Browsing by Author "Audin, Laurence"
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Item Open Access Ejemplos de deformación producto de la tectónica extensiva en las zonas de Huambo-Cabanaconde en Arequipa y Calacoa-Huaytire en Moquegua, de los Andes centrales vistos por interferometría radar - INSAR(Sociedad Geológica del Perú, 2009) Gonzales Zuñiga, Katherine; Froger, Jean-Luc; Audin, Laurence; Macedo Sánchez, Orlando EfraínEn este trabajo se presentan los primeros resultados obtenidos por el método InSAR para la detección y medida del campo de deformación co-sísmico asociado a eventos sísmicos ocurridos en el sur del Perú. Interferogramas calculados sobre la zona de los poblados Huambo-Cabanconde (departamento de Arequipa) y sobre la zona de Calacoa (departamento de Moquegua), han permitido registrar procesos de deformación del suelo asociados a la tectónica extensiva superfi cial, la que viene actuando en los Andes Centrales desde el Mioceno medio. El primer ejemplo de deformación ha sido detectado en la zona Huambo-Cabanaconde. El interferograma calculado con imágenes adquiridas el 06/12/2002 y 12/09/2003, muestra una subsidencia en la Pampa Mojonpampa, hacia el sur de la falla normal Solarpampa, que forma parte del sistema de fallas Huambo-Cabanaconde. Esta subsidencia habría sido producida por sismos de magnitud Mb > 4 ocurridos entre el 13/12/2002 y 14/12/2002, los mismos que se producen por esfuerzos extensivos que actúan en dirección N-S. Un segundo ejemplo de deformación ha sido detectado en dos interferogramas de la zona de Calacoa (departamento de Moquegua), calculados con imágenes adquiridas entre el 01/12/2004 y el 13/05/2006. Esta deformación esta muy probablemente relacionada a un sismo de magnitud Mw 5.4 que corresponde al evento principal de la crisis sísmica ocurrida en octubre del 2005 en la región del volcán Ticsani. Esta crisis sísmica consiste en una sismicidad superfi cial intracrustal asociada a la actividad de una falla local N155º. El área de deformación producida fue de 15 x 12 km aproximadamente, y registró una amplitud máxima de 14 cm a 3.5 km al NO de la cima del volcán Ticsani. Las características de la falla N155º han sido puestas en evidencia por los datos interferométricos. Un tercer ejemplo de deformación ha sido observado a 25 km al SE del volcán Ticsani, en un área elíptica de aproximadamente 24.5 x 11.7 km orientada en dirección NO-SE y cuya amplitud máxima de deformación fue de 5.5 cm (subsidencia). Esta deformación se habría producido entre Diciembre de 2004 y Mayo de 2006 y puede ser atribuida a la ocurrencia de una crisis sísmica durante este periodo.Item Restricted Monumental inca remains and past seismic disasters: a relational database to support archaeoseismological investigations and cultural heritage preservation in the Andes(Elsevier, 2021-11) Combey, Andy; Tricoche, Agnès; Audin, Laurence; Gandreau, David; Escóbar, Carlos Benavente; Abuhadba, José Bastante; Tavera, Hernando; Rodríguez-Pascua, Miguel ÁngelAs recent dramatic and numerous examples demonstrate, earthquakes still constitute a significant threat to cultural heritage (Bam 2003; L’Aquila 2009; Haiti 2010; Nepal 2015). By damaging the historical legacy, telluric phenomena affect economic and touristic incomes and alter regional identities and collective psyche. In the Andes, as in other emerging regions across the globe, deficient seismic hazard assessments, constant lack of resources, and inadequate maintenance programs are additional challenges for cultural heritage management. As part of our archaeoseismological investigation in the Cusco area (Peru), we developed a relational database, which seeks to identify, record and inventory seismic damage in pre-Columbian architecture. This work presents the main characteristics of the structure and design of the RISC (“Risque sismique, Incas et Société à Cusco”) database and its contribution in supporting the fieldwork organization and facilitating the data acquisition. The collected architectonical evidence constitutes the first large archaeoseismological dataset in South America and will provide valuable complementary data in Peru to regional seismic hazard studies. We here aim to demonstrate that an ergonomic and user-friendly interface has a role to play in supervising and preserving the cultural heritage in active seismic areas. By converting ad-hoc surveys into routine inspections, RISC could become an effective low-tech monitoring system, providing relevant support for disaster risk reduction plans in archaeological sites conservation. We stress the necessity of adopting cost-effective and easy-to-implement tools for cultural heritage monitoring in emerging countries through this case study. Our database may represent a relevant methodological background and template for further initiatives in both fields of archaeoseismology and cultural heritage protection.Item Open Access Parámetros de la fuente del sismo de Sama (Tacna), 20 de noviembre de 2006 (5.4Mw)(Sociedad Geológica del Perú, 2007) Tavera, Hernando; Audin, Laurence; Bernal Esquia, Yesenia IsabelEl 20 de Noviembre de 2006 (14:48 UTC) cerca de la localidad de Sama (Tacna) ocurre un inusual evento sísmico con posible origen en una de las trazas de falla ubicada en el borde oeste del sistema de fallas de Incapuquio. Este sismo de foco superficial (17 km) y magnitud moderada (5.3ML), presenta su epicentro próximo a la traza de la falla Sama-Calientes, siendo su mecanismo focal del tipo compresional con planos orientados en la misma dirección que la falla (NO-SE). Los espectros de amplitud del desplazamiento de ondas S indican un momento sísmico (Mo) de 1.2E+24 dina-cm equivalente a una magnitud de 5.4Mw, además de un radio de ruptura de 3.7 km. De acuerdo a la traza de la falla Sama-Calientes y ~ los parámetros de la fuente del sismo, se sugiere que dicha falla es del tipo inversa con posible geometrí~ de bajo ángulo en profundidad.Item Restricted Seismic and aseismic slip on the Central Peru megathrust(Nature Research, 2010-05-06) Perfettini, Hugo; Avouac, Jean-Philippe; Tavera, Hernando; Kositsky, Andrew; Nocquet, Jean-Mathieu; Bondoux, Francis; Chlieh, Mohamed; Sladen, Anthony; Audin, Laurence; Farber, Daniel L.; Soler, PierreSlip on a subduction megathrust can be seismic or aseismic, with the two modes of slip complementing each other in time and space to accommodate the long-term plate motions. Although slip is almost purely aseismic at depths greater than about 40 km, heterogeneous surface strain1–8 suggests that both modes of slip occur at shallower depths, with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods9–11. Thus, active faults seem to comprise areas that slip mostly during earthquakes, and areas that mostly slip aseismically. The size, location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place, and what fraction of the long-term slip rate it accounts for. Here we address this issue by focusing on the central Peru megathrust. We show that the Pisco earthquake, with moment magnitude Mw 5 8.0, ruptured two asperities within a patch that had remained locked in the interseismic period, and triggered aseismic frictional afterslip on two adjacent patches. The most prominent patch of afterslip coincides with the subducting Nazca ridge, an area also characterized by low interseismic coupling, which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past. The seismogenic portion of the megathrust thus appears to be composed of interfingering rate-weakening and ratestrengthening patches. The rate-strengthening patches contribute to a high proportion of aseismic slip, and determine the extent and frequency of large interplate earthquakes. Aseismic slip accounts for as much as 50–70% of the slip budget on the seismogenic portion of the megathrust in central Peru, and the return period of earthquakes with Mw 5 8.0 in the Pisco area is estimated to be 250 years.Item Restricted Source model of the 2007 Mw 8.0 Pisco, Peru earthquake: implications for seismogenic behavior of subduction megathrusts(American Geophysical Union, 2010-02-09) Sladen, A; Tavera, Hernando; Simons, M; Avouac, J. P.; Konca, A. O.; Perfettini, Hugo; Audin, Laurence; Fielding, E. J.; Ortega, F.; Cavagnoud, R.We use Interferometric Synthetic Aperture Radar, teleseismic body waves, tsunami waveforms recorded by tsunameters, field observations of coastal uplift, subsidence, and runup to develop and test a refined model of the spatiotemporal history of slip during the Mw 8.0 Pisco earthquake of 15 August 2007. Our preferred solution shows two distinct patches of high slip. One patch is located near the epicenter while another larger patch ruptured 60 km further south, at the latitude of the Paracas peninsula. Slip on the second patch started 60 s after slip initiated on the first patch. We observed a remarkable anticorrelation between the coseismic slip distribution and the aftershock distribution determined from the Peruvian seismic network. The proposed source model is compatible with regional runup measurements and open ocean tsunami records. From the latter data set, we identified the 12 min timing error of the tsunami forecast system as being due to a mislocation of the source, caused by the use of only one tsunameter located in a nonoptimal azimuth. The comparison of our source model with the tsunami observations validate that the rupture did not extend to the trench and confirms that the Pisco event is not a tsunami earthquake despite its low apparent rupture velocity (<1.5 km/s). We favor the interpretation that the earthquake consists of two subevents, each with a conventional rupture velocity (2–4 km/s). The delay between the two subevents might reflect the time for the second shock to nucleate or, alternatively, the time it took for afterslip to increase the stress level on the second asperity to a level necessary for static triggering. The source model predicts uplift offshore and subsidence on land with the pivot line following closely the coastline. This pattern is consistent with our observation of very small vertical displacement along the shoreline when we visited the epicentral area in the days following the event. This earthquake represents, to our knowledge, one of the best examples of a link between the geomorphology of the coastline and the pattern of surface deformation induced by large interplate ruptures.Item Restricted Structure of the subduction system in southern Peru from seismic array data(American Geophysical Union, 2012-11-28) Phillips, Kristin; Clayton, Robert W.; Davis, Paul; Tavera, Hernando; Guy, Richard; Skinner, Steven; Stubailo, Igor; Audin, Laurence; Aguilar, VictorThe subduction zone in southern Peru is imaged using converted phases from teleseismic P, PP, and PKP waves and P wave tomography using local and teleseismic events with a linear array of 50 broadband seismic stations spanning 300 km from the coast to near Lake Titicaca. The slab dips at 30° and can be observed to a depth of over 200 km. The Moho is seen as a continuous interface along the profile, and the crustal thickness in the back-arc region (the Altiplano) is 75 km thick, which is sufficient to isostatically support the Andes, as evidenced by the gravity. The shallow crust has zones of negative impedance at a depth of 20 km, which is likely the result of volcanism. At the midcrustal level of 40 km, there is a continuous structure with a positive impedance contrast, which we interpret as the western extent of the Brazilian Craton as it underthrusts to the west. Vp/Vs ratios estimated from receiver function stacks show average values for this region with a few areas of elevated Vp/Vs near the volcanic arc and at a few points in the Altiplano. The results support a model of crustal thickening in which the margin crust is underthrust by the Brazilian Shield.Item Restricted Upper plate deformation and seismic barrier in front of Nazca subduction zone: The Chololo Fault System and active tectonics along the Coastal Cordillera, southern Peru(Elsevier, 2008) Audin, Laurence; Lacan, Pierre; Tavera, Hernando; Bondoux, FrancisThe South America plate boundary is one of the most active subduction zone. The recent Mw = 8.4 Arequipa 2001 earthquake ruptured the subduction plane toward the south over 400 km and stopped abruptly on the Ilo Peninsula. In this exact region, the subduction seismic crisis induced the reactivation of continental fault systems in the coastal area. We studied the main reactivated fault system that trends perpendicular to the trench by detailed mapping of fault related-geomorphic features. Also, at a longer time scale, a recurrent Quaternary transtensive tectonic activity of the CFS is expressed by offset river gullies and alluvial fans. The presence of such extensional fault systems trending orthogonal to the trench along the Coastal Cordillera in southern Peru is interpreted to reflect a strong coupling between the two plates. In this particular case, stress transfer to the upper plate, at least along the coastal fringe, appears to have induced crustal seismic events that were initiated mainly during and after the 2001 earthquake. The seafloor roughness of the subducting plate is usually thought to be a cause of segmentation along subduction zones. However, after comparing and discussing the role of inherited structures within the upper plate to the subduction zone segmentation in southern Peru, we suggest that the continental structure itself may exert some feedback control on the segmentation of the subduction zone and thus participate to define the rupture pattern of major subduction earthquakes along the southern Peru continental margin.