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Lateral Crustal Velocity Variations across the Andean Foreland in San Juan, Argentina from the JHD Analysis.

ASMEROM, B.B., University of Memphis, Memphis,TN,; CHIU, J.M, University of Memphis, Memphis,TN,; PUJOL, J., University of Memphis, Memphis,TN,; SMALLEY, R., University of Memphis, Memphis,TN,

P and S wave station corrections obtained from JHD re-analysis of local earthquakes recorded by PANDA network (1987-1988) show significant lateral crustal velocity variations across the Andean foreland near San Juan, Argentina. This study uses six times more events around Pie de Palo, a basement uplift surrounded by thick sedimentary basins, than the previous study (Pujol et al., 1991). Crustal events beneath the Pie de Palo are grouped into three clusters. Station corrections obtained from these clusters show similar but slightly different spatial patterns. Except for one station directly above thick valley sediment, all stations surrounding Pie de Palo show prominent negative station corrections using cluster-1 events that are directly underneath Pie de Palo. However, positive station corrections are observed for stations across the southeastern edge of Pie de Palo when cluster-2 events are used. The magnitude and distribution of these positive station corrections become even more pronounced from cluster-3, extending further east of Pie de Palo. The patterns of station corrections strongly imply the existence of a localized low velocity zone that may extend more to the south in the upper crust beneath the southeastern edge of Pie de Palo. The area between this low velocity region and eastern Precordillera shows a consistent negative station correction that reveals the existence of high velocity material in the upper crust. Station corrections also reveal that upper crustal velocities are low immediately to the west of eastern Precordillera. A well-defined west-dipping fault is apparent from cross-sectional views of seismicity across the northern Pie de Palo, while poorly defined, gently west- as well as east-dipping faults are observed in the southern part. Moreover, the spatial patterns of station corrections help to set up important priori information to be implemented in the initial model of upper crust for 3-D velocity inversion.


Last Modified: 2011 Aug 10