SCIENTIFIC JUSTIFICATION AND WORKPLAN
1. Detailed description of the research topic
Seismogenic fault models and active deformation models together with earthquake rate models and earthquake probability models were recently collectively used in time-independent models that allow to estimates the magnitude, location, and likelihood of potentially damaging earthquake ruptures in regions with high natural seismic hazard (e.g. the California region; Field et al., 2015 and references therein). Improvements of seismogenic fault models imply the recognition of the spatial geometry of the larger, more active faults, deemed to be the source of the most damaging future earthquakes, performed through the acquisition of new data as well as the revision of compilation of active fault systems from a review of the literature or existing databases. However, identifying active faults and calculating their geologic slip rates for deriving their earthquake rates are not an easy task for regions inaccessible to direct field studies like active offshore area. This is an important limitation for Probabilistic Seismic Hazard Assessment (PSHA) of densely populated coastal areas, such as the regions around the central Mediterranean. In recent years, many government funded research projects aimed at realizing databases of active and seismogenic faults. For example, the European Community has funded the project “SHARE” that aimed to establish new standards in PSHA, by using data derived from multiple disciplines spanning from geology to seismology and earthquake engineering, and to compile an European database of active faults and seismogenic sources that cover the Euro-Mediterranean area. In Italy, the Database of Individual Seismogenic Sources (DISS) represents “the most advanced georeferenced repository of tectonic faults and paleoseismological information devoted, but not limited, to potential applications in the assessment of seismic hazard at regional and national scale”. Nevertheless, although these projects represent a synthesis of the most advanced knowledge regarding the active fault systems in Europe, at present little information is available in these databases on the geometry of the larger and more active faults present in the offshore areas, or when active fault systems have been included only in few cases their identification was based on modern studies.
A review of the recent literature shows that active tectonic studies in offshore areas generally use high-resolution seafloor imaging to identify the surficial expression of active faults in terms of sea-floor displacements, while high-resolution seismic profiles collected perpendicular to the active structures are used to identify growth strata in the Quaternary units, to be used for quantifying their present-day tectonic activity (e.g. Gràcia et al., 2006). Major issue of the active tectonic studies in the offshore areas is the impossibility of having direct evidence of active deformation and their incomplete record. Hence, most of the times the identification of active structures is 1) guided by onshore and coastal studies, when the fault systems are located in both offshore and onland sectors, and 2) relies at first on low-resolution regional studies that mapped the tectonic structures. However, this approach is very expensive and time-consuming in term of data acquisition, processing and interpretation. For these reasons, the spatial geometry of many active faults system and their Late Pleistocene-Holocene activity and slip rates are mostly unknown. As consequence, active faults in offshore area are often not considered in seismogenic fault and active deformation models. Consequently, a crucial research question to improve the Probabilistic Seismic Hazard Assessment of coastal areas characterized by high probability for earthquake occurrence is “how can we identify the spatial geometry and slip rates of the active offshore fault systems fundamental for probabilistic long-term earthquakes forecasting of coastal regions?”
Recently, it has been proposed that Infralittoral Prograding Wedges (IPWs) and their associated terrace-shaped upper boundary are reliable indicators of the paleo sea level and, as consequence, can be used as vertical movement indicators in offshore settings (e.g. Chaytor et al., 2008; Fraccascia et al., 2013 and references therein). The SPW formed worldwide during the sea level still-stand of the Last Glacial Maximum (LGM). They can be detected in high-resolution seismic reflection profiles along the distal sector of the continental shelf and upper slope. Pepe et al., 2014 on the basis of the analysis of the present-day depth variation of the edges of SPWs documented a difference in the post-LGM vertical tectonic movements between the SW and NE offshore sectors of the Capo Vaticano Promontory (western Calabria, southern Italy). The result was consistent with that recorded onshore by Pleistocene coastal terraces, which were widely used as markers to reconstruct the vertical movements along the coastal area at 102 ka timescale (e.g. Cucci et Tertulliani, 2010 and references therein). Thus, the magnitude and rate of Late Pleistocene-Holocene vertical tectonic movements that can be inferred from SPWs fill an information gap between the underwater and exposed domains and reconcile independent observations on the pattern and rate of vertical motion at local scale between the 102 ka to the 1 ka timescale. This finding is particularly significant because vertical tectonic motions (uplift/subsidence) are typically difficult to estimate in offshore settings. However, the methodological approach that allow to infer differential vertical movements along the continental shelf and upper slope that are the result of movements along active offshore faults on the basis of analysis of the present-day depth variations of the rollower of the IPWs has never been rigorously proposed.
To fill the data gap and provide additional constraints for probabilistic seismic hazard analysis of urban centers located near coastal areas, we aim at developing a novel, low-cost method to identify and characterize active faults or fault systems in near offshore areas and to reconstruct the recent history of movements along the fault planes. The development of the methods will focus on the innovative combination of geophysical data obtained from high-resolution, underwater acoustic methods (i.e. seismic reflections and multibeam echosounder) and potential fields with constrains derived from physical experimental investigation of geomorphological indicators (i.e. infralitoral prograding wedge), and absolute age of benchmarks recognized on gravity core data.
Experimental campaign will be focused on the analysis of the bed morphology under different hydrodynamic conditions with the aim of understanding the geological/oceanographic factors (e.g. sedimentary supply, fetch, bottom current, tide, eustatic sea-level change) that control the depth of formation of the SPW. The addition of an orthogonal current will allow to better understanding the effect of wave current interaction on the structure of the bed boundary layer, which in turn has repercussions on sediment transport and bed morphology. Potential fields are fruitfully used to decipher active tectonics structures in offshore areas. As matter of fact, fault activity may put in contact rocks with different susceptibility and/or density creating the condition to develop crustal magnetic and/or gravimetric anomalies. Physical properties variations may also arise from the temperature and pressure changes occurring along the fault planes. This usually happens inside the sedimentary bodies and in the underlying basement which is generally characterized by a higher magnetic susceptibility. The above mentioned conditions may possibly illuminate fault position and kinematics where has not a surficial expression. In some cases it may help to overcome the aforesaid lack of seafloor geomorphic evidences in identifying active faults. Several examples in different geodynamic environments exist worldwide, among them the more meaningful are the Canadian and United States Western Coast (Blakely at al., 2002, Brian et al., 2007, Sherrod et al., 2007, Klemperer and Gary Ernst, 2003) in the Cascade Range-Juan de Fuca Strait and the S. Francisco Bay- northern strand of the S. Andreas Fault. In these contexts magnetic and gravimetric data interpretation have allowed to revise and extend the position of buried or partially buried faults in between offshore and onshore sectors, also shading light on their potential active nature (Grauch and Ruleman; 2013).
2. The expected impact of the project is in five levels:
The main scientific impact of the project is to develop:
- an innovative, accurate, reliable and cost-effective geophysical method to specify the spatial geometry of active offshore faults at local and regional scale by using SPWs and associated abrasion platforms as short-term displacement markers. Our method is expected to be useful for improving seismogenic fault modeling and active deformation modeling for regions with high seismic hazard.
- an innovative method to quantitatively reconstruct the Holocene to late Pleistocene history of movements along active offshore faults through absolute dating of benchmarks from gravity cores collected in the near-faults area, where high-resolution seismic imaging highlights stratigraphic evidence of seismic activity.
- a guideline for required data collection (e.g. high-resolution seismics, multibeam and coring data) to employ the newly developed method.
- a strong basis for future collaboration and scientific international networking for scientists and academic research organizations from both Italy and Israel. This collaboration will result in scientific publications in peer-reviewed journals and international conferences, and can provide a basis for formation of joint EU/international workgroups in the fields of tectonics and earthquake hazard in the future.
At the EU and Italian level:
- The main impact of the project is to help at developing innovative geophysical methodologies that can be applied within Collaborative Project in the Cooperation Programme of the Seventh Framework Program of the European Commission like ‘European Database of Seismogenic Faults’ (EDSF, http://diss.rm.ingv.en/share-EDSF/), and the Italian ‘Database of Individual Seismogenic Sources (DISS, http://diss.rm.ingv.it/diss/)’ that have many shortcomings in terms of the completeness and the source model geometry in offshore areas.
At the Israeli level:
- The main impact of the project is to help at developing innovative geophysical methodologies for earthquake forecasting to apply in active tectonic basins offshore (which are relevant in Israel too: e.g. the Gulf of Eilat in the Red Sea, the Sea of Galilee, or the Dead Sea).
- The Italian researchers will transfer their vast knowledge and experience in using seismic methodologies to study active tectonic marine environments to the Israeli researchers (which usually work on less tectonic basins in the Mediterranean). Although the Israeli PI (Dr. Mor Kanari) is an early career scientist, he will be escorted and advised by the experienced Israeli Co-Investigator (Dr. Gideon Tibor). Additionally, he will benefit much from working with the experienced researchers from Italy.
The social impact of the project:
- Developing a new methodology for earthquake forecasting based on relatively simple geophysical data collection contributes and augments the ability of human society for planning and preparing for earthquake occurence. The end-users of all earthquake hazard and preparation policies are the people and infrastructure subjected to earthquake hazard.
The economic impact of the project is to provide:
- contribution to develop low-cost, geophysical methodology for the definition of ‘Probabilistic Long-Term Forecasting Models’ of offshore areas that uses the large amount of geophysical data acquired by marine research institutes over the last decades in the frame of national geological hazard project (e.g. project Magic, Carg, PRIN). For the past two years, the Israeli Ministry of Infrastructures, Energy and Water Resources is leading a project of creating a geo-hazard map in the frame of planning future marine infrastructure. Additionally, IOLR is involved in developing the Israeli Tsunami Warning System, which is based on modeling and detailed bathymetry and fault location. We expect the tools developed in the proposed study to provide important data and knowledge basis for the tsunami hazard project.