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TitleSlow slip and inter-transient locking on the Nicoya megathrust in the late and early stages of an earthquake cycle
AuthorXie, SORCID logo; Dixon, T H; Malservisi, R; Jiang, YORCID logo; Protti, M
SourceJournal of Geophysical Research, Solid Earth 2020 p. 1-22,
Alt SeriesNatural Resources Canada, Contribution Series 20200459
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf
AreaCosta Rica
Lat/Long WENS -86.0000 -84.0000 11.0000 9.0000
SubjectsNature and Environment; Science and Technology; tectonics; plate tectonics; faults, slip; earthquakes; earthquake studies; seismic energy; seismic surveys; seismic data; Caribbean Plate
Illustrationslocation maps; plots; graphs; tables; models
ProgramPublic Safety Geoscience Plate Boundary Earthquakes
Released2020 10 20
AbstractWe analyzed continuous GPS data collected from 2002-2020 to characterize slow slip events (SSEs) in and near the Nicoya Peninsula, Costa Rica. These data are bisected by the 5 September 2012 Mw 7.6 earthquake. The displacement time series contain multiple signals, including plate convergence, plate interface locking, coseismic and postseismic deformation, seasonal oscillations, SSEs, and noise. GPS-measured coseismic and postseismic displacements associated with the Mw 7.6 earthquake are modeled and removed by a step function plus multiple timescale relaxation processes with four characteristic times: 11, 94, 470, and 1,865 days. Seasonal oscillations are eliminated using a multichannel singular spectrum analysis (M-SSA). Ten major SSEs (Mw > 6.6) are observed in the remaining time series, with a constant recurrence interval of 21.7 ± 2.6 months. SSEs occur in both shallow (~10 km) and deep (~35 km) portions of the plate interface, but the latter last longer and have larger magnitudes. There is minimum to no slow slip in theMw 7.6 seismic rupture area and a persistent slow slip patch beneath the Nicoya Gulf entrance. Despite strong earthquake-related stress perturbations, the inter-SSE locking status on the megathrust is very similar between the late and early stages of the earthquake cycle and includes locked patches that ruptured in the 2012 earthquake or continue to rupture via SSEs. Some locked patches offshore south of the Nicoya Peninsula did not rupture in 2012, do not participate in SSEs, and may be indicative of supercycle behavior, that is, strain accumulation over several seismic cycles. These areas warrant heightened monitoring.
Summary(Plain Language Summary, not published)
Slow slip events are different ways than earthquakes to release stored energy in Earth's crust, but they do not cause damage. We build a database of slow slip events in Northwestern Costa Rica from GPS measurements with millimeter precision. We found that these events happened about every 22 months, and the repeating time remain unchanged by the 5 September 2012 Mw 7.6 Costa Rica earthquake. Modeling work that connects ground GPS measurements with crustal motion suggests the largest slow slip motion is under the entrance of the Nicoya Gulf. Strain accumulation patterns before and after the 5 September 2012 Mw 7.6 are similar.

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