The Corinth Rift Laboratory (Greece): What Can Micro-Seismicity Reveal?

In the framework of the Corinth Rift Laboratory, the seismic activity in the western part of the rift is monitored since 2000 by a network of 15 three-component stations (CRLNET). It is characterized by several instrumental and historical large earthquakes with magnitude larger than 5.5, and numerous active swarms. More than 12 years of seismicity (about 100,000 events) that covers seven orders of magnitude of seismic moment Mo (10¹⁰ – 10¹⁷ Nm) is available. The detailed analysis of the whole seismicity brings insights into the geometry of faults at depth, the nature and the structure of the active zone at 6-8 km depth previously interpreted as a possible detachment, and more generally into the rifting process and mechanical processes at various space-time scales. For this purpose, we identified multiplets and precisely relocated the seismicity using double difference techniques. The seismicity exhibits a complex structure, strongly varying along the rift axis. We will present some specific structures of the seismicity and swarms. The spatio-temporal evolution of earthquake sequences, which repeatedly occur in specific sub-areas of the fault segments, and the relationship with the distribution of the elastic/anelastic structure, the VP/VS ratio and physical properties of the micro-earthquakes (such as seismic moment, static stress-drop, corner frequency and source size) provide important insights on the presence and the role of fluids during the generation of fractures. The variability of the stress release would suggest, in fact, the presence of heterogeneities in the friction distribution and fluid pressure, and normal stress and elastic properties variability in the fault zone. Finally, according with seismic and geodetic observations, we proposed a new mechanical model for the rifting process in this region, implying a non-elastic, mostly aseismic uniform NS opening below the rift axis, coupled with the downwards growth of a yet unmature detachment.