Seismic ruptures and slow earthquakes in subduction zones
In a study recently published in the journal Science Advances, a team of French and Ecuadorian researchers have highlighted the relationships between different slip modes on the subduction fault along the coast of Ecuador. This study suggests that taking into account the low seismogenic potential of apparently coupled zones in the interseismic phase should enable a finer characterization of the rupture zones of future great earthquakes.
Publication date: 21/02/2018
General public, Press, Research
Related teams :
Tectonics and Mechanics of the Lithosphere
Related themes : Natural Hazards
Although the tectonic plates move continuously (with a homogeneous speed and direction) at their boundaries, the contact zones between plates prevent this movement. Along this interface, several types of slip can accommodate the movement of the tectonic plates, depending on the parameters of the fault zone (coupling, friction, role of fluids, etc.). Some parts of the fault slide stably over time in line with the global movement of the plates, while other zones are blocked. Earthquakes are caused by the rapid sliding of the plates, releasing the accumulated stresses.
But even within seismic zones, GPS networks deployed in subduction zones over the last twenty years or so have shown that transient asismic slip exists, either in the form of spontaneous events (called “slow earthquakes”) during the period between major earthquakes, or in the form of accelerated slip immediately after major earthquakes (“post-seismic” slip).
The magnitude 7.8 Pedernales earthquake that took place on April 16th 2016 along the subduction in Ecuador provided an opportunity to study the relationships between these different slip modes. Before the earthquake, the interface appears locked along well-defined zones. Several slow earthquakes were detected, releasing without shaking the stresses accumulated in these zones. The 16 April earthquake appears to have ruptured the part of the coupled zone for which no slow earthquakes were detected. Finally, after the earthquake, the zones of slow earthquakes are again activated in the post-seismic phase. All these observations are summarised in the diagram in Figure 1.
This study suggests that the spatial extension of seismic rupture remains confined to coupled zones that do not experience slow earthquakes. Zones that slip in slow earthquakes retain their seismic behaviour before and after the earthquake. By regularly releasing stresses through slow earthquakes, they provide an unfavourable environment for the propagation of seismic rupture. If new observations confirm this result for other subduction zones, observing slow earthquakes in detail will considerably improve our ability to define scenarios for future earthquakes.
Ref: F. Rolandone, J.-M. Nocquet, P. A. Mothes, P. Jarrin, M. Vallée, N. Cubas, S. Hernandez, M. Plain, S. Vaca, Y. Font, Areas prone to slow slip events impede earthquake rupture propagation and promote afterslip. Sci. Adv. 4, eaao6596 (2018). http://advances.sciencemag.org/content/4/1/eaao6596
