Stripe of normal mechanisms for crustal earthquakes with M ≤ 3.5 flanking the western side of the thrust front zone in the Andes backarc


Earthquakes with magnitudes M ≤ 3.5 were registered in the Andes backarc between ~32.5°S 33.75°S within a temporary experiment from November 2002 to March 2003. Data were collected from 15 seismological broad band stations, deployed above flat subduction section and also above the transitional to normal section of the Nazca plate. Seismic events were located mostly in part of the Southern Precordillera and Cerrilladas Pedemontanas of Mendoza Province. Focal mechanism solutions were obtained, for selected data between15 kmand35 kmdepths, from P wave first motion using FOCMEC software. A band trending NW-NNW of normal focal mechanism earthquakes is located just by the thrust front towards West, and covers the Southern tip of the Southern Precordillera and the Western side of the Cerrilladas Pedemontanas, Mendoza Province, Argentina. Thrust focal mechanism solutions obtained in the present work for events with magnitude less than or equal to 3.5 also show that the thrust front South of ~33.1°S is located in the same place as Mw ≥ 3.6 earthquakes. The most significant findings in this work are these signals of extensional regimen which appear in a compressional subduction tectonic regimen. Nevertheless the short temporal experiment precludes firm interpretations about this particular phenomenon. Probably it is related to a temporary stress relaxation. The normal earthquakes are likely associated to normal faults, and/or to their subsidiaries, that were inverted by contraction and now re-inverted at least transitorily as normal. These faults, which are near and to the East of the suture between Chilenia and Cuyania Paleozoic terranes, were originally involved in the Cuyo Triassic basin formation.

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Nacif, S. , Triep, E. , Furlani, R. and Spagnotto, S. (2013) Stripe of normal mechanisms for crustal earthquakes with M ≤ 3.5 flanking the western side of the thrust front zone in the Andes backarc. Natural Science, 5, 18-26. doi: 10.4236/ns.2013.58A1003.

Conflicts of Interest

The authors declare no conflicts of interest.


[1] Chinn, D.S. and Isacks, B.L. (1983) Accurate source depths and focal mechanism of shallow earthquakes in western South America and New Hebrides Island Arc. Tectonics, 2, 529-563. doi:10.1029/TC002i006p00529
[2] Kadinsky-Cade, K. (1985) Seismotectonics of the Chilean margin and the 1977 Caucete Earthquake of western Argentina. Ph.D. Thesis, Cornell University, Ithaca, New York.
[3] Alvarado, P., Beck, S., Zandt, G., Araujo, M. and Triep, E. (2005) Crustal deformation in the south-central Andes backarc terranes as viewed from regional broad-band seismic waveform modelling, GJI. Seismology, 163, 580598. doi:10.1111/j.1365-246X.2005.02759.x
[4] Alvarado, P. and Beck, S., (2006) Source characterization of the San Juan (Argentina) crustal earthquakes of 15 January 1944 (Mw 7.0) and 11 June 1952 (Mw 6.8). Earth and Planetary Science Letters, 243, 615-631. doi:10.1016/j.epsl.2006.01.015
[5] Alvarado, P., Beck, S. L. and Zandt, G. (2007) Crustal structure of the southcentral Andes Cordillera and backarc region from regional waveform modeling. Geophysical Journal International, 170, 858-875.
[6] Cortes, J., Casa, A., Pasini, M., Yamin, M. and Terrizzano, C. (2006) Fajas oblicuas de deformación neotectónica en Precordillera y Cordillera Frontal (31°30' 33°30' LS): Controles Paleotectónicos. Revista de la Asociación Geológica Argentina, 61, 639-646.
[7] Giambiagi, L., Mescua, J., Bechis, F., Martínez, A. and Folguera, A. (2013) Pre-Andean deformation of the Precordillera southern sector, southern Central Andes. Geosphere, 7, 219-239. doi:10.1130/GES00572.1
[8] Brooks, B., Bevis, M., Smalley, R., Kendrick, E., Manceda, R., Lauria, E., Maturana, R. and Araujo, M. (2003) Crustal motion in the Southern Andes (26° 36S°): Do the Andes behave like a microplate? Geochesmitry Geophysics Geosystems, 4, 1085. doi:10.1029/2003GC000505
[9] Anderson, M.L., Alvarado P., Zandt G. and Beck S. (2007) Geometry and brittle deformation of the subducting Nazca Plate Central Chile and Argentina. Geophysical Journal International, 171, 419-434. doi:10.1111/j.1365-246X.2007.03483.x
[10] Barazangi, M. and Isacks, B.L. (1976) Spatial distribution of earthquakes and subduction of the Nazca plate beneath South America. Geology, 4, 686-692. doi:10.1130/0091-7613(1976)4<686:SDOEAS>2.0.CO;2
[11] Yanez, G., Ranero, G. R., von Huene, R. and Díaz, J., (2001) Magnetic anomaly interpretation across a segment of the Sourthern Central Andes (32° 34°): Implications on the role of the Juan Fernández Ridge in the tectonic evolution of the margin during the upper Tertiary. Journal of Geophysical Research, 106, 6325-6345.
[12] Gans, C., Beck, S., Zandt, G., Gilbert, H. and Alvarado, P. (2011) Continental and oceanic crustal structure of the Pampean flat slab region, western Argentina, using receiver function analysis: New high-resolution results. Geophysical Journal International, 186, 45-58. doi:10.1111/j.1365-246X.2011.05023.x
[13] Allmendinger, R., Figueroa, D., Zinder, D., Beer, J., Mpodozis, C. and Isacks, B. L. (1990) Foreland shortening and crustal balancing in the Andes at 30° latitude. Tectonics, 9, 789-809. doi:10.1029/TC009i004p00789
[14] Kay, S., Godoy, E. and Kurtz, A. (2005) Episodic arc migration, crustal thickening, subduction erosion, and magmatism in the south-central Andes. Geological Society of America Bulletin, 117, 67-88. doi:10.1130/B25431.1
[15] Ramos, V., Dallmeyer, R. D. and Vujovich, G. (1998) Time constraints on the Early Paleozoic docking of the Precordillera, central Argentina. Special Publications, 142, 143-158. doi:10.1144/GSL.SP.1998.142.01.08
[16] Ramos, V.A. (2004) Cuyania, an exotic block to Gondwana: Review of a historical success and the present problems: Gondwana Research, 7, 1009-1026. doi:10.1016/S1342-937X(05)71081-9
[17] Liener, B.R. and Havskov, J. (1995) A computer program for locating earthquakes locally, regionally and globally. Seismological Research Letters, 66, 26-36. doi:10.1785/gssrl.66.5.26
[18] Furlani, R. and Triep, E. (2007) Modelo mínimo de velocidades de ondas P y ondas S por encima de la transición de plana a normal de placa de Nazca entre latitudes 31.5° 33.5°S y longitudes 67°-70°. 17th Congreso Geológico Argentino, Jujuy, 7 al 10 de Octubre del 2008.
[19] Snoke, J.A., Munsey, J.W., Teague, A.C. and Bollinger, G.A. (1984) A program for focal mechanism determination by combined use of polarity and SV-P amplitude ratio data. Earthquakes Notes, 55, 3-15.
[20] Sokos, E. N. and Zahradnik, J. (2008) ISOLA a FORTRAN code and a Matlab GUI to perform multiple-point source inversion of seismic data. Computers & Geosciences, 34, 967-977. doi:10.1016/j.cageo.2007.07.005
[21] Aki, K. and Richards, P. (1980) Quantitative seismology. Theory and methods. Volume I. W.H. Freeman, San Francisco.
[22] Cortés, J.M., Yamin, M.. and Pasini, M. (2005) La precordillera sur, provincias de mendoza y san juan. Actas del XVI Congreso Geológico Argentino, La Plata, 2005.
[24] Costa, C., Machette, M. N., Dart, R. L., Bastias, H. E., Paredes, J. D., Perucca, L. P., Tello, G. E. and Haller, K.M. (2000) Map and database of quaternary faults and folds in argentina. Open-File Report 00-0108, Department of the interior, United States Geological Survey, Reston.
[25] Ploszkiewicz, V. (1993) Yacimiento tupungato. Egeología y Recursos naturales de mendoza. 12o Congreso Geológico Argentino y 2o Congreso de Exploración de Hidrocarburos, Relatorio, Mendoza, 391-396.
[26] Kostoglodov V., Singh, S.K., Santiago, J.A., Franco, S.I., Larson, K.M., Lowry, A.R. and Bilham, R. (2003) A large silent earthquake in the Guerrero Seismic gap, Mexico. Geophysical Research Letters, 30, 1807. doi:10.1029/2003GL017219

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