Browsing by Author "Norabuena Ortiz, Edmundo"
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Item Restricted A new South American network to study the atmospheric electric field and its variations related to geophysical phenomena(Elsevier, 2014-12) Tacza, J.; Raulin, J. P.; Macotela, E.; Norabuena Ortiz, Edmundo; Fernández, G.; Correia, E.; Rycroft, M. J.; Harrison, R. G.In this paper we present the capability of a new network of field mill sensors to monitor the atmospheric electric field at various locations in South America; we also show some early results. The main objective of the new network is to obtain the characteristic Universal Time diurnal curve of the atmospheric electric field in fair weather, known as the Carnegie curve. The Carnegie curve is closely related to the current sources flowing in the Global Atmospheric Electric Circuit so that another goal is the study of this relationship on various time scales (transient/monthly/seasonal/annual). Also, by operating this new network, we may also study departures of the Carnegie curve from its long term average value related to various solar, geophysical and atmospheric phenomena such as the solar cycle, solar flares and energetic charged particles, galactic cosmic rays, seismic activity and specific meteorological events. We then expect to have a better understanding of the influence of these phenomena on the Global Atmospheric Electric Circuit and its time-varying behavior.Item Open Access An 8 month slow slip event triggers progressive nucleation of the 2014 Chile megathrust(American Geophysical Union, 2017-05-16) Socquet, Anne; Piña Valdes, Jesús; Jara, Jorge; Cotton, Fabrice; Walpersdorf, Andrea; Cotte, Nathalie; Specht, Sebastian; Ortega‐Culaciati, Francisco; Carrizo, Daniel; Norabuena Ortiz, EdmundoThe mechanisms leading to large earthquakes are poorly understood and documented. Here we characterize the long‐term precursory phase of the 1 April 2014 Mw8.1 North Chile megathrust. We show that a group of coastal GPS stations accelerated westward 8 months before the main shock, corresponding to a Mw6.5 slow slip event on the subduction interface, 80% of which was aseismic. Concurrent interface foreshocks underwent a diminution of their radiation at high frequency, as shown by the temporal evolution of Fourier spectra and residuals with respect to ground motions predicted by recent subduction models. Such ground motions change suggests that in response to the slow sliding of the subduction interface, seismic ruptures are progressively becoming smoother and/or slower. The gradual propagation of seismic ruptures beyond seismic asperities into surrounding metastable areas could explain these observations and might be the precursory mechanism eventually leading to the main shock.Item Restricted Atmospheric electric field variations and lower ionosphere disturbance during the total solar eclipse of 2010 July 11(Elsevier, 2016-11) Tacza, José C.; Raulin, Jean-Pierre; Macotela, Edith L.; Norabuena Ortiz, Edmundo; Fernández, GermánIn this paper, we study the variations of atmospheric electric field during the total solar eclipse (TSE) of July 11, 2010, at Complejo Astronómico El Leoncito (CASLEO). These variations observed with two identical sensors separated by 0.4 km, show a significant increase (∼55 V/m) when compared with averaged values measured during previous and subsequent fair weather days. Furthermore, identical changes are detected on the measured phases of Very Low Frequency waves received at CASLEO. The latter suggests a possible connection between the lower ionosphere and the lower atmosphere during the period of the eclipse.Item Open Access Decelerating Nazca-South America and Nazca-Pacific plate motions(American Geophysical Union, 1999) Norabuena Ortiz, Edmundo; Dixon, Timothy H.; Stein, Seth; Harrison, Christopher G. A.Space geodetic estimates of the rate of Nazca-South America convergence and Nazca-Pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average NUVEL-1A model. The implied rates of deceleration are consistent with longer term trends extending back to at least 20 Ma, about the time of initiation of Andes growth, and may reflect consequences of ongoing subduction and construction of the Andes, e.g., increased friction and viscous drag on the subducted slab as the leading edge of South America thickens.Item Restricted Geological setting, field survey and modeling of the Chimbote, northern Peru, tsunami of 21 february 1996(Springer, 1999) Buorgeois, J.; Petroff, C.; Yeh, H.; Titov, V.; Synolakis, C. E.; Benson, B.; Kuroiwa, J.; Lander, J.; Norabuena Ortiz, EdmundoWhereas the coast of Peru south of 10°S is historically accustomed to tsunamigenic earthquakes, the subduction zone north of 10°S has been relatively quiet. On 21 February 1996 at 21:51 GMT (07:51 local time) a large, tsunamigenic earthquake (Harvard estimate M w =7.5) struck at 9.6°S, 79.6°W, approximately 130 km off the northern coast of Peru, north of the intersection of the Mendana fracture zone with the Peru-Chile trench. The likely mechanism inferred from seismic data is a low-angle thrust consistent with subduction of the Nazca Plate beneath the South American plate, with relatively slow rupture characteristics. Approximately one hour after the main shock, a damaging tsunami reached the Peruvian coast, resulting in twelve deaths. We report survey measurements, from 7.7°S to 11°S, on maximum runup (2–5 m, between 8 and 10°S), maximum inundation distances, which exceeded 500 m, and tsunami sediment deposition patterns. Observations and numerical simulations show that the hydrodynamic characteristics of this event resemble those of the 1992 Nicaragua tsunami. Differences in climate, vegetation and population make these two tsunamis seem more different than they were. This 1996 Chimbote event was the first large (M W>7) subduction-zone (interplate) earthquake between about 8 and 10°S, in Peru, since the 17th century, and bears resemblance to the 1960 (M w 7.6) event at 6.8°S. Together these two events are apparently the only large subduction-zone earthquakes in northern Peru since 1619 (est. latitude 8°S, est. M w 7.8); these two tsunamis also each produced more fatalities than any other tsunami in Peru since the 18th century. We concur with Pelayo and Wiens (1990, 1992) that this subduction zone, in northern Peru, resembles others where the subduction zone is only weakly coupled, and convergence is largely aseismic. Subduction-zone earthquakes, when they occur, are slow, commonly shallow, and originate far from shore (near the tip of the wedge). Thus they are weakly felt, and the ensuing tsunamis are unanticipated by local populations. Although perhaps a borderline case, the Chimbote tsunami clearly is another wake-up example of a 'tsunami earthquake'.Item Open Access Gestión del conocimiento científico con valor social y gerencia pública(Instituto Geofísico del Perú, 2018-11-30) Mollo, Mary; Tavera, Hernando; Norabuena Ortiz, EdmundoEl IGP requiere sumarse al proceso de reforma y modernización del Estado a través del presupuesto por resultados (PPR) y las nuevas políticas del Consejo Nacional de Ciencia Tecnología e Innovación Tecnológica (Concytec) para lograr una mayor cobertura de la investigación científica. Este nuevo posicionamiento no solo está en marcha, sino que requiere de una redefinición estratégica en la gestión institucional que genere mayor valor en la producción científica para lograr que sea considerada un bien público por su contribución e impacto social. En este marco y contexto, en el año 2017, el IGP inicia una nueva etapa de gestión y desarrolla un diagnóstico de gestión institucional, cuyo análisis conduce a un nuevo modelo de gestión que propone desarrollar capacidades institucionales en la gestión del conocimiento geofísico. Para ello, se reconoce la especificidad de la naturaleza de la institución y se le diferencia en su quehacer planteando nuevos desafíos para la producción del conocimiento científico; más allá de su difusión en esta nueva etapa de gestión es de interés prioritario generar valor público y la necesidad de usar el conocimiento científico en la toma de decisiones de la política pública nacional y en las labores de la sociedad científica internacional y nacional.Item Open Access Heterogeneous Locking and Earthquake Potential on the South Peru Megathrust From Dense GNSS Network(American Geophysical Union, 2024-01-30) Lovery, B.; Chlieh, M.; Norabuena Ortiz, Edmundo; Villegas Lanza, Juan Carlos; Radiguet, M.; Cotte, N.; Tsapong-Tsague, A.; Quiroz Sifuentes, Wendy; Sierra Farfán, C.; Simons, M.; Nocquet, J. M.; Tavera, Hernando; Socquet, A.The Central Andes subduction has been the theater of numerous large earthquakes since the beginning of the 21st Century, notably the 2001 Mw = 8.4 Arequipa, 2007 Mw = 8.0 Pisco and 2014 Mw = 8.1 Iquique earthquakes. We present an analysis of 47 permanent and 26 survey global navigation satellite system (GNSS) measurements acquired in Central-South Peru between 2007 and 2022 to better understand the frictional properties of the megathrust interface. Using a trajectory model that mimics the different phases of the cycle, we extract a coherent interseismic GNSS field at the scale of the Central Andes from Lima to Arica (12–18.5°S). Interseismic models on a 3D slab geometry indicate that the locking level is relatively high and concentrated between 20 and 40-km depth. Locking distributions indicate a high spatial variability of the coupling along the trench, with the presence of many locked patches that spatially correlate with the seismotectonic segmentation. Our study confirms the presence of a creeping segment where the Nazca Ridge is subducting; we also observe a lighter apparent decrease of coupling related to the Nazca Fracture Zone (NFZ). However, since the Nazca Ridge appears to behave as a strong barrier, the NFZ is less efficient to arrest seismic rupture propagation. Considering various uncertainty factors, we discuss the implication of our coupling estimates with size and timing of large megathrust earthquakes considering both deterministic and probabilistic approaches. We estimate that the South Peru segment could have a Mw = 8.4–9.0 earthquake potential depending principally on the considered seismic catalog and the seismic/aseismic slip ratio.Item Restricted Morphology, structure and kinematics of a rainfall controlled slow‐moving Andean landslide, Peru(Wiley, 2016-09-15) Zerathe, Swann; Lacroix, Pascal; Jongmans, Denis; Marino, Jersy; Taipe, Edu; Wathelet, Marc; Pari, Walter; Smoll, Lionel Fidel; Norabuena Ortiz, Edmundo; Guillier, Bertrand; Tatard, LucileThe large slow‐moving landslide of Maca is located in the upper Colca valley (southern Peru), a region characterized by a well pronounced rainy period, and intense and recurrent sustained seismicity. The landslide, developed in deep lacustrine deposits, has recently accelerated, threatening the Maca village. This work aims at understanding the rupture mechanism and the causes of the recent landslide reactivation/acceleration. We present a multidisciplinary characterization of the Maca landslide that includes: (i) geological and morphological mapping in the field; (ii) remote sensing analysis using an historical aerial photograph of 1955 and the Pléiades satellite images (2013); (iii) global positioning system (GPS) including time‐series of surveys over 13 years, and continuous measurements over 14 months; (iv) a geophysical campaign with deep electrical resistivity tomography profiles acquired across the landslide mass. Our study shows that this 60 Mm3 landslide, which can be classified as a clay/silt compound landslide, moved by 15 m between 2001 and 2014 with a large inter‐annual velocity variation (up to a factor of 500) depending on the rainfall intensity. We suggest that these dramatic changes in velocity are the result of the combination of a threshold mechanism and the short intense rainy season in Peru. This study reveals three main driving factors acting at different timescales: (i) over several decades, the river course has significantly changed, causing the Maca landslide reactivation in the 1980s due to the erosion of its toe; (ii) at the year scale, a minimum amount of rainfall is required to trigger the motion and this amount controls the landslide velocity; (iii) transient changes in slide velocity may occur anytime due to earthquakes. This study particularly highlights the non‐linear behaviour of the motion with rainfall.Item Restricted Paleoseismology and global positioning system: earthquake-cycle effects and geodetic versus geologic fault slip rates in the Eastern California shear zone(Geological Society of America, 2003) Norabuena Ortiz, Edmundo; Dixon, Timothy H.; Hotaling, L.Published slip rates for the Owens Valley fault zone in eastern California based on geodetic data and elastic half-space models (5–7 mm/yr) are faster than longer term geologic rates (2–3 mm/yr). We use Global Positioning System data spanning the central Owens Valley, a more realistic rheological model with an elastic upper crust over a viscoelastic lower crust and upper mantle, and paleoseismic data from adjacent faults, to show that this difference could reflect earthquake-cycle effects. We estimate a long-term rate (2.1 ± 0.7 mm/yr) and earthquake recurrence interval (2750 +350/−1000 yr) from the geodetic data, both in agreement with independent geologic estimates.Item Open Access Retraso en el inicio de la temporada de lluvias e incremento de la ocurrencia de incendios(Instituto Geofísico del Perú, 2023-07) Zubieta Barragán, Ricardo; Ccanchi, Yerson; Martínez Grimaldo, Alejandra; Saavedra Huanca, Miguel; Norabuena Ortiz, Edmundo; Alvarez, Sigrid; Ilbay, MercyAl ocurrir un incendio forestal en los Andes, se suele pensar que la causa de este fuego que se propaga surge de la quema agrícola realizada por la propia población. Durante el año 2020, el periodo de la pandemia de la COVID-19, se registró la ocurrencia sin precedentes de incendios forestales en los Andes peruanos. Este estudio evalúa las condiciones climáticas y vegetativas propicias para la ocurrencia de dichos eventos haciendo uso de los datos de precipitación, reflectividad y el registro nacional de incendios (MINAM). El análisis de la precipitación estacional del año 2020 indica que este periodo no está estadísticamente asociado con un periodo de sequía; no obstante, el alto incremento de la frecuencia acumulada de días secos entre agosto y noviembre de 2020, durante el periodo de inicio de lluvias (al igual que los periodos de sequía de 2005, 2010 y 2016), habría desempeñado un rol importante en el aumento de condiciones favorables para la propagación de quemas y, por tanto, de incendios forestales. A ello se añade el contexto de la pandemia de la COVID-19, situación que propició el retorno por parte de la población a la actividad agrícola, lo cual habría favorecido la práctica de quemas con la finalidad de limpiar el terreno previo al cultivo.Item Restricted Space geodetic observations of Nazca-South America convergence across the Central Andes(American Association for the Advancement of Science, 1998-01-16) Norabuena Ortiz, Edmundo; Leffler-Griffin, Lisa; Mao, Ailin; Dixon, Timothy; Stein, Seth; Selwyn Sacks, I.; Ocola, Leonidas; Ellis, MichaelSpace geodetic data recorded rates and directions of motion across the convergent boundary zone between the oceanic Nazca and continental South American plates in Peru and Bolivia. Roughly half of the overall convergence, about 30 to 40 millimeters per year, accumulated on the locked plate interface and can be released in future earthquakes. About 10 to 15 millimeters per year of crustal shortening occurred inland at the sub-Andean foreland fold and thrust belt, indicating that the Andes are continuing to build. Little (5 to 10 millimeters per year) along-trench motion of coastal forearc slivers was observed, despite the oblique convergence.Item Restricted Spatial distribution and B value of intermediate-depth earthquakes beneath central Peru(American Geophysical Union, 1988-11) Schneider, John F.; Selwyn Sacks, I.; Huaco, Daniel; Ocola, Leonidas; Norabuena Ortiz, Edmundo; Flores, AntonioWe have investigated the spatial distribution of microseismicity at intermediate depth in the Wadati-Benioff (W-B) zone beneath central Peru. Within a 100 to 150 km depth range in the subducting Nazca plate, 67 event hypocenters define a horizontally subducting zone (horizontal zone) 450 to 600 km from the trench, and a zone of increasing dip (resubduction zone) 600 to 700 km from the trench. Although the shape of the W-B zone is generally consistent with previous observations from teleseismic data, the distribution of seismicity is not. In a 550 km wide band extending from 400 to 750 km from the trench, the density of teleseismicity (mb > 4, 1971–1981) increases as a function of distance from the trench, while the density of microseismicity (1.6 < mb < 4.2) decreases. Combining local and teleseismic data, the b value changes from .84 in the horizontal zone to .57 in the resubduction zone. This result suggests that the minimum earthquake size and/or stress drop increases in the resubduction zone. Low b-values may also be intrinsic to proximity to the seismic cut-off at 150 km depth.Item Open Access Tectonic inversion in the Caribbean-South American plate boundary: GPS geodesy, seismology, and tectonics of the Mw 6.7 22 April 1997 Tobago earthquake(American Geophysical Union, 2015-06) Weber, John C.; Geirsson, Halldor; Latchman, Joan L.; Shaw, Kenton; La Femina, Peter; Wdowinski, Shimon; Higgins, Machel; Churches, Christopher; Norabuena Ortiz, EdmundoOn 22 April 1997 the largest earthquake recorded in the Trinidad‐Tobago segment of the Caribbean‐South American plate boundary zone (Mw 6.7) ruptured a shallow (~9 km), ENE striking (~250° azimuth), shallowly dipping (~28°) dextral‐normal fault ~10 km south of Tobago. In this study, we describe this earthquake and related foreshock and aftershock seismicity, derive coseismic offsets using GPS data, and model the fault plane and magnitude of slip for this earthquake. Coseismic slip estimated at our episodic GPS sites indicates movement of Tobago 135 ± 6 to 68 ± 6 mm NNE and subsidence of 7 ± 9 to 0 mm. This earthquake was anomalous and is of interest because (1) its large component of normal slip and ENE strike are unexpected given the active E‐W dextral shearing across the Caribbean‐South American plate boundary zone, (2) it ruptured a normal fault plane with a low (~28°) dip angle, and (3) it reactivated and inverted the preexisting Tobago terrrane‐South America ocean‐continent (thrust) boundary that formed during early Tertiary oblique plate convergence.Item Restricted The role of drought conditions on the recent increase in wildfire occurrence in the high Andean regions of Peru(CSIRO Publishing, 2023-01-24) Zubieta Barragán, Ricardo; Ccanchi, Yerson; Martínez Grimaldo, Alejandra; Saavedra Huanca, Miguel; Norabuena Ortiz, Edmundo; Alvarez, Sigrid; Ilbay, MercyWildfire occurrence has increased sharply in the last two decades in the Peruvian Andes. There is, however, little research on wildfires and their impacts. This study explores the conditions conducive to wildfire during 2020. MODIS images were collected to estimate the development of vegetation. In addition, ground-based monthly and satellite-based daily precipitation data were collected. Daily precipitation regularity was evaluated using a concentration index (CI), while monthly precipitation was used to estimate the Standard Precipitation Index (SPI). We used also the Global Vegetation Moisture Index (GVMI), which is a useful indicator of vegetation dynamics based on vegetation moisture. Our results do not indicate a direct link between rainfall regularity (lowest CI values) and development of vegetation. Although the SPI drought analysis using seasonal rainfall indicated nearly normal conditions during 2019–2020, analysis of dry-day frequency (DDF) suggests that the dry period played an important role between September and November 2020, producing conditions similar to the droughts of 2005, 2010 and 2016. GVMI also showed below-average values from April to November. We corroborate the usefulness of DDF for monitoring the potential increase in wildfire conditions. A controlled burn policy could offer a more useful way to reduce the impacts of wildfire.