2012 Seismological Society of America Meeting, Program with Abstracts, p. 370

 

 

Morphotectonic segmentation along the Nicoya Peninsula seismic gap, Costa Rica, Central America

 

Jeff Marshall 1, Shawn Morrish 1, Eli LaFromboise 2, Amber Butcher 1, Brent Ritzinger 1, Kacie Wellington 1, Andrew Barnhart 1, Kelly Kinder 1, John Utick 1, Marino Protti 3, Tom Gardner 4, Don Fisher 5, Gerry Simila 2, Jim Spotila 6, Lewis Owen 7, Madhav Murari 7, Matthew Cupper 8

 

1. Geological Sciences Department, Cal Poly Pomona, Pomona, CA, 91768, USA

2. Geological Sciences Department, California State University, Northridge, CA, 91330, USA

3. OVSICORI, Universidad Nacional, Heredia, Costa Rica

4. Geosciences Department, Trinity University, San Antonio, TX, 78212, USA

5. Department of Geosciences, Penn State University, University Park, PA, 16802, USA

6. Department of Geosciences, Virginia Tech University, Blacksburg, VA 24061, USA

7. Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA

8. School of Earth Sciences, The University of Melbourne, Victoria, 3010, Australia

 

 

The Nicoya Peninsula, Costa Rica forms a prominent forearc high along the erosive Middle America convergent margin. This emergent landmass overlies the seismogenic zone and occupies a seismic gap that last ruptured in 1950 (M7.7). The edges of both the Nicoya gap and the peninsula’s abrupt shorelines correspond with aftershock limits of recent earthquakes to the north (1992 M7.2) and south (1990 M7.0). The coincidence of emergent topography and historic rupture zones suggests persistence of the Nicoya segment through multiple seismic cycles. Uplift along the Nicoya coast is recorded by emergent Quaternary strandlines, marine terraces, and incised valley-fill alluvium. Field mapping, surveying, and isotopic dating reveal uplift variations along the Nicoya margin that coincide with three contrasting domains of subducting seafloor (EPR, CNS-1, CNS-2). Variable uplift may reflect along-strike differences in subducting-plate roughness, thermal structure, fluid flow, and seismogenic-zone locking. Based on convergence rate (9 cm/yr) and historic seismicity, the repeat time for large Nicoya earthquakes is estimated at 50 +/-10 years. The most recent event (1950) generated >1m of coseismic uplift along the central Nicoya coast. Since then, most of this has been recovered by gradual interseismic subsidence, reflecting strain accumulation toward the next event. While elastic seismic-cycle strain produces high frequency shoreline fluctuations, long-term net uplift results in gradual coastal emergence and the growth of topographic relief. We suggest that net uplift along the Nicoya segment is the product of irrecoverable upper plate shortening associated with the seismic cycle, coupled with tectonic erosion at the trench and underplating of eroded material at depth beneath the peninsula. The persistence of the Nicoya segment may result from a feedback between subduction generated upper plate thickening and increased coupling along the plate interface due to isostatic loading.