Coseismic displacements and Holocene slip rates for two active thrust faults at the mountain front of the Andean Precordillera (∼33°S)

During the last few hundred years several destructive earthquakes occurred along the eastern margin of the Andean Precordillera, where GPS data reveal a shortening rate of ∼4.5 mm/a. We use fault scarp profiles and age determinations of deformed terraces (T<inf>1</inf>-T<inf>4</...

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Detalles Bibliográficos
Autores principales: Schmidt, S., Hetzel, R., Mingorance, F., Ramos, V.A.
Formato: JOUR
Materias:
Earthquakes
Risk assessment
Age determination
Co-seismic displacement
Fault dip
Fault scarp
GPS data
Holocenes
Seismic hazards
Slip rates
Thrust faults
Landforms
coseismic process
displacement
earthquake
earthquake magnitude
GPS
Holocene
mountain region
seismic hazard
slip rate
thrust fault
Precordillera
Pisum sativum
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_02787407_v30_n5_p_Schmidt
Aporte de:
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
Descripción
Sumario:During the last few hundred years several destructive earthquakes occurred along the eastern margin of the Andean Precordillera, where GPS data reveal a shortening rate of ∼4.5 mm/a. We use fault scarp profiles and age determinations of deformed terraces (T<inf>1</inf>-T<inf>4</inf>) to infer coseismic displacements and quantify slip rates for the Peas and Cal thrust faults near Mendoza city. Scarps on the lowest terrace level T<inf>1</inf> reveal vertical offsets of 0.8-1.0 m for both faults, which are interpreted as coseismic displacements during the last earthquake. Together with the fault dip these offsets indicate that both faults are capable of producing magnitude M<inf>W</inf> ∼6.9 earthquakes, which is corroborated by a magnitude M <inf>S</inf> = 7.0 event on the Cal fault that destroyed Mendoza in 1861. At the Peas thrust fault, terrace T<inf>2</inf> has an age of ∼3.3 ka and is offset by ∼1.9 m, whereas the ∼12-ka-old terrace T<inf>3</inf> is displaced by ∼11 m. Combined with the fault dip of ∼25 °, the age and offset of terrace T<inf>3</inf> define a shortening rate of ∼2.0 mm/a on the Peas fault, i.e., about half of the present-day shortening at the eastern margin of the Precordillera. At the Cal fault, terraces T<inf>2</inf> to T <inf>4</inf> have ages of ∼0.8 ka (OSL), ∼3.9 ka (14C), and 12 ka (10Be) and are vertically offset by ∼2.6, ∼3.6, and ∼7.0 m, respectively, which implies that slip on the fault has recently accelerated. Hence, the Cal fault poses a serious seismic hazard to the one million inhabitants of Mendoza. Copyright 2011 by the American Geophysical Union.

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