loading page

Shallow Slow Earthquake Episodes Near the Trench Axis Off Costa Rica
  • +2
  • Satoru Baba,
  • Kazushige Obara,
  • Shunsuke Takemura,
  • Akiko Takeo,
  • Geoffrey A. Abers
Satoru Baba
Earthquake Research Institute, the University of Tokyo, Earthquake Research Institute, the University of Tokyo, Earthquake Research Institute, the University of Tokyo, Earthquake Research Institute, the University of Tokyo

Corresponding Author:[email protected]

Author Profile
Kazushige Obara
Earthquake Research Institute, The University of Tokyo, Earthquake Research Institute, The University of Tokyo, Earthquake Research Institute, The University of Tokyo, Earthquake Research Institute, The University of Tokyo
Author Profile
Shunsuke Takemura
Earthquake Research Institute, the University of Tokyo, Earthquake Research Institute, the University of Tokyo, Earthquake Research Institute, the University of Tokyo, Earthquake Research Institute, the University of Tokyo
Author Profile
Akiko Takeo
Earthquake Research Institute, the University of Tokyo, Earthquake Research Institute, the University of Tokyo, Earthquake Research Institute, the University of Tokyo, University of Tokyo
Author Profile
Geoffrey A. Abers
Cornell University, Cornell University, Cornell University, Cornell University
Author Profile

Abstract

Slow earthquakes are mainly distributed in regions surrounding seismogenic zones along the plate boundaries of subduction zones. In the Central American subduction zone, large regular interplate earthquakes with magnitudes of 7–8 occur repeatedly around the Nicoya Peninsula, in Costa Rica, and a tsunami earthquake occurred off Nicaragua, just north of Costa Rica, in 1992. To clarify the spatial distribution of various slip behaviors at the plate boundary, we detected and located very low frequency earthquakes (VLFEs) around the Nicoya Peninsula using a grid-search matched-filter technique with synthetic templates based on a regional three-dimensional model. VLFEs were active in September 2004 and August 2005, mainly near the trench axis, updip of the seismogenic zone. The distribution of VLFEs overlapped with large slip areas of slow slip events. Low frequency tremor signals were also found in high-frequency seismogram envelopes within the same time windows as detected VLFEs; thus, we also investigated the energy rates of tremors accompanied by VLFEs. The range of scaled energy, which is the ratio of the seismic energy rate of a tremor to the seismic moment rate of accompanying VLFE and related to the rupture process of seismic phenomena, was 10-9–10-8. The along-dip separation of shallow slow and large earthquakes and the range of the scaled energy off Costa Rica are similar to those in shallow slow earthquakes in Nankai, which shares a similar thermal structure along the shallow plate boundary.
Sep 2021Published in Journal of Geophysical Research: Solid Earth volume 126 issue 9. 10.1029/2021JB021706