Source identification of Middle Age extreme event deposits in the Lesser Antilles using forward numerical modeling of tsunami

<p><span>The arc of the Lesser Antilles is one of the most quiet subduction zone in the world. In this region, the convergence of the Atlantic and the Caribbean plates is low (</span><span>few </span><span>mm/year) and most of the seismicity is a</span><span>n</span><span> intraplate and crustal seismicity. Among the Mw>7 earthquakes recorded in the historical catalog (1690 near Barbuda, 1843 near Guadeloupe, 1867 near the Virgin Islands, 1839 offshore Martinica, 1969 offshore Dominica, 1974 near Antigua), only the 1839 and 1843 events are suspected to be interplate earthquakes. The 1867 Virgin Island earthquake generated an important tsunami with waves of 10m that devastated the closest islands. A tsunami followed the 1843 earthquake but without much damage. These two events are the only known damaging tsunami in this region, but another older one might be added to the list. Indeed, an increasing number of tsunami deposits have been identified in the recent years on several islands of the arc, all of them being around 500 years old (~1450 AD). These deposits are all located in the northern segment of the arc, between Antigua and Puerto-Rico, in Anegada, St-Thomas (Virgin Islands), Anguilla </span><span>and</span><span> Scrub islands. There is </span><span>unfortunately</span><span> no record and no testimonies of an extreme event at that time.</span></p><p><span>The northern segment of the arc is particularly complex because located at the transition </span><span>between</span><span> the Greater Antilles </span><span>and the Lesser Antilles</span><span>. </span><span>It</span><span> is crossed by the Anegada Passage, a series of faults and basins cutting through the arc, which defines the limit between the Puerto-Rico micro-plate and the Caribbean plate. This passage and the numerous intra-arc fault systems present between the islands are active and likely compensate for the plates motion. The very low slip deficit detected with GPS measurements at the subduction contacts of Puerto-Rico and the Lesser Antilles indicates that the interface from Guadeloupe to Puerto-Rico can be considered as totally uncoupled or holding the characteristics of a very long seismic cycle. A tsunami generated by an extreme event 500 years ago in this region could be related to </span><span>intra-arc, outer-rise,</span><span> intraplate </span><span>or</span><span> interface fault rupture. The identification of the source </span><span>would</span><span> enable a better understanding of the seismic cycle and the dynamic of this part of the arc.</span></p><p><span>This study lists </span><span>and set models of</span><span> all the potential faults that could trigger an earthquake in the area encompassing the three islands : Anguilla, Anegada and StThomas. </span><span>We have created high-resolution bathymetric grids and</span><span> performed tsunami simulations </span><span>for each fault model</span><span>. </span><span>W</span><span>e uses run-up models to compare the simulated wave heights </span><span>and run-up distance</span><span> to all the deposits heights </span><span>and positions</span><span>. The magnitudes of our fault models range between 7 and </span><span>9,</span><span> but very few of them generate a strong enough tsunami t</span><span>o</span> <span>match</span><span> the observ</span><span>ed deposits</span><span>.</span></p>

Deformation Pattern of the Northern Sector of the Malta Escarpment (Offshore SE Sicily, Italy): Fault Dimension, Slip Prediction, and Seismotectonic Implications

Marine seismic reflection data coupled with on-land structural measurements improve our knowledge about the active deformation pattern of the northern sector of the Malta Escarpment, a bathymetric and structural discontinuity in the near-offshore of Eastern Sicily. As favourably oriented to be reactivated within the Neogene Africa–Europe convergence, it is believed that the Malta Escarpment has a significant role in the recent seismotectonic framework of the Western Ionian Basin and the Hyblean foreland domain of SE Sicily, where some of the largest and most destructive Mediterranean earthquakes are located according to available historical catalogs. Offshore seismic data along with bathymetric grids illuminate the shallow subseafloor setting and allow more accurate mapping of the seafloor expression of previously identified faults in the area. The seismic interpretation and the near-fault sediment pattern analysis provide constraints on fault 3D geometries as well as on their through-time tectonic activity, suggesting also that part of the observed deformation may have been caused by nontectonic processes. Identified faults form currently an E-dipping, roughly N–S trending, and 60 km-long extensional belt deforming the seafloor with a significant displacement amount in the Ionian offshore between Catania and Siracusa. 3-dimensional parameters of faults were then used to derive expected magnitudes and their reactivation propensity. Empirical scaling relationships and forward methods point to a high seismic potential for the detected fault as well as predict the fault slip behavior according to the field-derived differential stress. This combined analysis along with faults displacement measurements pointed out how the longest and most continuous fault could be capable of generating M > 7 seismic events, putting forward strong seismotectonic implications for the adjacent and densely populated Hyblean Plateau. The expected magnitude and the estimated recurrence time interval are compatible with those inferred for large historical earthquakes in the area even if other offshore seismic sources cannot be ruled out.

Marie Tharp’s Ongoing Legacy in Global Seabed Mapping Efforts

<p>The illumination of the seafloor through Marie Tharp’s lens was instrumental in the plate tectonics revolution and fundamentally transformed our understanding of earth processes. Rather than creating traditional contour maps from isolated soundings, her work yielded physiographic diagrams based on sparse echo-sounding profiles that were complemented by stylized views based on her interpretation of the trends and texture of the seafloor. These maps showed the fabric of seafloor in ways that could not have been achieved or communicated with traditional contour plots. Despite the sparseness of the input data, Marie Tharp and Bruce Heezen’s early seafloor maps are remarkably consistent with modern bathymetric maps that are based on orders of magnitude more observations.</p><p>An important part of the legacy of Tharp’s work is codified in the evolution of bathymetric data synthesis efforts led by several of her contemporaries and successors at the Lamont-Doherty Earth Observatory (LDEO). After Tharp’s seminal work transforming bathymetric profiles into the first maps of the global seafloor, efforts were undertaken to digitize echo-sounding profiles creating new opportunities for analysis and integration as well as the development of new software tools and approaches for working with those data. In the 1980s, the availability of multibeam sonars in the academic sector ushered in a new era of mapping by extending the data coverage from profiles to swaths that revealed spatially-continuous areas of the seafloor. The Ridge Multibeam Synthesis (RMBS) Project, which began in the 1990s, built upon Tharp’s early work and sought to advance understanding of the global mid-ocean ridge system by integrating swath data from multiple ships and cruises to create detailed bathymetric grids served online via the early web. Just over a decade later, the Global Multi-Resolution Topography (GMRT) Synthesis emerged as the next generation product under the inspiration of William Haxby. GMRT shifted the focus of effort from the mid-ocean ridges to the global ocean, and presented an efficient scalable solution using a tiled approach for providing access to global bathymetric data at native resolution. GMRT continues today and includes a curated collection of bathymetry data from over 1,100 research expeditions covering more than 9% of the global ocean at 100m spatial resolution. This presentation will describe the legacy of Marie Tharp in the context of the continuity of seabed mapping work at LDEO, including the evolution of bathymetry data synthesis and integration projects and how they connect to complementary efforts in the international arena including the Nippon Foundation – GEBCO Seabed 2030 Project.</p>