Browsing by Autor "Lawrence A. Drake"

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Crustal-thickness variations in the central Andes
(Geological Society of America, 1996) S. L. Beck; G. Zandt; Stephen C. Myers; Terry C. Wallace; Paul G. Silver; Lawrence A. Drake
Research Article| May 01, 1996 Crustal-thickness variations in the central Andes Susan L. Beck; Susan L. Beck 1SASO and Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar George Zandt; George Zandt 2IGPP, Lawrence Livermore National Laboratory, Livermore, California, and SASO and Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar Stephen C. Myers; Stephen C. Myers 1SASO and Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar Terry C. Wallace; Terry C. Wallace 1SASO and Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar Paul G. Silver; Paul G. Silver 3Carnegie Institution of Washington, Washington, D.C. Search for other works by this author on: GSW Google Scholar Lawrence Drake Lawrence Drake 4Observatorio San Calixto, La Paz, Bolivia Search for other works by this author on: GSW Google Scholar Author and Article Information Susan L. Beck 1SASO and Department of Geosciences, University of Arizona, Tucson, Arizona 85721 George Zandt 2IGPP, Lawrence Livermore National Laboratory, Livermore, California, and SASO and Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Stephen C. Myers 1SASO and Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Terry C. Wallace 1SASO and Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Paul G. Silver 3Carnegie Institution of Washington, Washington, D.C. Lawrence Drake 4Observatorio San Calixto, La Paz, Bolivia Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1996) 24 (5): 407–410. https://doi.org/10.1130/0091-7613(1996)024<0407:CTVITC>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Susan L. Beck, George Zandt, Stephen C. Myers, Terry C. Wallace, Paul G. Silver, Lawrence Drake; Crustal-thickness variations in the central Andes. Geology 1996;; 24 (5): 407–410. doi: https://doi.org/10.1130/0091-7613(1996)024<0407:CTVITC>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We estimated the crustal thickness along an east-west transect across the Andes at lat 20°S and along a north-south transect along the eastern edge of the Altiplano from data recorded on two arrays of portable broadband seismic stations (BANJO and SEDA). Waveforms of deep regional events in the downgoing Nazca slab and teleseismic earthquakes were processed to isolate the P-to-S converted phases from the Moho in order to compute the crustal thickness. We found crustal-thickness variations of nearly 40 km across the Andes. Maximum crustal thicknesses of 70–74 km under the Western Cordillera and the Eastern Cordillera thin to 32–38 km 200 km east of the Andes in the Chaco Plain. The central Altiplano at 20°S has crustal thicknesses of 60 to 65 km. The crust also appears to thicken from north (16°S, 55–60 km) to south (20°S, 70–74 km) along the Eastern Cordillera. The Subandean zone crust has intermediate thicknesses of 43 to 47 km. Crustal-thickness predictions for the Andes based on Airy-type isostatic behavior show remarkable overall correlation with observed crustal thickness in the regions of high elevation. In contrast, at the boundary between the Eastern Cordillera and the Subandean zone and in the Chaco Plain, the crust is thinner than predicted, suggesting that the crust in these regions is supported in part by the flexural rigidity of a strong lithosphere. With additional constraints, we conclude that the observation of Airy-type isostasy is consistent with thickening associated with compressional shortening of a weak lithosphere squeezed between the stronger lithosphere of the subducting Nazca plate and the cratonic lithosphere of the Brazilian craton. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Seismic hazard assessment in the Northern Andes (PILOTO Project)
(National Institute of Geophysics and Volcanology, 1999) C. Dimaté; Lawrence A. Drake; H. Yepez; Leónidas Ocola; Herbert Rendón; Gottfried Grünthal; Domenico Giardini
Five Andean countries (Bolivia, Peru, Ecuador, Colombia, Venezuela) and four European countries (Italy, Spain, Holland, Germany) cooperated in the PILOTO program ("Test area for earthquake monitoring and seismic hazard assessment"), launched under GSHAP and sponsored by the European Union (Ct.94-0103) to produce a unified SHA for the Andean region. Activities included the integration of national earthquake catalogues and source zonings in common regional databases and joint technical workshops for the assessment of the regional hazard, expressed in terms of expected peak ground acceleration with 10% exceedance probability in 50 years.
The propagation of Love and Rayleigh waves in the Andean Region
(1996) Lawrence A. Drake; Estela Minaya Ramos
El patrón distintivo desde la fuente sísmicas de un campo irradiado de ondas sísmicas se modifica profundamente al pasar por una región irregular como la Cordillera de los Andes de América del Sur. La onda Lg guiada por la corteza es útil en la discriminación de fuentes sísmicas, pero, aún para una sola fuente, las amplitudes de ondas de perlodo corto como Lg pueden variar significativamente. La Cordillera de los Andes de Bolivia forma una parte de la cadena de los Andes, que se originó en los dos principales ciclos orogénicos del Fanerozoico, un Cicio Preandino Precarnbrico-Paleozoico Superior y el Cicio Andino Mesozoico-Cenozoico. Durante el último Cicio, cuatro sistemas del arco magmático se desarrollaron sucesivamente hacia el este: un arco Jurasico-Cretacico Temprano en la Cordillera Costera de Chile, un arco Cretacico Medio en el Vaile Longitudinal de Chile, un arco Cretácico Tardlo-Paleogénico en la Precordillera Chilena y el arco Mioceno-Holoceno en la Cordiflera Occidental (Omarini et al., 1991; Dorbath et al., 1993; Scheueer et al., 1994). En la región del Cabalgamiento Andino Principal entre la Cordillera Oriental (o Real) y las Sierras Subandinas en Bolivia septentrional, hay superposición de aproximadamente 230 km de edad Neogena (Roeder, 1988). Las areniscas cloríticas Perrnicas marinas cerca de Copacabana sobre el Lago Titicaca y las diamictitas, areniscas, cuarcitas y lutitas Ordovlcico-Silliricas apretadamente plegadas, expuestas abundantemente en los cortes del camine entre Cochabamba y Caracollo, se encuentran a elevaciones desde 3800 m a 4500 m sobre el nivel del mar. El sistema de fallas de la Cordillera Real, en el borde sudoccidental, marca un limite subvertical, con buzarniento al sudoeste, que separa dos unidades de velocidad contrastante hasta una profundidad de 140 km. La profundidad al Moho debajo del Altiplano fue encontrada por Dorbath et al. (1993) aproximadamente a 60 km y, debajo de la Cordillera Real, aproximadamente a 50 km. Mas al sur, a través del Sur de Bolivia y Norte de la Argentina, Wigger et a/. (1994) encontraron que la profundidad al Moho debajo del Altiplano es aproximadamente de 72 km y, debajo de la Cordillera Real aproximadamente a 65 km. La propagación de las ondas de Love y de Rayleigh de perlodo corto, a lo largo de un perfil que atraviesa estas unidades del Altiplano y de la Cordillera Real de Bolivia septentrional, ha sido analizada por el método de elementos finitos. Un resultado preliminar es que, sin tener en cuenta la absorción, a un período de 2 s, 91.69% de la energía del modo fundamental de la onda Love y 98.60% de la energía del modo fundamental de la onda Rayleigh son transmitidos.