HR: 13:55h
AN: T42C-02    [PDF]
TI: Inter-plate coupling in Nicoya Peninsula, Costa Rica, as deduced from trans-peninsula GPS experiment
AU: * Iinuma, T
EM: iinuma@eri.u-tokyo.ac.jp
AF: ERI, Univ. of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Protti, J M
EM: jprotti@una.ac.cr
AF: OVSICORI-UNA, Apartado 2346-3000, Heredia, {} Costa Rica
AU: Obana, K
EM: obanak@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Gonz\'alez, V
EM: vgonzale@una.ac.cr
AF: OVSICORI-UNA, Apartado 2346-3000, Heredia, {} Costa Rica
AU: Van der Laat, R
EM: rvanderl@una.ac.cr
AF: OVSICORI-UNA, Apartado 2346-3000, Heredia, {} Costa Rica
AU: Kato, T
EM: teru@eri.u-tokyo.ac.jp
AF: ERI, Univ. of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Miyazaki, S
EM: miyagsi@pangea.stanford.edu
AF: ERI, Univ. of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Hernandez, E
EM: ehernan@una.ac.cr
AF: OVSICORI-UNA, Apartado 2346-3000, Heredia, {} Costa Rica
AB: We investigate state of plate coupling at the subduction zone beneath Nicoya Peninsula, northwestern Costa Rica, from 1.5-years of trans-peninsula GPS campaign measurement. Inter-plate coupling zone beneath Nicoya Peninsula is recognized as a clear seismic gap named "Nicoya seismic gap". In this area, Cocos plate is subducting beneath the Caribbean plate from the Mid American Trench with large convergence rate about 90mm/yr, and because of this, large earthquakes have occurred in 1853, 1900, and 1950 at this segment, and two large earthquakes occurred around Nicoya peninsula ($M_W 7.0$ in 1990 to the SE and the 1992 $M_W 7.6$ off Nicaragua to the NW). In the Nicoya seismic gap, a strong coupling of the two plates is manifested by low background seismicity, the sharp edge of aftershock zone of the 1990 and 1992 earthquakes, and the northeastward movement of the Nicoya peninsula recorded with GPS observations.\\ We started a new GPS survey program in Nicoya peninsula in 2001 to obtain new knowledge about the seismic coupling and the potential earthquake. 7 new benchmarks for GPS campaign observation were installed completing a 10-sites transect across Nicoya peninsula. We have done 3 times of GPS campaign observation on this array.\\ Crustal deformation on inter-seismic period above Nicoya seismic gap is estimated from 1.5 years of GPS observations. Obtained velocity field suggests that the forarc sliver motion along the pacific coast of Nicoya peninsula produces 8.5mm/yr of northwestward motion parallel to the Mid American Trench.\\ We performed an inversion analysis to infer inter-plate coupling at Nicoya seismic gap. The result of the inversion shows that upper and lower limits of coupling zone are corresponding with ones of seismogenic zone, which was investigated by Newman \textit{et al.} (2002) with seismological methods. Accumulated strain in the Nicoya seismic gap is able to bring earthquake whose moment magnitude is larger than $7.5$.
DE: 1206 Crustal movements--interplate (8155)
DE: 1243 Space geodetic surveys
DE: 7223 Seismic hazard assessment and prediction
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting