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 ProfileKazushige 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 ProfileShunsuke 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 ProfileAbstract
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.