AN EXTENSIVE VIRTUAL OUTREACH APPROACH BY SPE DHAKA UNIVERSITY CHAPTER FOR GEOSCIENCE EDUCATION AMIDST THE COVID-19 PANDEMIC

The Society of Petroleum Engineers (SPE) Dhaka University (DU) Chapter in Bangladesh commenced its journey on 1st October 2007. From the beginning, it has always been students-centered and fixated to pique broader geoscience disciplined-based interests of the members and arrange several annual seminars, conferences, lecture programs, workshops, and general meetings. Many of these webinars were led by distinguished geoscience professionals known domestically and globally. Engaging and inspiring students, particularly females, in practical and innovative thinking concerning the present energy crisis and exploring the world’s energy sectors remain the central theme in its offerings. The SPE DU Chapter organized a wide variety of events, emphasizing on technical knowledge regarding the exploration, development & production of petroleum and strengthening the students’ professional and improving soft skills. The COVID-19 pandemic forced the SPE to shift the technical sessions, symposium, and quiz competition online. The SPE also conducted an awareness campaign for COVID-19 via social media. Notably, the SPE organized a webinar on the right mindsets in the new normal situation and stepped in to disseminate general geology-related essential contents to its members and invitees to reduce the learning loss due to the pandemic. Noticing the dwindling oil price because of COVID-19, this chapter arranged a timely virtual lecture program on the future of oil and gas. The SPE DU chapter effectively adjusted its whole operation concerning COVID-19 and the safety of its members. The Geological Excursion and Gas field Visit, Petromania, and Geo-modelling Jumpstart: Software Experience are the other signature events of SPE DU Chapter. The former president of the SPE DU Chapter, Noshin Sharmili, attended the International Petroleum Technology Conference (IPTC) 2020 in Saudi Arabia and obtained the second position in the “Unlock the Reserve” competition. Being motivated, the chapter hosted a pivotal session delivering the tips of a successful application for IPTC Education Week. The SPE DU Chapter and its executive members have received the AAPG Foundation L. Austin Weeks Undergraduate Grant in 2020 and 2021. Furthermore, the SPE DU Chapter has been awarded the Student Chapter Excellence Award for 2021 and 2020. This prestigious award is the second-highest honor a student chapter may receive and is awarded to only 20% of student chapters around the world

Synthesis of the distribution of subsidence of the lower Ganges-Brahmaputra Delta, Bangladesh

Deltas, the low-lying land at river mouths, are sensitive to the delicate balance between sea level rise, land subsidence and sedimentation. Bangladesh and the Ganges-Brahmaputra Delta (GBD) have been highlighted as a region at risk from sea-level rise, but reliable estimates of land subsidence have been limited. While early studies suggested high rates of relative sea-level rise, recent papers estimate more modest rates. Our objective is to better quantify the magnitude, spatial variability, and depth variation of sediment compaction and land subsidence in the lower GBD to better evaluate the processes controlling them and the pattern of relative sea level rise in this vulnerable region. We combine subsidence and compaction estimates from hand-drilled tube wells and historic sites (1–5 mm/y), GNSS and river gauges (4–8 mm/y) and RSET-MH and borehole vertical strainmeters (9–10 mm/y) in SW Bangladesh. The differences between the different types of measurements reflect the different timescales, spatial distribution and depth sensitivity of the different observations. Rates are lower for times >300y providing data on the timescale of compaction. We also observe differences related to the degree to which different devices measure shallow and deep subsidence. Higher values reflect a greater component of subsidence from young shallow deposits from soil compaction and organic matter degradation. Thus, we observe different rates for different environments and physical settings. These differences indicate that in planning adaptation for rising sea level, hard construction with a solid foundation may experience different subsidence rates than open fields or reclaimed land with recent natural or anthropogenic sedimentation. Significance statement: Land subsidence increases the impact of sea level rise. We combine six different types of measurements that examine land subsidence in coastal Bangladesh. The results show that causes of subsidence, including compaction of the sediments varies both spatially and with depth, and that compaction and organic matter degradation from young shallow deposits is a significant contribution to subsidence. This suggests that hard construction with a solid foundation, such as buildings and embankments, may experience a lower subsidence rates than open fields or reclaimed land with recent natural or anthropogenic sedimentation

Sediment Delivery to Sustain the Ganges-Brahmaputra Delta Under Climate Change and Anthropogenic Impacts

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

Locked and loading megathrust linked to active subduction beneath the Indo-Burman Ranges

The Indo-Burman mountain rangesmarkthe boundary between the Indian and Eurasian plates, north of the Sumatra–Andaman subduction zone. Whether subduction still occurs along this subaerial section of the plate boundary, with 46mm/yr of highly oblique motion, is contentious. About 21mm/yr of shear motion is taken up along the Sagaing Fault, on the eastern margin of the deformation zone. It has been suggested that the remainder of the relative motion is taken up largely or entirely by horizontal strike-slip faulting and that subduction has stopped. Here we present GPS measurements of plate motions in Bangladesh, combined with measurements from Myanmar and northeast India, taking advantage of a more than 300 km subaerial accretionary prism spanning the Indo-Burman Ranges to the Ganges–Brahmaputra Delta. They reveal 13–17mm/yr of plate convergence on an active, shallowly dipping and locked megathrust fault. Most of the strike-slip motion occurs on a few steep faults, consistent with patterns of strain partitioning in subduction zones. Our results strongly suggest that subduction in this region is active, despite the highly oblique plate motion and thick sediments. We suggest that the presence of a locked megathrust plate boundary represents an underappreciated hazard in one of the most densely populated regions of the world

Lithologic mapping of a forested montane terrain from Landsat 5 TM image

Thick forest cover and poor infrastructures are the major hindrances for detailed lithologic mapping in an inaccessible montane landscape. To overcome these limitations, we utilize a Landsat 5 TM image to map lithology using vegetation and drainage pattern as an indicator of underlying rock types in a heavily forested region of the Chittagong Hill Tracts area located in southeastern Bangladesh. We use supervised and unsupervised classifiers for a vegetation-based approach while on-screen digitization is used for drainage patterns-based mapping. Field observations were used for mapping lithology and evaluating accuracy. Overall, our results agree well with the current geologic map and improve it by providing a more spatially detailed distribution of the sandstone and shale. The performances of all approaches are good at the inner and outer flanks of anticlines located in the study area while the drainage pattern mapping performs best at the mid-flank area

Geometry of the décollement below eastern Bangladesh and implications for seismic hazard

Eastern Bangladesh sits on the seismically active Chittagong-Myanmar fold and thrust belt (CMFB), a north-trending accretionary wedge on the eastern side of the India-Eurasia collision. Earthquakes on the basal décollement and associated thrusts within the CMFB present a hazard to this densely populated region. In this study, we interpret 28 seismic reflection profiles from both published and unpublished sources to constrain the depth of the basal décollement. To convert profiles from the time domain to the depth domain, we integrate sonic log and seismic stacking velocity data to generate time-velocity relationships for different parts of the CMFB. Our analysis reveals that the décollement is ∼9 km deep in northeast and southeast Bangladesh, but shallows to ∼5 km in east-central Bangladesh. The décollement has an area of 7.25 × 104 km2 (∼150 × 450 km), making it capable of an Mw 8.5 earthquake. However, the warped geometry of this fault might act as a rupture barrier were a large earthquake to occur on the décollement. Our combined velocity and fault model lay the groundwork for future studies to address seismic segmentation, ground shaking, and rupture modeling in the CMFB. Finally, we use our compiled data set to analyze the evolution of fold kinematics in the CMFB. We observe that folding style and failure mode varies, from mainly ductile deformation in the foreland to mainly brittle in the hinterland. The dual-failure modes within the CMFB support the hypothesis that a region with ductile deformation may still be capable of seismic behavior.Ministry of Education (MOE)Nanyang Technological UniversityNational Research Foundation (NRF)Published versionThis research was supported by the National Research Foundation Singapore under its Singapore NRF Fellowship scheme (NRF award NRF-NRFF2013-06), by the Earth Observato-ry of Singapore (EOS), by the Singapore Ministry of Education (MOE) under the Research Centers of Excellence initia-tive, and by a Nanyang Technological University Startup grant. This is EOS contribution number 255

Maintenance of a seismic network in Bangladesh and an initial earthquake catalog

Bangladesh is a densely populated country located on the north-eastern side of the India-Eurasia collision zone. The eastern half of the country is underlain by the seismically active Chittagong-Myanmar Fold and Thrust Belt, which forms the accretionary prism associated with the eastward-subducting Indian Plate, and is bordered to the north by the Dauki thrust fault, which bounds the southern margin of the actively rising Shillong Plateau. Two great earthquakes occurred here in 1897 (~Mw8.0) and 1762 (~Mw8.5). The seismic hazard in this region is poorly constrained due to questions about slip partitioning between the frontal and splay faults of the fold and thrust belt, whether faults will eventually slip at seismic speeds, and how shaking will be amplified and/or attenuated by the thick sedimentary cover. Seismic monitoring of the region can help to address these questions. In 2016, a collaborative effort between the Earth Observatory of Singapore and Dhaka University led to the installation of a network of 22 Lennartz 1-Hz (Short-period) and 6 Trillium Compact 120-s (Broadband) seismometer stations along the north-eastern (Sylhet region) and south-eastern (Chittagong region) parts of Bangladesh. The aim of this network is to monitor seismicity and to develop a better understanding of the subsurface structure in the region. This network has been actively running for over 4 years. The stations are spaced about 15 to 30 km apart, and are installed in either outdoor shallow vaults, or in above ground indoor locations on solid foundations, depending on local conditions. The stations are visited every 3 to 5 months for data collection, as well as repair and maintenance work. Here we discuss challenges faced and overcome during the deployment associated with environmental conditions (soil, plant growth, monsoon flooding, soil erosion, and cyclones) as well as arising from human and wildlife interference, political instability, and the COVID pandemic. We present various solutions that were implemented to mitigate or eradicate these problems. We have derived a preliminary catalog of earthquake locations consisting of >1100 events, and also detected >130 teleseismic events; event locations are currently being refined. Our data will provide a better understanding of the seismic activity and subsurface geology of the region

DataSheet1_Characterization and spatiotemporal variations of ambient seismic noise in eastern Bangladesh.docx

This study analyses the ambient noise field recorded by the seismic network, TREMBLE, in Bangladesh, operational since late 2016. Horizontal-vertical spectral ratios confirm the placement of stations on sediment, many situated on thick sedimentary columns, consistent with local geology. Noise across the broadband spectrum is systematically examined. A high amplitude local microseism (0.4–0.8 Hz) is recorded, originating near the coast and modulated by local tides. The secondary microseism (0.15–0.35 Hz) correlates strongly with wave height in the Bay of Bengal and varies with seasons, with greater power and higher horizontal amplitude in the monsoon season when the wave height is highest. The microseism increases in amplitude and decreases in frequency as a tropical depression moves inland. The primary microseism (∼0.07–0.08 Hz) exhibits no seasonal changes in power but display strong horizontal energy which changes with seasons. Low frequency (0.02–0.04 Hz) noise on the horizontal components has a 24-h periodicity, due to instrument tilt caused by atmospheric pressure changes. A station located next to the major Karnaphuli River shows elevated energy at ∼5 Hz correlated to periods of high rainfall. Anthropogenic noise (∼4–14 Hz) is station-dependent, demonstrating changing patterns in human activity, such as during Ramadan, national holidays and the COVID pandemic. Our work holds implications for seismic deployments, earthquake, and imaging studies, while providing insights into the interaction between the atmosphere, ocean, and solid Earth.</p

Stepwise, earthquake-driven coastal subsidence in the Ganges-Brahmaputra Delta (Sundarbans) since the eighth century deduced from submerged in situ kiln and mangrove remnants

This study reconstructs the coastal subsidence over the past 1300 years in a mangrove region along the coast of the Ganges-Brahmaputra Delta, an area not affected by anthropogenic interference. The relative sea level (RSL) history is based on radiocarbon and luminescence ages measured on 108 submerged kilns and in situ mangrove stumps. While the regional, long-term average subsidence rate is calculated to be 2.7 +/- 0.3 mm/yr, modern RSL (including eustacy, isostasy, ocean level, and subsidence) rises by 8.7 +/- 0.4 mm/yr. This rate has been balanced by natural sediment accretion so far. A reduction in sediment supply by engineering projects along rivers and coasts may, however, accelerate coastal inundation and retreat. Subsidence has accelerated during specific episodes since the eighth century. A major land-sinking event happened in the eighteenth century, with a downward displacement of 1-2 m, depending on geographic area. We propose that the subduction-related 1762 Arakan earthquake caused this sudden lowering. Prior to this event, RSL was nearly stable for 900 years. An earlier major subsidence event occurred around 900 CE, when the land suddenly sank by about 1 m, which also coincided with a major earthquake along the Arakan coast. Event-driven, sudden, significant subsidence, thus, needs to be considered a potential major hazard for coastal Bangladesh