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GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L04613, doi:10.1029/2003GL018863, 2004

Along-strike variations in underthrust sediment dewatering on the Nicoya margin, Costa Rica related to the updip limit of seismicity

Glenn A. Spinelli

Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA


Demian M. Saffer

Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, USA


Abstract

Along the Costa Rican subduction zone offshore the Nicoya peninsula, an offset in the updip limit of seismicity coincides with a transition between subduction of warm crust generated at the Cocos-Nazca Spreading Center and cool crust formed at the East Pacific Rise. We evaluate whether the observed difference in thermal state of incoming crust would result in significant differences in sediment dehydration reaction progress along strike, thought to be a control on the updip limit of seismicity. We combine thermal models with models of dehydration reaction kinetics for opal and smectite to estimate the distribution of diagenetic fluid sources. The modeled distribution of diagenetic fluid sources mimics the pattern of the updip limit of seismicity; seismicity begins ∼15–20 km landward of most of the smectite-to-illite transition. This suggests that the location of the updip limit of seismicity may be influenced by the dissipation of fluid overpressures landward of smectite-to-illite dehydration.

Received 17 October 2003; accepted 20 January 2004; published 28 February 2004.

Index Terms: 3015 Marine Geology and Geophysics: Heat flow (benthic) and hydrothermal processes; 3022 Marine Geology and Geophysics: Marine sediments—processes and transport; 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); 7209 Seismology: Earthquake dynamics and mechanics; 8105 Tectonophysics: Continental margins and sedimentary basins.

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Citation: Spinelli, G. A., and D. M. Saffer (2004), Along-strike variations in underthrust sediment dewatering on the Nicoya margin, Costa Rica related to the updip limit of seismicity, Geophys. Res. Lett., 31, L04613, doi:10.1029/2003GL018863.