Browsing by Author "Selwyn Sacks, I."

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    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, Michael
    Space 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.
    Palabras clave:Collision zoneGeodesySpace geodesy
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    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, Antonio
    We 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.
    Palabras clave:EarthquakesMicroseismicitySubduction