Properties Of Crust Research Articles

Crustal Heterogeneity of the Bhutan Himalaya: Insights from PgQ Tomography

Abstract We present the results of a seismic investigation conducted in Bhutan using data from the Geodynamics and Seismic Structure of the Eastern Himalaya Region broadband network, focusing on variations in crustal structure and seismic attenuation properties. Through analysis of seismic data from 56 events recorded between 2013 and 2014, with magnitudes exceeding 4.5 and depths shallower than 50 km, we examined 1 Hz PgQ (Q0)-values among multiple station pairs using the two-station method. Our findings reveal significant disparities in PgQ0-values across Bhutan. The western region exhibits low PgQ0 values, indicating high seismic attenuation, whereas the central region shows medium-to-high PgQ0 values, suggesting lower attenuation. Notably, these results are consistent with the geometry of the Moho, providing valuable insights into crustal geometry and rheology. This study contributes to a deeper understanding of Bhutan’s complex crustal structure, offering insights into crustal properties and seismic attenuation mechanisms in this geologically significant region.

Temporal variation of S-wave attenuation during the 2009 L'Aquila, Central Italy, seismic sequence

Summary We investigate temporal and spatial variations of the spectral decay parameter kappa (κ) before and after the April 6, 2009, L'Aquila earthquake (Mw 6.1), in central Italy. We analyzed foreshocks ten days before and aftershocks occurring ten days and six months after this main event. We select earthquakes with magnitudes Mw ≥ 3.2 registered by the seismic network of central Italy within a radius of 20 km from the epicenter of the L'Aquila mainshock and having hypocenter distances of less than 170 km. We separate near-source, along-path and near-site contributions of κ for each group of events and we detected temporal variations of this S-wave attenuation parameter. We find that ten days before the mainshock κ along the path has the lowest values, probably due to high tectonic stress accumulated, in agreement with previous investigations performed with other techniques, then κ increases during the main event and remains constant during the first ten days of aftershocks. The aftershocks that occurred six months after show an increase in the regional attenuation probably due to the tectonic stress released during the main shock and the earlier aftershocks. From the spatial point of view, ten days before the principal event the foreshocks located to the south show an increase in the near-source attenuation towards the northeast, in the direction of the mainshock. These spatial variations of κ may be related to the presence of crustal fluids near the rupture area, as evidenced by other previous studies. The first ten days of aftershocks that concentrate around the main earthquake have high near-source κ, and those located north of the main rupture have lower values. These observations are consistent with previous investigations that show variations of elastic and anisotropic crustal properties during the L'Aquila earthquake sequence due to dilatancy and fluid diffusion processes within the nucleation zone. We conclude that temporal variations of the spectral decay parameter κ provide important clues for the earthquake cycle in central Italy.

Investigating Subsurface Properties of the Shallow Lunar Crust Using Seismic Interferometry on Synthetic and Recorded Data

AbstractIn the past few years, the remarkable progress of commercially operated spacecrafts, the success with reusable rocket engines, as well as the international competition to explore space, has led to a substantial acceleration of activities in the design and preparation of ambitious future lunar missions. In the search for ice and/or cavities imaging the shallow subsurface structure is of vital importance. Hereby, previous studies have shown that seismic interferometry is a promising method to investigate the subsurface properties from passive lunar data. In this study, we want to evaluate the potential of this method further by examining the required duration of seismic measurements and the influence of scattering on the Green's function retrieval. Therefore, we applied seismic interferometry to both measured Apollo 17 data and synthetic data. Our findings indicate that, under optimal conditions, a few hours of data are sufficient when using the method of time‐scaled phase‐weighted stack (ts‐PWS). However, this strongly depends on the inter‐station distance, the orientation toward the principal noise sources, and the timing of the measurement during the lunar cycle. Additionally, we were able to reproduce the measured data using numerical simulations in 2D. The synthetic results show that scattering effects clearly influence the Green's function extraction, especially for larger station distances.

The 3D Crustal Structure of the Wilkes Subglacial Basin, East Antarctica, Using Variation of Information Joint Inversion of Gravity and Magnetic Data

AbstractDirect geological information in Antarctica is limited to ice free regions along the coast, high mountain ranges, or isolated nunataks. Therefore, indirect methods are required to reveal subglacial geology and heterogeneities in crustal properties, which are critical steps toward interpreting geological history. We present a 3D crustal model of density and susceptibility distribution in the Wilkes Subglacial Basin (WSB) and the Transantarctic Mountains (TAM) based on joint inversion of airborne gravity and magnetic data. The applied “variation of information” technique enforces a coupling between inferred susceptibility and density, relating these quantities to the same gravity and magnetic sources to give an enhanced inversion result. Our model reveals a large body located in the interior of the WSB interpreted as a batholithic intrusive structure, as well as a linear dense body at the margin of the Terre Adélie Craton. Density and susceptibility relationships are used to inform the interpretation of petrophysical properties and the reconstruction of the origin of those crustal bodies. The petrophysical relationship indicates that the postulated batholitic intrusion is granitic, but independent from the Granite Harbor Igneous Complex described previously in the TAM area. Emplacement of a large volume of intrusive granites can potentially elevate local geothermal heat flow significantly. Finally, we present a new conceptual tectonic model based on the inversion results, which includes development of a passive continental margin with seaward dipping basalt horizons and magmatic underplating followed by two distinct intrusive events associated with the protracted Ross Orogen.

Crustal-mantle layering deposits in the Von Kármán crater, South Pole-Aitken basin

Comprehending the properties of the Moon's crust and mantle materials is essential for decoding its interior. Whether the South Pole-Aitken (SPA) basin potentially excavated the upper mantle materials remains mysterious. The Chang'E Four Lunar Penetrating Radar (LPR) has provided an unprecedented opportunity to investigate the SPA basin in the Von Kármán (VK) crater. Utilizing a data-driven generative deep learning inversion algorithm, the subsurface physical properties along the Yutu-2 path were determined. 4 distinct deposit zones were discovered beneath the surface. All zones feature an upper low-permittivity (paleo-)regolith layer overlaying on a lower high-permittivity layer of rockier ejecta or basal basalt. Zone 1, an ejecta layer from the Finsen crater within the SPA Compositional Anomaly, has a bulk density (2.81±0.22g/cm3) denser than that of highland crust represented by materials originating from VKL and VKL' craters in the Mg-Pyroxene Annulus, which are present in Zones 2 and 3. This suggests the possible presence of mantle materials in Zone 1, providing the first diagnostic evidence that the SPA impact may have penetrated the upper lunar mantle.

Crater Morphometry on Callisto

Impact crater formation is affected by the physical properties of planetary crusts, allowing comparison of crater dimensions to serve as a proxy for comparing the crustal properties of different planetary bodies. New topographic profiles of Callisto craters, derived from Galileo-based digital terrain models, are presented, and the crater dimensions recorded. These data were used to derive crater morphometry scaling trends, which were then compared to the established trends of Ganymede and the Moon. Our comparative study suggests that the upper brittle portion of Callisto’s ice crust allows for the retention of steep-sided and elevated rim scarps, while subsurface warmer ice leads to an enhanced uplift and shallowing of the crater bowl. Crater dimensions are similar between Callisto and Ganymede, suggesting that the bulk properties of their near-surface crusts are comparable. The most notable difference between craters on these two Galilean moons were the smaller central pit diameters on Callisto. This difference can be explained if the pit formation on these bodies is controlled by the presence and movement (drainage and/or volatile loss) of impact melt water: the lower impact velocity and/or lower expected crustal heat flow on Callisto will result in less impact melt generation, and thus smaller central pits.

The Role of Lower Crustal Rheology on Surface Deformation During Oblique Extension: Insights From Sandbox Modeling

AbstractExtensive researches have been conducted on the relationship between surface deformation and the properties of upper crust. However, the link between surface deformation and lower crustal rheology, especially in a three‐dimensional context, remains unclear. In this study, we utilize sandbox modeling to investigate the impact of lower crustal rheology on surface deformation during oblique extension. Under the same conditions, six models with different lower crustal viscosities, both with and without syn‐kinematic deposits, are conducted. The results indicate that a decrease in lower crustal viscosity may contribute to an increase in: (a) graben width, (b) graben length, (c) graben spacing, (d) the number of isolated rifts and (e) topographic relief of oblique extensional systems, while also leading to a reduction in the total number of grabens. Notably, there exists a negative linear correlation between graben spacing and lower crustal viscosity. In map view, the angle between fault strike and the direction of pre‐existing discontinuities increases as the viscosity of the lower crust decreases. Furthermore, the frequency of large rakes (>50°) decreases with decreasing lower crustal viscosity. These findings align with natural examples such as the East African Rift System, Weihe Graben and the South Tibetan Rift in terms of geomorphology, tectonics, and crustal rheology. Through a comprehensive comparison of the graben width, spacing, and the angle between fault strike and the direction of pre‐existing discontinuities, our study provides valuable insights into the rheology of the lower crust in natural settings.

Spatiotemporal Evolution of Slow Slip Events at the Offshore Hikurangi Subduction Zone in 2019 Using GNSS, InSAR, and Seafloor Geodetic Data

AbstractDetecting crustal deformation during transient deformation events at offshore subduction zones remains challenging. The spatiotemporal evolution of slow slip events (SSEs) on the offshore Hikurangi subduction zone, New Zealand, during February–July 2019, is revealed through a time‐dependent inversion of onshore and offshore geodetic data that also accounts for spatially varying elastic crustal properties. Our model is constrained by seafloor pressure time series (as a proxy for vertical seafloor deformation), onshore continuous Global Navigation Satellite System (GNSS) data, and Interferometric Synthetic Aperture Radar displacements. Large GNSS displacements onshore and uplift of the seafloor (10–33 mm) require peak slip during the event of 150 to >200 mm at 6–12 km depth offshore Hawkes Bay and Gisborne, comparable to maximum slip observed during previous seafloor pressure deployments at north Hikurangi. The onshore and offshore data reveal a complex evolution of the SSE, over a period of months. Seafloor pressure data indicates the slow slip may have persisted longer near the trench than suggested by onshore GNSS stations in both the Gisborne and Hawkes Bay regions. Seafloor pressure data also reveal up‐dip migration of SSE slip beneath Hawke Bay occurred over a period of a few weeks. The SSE source region appears to coincide with locations of the March 1947 Mw 7.0–7.1 tsunami earthquake offshore Gisborne and estimated great earthquake rupture sources from paleoseismic investigations offshore Hawkes Bay, suggesting that the shallow megathrust at north and central Hikurangi is capable of both seismic and aseismic rupture.

High-precision U[sbnd]Pb geochronology of an ignimbrite flare-up in a silicic large igneous province (Chon Aike, Patagonia)

Silicic large igneous provinces (SLIPs) are periods of particularly voluminous felsic volcanism in the geologic record. Previous work has suggested an overall long lifespan for SLIPs of 20 to 40 Myr, commonly punctuated by shorter-lived ‘flare-ups’ of higher volcanic productivity (1–5 Myr), but detailed studies of individual flare-up events are lacking. The Jurassic Chon Aike SLIP (CASP) is the product of an exceptional geological event wherein voluminous felsic volcanism (ca. 219,000 km3) was generated predominately via crustal anatexis over 45 Myr. We focus on the Late Jurassic El Quemado Complex (EQC), which marked the final stages of felsic volcanism for the CASP. In-situ U-Pb ages for the EQC previously suggested a duration of ∼5 Myr; however, new high-precision CA-ID-TIMS ages indicate the total durations of ignimbrite successions were shorter than 350 kyr. A compilation of zircon U-Pb ages for the eight CASP formations in Patagonia and the Antarctic Peninsula reveals changes in volcanic duration between formations deposited in the intraplate relative to the continental margin, suggesting a spatial control over the magmatic lifespans of geographically restricted systems. We suggest that the rate of magmatism in the CASP was primarily controlled by heterogeneities in the crust, largely between Proterozoic igneous crust and younger, metasedimentary crust that was recently accreted relative to the timing of Jurassic volcanism. The observed duration of volcanism was modulated by these differences in crustal properties from the injection of mafic magmas into the lower crust during extension and mantle upwelling, following rollback of the subducting oceanic slab towards the Paleo-Pacific margin of Gondwana. The short duration in the EQC is the product of unique overlapping conditions that favored crustal melting and resulted in the voluminous ignimbrite flareup (104 km3) of some of the Earth's highest δ18O magmas measured.

Lithospheric Evolution of the South‐Central United States Constrained by Joint Inversion of Receiver Functions and Surface Wave Dispersion

AbstractIn the present study, we use broadband seismic data recorded by 190 stations of the EarthScope program's Transportable Array to construct a 3‐D shear wave velocity model for the upper 180 km using a non‐linear Bayesian Monte‐Carlo joint inversion of receiver functions (RFs) and Rayleigh wave dispersion curves. Ambient noise and teleseismic data are used for obtaining Rayleigh wave phase velocity dispersion curves. A resonance removal filtering technique is applied to the RFs contaminated by reverberations from the thick sedimentary layers that cover most of the region. Our observations of the higher crustal shear velocities (∼3.40 km/s) beneath the Sabine Block (SB), along with the estimated relatively thicker crust (∼34.0 km) and lower crustal Vp/Vs estimates (∼1.80) in comparison with the rest of the Gulf Coastal Plain (GCP) (∼3.10 km/s for crustal shear velocities, ∼29.0 km for crustal thickness, and ∼1.90 for crustal Vp/Vs estimates), indicating that this crustal block has different crustal properties from the surrounding coastal plain regions. The southern Ouachita Mountains have a thin crust (∼30.0 km) and low mean crustal Vp/Vs value (∼1.73), suggesting that lower crustal delamination has occurred in this region. Low velocities in the upper mantle beneath most of the GCP are interpreted as a combined result of thin lithosphere, higher‐than‐normal temperatures, and possibly compositional variations.

Experimental test and mechanism analysis of soil crust erosion resistance of rammed earth Great Wall in rainy season

Rammed earth is a kind of cleaning material, widely used in all kinds of buildings in the world. The Great Wall of ancient China is a typical world cultural site built from rammed earth. The rammed earth Great Wall of Shanhaiguan is close to Bohai Bay, which has suffered from long-term erosion by rain, causing a series of problems such as soil loss, collapse and gully flushing. The protection materials of the rammed earth site have always puzzled scholars. However, during the rainy season, it was found that some of the walls at Xiaowan Gouge and Nantuzhuang Gouge in the Shanhaiguan Great Wall had unwashed traces, the soil surface of the walls was intact, and the anti-erosion ability of the walls was significantly higher than that of other places. In order to explore the reasons for its strong anti-erosion ability in the natural state of rammed earth wall, guide the protection of rammed earth Great Wall, and carry out different experimental tests to explore its anti-erosion reasons and internal mechanisms. Firstly, the characteristics of rammed soil were understood through the composition test of rammed soil, and the indoor and outdoor erosion test was carried out to determine that the anti-erosion reason was the protection of gray-green soil crust. The property and composition of soil crust were determined through the immersion test and genome sequencing. Finally, the protection mechanism of soil crust was analyzed by scanning electron microscopy.

Post-collisional lithospheric delamination in eastern Iran, revealed by non-linear teleseismic tomography and residual topography

The Eastern Iranian Mountain Ranges (EIR) emerged as a consequence of the Late Cretaceous collision between the Afghan and Lut blocks. However, the response of the uppermost mantle to this collision remains enigmatic. Additionally, although petrological evidence suggests that post-collisional delamination is possible, it has not been conclusively identified in prior regional seismic imagery. This observation leads us to further explore this possibility using a dense seismic network. To gain insight into the geodynamic implications for eastern Iran and address knowledge gaps, we extensively investigated the seismic structure of the uppermost mantle beneath the EIR using a dense seismic network of 34 temporary stations, complemented by data from nine additional local permanent stations. By meticulously analyzing 6589 relative arrival time residuals from teleseismic records with favorable signal-to-noise ratios, we applied a non-linear tomography method to map P-wave velocity perturbations in a relative sense. Our tomographic images unveiled distinct instances of rapid high-velocity anomalies beneath low-velocity regions in the shallow mantle, suggesting the potential occurrence of lithospheric dripping, followed by subsequent asthenospheric upwelling. This observation offers a plausible explanation for the observed post-collisional magmatism over the Lut Block. Furthermore, to maintain the approximately 1.5-km positive residual topography across the EIR, beyond the influence of crustal properties, additional support from the hot and buoyant asthenosphere becomes crucial, particularly in the absence of a substantial lithospheric mantle.

Unveiling attenuation structures in the northern Taiwan volcanic zone.

This cutting-edge study delves into regional magmatism in northern Taiwan through advanced 3-D P- and S-wave frequency-dependent attenuation tomography. Positioned at the dynamic convergence boundary between the Philippine Sea Plate and the Eurasian Plate, Taiwan experiences moderate earthquakes and intriguing volcanic activity, with a focus on the Tatun volcano group. Employing the Formosa seismic array for high-resolution results, our research identifies high-attenuation anomalies (low Q) beneath the northern Taiwan volcanic zone (NTVZ) and offshore submarine volcanoes, indicative of potential hydrothermal activities and magma reservoirs at varying depths. Additionally, we explore low-attenuation anomalies (high Q) in the forearc region of the Ryukyu subduction zone, suggestive of partial saturation linked to serpentinization processes resulting from seawater infiltration or forearc mantle hydration. These findings shed light on the complex geological features and provide essential insights into the crustal properties of northern Taiwan, contributing to a deeper understanding of its magmatic evolution and tectonic processes.

The contribution of Rob Westaway to the study of fluvial archives

Robert Westaway was a structural and hard-rock geologist who turned his attention to the study of Late Cenozoic fluvial archives, believing that the preservation of staircases of river terraces, particularly representing the Middle and Late Pleistocene, could only be explained in terms of crustal activity in response to surface processes, the latter affected by climatic change. His entry into this research area coincided with the realisation that such terrace sequences required surface or crustal uplift to have taken place over the time interval represented. Workers were unable to explain the observed amounts of uplift in terms of erosional isostasy, a process that could potentially have explained such one-way crustal movement. Westaway envisaged a mechanism by which mobile lower crust migrated to beneath uplifting areas, maintaining and reinforcing their uplift. The mechanism requires complex mathematics to explain it, as well as lending itself to mathematical modelling of the process, based on varying crustal properties and changes in the rates of surface processes in response to climatic fluctuation. Essentially the lower-crustal effect can be envisaged as a positive-feedback enhancement of erosional isostasy.It became apparent that Westaway's theories could explain geomorphological and sedimentary fluvial archives that were otherwise difficult to elucidate. Mantle-based erosional isostasy could not explain terrace staircases, for example. Many of these occur in regions that are tectonically inactive, and so cannot be attributed to neotectonic activity. A game-changer in terms of persuading the wider community came from the recognition of crustally ultrastable regions in which progressive long-timescale uplift has not occurred: Archaean cratons. Westaway's envisaged lower-crustal flow would not be expected in such regions, which have cold, brittle and immobile crust to its full depth. Ancient fluvial deposits are found close to modern valley-floor levels in such areas. Regions of younger Precambrian crust (Proterozoic) showing intermediate situations were subsequently identified. Other dilemmas could be resolved, such as the ‘back-tilting’ of the early-Middle Pleistocene Bytham River in the English Midlands, caused by its drainage crossing crustal blocks with different properties that have accordingly experienced differential uplift. Although glacio-isostasy, mostly seen in the effects of rebound since the Last Glacial Maximum (LGM), is largely accommodated in the mantle, and thus is reversed as a response to glacial loading and unloading, in areas of suitable crustal type there is evidently a small lower-crustal component that is less readily reversible.Westaway's important contribution has yet to be fully integrated into received wisdom in geomorphological and Quaternary circles, although much of it is now widely accepted and more will be explored and published in due course.

Hydrothermal Seepage of Altered Crustal Formation Water Seaward of the Middle America Trench, Offshore Costa Rica

AbstractChemical compositions of sediment pore waters are presented from 13 piston and gravity cores that were collected on ∼24 Ma crust of the Cocos Plate seaward of the Middle America Trench and near the onset of crustal faulting from subduction. Cores were collected mainly within a 1.75 km2 area overlying a buried basement topographic high that supports an elevated heat flux, consistent with seawater transport within the upper volcanic crust. Systematic variations in pore water chemical profiles indicate upward seepage speeds (up to 1.7 cm yr−1 providing a net flux of 0.1 L s−1), constrain the chemical composition of the formation water within the underlying upper basaltic basement, and elucidate diagenetic reactions in the sediment. Relative to seawater, formation water has an elevated temperature (70–80°C) and concentrations or values of Ca, chlorinity, Sr, Ba, Li, Fe, Mn, Si, Cs, D/H, and Mo, and lower concentrations or values of Mg, Na, sulfate, alkalinity, TCO2, K, B, F, phosphate, 87Sr/86Sr, δ13C, δ18O, U, and Rb. Although this site is located only 30 km from the trench axis, there is no chemical evidence for subduction‐related hydrologic influences. Instead, the data are explained by a combination of seawater‐basalt reactions within the upper basement and diffusive exchange with overlying sediment, as part of a shallow, ridge‐flank hydrothermal system. It is unclear why this site has an elevated heat flux relative to neighboring crust, but this may result from variations in crustal properties or modification related to flexural faulting outboard of the trench.

Geodetic slip rate partitioning in the central Anninghe and Daliangshan faults: Effects of fault geometry, elastic heterogeneity, and viscoelastic rheology

Geodetic measurements can be employed to estimate the secular slip rates and locking depths of crustal faults, two key parameters which influence assessment of long-term seismic hazard presented by a fault. However, this process requires making assumptions about the rheological properties of the Earth's crust and lithosphere, as well as the fault geometry at depth. Previous geodetic studies have inferred widely varying slip rates and locking depths for the central Xianshuihe-Xiaojiang Fault System, located along the southeastern margin of the Tibetan plateau. In this study, we use updated GNSS measurements, including 13 new velocities, to explore the effects of assumed rheology and fault geometry on the inferred slip rates and locking depths of the subparallel Anninghe (ANH) and Daliangshan (DLS) faults in this region. We demonstrate that only models taking into account the viscoelastic relaxation of the lower crust can resolve the apparent discrepancies. Models assuming a fully elastic rheology suggest very deep locking depths (∼35 km) and a lower slip rate on the ANH fault (∼5 mm/yr) than the DLS fault (∼7 mm/yr). Neither the relative slip rates nor the locking depths agree with seismic or geologic observations. We also consider models assuming a heterogeneous elastic rheology, but find they are indistinguishable from the homogeneous models. Modifying the fault geometry can impact the relative slip rates of the two faults but does not produce a reasonable locking depth either. In contrast, viscoelastic models accounting for seismic cycle effects indicate a faster ANH slip rate (∼5–7 mm/yr), a slower DLS rate (∼4–5 mm/yr), and a shallower locking depth for both faults (∼18 km), all of which are more consistent with independent seismic and geological observations. Our study suggests that steady long-term motion on these faults is modulated by long-lasting viscoelastic effects over a relatively broad region.

Impact of batter solid-water ratio and frying time on meat-analog based coated fried food

In response to recent demand of animal-meat alternatives, plant derived composites based meat-analog is at the center of attention. This study investigated the impact of batters’ solid-to-water ratio (SWR) and frying time (FT) on the evolution of physicochemical, thermal and structural properties of meat-analog (MA) based batter coated fried products. Wheat and rice flour-based batter systems of different SWR (1:1.1, 1:1.3, 1:1.5) was used to coat a MA model, and were deep-fried at 180 °C for 2, 4 and 6 min in canola oil. Results revealed that SWR of batter coatings negatively correlated with batter-pickup (BP), water-retention-ability (WRA), cooking yield (CY), moisture and structural properties (thickness, densities) of the fried foods crust. Batters' SWR positively correlated with frying loss (FL), fat, textural attributes (hardness, brittleness, crispiness) and glass-transition-temperature (Tg) of the fried foods crust. The FL, crust thickness, fat content, Tg, and textural attributes positively correlated with frying time (FT); whereas CY, moisture content and crust densities were negatively correlated with FT. The Tg of MA-based batter coated fried foods crust were ranged between −23.51 °C and −20.16 °C. Higher SWR and FT diminishes post-fry mass redistribution, textural evolution, and color changes; whereas lower SWR and FT retained the juiciness of food-core substrate. Scanning electron microscopy analysis revealed that both the SWR and FT impacted surface microstructural properties (roughness, micro-opening) of MA-based batter coated fried products. Surface openings (SO) were negatively correlated with the moisture content, while positively correlated with the fat content of MA-based batter coated fried foods crust.

Crustal properties investigation in the Meratus Complex Zone, Southeast Borneo, using H-κ stacking of receiver function analysis

We study crustal properties using teleseismic receiver functions extracted from two broadband seismic stations around the Meratus Complex region, Southeast Borneo. The two seismic stations, BBKI and KBKI, are distributed in the Meratus Mountains and Pulau Laut. We then employ the H-κ stacking technique to measure the crustal thickness (H) and the crustal average Vp/Vs ratio (κ). The method works quite well for receiver functions recorded on seismic station KBKI. The thickness of the crust and Vp/Vs ratio underneath this station are around 38 km and 1.64, respectively. On the contrary, the standard H-κ method fails in estimating the crustal properties beneath station BBKI due to significant sedimentary contamination on the receiver functions. Thus, we apply the sequential H-κ stacking analysis by removing the sedimentary effect and increasing the Moho Ps amplitude. The result shows the thickness of the crust is around 29 km, although the Vp/Vs is not well determined. The research findings from both stations are comparable to those derived from the previous receiver function study using inversion modelling. The crustal properties around this area may reflect the continental material part of the Sunda continental block.

Bayesian inversion for modelling 3-D density structures in the eastern margin of Bayan Har block and its tectonic implications

SUMMARY Recently, the eastern margin of the Tibetan plateau has experienced three moderate earthquakes. Deep crustal structure is a critical factor for understanding the seismotectonic environment and deformations in this region. Although several multidisciplinary geophysical approaches have been used to develop crustal structure models for this area, substantial inconsistencies still persist in the results due to the intricate structural properties of crust. In this study, we introduce a novel approach to construct a 3-D crustal model with assimilated density structure (MADS) at a resolution of 0.2° × 0.2° × 5 km. This model is built by integrating data from various source, including multisource gravity anomalies and diverse available crustal structure reference models. We use a model-assimilated gravity inversion process with Bayesian parameter optimization. First, we combine the terrestrial gravity profiles data set with published global gravity field models to create a data set rich in reliable high-frequency anomaly information. Secondly, we incorporate three reference models derived from different seismological methods as prior constraints for our model. These models encompass seismic tomography, surface wave dispersion and receiver function data. We optimize the hyper-parameters of these constraints using the Bayesian criterion. The results demonstrate that the MADS not only captures significant changes in the crustal density but also discerns subtle variations in the upper and middle crust, thereby providing detailed insights into the morphologies of major faults. For instance, the central section of the Longmenshan fault is revealed as a high-angle deep thrust feature, while the frontal section of the Longmenshan fault appears as a low-angle mid-deep thrust feature, and the Xianshuihe fault exhibits a vertical deep subduction feature. Additionally, our findings indicate a correlation between the locations of moderate-to-large earthquakes in this region and the high density-gradient zones or asperities with high density within MADS. We believe that the insights into density characteristics offered by the new MADS model can shed light on the study of asperities associated with recent moderate earthquakes and enhance our understanding of deformation in this region.

Effect of a commercial peptidase on volatile composition and sensory properties of wheat bread crumb and crust

Flavourzyme is a commercial peptidase, primarily exhibiting exopeptidase activity. The effects of Flavourzyme addition (0–1.6 g/kg, flour basis) on chemical composition, volatile profile and sensory properties of bread crumb and crust were systematically studied. Free amino acids (from 999 to 2156 mg/kg with 1.6 g/kg Flavourzyme addition) and trichloroacetic acid-soluble small peptides in dough remarkably increased with Flavourzyme addition. Gas chromatography-mass spectrometry analysis revealed that 3-methyl-1-butanol, 3-(methylthio)-1-propanol, 2-phenylethanol, acetoin and indole enhanced in crumb after Flavourzyme addition. Meanwhile, pyrazines, benzaldehyde, 5-methyl-2-furanmethanol, maltol and 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one accumulated in crust. Descriptive sensory analysis revealed that the cheesy and alcoholic notes of crumb and the caramel, toasted and nutty notes of crust were strengthened with Flavourzyme addition. The Flavourzyme hydrolysis products enhanced yeast activity in fermentation and facilitated Maillard reactions in baking, leading to the accumulation of related volatile compounds. These compounds subsequently modified the aroma properties of crumb and crust.