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

Abstract

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 (Figure 1). They use different datasets (i.e., bathymetry, seismicity from a local seismic network, sub-bottom profiling, reflection seismic profiles or sedimentary cores) to identify and characterize the seismic cycle of active faults using multidisciplinary approaches and innovative methodologies. The main goal of this Research Topic has been to show the present advance in underwater active tectonics and paleoseismology in order to improve our understanding about the seismic and tsunami hazard. Here we provide a short review of the contributions grouped by the main topics.