Arroyo, Ivonne G., Husen, S. and Flüh, Ernst R. (2014) The seismogenic zone in the Central Costa Rican Pacific margin: high-quality hypocenters from an amphibious network. International Journal of Earth Sciences, 103 (7). pp. 1747-1764. DOI 10.1007/s00531-013-0955-8.

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Abstract

Transition from subduction of normal to
thickened oceanic crust occurs in the central portion of the
Costa Rican margin, where large interplate earthquakes
(M * 7) and abundant interseismic seismicity have been
associated with subduction of bathymetric highs. We
relocated *1,300 earthquakes recorded for 6 months by a
combined on- and offshore seismological network using
probabilistic earthquake relocation in a 3D P-wave velocity
model. Most of the seismicity originated at the seismogenic
zone of the plate boundary, appearing as an 18° dipping,
planar cluster from 15 to 25–30 km depth, beneath the
continental shelf. Several reverse focal mechanisms were
resolved within the cluster. The upper limit of this interseismic
interplate seismicity seems to be controlled
primarily by the overlying-plate thickness and coherency,
which in turn is governed by the erosional processes and
fluid release and escape at temperatures lower than *100
to 120° C along the plate boundary. The downdip limit of
the stick–slip behaviour collocates with relative low temperatures
of *150 to 200° C, suggesting that it is controlled
by serpentinization of the mantle wedge. The
distribution of the interseismic interplate seismicity is
locally modified by the presence of subducted seamounts at
different depths. Unlike in northern Costa Rica, rupture of
large earthquakes in the last two decades seems to coincide
with the area defined by the interseismic interplate seismicity.

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