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| Titel |
Slip rates of active thrusts at the front of the Precordillera revealed by exposure dating and fault scarp profiles, Mendoza, Argentina |
| VerfasserIn |
Silke Schmidt, Ralf Hetzel, Jan Kuhlmann, Francisco Mingorance, Victor Ramos |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250032924
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| Zusammenfassung |
| Although large historical earthquakes occurred in the Andean back-arc region between
28° and 34°S, the slip rates of active reverse faults remain unknown; hence the
seismic hazard related to these faults is poorly constrained. Here we report long-term
slip rates for two faults - the Peñas and the Cal thrust - which define the front of
the Andean Precordillera north of Mendoza. Both thrusts displace several Late
Pleistocene to Holocene river terraces and form well-preserved fault scarps. At the Peñas
thrust three terraces (T1, T2, and T3) are displaced vertically by ~0.9, ~1.9 and
~11 m, respectively. 10Be exposure dating constrains the age of T2 and T3 as 2.9
± 0.8 ka and 11.1 ± 1.7 ka, which yields an uplift rate of 0.9 ± 0.1 mm/a. The
horizontal shortening rate of the Peñas thrust - calculated by using the age of T3
and the dip angle of 25° - is 1.9 ± 0.2 mm/a. At the Cal thrust a fault scarp has
displaced a terrace with a maximum age of 12 ka by 7 m. As the Cal thrust dips
~25°, this yields a shortening rate of -¥ 1.3 mm/a. Our results demonstrate that
the two thrusts accomodate about half of the present-day shortening rate in the
back-arc region of the Andes, which is constrained as 4.5 ± 1.7 mm/a (Brooks et al.,
2003).
Using the compilation of Well & Coppersmith (1994), the 50-km-long Peñas and the
31-km-long Cal thrusts are capable of producing earthquakes with a magnitude of Mw 6.7 to
7.0. This is supported by a magnitude Ms ~ 7.0 earthquake on the Cal fault, which devastated
Mendoza in 1861 and killed two thirds of its population. Earthquakes of this magnitude have
presumably generated the smallest fault scarps (~0.9 m vertical offset) present at both
thrusts. The higher scarps are interpreted to record multiple offsets generated during several
Holocene earthquakes.
References
Brooks, B.A., Bevis, M., Smalley, R., Kendrick, E., Manceda, R., Lauria, E., Maturana, R. &
Araujo, M. (2003): Crustal motion in the Southern Andes (26° - 36°S): Do the Andes
behave like a microplate? Geochem. Geophys. Geosyst., 4 (10), pp. 14, 1085, doi
10.1029/2003GC000505.
Wells, D.L. & Coppersmith, K.J. (1994): New empirical relationships among magnitude,
rupture length, rupture width, rupture area, and surface displacement. Bull. Seis. Soc. Am.,
84, 974-1002. |
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