Geometry of the Décollement Below Eastern Bangladesh and Implications for Seismic Hazard

Abstract

With a population of over 160 million, Bangladesh is one of the most densely populated countries in the world (Figure 1a, inset). The country sits on a seismically active fold and thrust belt on the eastern side of the India-Eurasia collision zone that represents the updip tip of an active, oblique subduction zone diving to the east beneath Myanmar (Figures 2 and 3;

New GNSS and Geological Data From the Indo‐Burman Subduction Zone Indicate Active Convergence on Both a Locked Megathrust and the Kabaw Fault

“…We attribute this improvement to the addition of vertical rates and introducing non‐planar faults in our geodetic analysis. Although we cannot determine the shape of the locked portion of the megathrust, we note that the curved geometries determined here are in good agreement with the geologically and geophysically estimated structure of the megathrust (Abdullah et al., 2022; Betka, Seeber, Thomson, Steckler, et al., 2018; Bürgi et al., 2021). Our preferred convergence rate (∼12 mm/yr) is on the lower end of values suggested by previous geodetic work (R. Mallick et al., 2019; Steckler et al., 2016) as our models show that a portion of the Indian‐Shan shortening is also absorbed by the Kabaw Fault, reducing the convergence rate on the megathrust.…”

“…Our megathrust analysis employs interseismic geodetic data sets that predominantly records deep aseismic slip that cannot shed light on the geometry of the locked portion of the megathrust. Nevertheless, our results suggest that the shift from a fully coupled to freely slipping megathrust detachment occurs at a depth of 10-20 km and a longitude of ∼92.4° E. While uncertainty remains as to the exact locking depth, our work specifies the shallowest part of the megathrust that is detectable with our interseismic data set is in reasonable agreement to the depth estimates stemming from geological and seismic constraints (∼7 km; Bürgi et al, 2021;Abdullah et al, 2022). This is an improvement from previous geodetic work that determined locking depths of 25-35 km in a similar position (e.g., R. Mallick et al, 2019;Steckler et al, 2016).…”

“…This line of reasoning follows previous arguments claiming the Indo‐Burma subduction zone is incapable of hosting large megathrust events (Gahalaut et al., 2013; Kundu & Gahalaut, 2012; Le Dain et al., 1984; Ni et al., 1989; Panda et al., 2022). These arguments lean on three lines of evidence regarding the Indo‐Burma interface: (a) it is considered to be a shallow dipping and weak structure (Abdullah et al., 2022; Betka, Seeber, Thomson, Steckler, et al., 2018; Bürgi et al., 2021; Steckler et al., 2008), (b) it lacks evidence for moderate interseismic interplate activity (Kundu & Gahalaut, 2012), and (c) seismic activity in the slab is dominated by North‐South P axes (Purnachandra Rao & Kumar, 1999). We address all of these arguments in the following paragraphs.…”

“…The outermost western folds of the accretionary prism extend above the detachment and are blind, buried by the rapid sedimentation of the GBD (Sikder & Alam, 2003). The anticlines overlie a detachment that is as shallow as 3–4 km in Tripura, India (Betka, Seeber, Thomson, Steckler, et al., 2018), but deepens to the north and south of that culmination (Abdullah et al., 2022; Bürgi et al., 2021; Najman et al., 2016). Farther east in the inner foldbelt, the surface slope increases to 0.5° and structures that overlie the detachment indicate that it dips ∼7° east and deepens to ∼10 km (Betka, Seeber, Thomson, Sincavage, et al., 2018).…”

Risk Analysis of Urban Water Infrastructure Systems in Cauayan City

“…Mapping broad territories for earthquake-induced soil liquefaction danger may appear to be an oxymoron, given that soil liquefaction is a spatially highly limited phenomena in and of itself [17]. In a recent study, they developed combined velocity and fault model that paved the way for further research into seismic segmentation, ground shaking, and rupture modeling [18]. Following the current national earthquake hazard models, the a newly constructed seismogenic source model was established in a paper which includes completely harmonized and cross-border seismogenic sources [19].…”