Inherited faults and deep fluids, the cocktail behind the Galician seismicity

Writing / Irene Vega

The research group TECVOLRISK from the Rey Juan Carlos University, has spent more than 20 years studying the singular intra-plate seismicity of the northwest of the peninsula. In the new publication of him in the magazine Global and Planetary Change, in collaboration with researchers from the GFZ (GeoForschungsZentrum) of Germany, present evidence on the possible causes of seismicity in this region.

The results of the investigation suggest that a large part of this seismicity is generated by the ascent of deep fluids through the faults, due to the fact that the seismicity migrates towards the surface and the presence in hot springs of mantle CO2 (that which comes from the mantle that exists below the earth's crust). “These fluids reduce the effort necessary to generate the rupture of the faults, that is, they would act like oil inside some gears, facilitating the rupture and movement of the faults”, explain the authors of the study.

This work opens a window with implications in seismic hazard studies, since it highlights how all potential inherited fault systems (old faults, but which are reactivated today) have the same probability of generating seismicity, regardless of whether there are instrumental seismicity record or little morphological expression. In short, all these faults must be taken into account in seismic hazard studies.

Seismicity in Galicia, the great unknown

Far from what we usually think, there are not only earthquakes in California, Japan, Murcia or Granada; Galicia also registers recent earthquakes, although their origin is less well known.

The seismicity of the Galician region is far from the edges of the tectonic plates located in southern Spain. These are known as intra-plate regions and they exhibit different characteristics compared to plate boundaries (eg longer recurrence periods between earthquakes, low strain rates, different seismic fault cycles, etc.). Due to this and the low earthquake awareness that exists in these regions, added to the lack of earthquake resistant structures, intra-plate earthquakes can be even more devastating than plate-edge earthquakes. For this reason, studies -such as the one carried out by the URJC research group- on the origin of earthquakes in these areas are of great interest, since they will allow us to understand and minimize the damage they generate.