Quaternary intraplate deformation in the southeastern Sierras Pampeanas, Argentina

• Published in: Journal of seismology Vol. 5; no. 3; pp. 399 - 409
• Main Authors: Costa, Carlos H, Murillo, M Victoria, Sagripanti, Guillermo L, Gardini, Carlos E
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.07.2001
• Subjects: Earthquakes; Geology; Plate tectonics; Seismology
• ISSN: 1383-4649; 1573-157X
• DOI: 10.1023/A:1011431827075

Neogene strain from the subducting Nazca plate is widely distributed in theAndean foreland as a result of flat-lying subduction beneath central westernArgentina (28^sup °^-33^sup °^S latitude). This fact is indicated byuplifted basement blocks bounded by reverse faults as far as 600 kms eastof the Chilean trench axis. Some deformation in the southern Sierras deCórdoba (southeastern Sierras Pampeanas) indicates significantdisplacements during Quaternary and even late Holocene time. Thisregion has low to moderate seismicity characterized by earthquakemagnitudes ≤ 6.7 with no associated noticeable surface ruptures.This paper presents information recently gathered on the most conspicuousregional structures of the area (El Molino, Sierra Chica and Las Lagunasfaults). The last movement along the El Molino fault thrust basement rocksover organic-rich (0.8-1.3 ka) sediment and fault relationships suggestprevious Quaternary displacements. Along the Sierra Chica fault,Precambrian basement has been thrust a minimum of 13.5 m overPleistocene conglomerates, and faulting also affects latePleistocene-Holocene fluvial sediments. The Las Lagunas fault has beenregarded as the source of the 1934 Ms 5.5 and 6.0 earthquakes, whichheavily damaged the nearby village of Sampacho. The faulted surface isburied under Holocene loess, but its trace is expressed as a 24-km-longrectilinear scarp, despite continuous modification due to land use.Although we lack detailed information on probable rupture lengths duringlarge Sierras Pampeanas thrust earthquakes, some preliminary considerationsare made for the regional seismic hazard of these structures. The geologicevidence described here identifies these faults as possible sources of strongearthquakes in the future.[PUBLICATION ABSTRACT]