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Submarine paleoseismology hinges on analyzing stratigraphic records to learn about past earthquakes. Marine microfossils, such as foraminifera, can reveal critical details about the water depth of the sediment remobilized during earthquakes.Although allochthonous foraminifera are typically excluded from age control studies, these faunas are useful in providing insight into the water depth from which a sediment transport deposit originated. As an example, we describe a ~16 m thick Holocene sedimentary deposit first defined by Kioka et al. (2019) and later dated to 1.77 (+0.49/−0.31) ka by Usami et al. (2021) and Schwestermann et al. (2021) based on bulk OC, C-14. Strasser et al. (InPress) identified the event at IODP Expedition 386 Sites M0084, M0086, and M0088, located at hadal depths in the northern Japan Trench. Each site features a basal 1 to2 m thick, fining-upward medium sand to silt with well-defined planar and ripple lamination. The sequence has been interpreted as a turbidite composed of basalsand grading into silty clay that is overlain by a mass transport deposit. Calcareous foraminifera occur in the deposit despite being well below the CCD. Foraminiferal abundance decreases from the basal sand to the fi ne silty clay due to gravitational size sorting. Most displaced foraminifera, including thin-shelled taxa, are moderatelyt o well-preserved, likely due rapid burial, high alkalinity, and low internal friction within the flow. The foraminiferal assemblages are consistent across the three sites. The sandy portion of the deposit is dominated by Elphidium batialis, Uvigerina akitaensis, Nonionellina labradorica, Chilostomellina fi mbriata, and species of Bulimina, indicative of upper to middle bathyal depths (200 to 1000 m). In contrast, the silty clay contains smaller foraminifera like Bolivina, Cassidulina, Stainforthia and Epistominella, suggesting outer neritic to upper bathyal depths (100 to 600 m). Radiocarbon dating of the foraminifers within the basal sand from each site reveals that M0086 (16750 to 16200 cal BP) and M0088 (16650 to 16050 cal BP) have younger source ages compared to M0084 (19350 to 18800 cal BP). These findings indicate that the ~1.77 ka sediment transport event entrained much older strata that had originated in upper to middle bathyal depths and outer neritic to upper bathyal depths. 

Abstract. Large subduction earthquakes can rupture the shallow part of the megathrust with unusually large displacements and tsunamis. The long duration of the seismic source and high upper-plate compliance contribute to large and protracted long-period motions of the outer upper plate. The resulting shear stress at the sediment–water interface in, for example, the Mw 9.0 2011 Tohoku–Oki earthquake could account for surficial sediment remobilization on the outer margin. We test this hypothesis by simulating in physical tank experiments the combined effects of high- and low-frequency seismic motions on sediment of different properties (chemistry, grain size, water content, and salinity). Our results show that low-frequency motion during a 2011-like earthquake can entrain several centimeters of surficial sediment and that entrainment can be enhanced by high-frequency vertical oscillations. These experiments validate a new mechanism of co-seismic sediment entrainment in deep-water environments. 

The largest known earthquakes ruptured megathrusts at subduction boundaries. The largest among these ruptured the entire seismogenic depth range up to the seafl oor and have generated enormous regionally destructive tsunamis. This type of rupture that breaches the sea-fl oor is fortunately rare, but, as a result, the most recent ones, M9.2 Sumatra in 2004 and the M9.0 Japan in 2011, were unexpected and thus caused great damage. We don’t know where and when they can occur again. Our approach has been to compare earthquake event deposits in various ocean settings (IODP Expedition 386, Japan 2021; Jamaica Passage 2022; Bay of Bengal 2024) and to study the entrainment processes (shaking tank experiments) and search for distinguishing features in the depositional record. We are now revealing techniques that involve the use of isotopes and chemistry to characterize earthquake related event deposits. We identifi ed thick, acoustically homogeneous layers “homogenites” that have homogeneous radiogenic isotope (Nd, Sr, Pb) signatures, unlike the background sediments. Additionally, TOC%, N% and d C, d N, show distinct signatures relative to the background. These isotopic signatures correspond perfectly well with lithology, physical properties and X-CT scans in the thick homogenites. Using these techniques we recognize the 1454 AD Kiatoka and 869 AD Jogan events in the Japan Trench that were tsunamigenic and possibly ruptured the seafl oor. While each of these events has unique signatures, there are common threads and these fi ndings lay the groundwork to go back in time and better characterize older Mw9.0 ruptures. One of the most signifi cant contributions to this effort is the recognition of M9.0 2011 Tohoku tsunamigenic earthquake in the Japan Trench. Short-lived radioisotopes help to document the extent of the remobilized sediment. This event has provided unique insights due to the Fukushima nuclear reactor radioisotopes measured in the Japan Trench as far as ~200km from its source. The use of these techniques provides tools for recognizing tsunamigenic earthquakes in other subduction boundaries such as Cascadia. 

Abstract The Enriquillo–Plantain Garden fault (EPGF), the southern branch of the northern Caribbean left-lateral transpressional plate boundary, has ruptured in two devastating earthquakes along the Haiti southern peninsula: the Mw 7.0, 2010 Haiti and the Mw 7.2, 2021 Nippes earthquakes. In Jamaica, the 1692 Port Royal and 1907 Great Kingston earthquakes caused widespread damage and loss of life. No large earthquakes are known from the 200-km-long Jamaica Passage segment of this plate boundary. To address these hazards, a National Science Foundation Rapid Response survey was conducted to map the EPGF in the Jamaica Passage south of Kingston, Jamaica, and east of the island of Jamaica. From the R/V Pelican we collected >50 high-resolution seismic profiles and 47 gravity cores. Event deposits (EDs) were identified from lithology, physical properties, and geochemistry and were dated in 13 cores. A robust 14C chronology was obtained for the Holocene. A Bayesian age model using OxCal 4.4 calibration was applied. Out of 58 EDs that were recognized, 50 have ages that overlap within their 95% confidence ranges. This allowed for their grouping in multiple basins located as much as 150 km apart. The significant age overlap suggests that EDs along the Enriquillo–Plantain Garden plate boundary resulted from large and potentially dangerous earthquakes. Most of these earthquakes may derive from the EPGF but also from thrust faulting at this strain-partitioned transpressional boundary. The recent increase in Coulomb stress on the EPGF from the Mw 7.2 Nippes earthquake in southwestern Haiti and the discoveries reported here enhance the significance for hazard in the Jamaica Passage.