Eastern Flank Research Articles

Comprehensive classification of Red-colored Serie rocks from the eastern flank of the South Caspian Basin (Jigalybek field) based on reservoir and geophysical properties

The Absheron-Prebalkhanian tectonic zone, known as the Absheron threshold, has been the subject of extensive study by researchers for nearly hundred years. This region holds significant interest due to its strategic location between the well-known oil and gas-bearing areas of Absheron and Cheleken. This paper presents a comprehensive classification of Red-colored Serie (RCS) rocks from the Jigalybek (Jdanov Bank) field (located in the eastern part of the South Caspian Basin) based on reservoir and geophysical properties. The study includes a detailed analysis and classification of rocks into different classes, considering both reservoir and non-reservoir properties. A total of 42 core samples were analyzed to determine key geophysical parameters, including R-1-R-5, ρLL, SP, ΔJγ, ΔJpγ, and Δd. The analysis revealed four distinct classes of rocks based on their reservoir properties, identifying two types of highly permeable and moderately permeable reservoirs, and two types of non-reservoirs comprising compacted low-permeability clays and pure clays. The geophysical classification further differentiated the rocks into oil-bearing, water-bearing, and non-reservoir types, emphasizing the geophysical signatures that distinguish between these categories. A comprehensive classification approach was also applied, combining six reservoir properties and ten geophysical parameters to refine the distinction between water-saturated and oil-saturated reservoirs. The study demonstrated that water-saturated reservoirs are generally more clay-rich and less porous than oil-saturated reservoirs, providing a robust methodology for identifying and characterizing different types of reservoirs in the field. Such a classification system is valuable for improving the accuracy of reservoir identification and characterization, leading to better resource management and extraction strategies in the Jigalybek field. The results underscore the importance of integrating multiple geophysical and reservoir parameters to achieve a more precise classification and understanding of subsurface rock properties.

New insights into the thermo‐tectonic development of the Suez rift within the framework of the northern Arabian–Nubian Shield

AbstractThe Gulf of Suez is a young continental rift, the flanks of which make up the Arabian–Nubian Shield basement complex that formed during the East African Orogeny. The impact and significance of the consecutive tectono‐thermal activities on the Arabian–Nubian Shield and the rifting processes in the Gulf of Suez remain uncertain. Combining zircon and apatite fission‐track dating with time–temperature modelling has been effective in addressing these issues. We here present thermochronological data for 20 basement samples collected from the Samra Mountain region at the northern tip of the Gulf of Suez's eastern flank. Zircon fission‐track data revealed two age groups separated spatially and dating from ca. 652 ± 25 Ma and ca. 426 ± 31 Ma. In contrast, apatite fission‐track data revealed three spatially separated age groups dating from ca. 473 ± 10 Ma, ca. 269 ± 29 Ma and ca. 101 ± 12 Ma. Reconstructed time–temperature historical records revealed four distinct rapid cooling pulses (i.e. Neoproterozoic, Devonian–Carboniferous, Cretaceous and Oligocene–Miocene) consistent with the tectonic history and regional geology. By integrating our findings with the regional tectonic and sedimentation histories, the relationship between cooling events and exhumation events could be inferred. These cooling pulses were activated in response to four events: (1) the Precambrian–Cambrian post‐accretion erosional event, (2) the Devonian–Carboniferous Variscan tectonic event, (3) the Cretaceous Gondwana disintegration and (4) the Oligocene–Miocene Gulf of Suez rifting, respectively. In the studied region, no thermal overprint was seen in association with the rifting in the Gulf of Suez, suggesting that the region had been segmented into northern and southern segments. A southward thermal source, the Arabian margin plume, caused an increase in the rift flank elevation and heat flow in the southern Sinai.

Oil characteristics and the onset of biodegradation on the eastern flank of the Malay Basin, offshore Peninsular Malaysia

There is a great variety of oil types in the eastern Malay Basin flank area. We observe heavier, hence lower quality, oil at shallow reservoir levels, but mostly light oil in deeper petroleum reservoirs. The oils are characterized by varying amounts of wax, a fairly low sulphur content and, occasionally, significant levels of CO2. Many of the shallow reservoir oils appear to have been derived from originally light oils that suffered from biodegradation, and are slightly enriched in sulphur, compared to the native oils. Oils in reservoirs with a temperature of less than 75 °C appear to have been biodegraded, whereas hotter reservoirs with temperatures above 90 °C appear to have been unaffected.

Heat Flow of Continental Rift Zones: A New Approach to Data Evaluation

The features of heat flow distribution in some rift zones are considered, namely: the Baikal rift zone, the Shanxi–Liaohe rift, the Jordan rift, the Orel Trough (Sture) in the north of the Svalbard plate, as well as the rift zone of Iceland. Heat flow asymmetry relative to the rift centerline is also noted against the increased heat flow background in the rift zone compared to adjacent areas. The nature of such asymmetry is connected not only with the different faults permeability on the sides but also with planetary factors – forces acting on a rotating planet, in particular, with the Coriolis force. Heat flow increase on the eastern flanks compared with the western flanks in the considered rifts of the meridional strike is consistent with the Coriolis force vector in the Earth Northern Hemisphere.

3D seismic velocity models from local earthquake tomography furnish new insights on the Mount Etna volcano (Southern Italy)

We present a new seismotomography investigation providing a 3-D overall model of Vp, Vs and Vp/Vs for Mt. Etna, the largest and most active volcano in Europe. We estimated and jointly evaluated P- and S-wave velocity patterns together with the Vp/Vs ratio, particularly useful to discriminate the presence of groundwater, gas, and melts and thus very precious for volcano investigations. We applied the LOTOS software to ~ 4600 crustal earthquakes that occurred in the Etnean area during the last 26 years, the longest time-interval ever analysed for Mt. Etna. This wide dataset has allowed us to characterize the volcano velocity structure getting over possible singularities due to specific eruptive phases. Our results further refined the high velocity body widely recognized in the south-eastern sector of Mt. Etna by furnishing new clues on the possible former magma pathways. Moreover, the obtained 3D seismic velocity model depicted new anomalies revealing the presence of: (i) two shallow underground aquifers in the northern Etnean sector; (ii) a volume of strongly fractured rocks filled of fluids along the eastern flank; (iii) a quite deep region of probable fluid accumulation apparently not linked to the volcanic activity in the western sector.

Observed Pathways and Interannual Variability of the Warm Inflow Onto the Continental Shelf in the Southern Weddell Sea

AbstractModel projections suggest that the continental shelf in the southern Weddell Sea may experience a shift from today's near‐freezing temperature to a much warmer state, where warm water floods the shelf and basal melt rates beneath the Filchner Ronne Ice Shelf increase dramatically. Today, the Filchner Trough serves as a conduit for the southward flow of Warm Deep Water (WDW) during summer and, thus, requires continuous monitoring of its hydrographic conditions. An extensive network of moorings was installed at key sites along the inflow pathway from 2017 to 2021, to expand on existing mooring records starting in 2014. The moorings complemented with under‐ice profiling floats reveal two inflow pathways, where WDW enters along the eastern flank of the Filchner Trough as well as through a smaller trough east of there. Within the observed period, 2017 and 2018 feature anomalously warm inflows. The inflow is regulated by the heaving of isopycnals over the continental slope, and the southward propagation toward Filchner Ice Shelf is two times faster during these warm years. Furthermore, the warm years coincide with low summer sea ice concentration, which enhances surface stratification through increased freshwater input and modifies sea ice‐ocean stresses that both act to lift the warm water layer and increase the temperatures on the continental shelf. Finally, the recent record low sea ice conditions around the Antarctic emphasize the importance of our findings and raise concerns regarding a potentially increasing presence of WDW on the southern Weddell Sea shelf.

Glacial and periglacial geomorphology of the eastern flank of the north Patagonian Andes: Quaternary morphoclimatic evolution

The cold climate events of the Upper Cenozoic greatly modified the landscape of Patagonia, where a large number of relicts and active landforms of glacial, periglacial and paraglacial origin is preserved. To assess the regional paleoclimatic record when numerical ages are unavailable, the spatial distribution of local depositional landform sequences was analyzed in six mountain ranges located on the eastern margin of the North Patagonian Andes. The analysis of satellite images and digital elevation model, fieldwork research and its integration into a Geographical Information System were used to develop a detailed inventory of mountain landforms. A total of 67 glacial valleys, 97 glacial cirques, 94 moraines, 75 rock glaciers, 103 protalus ramparts, and more than 145 km2 and 100 km2 of surface affected by solifluction and mass wasting processes respectively were mapped. From the analysis of the spatial and altitudinal distribution of landforms, we defined temporal and spatial sequences of morpho-climate importance. We recognized four major morpho-climate events associated with local paleoclimate conditions and one stage of a recent paraglacial adjustment. The oldest cold climate event recognized might be correlated with the Last Glacial Maximum. The results show the rise in the average air temperature and an aridity trend for the study area since the Late Pleistocene. During this lapse, glacial environments evolved to periglacial environments, although was recognized their coexistence in some areas in the same mountain range.

Rupture behaviors of the southern Xianshuihe fault and seismicity around Mt. Gongga: Insights from the 2022 MW 6.6 Luding (China) earthquake sequence

The 2022 MW 6.6 Luding earthquake occurred on the Moxi segment of the Xianshuihe fault at the southeast margin of Tibetan Plateau, China. To assess the seismic potential of the Moxi segment, we examine the rupture process of the mainshock and aftershock sequence, along with historical seismicity. Our preferred slip model inverted from teleseismic body waves and regional GNSS static displacements shows a dominant southeastward rupture consisting of two distinct, prominent slip patches along strike extending by ∼15 km, with a peak slip of ∼2.8 m, approximately balancing the slip deficit since the last major earthquake in 1786. The northern section of the Moxi segment experienced minor coseismic slip, which, together with the significant slip deficits and positive Coulomb failure stress change induced by the 2022 mainshock indicates a high seismic potential. Several aftershock clusters are distributed along or near the Moxi segment, with strike-slip focal mechanisms around the downdip edge of the coseismic slip area at ∼8‐12 km. At the eastern flank of Mt. Gongga, another cluster of normal faulting aftershocks is located at shallower depths of ∼3‐7 km, with high seismicity rate over ∼9 months including two other M5 sequences in January and February 2023. Similar intense shallow normal faulting activity had occurred after the impoundment of the nearby Dagangshan reservoir in 2015. We speculate that some NW-SE trending normal faults were initially developed by the gravitational collapse of Mt. Gongga underneath the eastern flank, further weakened by fluid flow, as supported by the existence of hot springs and water impoundment, and reactivated by the tensional stress change induced by the 2022 mainshock. These results have important implications for assessing the seismic hazard in and around the Moxi segment, and the potential interplay between strike-slip fault and nearby mountain areas.

Subsurface floats in the Filchner Trough provide the first direct under-ice tracks of the circulation on shelf

Abstract. Bottom water formation in the Weddell Sea and mass loss from the Filchner–Ronne Ice Shelf are tightly linked by the supply of Warm Deep Water to the continental shelf. Heavy sea ice cover and icebergs restrict ship access and upper-ocean measurements by moorings, compelling us to try new sampling methods. We present results from the first dedicated under-sea-ice float experiment tracking circulation on the continental shelf of the eastern Weddell Sea. Seven Apex profiling floats were deployed in 2017 at three different locations on the eastern Weddell Sea continental shelf, targeting the inflowing modified Warm Deep Water (mWDW), as well as the outflowing Ice Shelf Water (ISW). The floats capture a warm mWDW regime with southward inflow over the eastern continental shelf and a cold ISW regime with a recirculation of ISW in the Filchner Trough throughout the 4 years of observations. We provide the first Lagrangian in situ confirmation that the mWDW flowing onto the continental shelf follows two pathways: the eastern flank of the Filchner Trough and a small trough on the shallow shelf farther east. In the present circulation regime, this warm water is blocked from reaching the ice shelf cavity due to the presence of the thick ISW layer inside the Filchner Trough. The floats' trajectories and hydrography reveal the dynamically active front, flow reversal, and eddying motion between these two water masses along the eastern flank of the Filchner Trough.

Evolution of Baltic Security: Analysis of Threats and Strategic Responses

This article explores the evolution of security in the Baltic region, focusing first on Estonia, Latvia and Lithuania, and analysing the key challenges posed by the Russian Federation since the annexation of Crimea in 2014 and the subsequent security measures taken by NATO through the Enhanced Forward Presence (eFP) mission. It details the strategic responses of the Baltic states, highlighting their military modernisation, defence cooperation with NATO and growing reliance on multinational exercises. The article also examines the role of Poland as a key player in NATO's eastern flank defence and the integration of Finland and Sweden into NATO, emphasising their contribution to strengthening the Baltic and Arctic security architecture. The analysis concludes with an examination of the multiple threats that characterise the region's security environment, underlining the importance of coherent multinational defence strategies.

Variscan basement tectonics and Alpine shear zones in the external Balkanides: Structural data from the Vezhen Massif, Central Stara Planina Mts., Bulgaria

The Alpine Balkanides in Bulgaria are developed over Variscan orogenic fragments, which are variously affected by late-stage thick-skinned thrust tectonics. Often, these fragments hold both Variscan and Alpine structural records. А key area to shed light on important aspects of the tectonic evolution of the external parts of the Alpine Balkanide orogen is the Vezhen Massif in the Central Stara Planina Mountains. Although it is built exclusively of Paleozoic crystalline rocks, its structure was long considered as an example of intense mid Eocene to early Oligocene (Late Alpine) shortening. Detailed fieldwork in the area shows a more complicated tectonic framework and provides evidence of a polyphase structural evolution, involving an important stage of Variscan metamorphism and deformation and two stages of north-vergent Alpine shortening. The Stargel-Boluvanya Tectonic Zone that affects the western Vezhen Massif is one of the most important Variscan structures in the Balkan fold-and-thrust belt. Structural data indicate that the metamorphic basement records initial top-to-north thrusting, followed by further shortening, which led to folding and localized strike-slip deformation. The Variscan syn-metamorphic fabric is cross-cut by several post-kinematic igneous bodies of late Carboniferous to Permian ages. The tectonic history continues with a development of a network of greenschist facies north-vergent mylonitic zones for which an Early Alpine (post-late Permian but pre-Late Cretaceous) age is assumed. Late Alpine north-vergent thrusting is evident only on the eastern and northern flanks of the Vezhen Massif. In a broad structural context, the documented record in the basement rocks of the Vezhen Massif is comparable with those of the external massifs of the Alps and Iberia.

New Insight on Stratigraphy and Lithofacies of Banten Tuff Revealed from Eastern Flank of Rawa Danau Volcanic Complex, Java, Indonesia

New Insight on Stratigraphy and Lithofacies of Banten Tuff Revealed from Eastern Flank of Rawa Danau Volcanic Complex, Java, Indonesia

Observation of deep currents around a seamount between the Japan and Kuril trenches

Hydrographic observations and two-year current measurements revealed the flow around the Erimo Seamount between the Japan and Kuril trenches. Northward currents were observed to flow both around the seamount and on the eastern flank of the trench. Since the dissolved oxygen concentration of the former is higher than that of the latter, these currents correspond to the western and eastern branch currents of the deep western boundary current in the North Pacific, respectively. The western branch current forms a Taylor cap over the seamount, although during certain periods, it joins the eastern branch current. During such periods, a strong jet forms around the seamount and the Taylor cap is washed away. Such alternately intensified currents are consistent with previous observations of the Japan Trench. On the western flank of the trench, a southward current flows near the seafloor, while an eastward current is formed at a depth of 3360 m due to the confluence of the currents from north and south.

Surface temperature modulations induced by Rossby Wave Breaking over Indian region

Abstract Upper-level Rossby Wave Breaking (RWB) significantly affects surface weather patterns in the subtropical Indian region through influencing wind circulation often resulting in extremes in rainfall and surface temperatures. While the impact of RWB on rainfall is relatively well understood, its role in modulating surface temperatures within the Indian subcontinent is less explored. This study examines the link between pre-monsoon (March to May) RWB events and the occurrence of extreme surface temperatures and heatwaves by considering long-term data of 43 years between 1979 and 2021. We identify 139 RWB events using a potential vorticity (PV) contour searching algorithm over the Indian sub-continent. Our analysis reveals a significant amplification in temperature both to the west and east of the breaking PV streamers. These temperature anomalies, which last for 3–4 days during the breaking events, strongly correlate with the maximum day of breaking. Further, regression analyses explain the reasons behind the temperature enhancement mainly on the western and eastern flank of RWB. It indicates a positive association between upper-level PV anomalies and anticyclonic circulations at 250 hPa, along with subsidence at 500 hPa, leading to drier conditions in the western and eastern regions of the PV streamers. Additionally, the decomposition of temperature anomalies during RWB events reveals that surface warming is primarily driven by diabatic heating on both sides of the centroid, with stronger adiabatic heating in regions of upper-level anticyclonic circulation and significant temperature advection predominantly on the western side of the centroid, resulting in dry weather and the poleward movement of warm air toward the ridges near the PV streamers.

Evaluación de los efectos secundarios tras el sismo del 18 de enero de 2021 (Mw 6,5) en San Juan, Argentina: determinación de la intensidad sísmica a través de la escala ESI-2007

This study focuses on evaluating the numerous secondary effects, such as mass wasting and soil liquefaction, caused by the Mw 6.5 earthquake that occurred on January 18, 2021, in the province of San Juan, Argentina. The epicenter was located on the eastern flank of the Las Osamentas range. Although it caused significant damage to buildings and cultivated areas, there were no fatalities. The aim is to identify and describe these secondary effects and determine the seismic intensity of the event using the INQUA’s (International Union for Quaternary Research) 2007 ESI (Environmental Seismic Intensity) scale. Field assessments were conducted shortly after the earthquake, documenting liquefaction and mass wasting structures through direct observations, digital photographs, GPS (Global Positioning System) localization, and data inventory, among other methods. This procedure validates a protocol for future applications in estimating seismic intensities for sparsely populated areas. Additionally, the study seeks to confirm the scientific and cultural importance of these ephemeral structures as assets that could be protected, therefore contributing to regional development.

The Bucharest Nine Part of NATO's Eastern Flank: an Analysis of Military Investment on Equipment

An important part of NATO's deterrence and defence role is its military presence in the eastern part of the Alliance's territory, represented by the Bucharest Nine (B9). The ability of this group to fulfil its strategic mission depends on the condition of the military equipment at its disposal. The number of pieces of military equipment and their combat capability are determined by the investment in military equipment. In the context of the pledge to spend at least 20 % of total defence expenditure on military equipment, it appears that between 2004 and 2022 there is a steep increase of defence investment gap, followed by a partial absorption of the investment gap after 2014. The investment gap is reflected in the volume and condition of military equipment. Rising spending in recent years is positively reflected in the increasing volume of acquisitions for new military equipment in all B9 countries. However, due to the delay, these investments are and will only be reflected in defence capabilities in the future.

The Gulf of Suez rifting: implications from low-temperature thermochronology

ABSTRACT The Gulf of Suez is a continental rift basin that has been developed during the Oligocene-Miocene as a northern extension of the Red Sea rift system. The Oligo-Miocene rift-activated flanks are represented by exposures of the Neoproterozoic basement rocks of the Arabian-Nubian Shield. An additional thermal overprint (i.e. mantle plume) and the preceding tectono-thermal events that also affected the rifting dynamics and the uplift of its flanks remain uncertain. We here present thermochronological data for 20 basement samples collected from the Gabal Somr ElQaa area at the northwestern flank of the Gulf of Suez. The resulted zircon fission-track ages could be divided temporospatially into two groups: the Cambrian and the Silurian-Devonian with average ages of 503 ± 14 Ma and 407 ± 11 Ma, respectively. While apatite fission-track data reveal three different age groups of the Devonian-Carboniferous, the Permian-Triassic, and the Late Cretaceous, with average ages of 349 ± 10 Ma, 246 ± 6 Ma, and 81 ± 5 Ma, respectively. The modelled t-T histories indicate four cooling pulses during the Neoproterozoic, the Devonian-Carboniferous, the Cretaceous, and the Oligocene-Miocene. Integrating our findings with the regional tectonism and depositional records indicates that these cooling pulses could be attributed to synchronous activities of the post-accretion erosional event, the Variscan tectonic event, the Mid-Atlantic Ridge spreading, and the Gulf of Suez rifting. The Gulf of Suez is a passive rift, formed by a single and rapid rifting pulse within the framework of the Red Sea rift system. An additional east-southward far-field thermal overprint from the Arabian marginal plume partially affected the Suez rifting process. This thermal print affected only the rift’s southern portion of its eastern flank, causing syn-rift cooling ages, highly elevated rift flanks, and an increased heat flow. The western rift flank and the northern segment of the eastern flank are characterized by pre-rift cooling ages, modest rift flanks, and reduction in heat flow.

Post-glacial stratigraphy and late Holocene record of great Cascadia earthquakes in Ozette Lake, Washington, USA

Ozette Lake is an ~100-m-deep coastal lake located along the outer coast of the Olympic Peninsula (Washington, USA); it is situated above the locked portion of the northern Cascadia megathrust but also relatively isolated from active crustal faults and intraslab earthquakes. Here we present a suite of geophysical and geological evidence for earthquake-triggered mass transport deposits (MTDs) and related turbidite deposition in Ozette Lake since ca. 14 ka. Comprehensive high-resolution bathymetry data, seismic reflection profiles, and sediment cores are used to characterize the post-glacial stratigraphic framework and examine paleoseismic evidence in the lacustrine sediments. Stacked sequences of MTDs along the steep eastern flanks of the lake appear to grade basin-ward from thick, chaotic, blocky masses to thin, parallel-bedded turbidite beds. The discrete turbidite event layers are separated by fine-grained (silt and clay) lake sedimentation. The event layers are observed throughout the lake, but the physical characteristics of the deposits vary considerably depending on proximity to primary depocenters, steep slopes, and subaqueous deltas. A total of 30–34 event deposits are observed in the post-glacial record. Radiometric dating was used to reconstruct a detailed sedimentation history over the last ~5.5 k.y., develop an age model, and estimate the recurrence (365–405 yr) for the most recent 12 event layers. Based on sedimentological characteristics, temporal overlap with other regional paleoseismic chronologies, and recurrence estimates, at least 10 of the dated event layers appear to be sourced from slope failures triggered by intense shaking during megathrust ruptures; the recurrence interval for these 10 events is 440–560 yr. Thus, Ozette Lake contains one of the longest and most robust geological records of repeated shaking along the northern Cascadia subduction zone.

Petrogenetic implications, geochemistry and tectonic framework of albitite hosted magnetite in North Delhi Fold Belt: Application of geochemistry and apatite chemistry

The iron ore bodies in the form of lensoidal and pocket type deposits occur within the Meso to Neo-Proterozoic meta-sedimentary rocks and albitites of Ajabgarh Group of Delhi Supergroup in Khetri basin, Western India. These are exposed as detached and linear ore bodies at the southern (western flank) and south-eastern (eastern flank) part of the Khetri copper deposit which follows the regional trend of the host rocks. The detailed field and petrographic studies reveal that the magnetite and hematite are associated with major silicates like quartz, actinolite, muscovite, biotite, albite and, K-feldspar. Some minor occurrences of apatite, sphene, ilmenite and monazite are also found. This work is focused on understanding the evolution of albitite-hosted magnetite with respect to tectonic signatures, the source of mineralizing fluid, and its spatial relationship with the regional albitites and meta-sediments. To interpret the above, whole rock geochemistry of albitite rocks, magnetite ore and mineral chemistry of fluorapatite, were adopted.The whole rock geochemistry of albitite suggests that the parent rocks are of calc-alkaline magma series that are originated from the subduction-related rift zone of volcanic arc environment. The apatite chemistry signifies that these are evolved from the highly fractionated granitic rocks (granitoid) at moderate to high oxidizing conditions. Some deformed apatite grains are also encountered having small distorted monazite inclusions. Thus, it has an indication of high-temperature metasomatic/hydrothermal fluids that may be responsible for the removal of REEs from apatite and re-nucleate as monazite inclusions within it. Therefore, the overall evidence and associations of albitite with apatite-magnetite is demonstrating that the source rock of the study area could have evolved from the arc system of active continental margin which was abundant with Fe, U, REEs, etc. Hence, the sources rocks were suitably metasomatized by hydrothermal fluids channelized through the regional shear zone and simultaneous precipitation of the magnetite in the study area. The dominance of magnetite, associated REEs, apatite, and non-association of sulfide minerals with the magnetite in the area of study has close similarities with the IOA type deposits.

Moisture dynamic processes of the westward propagation of quasi-biweekly oscillation in Asian tropical summer monsoon rainfall

The quasi-biweekly oscillation (QBWO) is an important component of tropical monsoon variations. In this study, the QBWO rainfall demonstrates a westward propagation across the tropical Asian monsoon region, originating from the western North Pacific, passing through the South China Sea and the Bay of Bengal, and ultimately reaching the northwestern Indian Peninsula. Notably, the rainfall anomalies over the South China Sea precede those over the Bay of Bengal by one quarter of the QBWO life cycle. Enhanced (suppressed) rainfall is closely associated with significant positive (negative) specific humidity anomalies, primarily induced by meridional moisture transport at the lower levels, as revealed by a moisture budget analysis. Specifically, the alternating presence and westward movement of northerly anomalies on the eastern (western) flank of anticyclonic (cyclonic) circulation anomalies are responsible for transporting low-frequency moisture across tropical Asia, thereby instigating the westward propagation of QBWO rainfall. Thus, the multiscale interactions between atmospheric circulation and moisture play a pivotal role in the development of QBWO monsoon rainfall, and understanding the moisture dynamics of this rainfall development would provide useful information for subseasonal rainfall prediction in tropical Asia.