Publication Date:
2001-01-01
Description:
Neogene strain from the subducting Nazca plate is widely distributed in the Andean foreland as a result of flatlying subduction beneath central western Argentina (28°-33°S latitude). This fact is indicated by uplifted basement blocks bounded by reverse faults as far as 600 kms east of the Chilean trench axis. Some deformation in the southern Sierras de Coŕdoba (southeastern Sierras Pampeanas) indicates significant displacements during Quaternary and even late Holocene time. This region has low to moderate seismicity characterized by earthquake magnitudes ≤ 6.7 with no associated noticeable surface ruptures. This paper presents information recently gathered on the most conspicuous regional structures of the area (El Molino, Sierra Chica and Las Lagunas faults). The last movement along the El Molino fault thrust basement rocks over organic-rich (0.8-1.3 ka) sediment and fault relationships suggest previous Quaternary displacements. Along the Sierra Chica fault, Precambrian basement has been thrust a minimum of 13.5 m over Pleistocene conglomerates, and faulting also affects late Pleistocene-Holocene fluvial sediments. The Las Lagunas fault has been regarded as the source of the 1934 Ms 5.5 and 6.0 earthquakes, which heavily damaged the nearby village of Sampacho. The faulted surface is buried under Holocene loess, but its trace is expressed as a 24-km-long rectilinear scarp, despite continuous modification due to land use. Although we lack detailed information on probable rupture lengths during large Sierras Pampeanas thrust earthquakes, some preliminary considerations are made for the regional seismic hazard of these structures. The geologic evidence described here identifies these faults as possible sources of strong earthquakes in the future.
Print ISSN:
1383-4649
Electronic ISSN:
1573-157X
Topics:
Geosciences
,
Physics
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