A tremor and slip event on the Cocos‐Caribbean subduction zone as measured by a global positioning system (GPS) and seismic network on the Nicoya Peninsula, Costa Rica

Abstract

[1] In May 2007 a network of global positioning systems (GPS) and seismic stations on the Nicoya Peninsula, of northern Costa Rica, recorded a slow-slip event accompanied by seismic tremor. The close proximity of the Nicoya Peninsula to the seismogenic part of the Cocos-Caribbean subduction plate boundary makes it a good location to study such events. Several centimeters of southwest motion were recorded by the GPS stations over a period of several days to several weeks, and the seismic stations recorded three distinct episodes of tremor during the same time span. Inversion of the surface displacement data for the depth and pattern of slip on the plate interface shows peak slip at a depth of 25-30 km, downdip of the main seismogenic zone. Estimated temperatures here are ∼250°-300°C, lower than in other subduction zones where events of this nature have been previously identified. There may also be a shallower patch of slip at ∼6 km depth. These results are significant in that they are the first to suggest that slow slip can occur at the updip transition from stick slip to stable sliding, and that a critical temperature threshold is not required for slow slip. Tremor and low-frequency earthquake locations are more difficult to determine. Our results suggest they occur on or near the plate interface at the same depth range as the deep slow slip, but not spatially colocated.

Slow slip events in Costa Rica detected by continuous GPS observations, 2002–2011

“…Plate convergence direction is 10 counter-clock wise from the trench-normal direction [DeMets, 2001]. The subduction rate in the trench-normal direction is 74-84 mmyr À1 [Outerbridge et al, 2010], while fore-arc motion is in the range of 8-14 mmyr À1 [DeMets, 2001;Norabuena et al, 2004;LaFemina et al, 2009]. The subducting Cocos plate is formed at both the fast spreading East Pacific Rise (EPR), with relatively smooth seafloor topography, and the slow-spreading Cocos-Nazca Ridge (CNR), with relatively rough seafloor topography [Protti et al, 1995;Barckhausen et al, 2001].…”

“…The subducting Cocos plate is formed at both the fast spreading East Pacific Rise (EPR), with relatively smooth seafloor topography, and the slow-spreading Cocos-Nazca Ridge (CNR), with relatively rough seafloor topography [Protti et al, 1995;Barckhausen et al, 2001]. The location of the Nicoya peninsula, close to the subduction plate boundary and above the seismogenic portion of the plate interface, provides an excellent location for geodetic and seismic studies of shallow subduction zone processes [Lundgren et al, 1999; Outerbridge et al, 2010;Feng et al, 2010;Walter et al, 2011].…”

“…However they may also "load" adjacent segments of the interface [Ito et al, 2007;Segall et al, 2006]. [3] The Nicoya Peninsula is located in northwest Costa Rica, and overlies part of the Middle America subduction zone, where the Cocos plate subducts northeastward beneath the Caribbean plate ( Figure 1) at a rate of $85 mm/yr [Dixon, 1993;DeMets, 2001;Outerbridge et al, 2010]. Plate convergence direction is 10 counter-clock wise from the trench-normal direction [DeMets, 2001].…”

Space geodetic observations of repeating slow slip events beneath the Bonin Islands

“…For example, SSEs under the Boso Peninsula, Kanto District, Japan, another well-studied series of SSEs (Ozawa et al 2003), recur every 5-7 yr, and those in the southwest Ryukyu Arc repeat biannually (Heki & Kataoka 2008;Nishimura 2014). Outside Japan, repeating SSEs are found, for example, in Cascadia, Western North America (Dragert et al 2001), Hikurangi, New Zealand (Douglas et al 2005), and the Nicoya Peninsula, Costa Rica (Outerbridge et al 2010). (Argus et al 2010).…”

Scientific Drilling

“…In many ways, our understanding of the origins of slow slip events has been hampered by the fact that many of the best-studied SSEs worldwide (e.g., Cascadia, Nankai) occur at depths of 30-40 km below the Earth's surface (Dragert et al, 2001;Obara et al, 2004), and scientists must rely on indirect evidence to investigate these fascinating phenomena. However, the discovery of shallow SSEs (at <10 km depth) at subduction margins in New Zealand, central Japan and Costa Rica (Douglas et al, 2005;Outerbridge et al, 2010Ozawa et al, 2007Sagiya, 2004;Wallace and Beavan, 2010) highlights the exciting potential for IODP drilling to gain direct access to the SSE source area, and thus to play a key role in unlocking the secrets of SSEs.…”