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Accomodation of the deformation in the Cocos-Caribbean-North America triple junction area, from GPS meaurements

Abstract : Northern Central America is located in a complex zone of interaction between three major tectonic plates: the North American (NA), the Caribbean (CA) and the Cocos (CO) plates. While the CO plate is subducting under the NA and CA plates along the Mid-American trench, the on-land relative motion between the NA and CA plates is mainly accommodated by the east-west trending left-lateral Polochic-Motagua fault system. We use GPS data to characterize the deformation in this CO-CA-NA triple junction area in terms of interactions and relative contributions of the different structures (Polochic and Motagua faults, a series of north-south grabens south of them and the Mid-American Volcanic Arc, MAVA), and coupling at the subduction interface. We analyse GPS-campaign data from different networks in Guatemala (24 sites measured in 1999-2003- 2006), Salvador (3 sites measured in 2003 and 2006) and Chiapas, southern Mexico (8 sites measured each year from 2002 to 2004). Data are processed and combined using the GAMIT/GLOBK softwares. The obtained velocity field is first fitted using simple elastic models. The Motagua fault seems to accomodate most of the present left-lateral motion between CA and NA, with less than 30 procent taken by the Polochic fault despite its comparable surface morphology, historical seismicity and microseismic activity (that we recorded during a 6 months experiment in 2005). This may suggest complex mechanical interactions between the Motagua and Polochic faults at the scale of several seismic cycles. A single fault model, centered on the Motagua fault, locked at a depth of 15 km, indicates a slip rate decrease from eastern (20 mm/yr) to central Guatemala (10 mm/yr) towards the CA-CO-NA triple junction (0 mm/yr?). This decrease seems to be consistent with east-west extension rates estimated across the Ipala and Guatemala city grabens south of the Motagua fault. We also observe a right-lateral movement across the MAVA: 15mm/yr in western Salvador and 10mm/yr in eastern Guatemala. This movement is consistent with that observed along the nicaraguan and costa-rican volcanic arcs. To take into account the rotation of blocks and the elastic deformation localized on faults at their boundaries in this area, we finally use the 3D-elastic inverse model DEFNODE (McCaffrey 2002) to fit the GPS-derived deformation field. Our 4 blocks (CO,CA, NA and a microplate in between the MAVA and the CO subduction interface) seems to suggest a coupling decrease at the subduction interface from Chiapas to Guatemala, although not fully resolved with the present data set.
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Conference papers
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https://hal-insu.archives-ouvertes.fr/insu-00355090
Contributor : Pascale Talour <>
Submitted on : Thursday, January 22, 2009 - 9:18:11 AM
Last modification on : Wednesday, September 30, 2020 - 2:36:03 PM

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  • HAL Id : insu-00355090, version 1

Citation

A. Franco, Cécile Lasserre, H. Lyon-Caen, E. Molina, V. Kostoglodov, et al.. Accomodation of the deformation in the Cocos-Caribbean-North America triple junction area, from GPS meaurements. AGU Fall Meeting, 2008, San Francisco, United States. ⟨insu-00355090⟩

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