A powerful 7.8-magnitude earthquake occurred on the Ecuadorian coast on 16 April 2016 at 19:00 local time. The latest reports indicate more than 272 fatalities and 2,500 injured, with severe damage in Guayaquil, the country’s largest business centre, and as far as the capital Quito. The tremor lasted more than a minute, causing displacement over several metres along the fault conveying the movement between the Nazca oceanic plate and the continent.
he seismic work conducted by IRD in close partnership with the Instituto Geofisico (IG-EPN) at the Quito Polytechnic College and other French partners, has clearly demonstrated, as part of long-standing cooperation that was strengthened in 2012 by research by the "Earthquakes and Volcanoes in the Northern Andes" (SVAN) international combined laboratory (ICL), that this sector was the most likely to suffer a violent rupture, given the seismotectonic context.
In 1906, this region experienced an 8.8-magnitude earthquake, the seventh most powerful since the start of the 20th century, with the formation of a tsunami that devastated the northern coast of Ecuador and southern Colombia. There were between 500 and 1,500 deaths according to estimates at the time. Since then, despite sustained seismic activity in the region, the absence of major quakes had led IG-EPN, Géoazur and ISTerre seismologists to step up their surveillance in the vulnerable sector under threat.
The violence of the tremor on 16 April 2016 and the dozens of aftershocks indicate that the telluric event was expected in the scenario anticipated by the IG-EPN and IRD researchers, and demonstrates the value in continuing with long-term research via long-standing partnerships such as the SVAN ICL.
During the 1990s, the research conducted jointly by IRD and researchers from the Quito IG-EPN first looked at vulnerability and site effects in urban sectors such as Quito.
Since then, throughout the 2000s and 2010s, investigations were broadened to include analysis of the seismic cycle across the entire subduction segment (from northern Peru to southern Colombia), most notably with focus on the role played by slow slips in deformation and on the conditions of seismicity and current and long-term deformation, specifically affecting the overlying plate margin which ruptured during the 16 April earthquake.
In addition, seismological studies endeavour to identify potentially active faults at the margin and in mountain ranges in Ecuador, focusing on the segments the most likely to rupture sometime soon. The geodetic data from GPS indicate that the displacement of the Nazca oceanic plate under the South American continent occurs at a speed of 6 cm/year in Ecuador and results in seismicity typical to the subduction zone at the thrust fault and the Ecuadorian plate margin, but also in the development of major faults in the mountain ranges, linked to northward retreat of a large section known as the North Andean Block.
This research was conducted on land in the coastal region and in the upper part of the country, and at sea where underwater seismology observation technologies (Ocean Bottom Seismometers or OBS) were able to track micro-seismic activity in active faults further away from the coast. This marine geophysical research was conducted during campaigns at sea in partnership with INOCAR (Instituto Oceanográfico de la Armada) and ESPO (Escuela Superior Politécnica del Litoral) with support from the IFREMER fleet.
Finally, there are studies designed to characterise and quantify the seismic risk by putting forward prevention measures to mitigate risk (paraseismic construction code, crisis management organisation) and to raise awareness of the concept of risk. These applications concern the country’s main urban areas, especially the city of Quito, which has been affected by earthquakes several times over recent years.
This work receives backing from the national research agency as part of the REMAKE project (Seismic Risk in Ecuador : Mitigation, Anticipation and Knowledge of Earthquakes) that began this year.
Continuing on from the valuable and productive scientific collaboration long established between the Ecuadorian and French scientific teams, logistics support has been provided by the IRD representation in Ecuador while French and Ecuadorian researchers have come together in the French post-earthquake unit (CNRS/INSU).