ProjectTitle : OLLIN–Identification (and characterization) of seismogenic faults in populated areas of Latin America and its incorporation into seismic hazard assessment
PI : María Ortuño Candela – Universitat de Barcelona
OLLIN is a project aiming to set up a new collaborative framework between specialists and young researchers from both sides of the Atlantic to improve geological knowledge and seismic hazard assessment (SHA) of two populated regions of Latin America. These are the Transmexican Volcanic belt (TMVB) and the Northern Southamerica Plate Boundary (NSAPB), which extends from Ecuador to Colombia and Venezuela. To do so, three fundamental steps are undertaken; Firstly, data on the seismogenic potential of faults in these areas is gathered, discussed and selected. The most likely fault rupturing mechanisms are discussed, which will lead us to focus the fieldwork on areas which are relevant to SHA but lack information on key seismic parameters (slip rates, segmentation, complex versus simple ruptures, maximum expected earthquakes, etc.). Secondly, the incorporation of that knowledge on seismogenic fault models into the SHA is conducted using existing Fault2SHA tools. This step includes the adaptation of those tools to these specific Latin American settings and the generation of new ones. Finally, results dissemination to society is ensured by the participation of stakeholders from civil protection, geological surveys and other end-users through special meetings, training courses and on-line access that allow to keep track of progress and results.
Understanding how successive earthquakes accrue on faults to produce tectonic landforms is still poorly understood. The way deformation is accommodated throughout the crust, in response to the far-field plate tectonics force imposes at plate boundaries, strongly affects the seismic cycle and may control earthquake triggering and the spatial pattern of fault ruptures. The Apennines range, host of the 2016 seismic sequence (5 shocks Mw5-6.5 over 9 months), is a unique area where the accumulation and release of slip over multiple seismic cycles, over time scales of 1yr-1 Myr and spatial scales of 1m-100km, can be determined. We will combine frontier methodologies in geochronology, remote sensing, geodesy, geophysics, high-resolution topographical data acquisition, seismic hazard modelling, all developed and/or mastered by our teams, to quantitatively constrain how portions of the seismic cycle scale up over multiple cycles to produce the cumulative escarpments we see in the landscape.
In the last months two papers concerning earthquake interactions and probabilistic seismic hazard of the WFZ were published by members of the FAULT2SHA Working Group (Verdecchia et al., 2019, GJI; Valentini et al., 2020, BSSA).
Verdecchia and coauthors used an approach based on physical (coseismic + postseismic Coulomb stress changes) and statistical (probability calculations) to determine if the stress changes due to the youngest paleoevents have significantly modified the present-day probability of occurrence of large earthquakes on each of the segments of the central WFZ. The authors show that regardless of any uncertainties in this approach, Coulomb stress changes strongly affect the time-dependent probability of a large earthquake on the Brigham City, Salt Lake City, and Provo segments. These results indicate that the seismic hazard connected with single-segment ruptures on the central WFZ might be underestimated, if the effects of stress changes are not considered.
Valentini and coauthors assess the impact that the Wasatch fault segmentation model has on seismic hazard by evaluating the time-independent long-term rate of ruptures on the fault that satisfy fault-slip rates and paleoseismic event rates, adapting standard inverse theory used in the Uniform California Earthquake Rupture Forecast (Vers. 3) and implementing a segmentation constraint in which ruptures across primary structural complexities are penalized.