Costa Rica Earthquakes

Author : Lise Alalouf
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (129 download)

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Download or read book Modeling Slow Slip Events and Megathrust Earthquakes in the Costa Rica Subduction Zone written by Lise Alalouf and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Subduction zones are where the largest earthquakes occur. In recent decades, scientists have also discovered the presence of episodic aseismic slip, including slow slip events (SSE), along most of the subduction zones. However, it is still unclear how these SSEs can influence megathrust ruptures. The Costa Rica subduction zone is a particularly interesting area as a SSE was recorded 6 months before the 2012 Mw7.6 earthquake, in the Nicoya Peninsula, suggesting potential stress transfer from the SSE to the earthquake slip zone. SSEs beneath the Nicoya Peninsula have also been recorded both updip and downdip of the seismogenic zone, making it a unique area to study the complex interaction between SSEs and earthquakes.We conducted an initial study, using GPS inversion from previous studies, to observe the empirical relationships of various source parameters between SSEs and megathrust earthquakes along the Costa Rica subduction zone. They highlight the differences and similarities between SSEs and megathrust earthquakes and allows to better explain the physical mechanisms at the base of the SSEs. It was observed that static stress drop of SSEs remains constant for different sized event but are 1-2 orders of magnitude lower for SSEs than for earthquakes. We also found that the duration-moment scale for SSEs of Costa Rica is M0 ~ T, where M0 is the equivalent moment and T is the event duration.Then, to better understand how updip and downdip SSEs and megathrust earthquakes may be related, we performed a numerical simulation study. As most of the SSEs (shallow and deep) were recorded around the Nicoya Peninsula, we used a 1D linear fault integrated in a homogeneous elastic half-space under the Nicoya Peninsula of the Costa Rica margin. This 1D modelling in the framework of the rate-and-state friction law, allows us to study the interaction between SSEs and megathrust ruptures with high numerical resolution and relatively short computation times. The model provides information on the long-term seismic history by reproducing the different stages of the seismic cycle (interseismic slip, shallow and deep episodic slow slip, and coseismic slip). We investigated the influence of the variation of numerical parameters and frictional properties on the recurrence interval, maximum slip velocity and cumulative slip of SSEs (both shallow and deep) and earthquakes, and their interaction. For an assumed friction parameters a-b profile, that we defined from thermal evolution of the Costa Rica subduction zone, we varied effective normal stress and characteristic slip distance until the model replicated the observed recurrence intervals for SSEs (~ 20-22 months) and earthquakes (~ 50 years) under the Nicoya Peninsula. Then, we compared our results with GPS and seismic observations to identify an optimal set of model parameters to understand the interaction between different modes of subduction fault deformation. We defined this set as L = 0.2 - 0.8 mm and Effective normal stress = 0.4 - 2.4 MPa for SSEs and L = 10 mm and Effective normal stress = 35 MPa for earthquakes. Our results show that parameters such as characteristic slip distance and effective normal stress strongly impact on the long-term history fault slip of Costa Rica, both on the recurrence interval between SSEs and on the SSE maximum slip velocity. We also found through simulation that deep SSEs have shorter recurrence intervals and higher maximum slip rates but shorter durations than shallow SSEs. In addition, we observe a deep loading phase prior to the earthquake rupture where, in the few years prior to the earthquake, SSEs occur more frequently and the maximum slip rate is higher, which could represent a distinctive earthquake preparation phase. While for shallow SSEs, the loading prior to an earthquake rupture is represented by more temporally spaced SSEs, with higher maximum slip rates"--