5 research outputs found
Gradual unlocking of plate boundary controlled initiation of the 2014 Iquique earthquake
On 1 April 2014, Northern Chile was struck by a magnitude 8.1 earthquake
following a protracted series of foreshocks. The Integrated Plate
Boundary Observatory Chile monitored the entire sequence of events,
providing unprecedented resolution of the build-up to the main event
and its rupture evolution. Here we show that the Iquique earthquake
broke a central fraction of the so-called northern Chile seismic gap,
the last major segment of the South American plate boundary that
had not ruptured in the past century. Since July 2013 three seismic
clusters, each lasting a few weeks, hit this part of the plate boundary
with earthquakes of increasing peak magnitudes. Starting with the
second cluster, geodetic observations show surface displacements that
can be associated with slip on the plate interface. These seismic clusters
and their slip transients occupied a part of the plate interface that
was transitional between a fully locked and a creeping portion. Leading
up to this earthquake, the b value of the foreshocks gradually decreased
during the years before the earthquake, reversing its trend a few days
before the Iquique earthquake. The mainshock finally nucleated at
the northern end of the foreshock area, which skirted a locked patch,
and ruptured mainly downdip towards higher locking. Peak slip was
attained immediately downdip of the foreshock region and at the margin
of the locked patch. We conclude that gradual weakening of the
central part of the seismic gap accentuated by the foreshock activity
in a zone of intermediate seismic coupling was instrumental in causing
final failure, distinguishing the Iquique earthquake from most
great earthquakes. Finally, only one-third of the gap was broken and
the remaining locked segments now pose a significant, increased seismic
hazard with the potential to host an earthquake with a magnitude
of 8.5