Editorial: Submarine Active Faults: From Regional Observations to Seismic Hazard Characterization

Since the beginning of the XXI Century, our society has witnessed a number of catastrophic
earthquakes with devastating consequences (e.g., Sumatra 2004, Haiti 2010, Japan 2010, Nepal 2015,
Italy 2009 and 2016). Localizing the active faults and understanding their earthquake history is key to
improve modern probabilistic seismic hazard assessment (PSHA) and, thus, to mitigate the
consequences of future events. Seismicity models to characterize the earthquake frequency in a
region in PSHA studies have been traditionally based on archaeological, historical and instrumental
earthquake records. However, the rapid advance of active tectonics and paleoseismological studies
has resulted in the development of seismicity models for faults, since they allow characterizing the
active faults, reconstructing their 3D geometry at depth, and determining their past earthquake
history and seismic potential based on the interpretation of the geological record.
Traditionally, active tectonics and paleoseismological research had been mainly conducted to study
onshore active faults. However, the occurrence of the offshore Sumatra (2004) and Japan (2010)
earthquakes and consequent tsunamis, which caused tens of thousands of casualties and extensive and
severe damage and economic losses, have brought into sharp focus the need to better understand the
geohazards related to submarine active faults. In the last few years, the availability of offshore geological and
geophysical data at various scales (e.g., deep and shallow borehole, wide angle seismic profiles, tomography,
3D and 2D seismic reflection surveys, high resolution bathymetry or seafloor imaging) has allowed for a
better definition of offshore fault systems. These studies focused on accurately constraining the kinematic,
architecture and linkage of active faults, and, in some cases, identify recent earthquake ruptures or
recognize and date individual events. In addition, underwater active tectonics and paleoseismological
studies benefit from: (1) low erosional rates that preserve fault morphology and segmentation; (2)
continuous sedimentation in time and space that allows for local and/or regional stratigraphic and
chronostratigraphic correlations; (3)multiscale seafloor mapping and sub-seafloor seismic imaging; and 4)
absence–or lowest amount–of human modification.
This Research Topic includes fourteen published articles focused in the study of underwater active
tectonic regions or active fault systems around the world