10. October 2015 Subducting seamounts control interplate coupling and seismic rupture in the 2014 Iquique earthquake area



In a recent study published in the international journal Nature Communications, IMAP member Jacob Geersen from the Cluster of Excellence “The Future Ocean” and the GEOMAR Helmholtz Centre for Ocean Research Kiel and co-authors present an explanation for the smaller than expected tremor during the April 2014 Iquique earthquake.

 

Chile is one of the countries that is most at risk from damaging earthquakes. The reason for the high earthquake frequency lies just off the coast where the oceanic Nazca plate subducts underneath the South American plate. This leads to the accumulation of stress that will sooner or later, be released during an earthquake. In northern Chile, however, there is a 550 kilometer wide gap that did not experience a major earthquake since 1877. Therefore, no one was caught by surprise when a series of tremors struck the area around the northern Chilean city of Iquique in spring 2014. The main quake on 1 April reached a magnitude of 8.1 and triggered a tsunami.

But experts were surprised that the quake was not as large and damaging as expected, and that it affected only a limited region. To understand the reason for the low intensity of the 2014 Iquique earthquake, Dr. Geersen and his colleagues studied the seafloor topography off northern Chile combined with seismic images that resolve the deep structure under the seafloor. It turned out that the seafloor of the Nazca plate in the affected region is not entirely flat. Instead, there are numerous extinct volcanos, so called seamounts, some of them thousands of meters high. These seamounts are, together with the Nazca plate, pushed beneath the South American Plate. Because of this roughness and the associated fractures created by the subducting seamounts, less stress is build up in the area and the resulting earthquake is smaller.

The risk of a future mega earthquake in the seismic gap of northern Chile is not yet reduced. Although a portion of the accumulated stress has now been released by the 2014 earthquake, the unbroken northern and southern portion of the seismic gap still hold enough energy that remains to be released during an earthquake with a magnitude larger than 8.5. Therefore, scientists from around the world continue to monitor the region. In autumn 2015, a team of GEOMAR scientists will visit the area onboard the German research vessel SONNE in order to install high-precision instrumentation on the seabed that is capable of detecting even small centimeter-scale movements of the subsurface

Original publication:
Geersen, J. et al. (2015), Subducting seamounts control interplate coupling and seismic rupture in the 2014 Iquique earthquake area. Nat. Commun. 6:8267 doi: 10.1038/ncomms9267
http://www.nature.com/ncomms/2015/150930/ncomms9267/full/ncomms9267.html

Read more:
www.geomar.de/en/news/article/erloschene-tiefseevulkane-als-erdbebenstopper

Contact:

Jacob Geersen, jgeersen@geomar.de