the present‐day boundary of the North Andean Sliver in Ecuador

Evidences of Surface Rupture Associated With a Low‐Magnitude (M_w5.0) Shallow Earthquake in the Ecuadorian Andes

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Paleoseismology and tectonic geomorphology of the Pallatanga fault (Central Ecuador), a major structure of the South-American crust

Cited by 38 publications

References 31 publications

A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment

A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment

Partitioning of oblique convergence in the Northern Andes subduction zone: Migration history and the present‐day boundary of the North Andean Sliver in Ecuador

Evidences of Surface Rupture Associated With a Low‐Magnitude (Mw5.0) Shallow Earthquake in the Ecuadorian Andes

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Evidences of Surface Rupture Associated With a Low‐Magnitude (M_w5.0) Shallow Earthquake in the Ecuadorian Andes