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Abstract Earthquakes present severe hazards for people and economies and can be primary drivers of landscape change yet their impact to river-channel networks remains poorly known. Here we show evidence for an abrupt earthquake-triggered avulsion of the Ganges River at ~2.5 ka leading to relocation of the mainstem channel belt in the Bengal delta. This is recorded in freshly discovered sedimentary archives of an immense relict channel and a paleo-earthquake of sufficient magnitude to cause major liquefaction and generate large, decimeter-scale sand dikes >180 km from the nearest seismogenic source region. Precise luminescence ages of channel sand, channel fill, and breached and partially liquefied floodplain deposits support coeval timing of the avulsion and earthquake. Evidence for reorganization of the river-channel network in the world’s largest delta broadens the risk posed by seismic events in the region and their recognition as geomorphic agents in this and other tectonically active lowlands. The recurrence of comparable earthquake-triggered ground liquefaction and a channel avulsion would be catastrophic for any of the heavily populated, large river basins and deltas along the Himalayan arc (e.g., Indus, Ganges, Brahmaputra, Ayeyarwady). The compounding effects of climate change and human impacts heighten and extend the vulnerability of many lowlands worldwide to such cascading hazards. 

We utilized shear wave splitting analysis of teleseismic SKS, SKKS, and PKS phases to infer upper mantle deformational fabrics across a substantial area of Southeast Asia, where splitting measurements were previously limited. We used newly available permanent and temporary broadband seismic networks deployed across the Indo-Burma subduction zone and the eastern Indochina peninsula. The resulting 492 well-constrained splitting and 654 null measurements from 185 stations reveal clear large-scale patterns in the mantle deformational fabrics in response to the highly oblique active subduction and a large transform plate boundary. We identified two distinct domains of mantle deformation fabrics in the western Burma microplate and the eastern Indochina peninsula. In the former, trench parallel N-S fast polarization directions with an average lag time (δt) of 1.9 s are observed beneath the Indo-Burman Ranges. We suggest the observed splitting is partly due to anisotropy in the sub-slab region and relates to shear induced by the north moving Indian plate. The lithospheric fabric within the Indo-Burman Ranges and underlying subducting slab fabric contribute to produce the observed average δt of 1.9 s. The δt value decreases to an average of 1.0 s towards the back-arc until we reach the dextral Sagaing fault. In the second domain, starting approximately 100 km east of the Sagaing fault, we observe a consistent E-W fast direction with an average δt of 1.10 s in the eastern Shan-Thai and Indochina blocks. We interpret the E-W fabric as due to the deformation associated with the westward spreading of the Hainan mantle plume, possibly driven by overriding plate motion. Low velocities in the shallow mantle and late Cenozoic intraplate volcanism in this region support the plume-driven asthenospheric flow model in the Indochina peninsula. The sudden transition of the fast polarization direction from N-S to E-W along the eastern edge of the Burma microplate indicates the Sagaing fault acts as a mantle flow boundary between the subduction dominated trench parallel flow to the west and plume induced asthenospheric flow to the east. We also observed no net splitting beneath the Bengal basin which is most likely due to the presence of frozen vertical fabric resulting from the Kerguelen plume activity during Early Cretaceous. 

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. 

This supplemental text (pp. 2-4) describes the analytical procedures for the detrital zircon fission track (dzFT) and detrital zircon U-Pb analyses (dzUPb). Sample locations are listed in supplemental file S1. The new dzUPb analytical data are presented in supplemental file S2. Supplemental files S3, S4, and S5 give the data sets used in the regional dzUPb compilations, a list of the compiled data, and the intersample comparison statistical results for the dzUPb compilations, respectively. Supplemental S6 contains the Monte-Carlo modeling results for the source terrane inversions using DZMix (Sundell and Saylor, 2017). Supplemental file S7 contains the full data tables and a summary of the dzFT results. All prior datasets were compiled from the supplemental files released with the original publications.</p> 

Abstract The principal nature-based solution for offsetting relative sea-level rise in the Ganges-Brahmaputra delta is the unabated delivery, dispersal, and deposition of the rivers’ ~1 billion-tonne annual sediment load. Recent hydrological transport modeling suggests that strengthening monsoon precipitation in the 21st century could increase this sediment delivery 34-60%; yet other studies demonstrate that sediment could decline 15-80% if planned dams and river diversions are fully implemented. We validate these modeled ranges by developing a comprehensive field-based sediment budget that quantifies the supply of Ganges-Brahmaputra river sediment under varying Holocene climate conditions. Our data reveal natural responses in sediment supply comparable to previously modeled results and suggest that increased sediment delivery may be capable of offsetting accelerated sea-level rise. This prospect for a naturally sustained Ganges-Brahmaputra delta presents possibilities beyond the dystopian future often posed for this system, but the implementation of currently proposed dams and diversions would preclude such opportunities. 

Abstract The Indo‐Burma subduction zone is a highly oblique subduction system where the Indian plate is converging with the Eurasian plate. How strain is partitioned between the Indo‐Burma interface and upper plate Kabaw Fault, and whether the megathrust is a locked and active zone of convergence that can generate great earthquakes are ongoing debates. Here, we use data from a total of 68 Global Navigation Satellite System (GNSS) stations, including newly installed stations across the Kabaw Fault and compute an updated horizontal and vertical GNSS velocity field. We correct vertical rates for fluctuating seasonal signals by accounting for the elastic response of monsoon water on the crust. We model the geodetic data by inverting for 11,000 planar and non‐planar megathrust fault geometries and two geologically viable structural interpretations of the Kabaw Fault that we construct from field geological data, considering a basin‐scale wedge‐fault and a crustal‐scale reverse fault. We demonstrate that the Indo‐Burma megathrust is locked, converging at a rate ofmm/yr, and capable of hosting >8.2M_wmegathrust events. We also show that the Kabaw Fault is locked and accommodating strike‐slip motion at a rate ofmm/yr and converging at a rate ofmm/yr. Our interpretation of the geological, geophysical, and geodetic datasets indicates the Kabaw Fault is a crustal‐scale structure that actively absorbs a portion of the convergence previously ascribed to the Indo‐Burma megathrust. This reveals a previously unrecognized seismic hazard associated with the Kabaw Fault and slightly reduces the estimated hazard posed by megathrust earthquakes in the region. 

ABSTRACT Constraining time is of critical importance to evaluating the rates and relative contributions of processes driving landscape change in sedimentary basins. The geomorphic character of the field setting guides the application of geochronologic or instrumental tools to this problem, because the viability of methods can be highly influenced by geomorphic attributes. For example, sediment yield and the linked potential for organic preservation may govern the usefulness of radiocarbon dating. Similarly, the rate of sediment transport from source to sink may determine the maturity and/or light exposure of mineral grains arriving in the delta and thus the feasibility of luminescence dating. Here, we explore the viability and quirks of dating and instrumental methods that have been applied in the Bengal Basin, and review the records that they have yielded. This immense, dynamic, and spatially variable system hosts the world's most inhabited delta. Outlining a framework for successful chronologic applications is thus of value to managing water and sediment resources for humans, here and in other populated deltas worldwide. Our review covers radiocarbon dating, luminescence dating, archaeological records and historical maps, short‐lived radioisotopes, horizon markers and rod surface elevation tables, geodetic observations, and surface instrumentation. Combined, these tools can be used to reconstruct the history of the Bengal Basin from Late Pleistocene to present day. The growing variety and scope of Bengal Basin geochronology and instrumentation opens doors for research integrating basin processes across spatial and temporal scales. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.