Hydrologic detection and finite element modeling of a slow slip event in the Costa Rica prism toe

Abstract

[1] We investigate transient fluid flux through the seafloor recorded near the Costa Rica trench during the 2000 Costa Rica Seismogenic Zone Experiment using a 2-D fully coupled poroelastic finite element model. We demonstrate that the observed hydrologic anomalies are consistent with a model of propagating slow slip at the subduction interface between the frontal prism and downgoing plate. There are two sources of volumetric strain that drive fluid flux at the seafloor in response to fault slip at depth: (1) compression and dilation in the vicinity of the tips of a slipping patch and (2) extension and compression due to flexure of the seafloor. The superposition of these two effects results in distinctive spatial and temporal patterns of fluid flow through the seafloor. In a forward modeling approach, time series from shear ruptures with a range of fault length-to-depth ratios in a heterogeneous crust are generated and compared with flow rate observations. Assuming a constant propagation rate and an elliptical profile for the distribution of slip along the decollement, the set of model predictions enables us to infer the probable rupture location, extent, propagation velocity, and duration from a single flow rate time series. The best fit model suggests that the slow slip event initiated within the toe at a depth of less than 4 km and propagated bilaterally at an average rate of 0.5 km dÀ1 . This interpretation implies that stress in the shallow subduction zone is relieved episodically. Furthermore, the Costa Rica data suggest that episodic slow slip events may initiate in the prism toe without being triggered by a seismic event further downdip.

Simultaneous long‐term and short‐term slow slip events at the Hikurangi subduction margin, New Zealand: Implications for processes that control slow slip event occurrence, duration, and migration

“…We suggest that this event may instead be located within the updip transition from seismic to aseismic behavior (Figure 10). The occurrence of episodic slow slip updip of the seismogenic zone has been suggested in Costa Rica based on evidence for hydraulic transients correlated with seismic tremor and slow slip [ Brown et al , 2005; LaBonte et al , 2009; Davis et al , 2011]. Outerbridge et al [2010]also suggest SSE slip updip of the seismogenic zone from shore‐based cGPS data, although the cGPS network in their study is comparatively sparse, and we contend that Outerbridge et al 's [2010] models for SSE slip updip of the seismogenic zone are not well constrained.…”

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

“…The phenomenon was observed on only three out of a total of 14 OBS instruments near the base of the continental margin. LaBonte et al [2009] used a 2‐D fully coupled poroelastic finite‐element model to show that the patterns of fluid flow could be matched by a dislocation on the plate interface at a depth of less than 4 km, propagating bilaterally at an average rate of ∼0.5 km d −1 and lasting 20 d or more. In 2003 pressure gauges in ODP (Ocean Drilling Program) boreholes approximately 60 km offshore of the Nicoya Peninsula recorded two transient events [ Davis and Villinger , 2006], also interpreted as evidence for a slow‐slip event.…”

“…Since the occurrence of the 2007 event, an additional coastal station (SAJU) has been installed, increasing offshore resolution in case of similar future events. The occurrence of a possible shallow slip event in 2000 [ Brown et al , 2005; LaBonte et al , 2009] and pressure transients observed in ODP boreholes offshore the Nicoya Peninsula in 2003 [ Davis and Villinger , 2006] and May 2007 [M. Hessemann, personal communication, 2009] suggests that the shallow slip patch in our low‐misfit model may be real, and we make that assumption in the following discussion.…”

Active deformation near the Nicoya Peninsula, northwestern Costa Rica, between 1996 and 2010: Interseismic megathrust coupling

“…Six slow‐slip episodes were observed near Nicoya with an average recurrence interval of 21 ± 6 months [ Jiang et al , 2012]. The first episode, in early 2000, including three pulses of transient slow‐slip propagating at the shallow subduction interface, was suggested by correlated flow rate transients detected across three flowmeters at the frontal prism of the forearc [ Brown et al , 2005; LaBonte et al , 2009]. The transient signal was also accompanied with tremor‐like noise recorded on collocated ocean bottom seismometers [ Brown et al , 2005].…”