Multiscale postseismic behavior on a megathrust: The 2012 Nicoya earthquake, Costa Rica

Abstract

The Nicoya Peninsula in northwest Costa Rica overlies a section of the subduction megathrust along the Middle America Trench. On 5 September 2012, a moment magnitude 7.6 megathrust earthquake occurred beneath a dense network of continuous GPS and seismic stations. Many of the GPS stations recorded the event at high rate, 1 Hz or better. We analyze the temporal and spatial evolution of surface deformation after the earthquake. Our results show that the main rupture was followed by significant afterslip within the first 3 h following the main event. The behavior of the surface displacement can be represented by relaxation processes with three characteristic times: 7, 70, and more than 400 days. We assume that the long relaxation time corresponds to viscoelastic relaxation and the intermediate relaxation time corresponds to afterslip on the main fault. The short relaxation time may represent a combination of rapid afterslip, poroelastic adjustment in the upper crust, or other processes. During the first few months that followed the earthquake, afterslip likely released a significant amount of slip deficit still present following the coseismic rupture, in particular updip of the rupture. Afterslip seems to be bounded updip by regions affected by slow slip events prior to the earthquake, suggesting that the two processes are influenced by different frictional properties.

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

“…Afterslip following the earthquake is bounded by the slow-slip area to the southeast, suggesting differences in frictional properties along strike (Malservisi et al, 2015) or that shear stress has been released in that area by slow slip. These results indicate a strong lateral variability in seismogenic zone properties that seem to correlate with subduction zone structure inferred from seismic and geophysical studies.…”

Slow slip events in the early part of the earthquake cycle

“…High precision GPS instruments in the Nicoya Peninsula of Costa Rica have facilitated detailed geodetic observations of key parts of the earthquake cycle: late interseismic [ Dixon et al , ; Jiang et al , ; Feng et al , ], coseismic [ Protti et al , ], and early postseismic stages [ Malservisi et al , ]. The peninsula lies along the Middle America subduction zone, where the Cocos plate is subducted beneath the Caribbean plate at a rate of 8 cm/yr (Figure ) [ DeMets , ].…”

Space geodetic observation of the deformation cycle across the Ballenas Transform, Gulf of California

“…The analysis generally followed Malservisi et al [2015], with the daily solutions that were aligned to IGb08 [Rebischung et al, 2012].…”

“…Assuming an exponential decay of the signal, we can invert the time series for the three components (north-south, east-west, and up-down) of each station for a single best fit relaxation time following Malservisi et al [2015]. The best fit relaxation time for the sites within the Baja peninsula varies from 178 to 195 days (Table 5).…”