Browsing by Autor "E. Minaya"

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Ambient noise tomography across the Central Andes
(Oxford University Press, 2013) Kevin M. Ward; Ryan Porter; G. Zandt; S. L. Beck; L. S. Wagner; E. Minaya; Hernando Tavera
The Central Andes of southern Peru, Bolivia, Argentina and Chile (between 12°S and 42°S) comprise the largest orogenic plateau in the world associated with abundant arc volcanism, the Central Andean Plateau, as well as multiple segments of flat-slab subduction making this part of the Earth a unique place to study various aspects of active plate tectonics. The goal of this continental-scale ambient noise tomography study is to incorporate broad-band seismic data from 20 seismic networks deployed incrementally in the Central Andes from 1994 May to 2012 August, to image the vertically polarized shear wave velocity (<it>V</it><inf>sv</inf>) structure of the South American Cordillera. Using dispersion measurements calculated from the cross-correlation of 330 broad-band seismic stations, we construct Rayleigh wave phase velocity maps in the period range of 8–40 s and invert these for the shear wave velocity (<it>V</it><inf>sv</inf>) structure of the Andean crust. We provide a dispersion misfit map as well as uncertainty envelopes for our <it>V</it><inf>sv</inf> model and observe striking first-order correlations with our shallow results (∼5 km) and the morphotectonic provinces as well as subtler geological features indicating our results are robust. Our results reveal for the first time the full extent of the mid-crustal Andean low-velocity zone that we tentatively interpret as the signature of a very large volume Neogene batholith. This study demonstrates the efficacy of integrating seismic data from numerous regional broad-band seismic networks to approximate the high-resolution coverage previously only available though larger networks such as the EarthScope USArray Transportable Array in the United States.
Anomalous crust of the Bolivian Altiplano, central Andes: Constraints from broadband regional seismic waveforms
(American Geophysical Union, 1996) G. Zandt; S. L. Beck; S. R. Ruppert; Charles J. Ammon; Don Rock; E. Minaya; Terry C. Wallace; Paul G. Silver
A one‐year deployment of broadband seismographs in the Bolivian Altiplano recorded numerous intermediate‐depth earthquakes at near‐regional distances. We modeled the associated broadband waveforms of two earthquakes to estimate an average crustal structure for the Altiplano. The resulting model is characterized by an anomalously low mean P velocity of 6.0 km/s, a low Poisson's ratio of 0.25, and a crustal thickness of 65 km. The combination of the low mean velocity and low Poisson's ratio can be explained only by a predominantly quartz‐rich, felsic bulk composition. This constraint precludes significant volumes of magmatic addition from the mantle contributing to the great thickness of the Altiplano crust, but is consistent with thickening by compressive shortening concentrated in a weak felsic layer.
Catálogo de terremotos de América del Sur homogéneo en Mw para el periodo pre-1964
(2018) A. A. Gómez Capera; M. Stucchi; L. Rodríguez; Mónica Arcila; M. Bufaliza; José E. Choy; E. Minaya; Lisette Leyton; Marlon Pirchiner; Herbert Rendón
En el marco del proyecto The South America Risk Assessment (SARA), se compilo un catalogo de terremotos para America del Sur, en terminos de magnitud momento (Mw), a partir de los datos disponibles en el Centro Regional de Sismologia para America del Sur (CERESIS), tanto de los estudios recientes de terremotos historicos, como de los analisis realizados durante el proyecto. En particular, se incluyen: i) la ultima version del catalogo CERESIS-91 preparado por CERESIS y publicado por el Consejo Nacional de Ciencia y Tecnologia CONCYTEC del Peru; ii) la determinacion de parametros por parte de estudios recientes, incluidos los propuestos por el catalogo ISC-GEM y, en su caso, los catalogos nacionales que cumplen con los criterios de transparencia requeridos por el proyecto. Los resultados descritos en el presente articulo se refieren a la ventana de tiempo pre-1964.} Para seguir leyendo descargue el archivo.
Central Andean crustal structure from receiver function analysis
(Elsevier BV, 2016) Jamie Ryan; S. L. Beck; G. Zandt; L. S. Wagner; E. Minaya; Hernado Tavera
Changes in ground deformation prior to and following a large urban landslide in La Paz, Bolivia, revealed by advanced InSAR
(Copernicus Publications, 2019) Nicholas J. Roberts; Bernhard Rabus; John J. Clague; Reginald L. Hermanns; Marco-Antonio Guzmán; E. Minaya
Abstract. We characterize and compare creep preceding and following the complex 2011 Pampahasi landslide (∼40 Mm3±50 %) in the city of La Paz, Bolivia, using spaceborne radar interferometry (InSAR) that combines displacement records from both distributed and point scatterers. The failure remobilized deposits of an ancient complex landslide in weakly cemented, predominantly fine-grained sediments and affected ∼1.5 km2 of suburban development. During the 30 months preceding failure, about half of the toe area was creeping at 3–8 cm a−1 and localized parts of the scarp area showed displacements of up to 14 cm a−1. Changes in deformation in the 10 months following the landslide demonstrate an increase in slope activity and indicate that stress redistribution resulting from the discrete failure decreased stability of parts of the slope. During that period, most of the landslide toe and areas near the head scarp accelerated, respectively, to 4–14 and 14 cm a−1. The extent of deformation increased to cover most, or probably all, of the 2011 landslide as well as adjacent parts of the slope and plateau above. The InSAR-measured displacement patterns, supplemented by field observations and optical satellite images, reveal complex slope activity; kinematically complex, steady-state creep along pre-existing sliding surfaces accelerated in response to heavy rainfall, after which slightly faster and expanded steady creeping was re-established. This case study demonstrates that high-quality ground-surface motion fields derived using spaceborne InSAR can help to characterize creep mechanisms, quantify spatial and temporal patterns of slope activity, and identify isolated small-scale instabilities; such details are especially useful where knowledge of landslide extent and activity is limited. Characterizing slope activity before, during, and after the 2011 Pampahasi landslide is particularly important for understanding landslide hazard in La Paz, half of which is underlain by similar large paleolandslides.
Changes in ground deformation prior to and following a large urbanlandslide in La Paz, Bolivia revealed by advanced InSAR
(2018) Nicholas J. Roberts; Bernhard Rabus; John J. Clague; Reginald L. Hermanns; Marco-Antonio Guzmán; E. Minaya
Abstract. We characterize and compare creep preceding and following the 2011 Pampahasi landslide (∼ 40 Mm3 ± 50 %) in the city of La Paz, Bolivia, using spaceborne RADAR interferometry (InSAR) that combines displacement records from both distributed and point scatterers. The failure remobilised deposits of an ancient landslide in weakly cemented, predominantly fine-grained sediments and affected ∼ 1.5 km2 of suburban development. During the 30 months preceding failure, about half of the toe area was creeping at 3–8 cm/a and localized parts of the scarp area showed displacements of up to 14 cm/a. Changes in deformation in the 10 months following the landslide are contrary to the common assumption that stress released during a discrete failure increases stability. During that period, most of the landslide toe and areas near the headscarp accelerated, respectively, to 4–14 and 14 cm/a. The extent of deformation increased to cover most, or probably all, of the 2011 landslide as well as adjacent parts of the slope and plateau above. The InSAR-measured displacement patterns – supplemented by field observations and by optical satellite images – indicate that kinematically complex, steady-state creep along pre-existing sliding surfaces temporarily accelerated in response to heavy rainfall, after which the slope quickly achieved a slightly faster and expanded steadily creeping state. This case study demonstrates that high-quality ground-surface motion fields derived using spaceborne InSAR can help to characterize creep mechanisms, quantify spatial and temporal patterns of slope activity, and identify isolated small-scale instabilities. Characterizing slope instability before, during, and after the 2011 Pampahasi landslide is particularly important for understanding landslide hazard in La Paz, half of which is underlain by similar, large paleolandslides.
Determination of the fault plane and rupture size of the 2013 Santa Cruz earthquake, Bolivia, 5.2 Mw, by relative location of the aftershocks
(Elsevier BV, 2016) Carolina Rivadeneyra‐Vera; Marcelo Assumpção; E. Minaya; Percy Aliaga; G. Avila
Erratum: Ambient noise tomography across the Central Andes
(Oxford University Press, 2013) Kevin M. Ward; Ryan Porter; G. Zandt; S. L. Beck; L. S. Wagner; E. Minaya; Hernando Tavera
Kevin M. Ward,1 Ryan C. Porter,2 George Zandt,1 Susan L. Beck,1 Lara S. Wagner,3 Estela Minaya4 and Hernando Tavera5 1Department of Geosciences, The University of Arizona, 1040 E. 4th Street Tucson, AZ 85721, USA. E-mail: wardk@email.arizona.edu 2Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015-1305, USA 3Department of Geological Sciences, University of North Carolina at Chapel Hill, 104 South Rd., Mitchell Hall, CB #3315, Chapel Hill, NC 27599-3315, USA 4El Observatorio San Calixto, Calle Indaburo 944, Casilla 12656, La Paz, Bolivia 5Instituto Geofisico Del Peru, Calle Badajo No. 169, Urb. Mayorazgo IV Etapa, Lima, Peru
Evidence for a meteoritic origin of the September 15, 2007, Carancas crater
(Wiley, 2008) Alexis Le Pichon; K. Antier; Yves Cansi; B. Hernandez; E. Minaya; B. BURGOA; D. P. Drob; Läslo Evers; Jérémie Vaubaillon
Abstract— On September 15th, 2007, around 11:45 local time in Peru, near the Bolivian border, the atmospheric entry of a meteoroid produced bright lights in the sky and intense detonations. Soon after, a crater was discovered south of Lake Titicaca. These events have been detected by the Bolivian seismic network and two infrasound arrays operating for the Comprehensive Nuclear‐Test‐Ban Treaty Organization, situated at about 80 and 1620 km from the crater. The localization and origin time computed with the seismic records are consistent with the reported impact. The entry elevation and azimuthal angles of the trajectory are estimated from the observed signal time sequences and back‐azimuths. From the crater diameter and the airwave amplitudes, the kinetic energy, mass and explosive energy are calculated. Using the estimated velocity of the meteoroid and similarity criteria between orbital elements, an association with possible parent asteroids is attempted. The favorable setting of this event provides a unique opportunity to evaluate physical and kinematic parameters of the object that generated the first actual terrestrial meteorite impact seismically recorded.
Hazardous faults of South America; compilation and overview
(Elsevier BV, 2020) Carlos H. Costa; Alexandra Alvarado; Franck Audemard; Laurence Audin; Carlos Benavente; Francisco H.R. Bezerra; José Cembrano; Gabriel González; Myriam López; E. Minaya
Imaging the transition from flat to normal subduction: variations in the structure of the Nazca slab and upper mantle under southern Peru and northwestern Bolivia
(Oxford University Press, 2015) A. C. Scire; G. Zandt; S. L. Beck; Maureen D. Long; L. S. Wagner; E. Minaya; Hernando Tavera
Two arrays of broad-band seismic stations were deployed in the north central Andes between 8° and 21°S, the CAUGHT array over the normally subducting slab in northwestern Bolivia and southern Peru, and the PULSE array over the southern part of the Peruvian flat slab where the Nazca Ridge is subducting under South America. We apply finite frequency teleseismic P- and S-wave tomography to data from these arrays to investigate the subducting Nazca plate and the surrounding mantle in this region where the subduction angle changes from flat north of 14°S to normally dipping in the south. We present new constraints on the location and geometry of the Nazca slab under southern Peru and northwestern Bolivia from 95 to 660 km depth. Our tomographic images show that the Peruvian flat slab extends further inland than previously proposed along the projection of the Nazca Ridge. Once the slab re-steepens inboard of the flat slab region, the Nazca slab dips very steeply (∼70°) from about 150 km depth to 410 km depth. Below this the slab thickens and deforms in the mantle transition zone. We tentatively propose a ridge-parallel slab tear along the north edge of the Nazca Ridge between 130 and 350 km depth based on the offset between the slab anomaly north of the ridge and the location of the re-steepened Nazca slab inboard of the flat slab region, although additional work is needed to confirm the existence of this feature. The subslab mantle directly below the inboard projection of the Nazca Ridge is characterized by a prominent low-velocity anomaly. South of the Peruvian flat slab, fast anomalies are imaged in an area confined to the Eastern Cordillera and bounded to the east by well-resolved low-velocity anomalies. These low-velocity anomalies at depths greater than 100 km suggest that thick mantle lithosphere associated with underthrusting of cratonic crust from the east is not present. In northwestern Bolivia a vertically elongated fast anomaly under the Subandean Zone is interpreted as a block of delaminating lithosphere.
Implications of spatial and temporal development of the aftershock sequence for the <i>M<sub>w</sub></i> 8.3 June 9, 1994 Deep Bolivian Earthquake
(American Geophysical Union, 1995) Stephen C. Myers; Terry C. Wallace; S. L. Beck; Paul G. Silver; G. Zandt; J. C. VanDecar; E. Minaya
On June 9, 1994 the M w 8.3 Bolivia earthquake (636 km depth) occurred in a region which had not experienced significant, deep seismicity for at least 30 years. The mainshock and aftershocks were recorded in Bolivia on the BANJO and SEDA broadband seismic arrays and on the San Calixto Network. We used the joint hypocenter determination method to determine the relative location of the aftershocks. We have identified no foreshocks and 89 aftershocks ( m > 2.2) for the 20‐day period following the mainshock. The frequency of aftershock occurrence decreased rapidly, with only one or two aftershocks per day occuring after day two. The temporal decay of aftershock activity is similar to shallow aftershock sequences, but the number of aftershocks is two orders of magnitude less. Additionally, a m b ∼6, apparently triggered earthquake occurred just 10 minutes after the mainshock about 330 km east‐southeast of the mainshock at a depth of 671 km. The aftershock sequence occurred north and east of the mainshock and extends to a depth of 665 km. The aftershocks define a slab striking N68°W and dipping 45°NE. The strike, dip, and location of the aftershock zone are consistent with this seismicity being confined within the downward extension of the subducted Nazca plate. The location and orientation of the aftershock sequence indicate that the subducted Nazca plate bends between the NNW striking zone of deep seismicity in western Brazil and the N‐S striking zone of seismicity in central Bolivia. A tear in the deep slab is not necessitated by the data. A subset of the aftershock hypocenters cluster along a subhorizontal plane near the depth of the mainshock, favoring a horizontal fault plane. The horizontal dimensions of the mainshock [ Beck et al., this issue; Silver et al., 1995] and slab defined by the aftershocks are approximately equal, indicating that the mainshock ruptured through the slab.
Lowermost mantle anisotropy near the eastern edge of the Pacific LLSVP: constraints from SKS–SKKS splitting intensity measurements
(Oxford University Press, 2017) Jie Deng; Maureen D. Long; Neala Creasy; L. S. Wagner; S. L. Beck; G. Zandt; Hernando Tavera; E. Minaya
Seismic anisotropy has been documented in many portions of the lowermost mantle, with particularly strong anisotropy thought to be present along the edges of large low shear velocity provinces (LLSVPs). The region surrounding the Pacific LLSVP, however, has not yet been studied extensively in terms of its anisotropic structure. In this study, we use seismic data from southern Peru, northern Bolivia and Easter Island to probe lowermost mantle anisotropy beneath the eastern Pacific Ocean, mostly relying on data from the Peru Lithosphere and Slab Experiment and Central Andean Uplift and Geodynamics of High Topography experiments. Differential shear wave splitting measurements from phases that have similar ray paths in the upper mantle but different ray paths in the lowermost mantle, such as SKS and SKKS, are used to constrain anisotropy in D″. We measured splitting for 215 same station-event SKS–SKKS pairs that sample the eastern Pacific LLSVP at the base of the mantle. We used measurements of splitting intensity(SI), a measure of the amount of energy on the transverse component, to objectively and quantitatively analyse any discrepancies between SKS and SKKS phases. While the overall splitting signal is dominated by the upper-mantle anisotropy, a minority of SKS–SKKS pairs (∼10 per cent) exhibit strongly discrepant splitting between the phases (i.e. the waveforms require a difference in SI of at least 0.4), indicating a likely contribution from lowermost mantle anisotropy. In order to enhance lower mantle signals, we also stacked waveforms within individual subregions and applied a waveform differencing technique to isolate the signal from the lowermost mantle. Our stacking procedure yields evidence for substantial splitting due to lowermost mantle anisotropy only for a specific region that likely straddles the edge of Pacific LLSVP. Our observations are consistent with the localization of deformation and anisotropy near the eastern boundary of the Pacific LLSVP, similar to previous observations for the African LLSVP.
Recent Landslide Activity in La Paz, Bolivia
(2014) Nicholas J. Roberts; Bernhard Rabus; Reginald L. Hermanns; Marco-Antonio Guzmán; John J. Clague; E. Minaya
Shallow seismicity, triggered seismicity, and ambient noise tomography at the long-dormant Uturuncu Volcano, Bolivia
(Springer Science+Business Media, 2011) Jennifer A. Jay; M. E. Pritchard; M. E. West; Douglas H. Christensen; M. M. Haney; E. Minaya; M. Sunagua; Stephen R. McNutt; Mario Zabala
Supplementary material to "Changes in ground deformation prior to and following a large urbanlandslide in La Paz, Bolivia revealed by advanced InSAR"
(2018) Nicholas J. Roberts; Bernhard Rabus; John J. Clague; Reginald L. Hermanns; Marco-Antonio Guzmán; E. Minaya
The 2011 Pampahasi landslide is one of seven historical landslides exceeding 1 Mm 3 in the La Paz area.Landslides of possibly similar size to the 2011 event happened in 1582 and 1873 in the southwest part of the La Paz valley system, but little is known of these events aside from sparse written accounts.The first event affected an area of 2 km 2 or more and buried the villages of Canoma and Ango Ango, which were likely located in Llojeta Valley (Fig. S1).This landslide claimed about 200 lives (Cabeza de Vaca, 1586; transcribed in Jiménez de la Espada, 1965, p. 342-351 andin Arispe, 2011).The second event involved extensive ground movement over an area of about 8 km 2 (Markham, 1874) and more rapid, localized movement that destroyed an area named Tembladerani (Markham, 1874) located southwest of the city centre, causing 32 deaths (Crespo, 1902).Its location may correspond to the modern area of the city called Tembladerani (Fig. S1), although Dobrovolny (1962) applies this name to a landslide deposit in Llojeta Valley.The loss of life from these two events suggests velocities exceeding several metres per second or, at the very least, a lack of prompt evacuation.Four smaller landslides happened in the twenty-first century in the Llojeta and Allpacoma valleys near the margins of the La Paz and Achocalla basins (Hermanns et al., 2012; Fig. 1B); they destroyed about 51 homes but did not claim any lives (Roberts, 2016) (Table S1).Most of these failures involved weakly lithified, fine-grained sediments of the middle part of the La Paz Formation, including large areas that had been previously mobilized by large paleolandslides.
The 1998 Aiquile, Bolivia earthquake: A seismically active fault revealed with InSAR
(Elsevier BV, 2005) G. J. Funning; R. Barke; Simon Lamb; E. Minaya; B. Parsons; Tim Wright