Rheological Structure Research Articles

The Growth of Europa's Icy Shell: Convection and Crystallization

AbstractThe thickness of Europa's icy shell, which controls its thermal and rheological structure, cannot currently be directly measured. However, it can be estimated through indirect methods, including geodynamic modeling. We simulate the crystallization of the ice shell from a liquid water ocean and its subsequent thermal equilibration in the presence of tidal heat. We evaluate the effects of solid‐state stagnant lid convection on the shell's thermal equilibrium thickness and shell formation timing. The thermal equilibrium thickness of the ice shell ranges from 5 to 30 km, depending on the imposed tidal flexure strain rate. The ice lithospheric thickness remains less than 8 km, independently of imposed tidal flexure strain rate, overall shell thickness, and surface temperature, suggesting the Europan ice lithospheric strength is globally uniform. Thermal convection significantly reduces the thermal equilibration time scale, with the Europan ice shell able to fully crystallize out from a liquid water ocean in less than 2 Myr. Heterogeneous thermal equilibrium thickness values across the satellite suggest that widespread crystallization and melting may occur at the base of the shell. Rapid melting and crystallization timing suggest that the young surface age of the Europan ice shell may be the result of rapid catastrophic whole‐shell melting and recrystallization entirely recycling the surface.

Differences in east-west thermo-rheological structure and lithospheric deformation in the Qaidam Basin, Northern Tibetan Plateau, China

ABSTRACT To investigate the differences in east-west lithospheric deformation in the Qaidam Basin, we present thermo-rheological models of two profiles across the western Qaidam Basin (WQB) and eastern Qaidam Basin (EQB). The differences in east-west geodynamic deformation styles are also described, involving GPS motions, focal mechanisms (P axes), seismic anisotropy (SKS-wave splitting), and low-velocity zones (LVZs). The WQB is characterized by a warm destabilized cratonic basin with a weak lower crust, and the rheological structure changes from a rather weak crème brûlée-1 regime into a strong jelly sandwich-1 regime, from the Altyn-Qaidam boundary to the northeastern corner of the WQB. Combined with the limited distribution of the LVZs and the strong crust-mantle decoupling revealed by the unmatched pattern between P axes (N20ºE) and SKS-wave splitting (N110°E), the crust-mantle mixing related to the under-thrusting of the Tarim Basin along the Altyn Tagh Fault is suggested as the primary tectonic dynamic inducement of the destabilized WQB craton, which weakens the lithospheric strength greatly and contributes to the shallow brittle deformation. However, the EQB performs as a typical cold and rigid cratonic basin characterized by a jelly sandwich-2 rheological regime, which is sufficiently strong to maintain crust-mantle coupling. The LVZs beneath the EQB revealed by recent wide-angle seismic profiles have only a small effect on the lithospheric strength drop. The EQB could be regarded as a solid basin, anchored in the NE Tibetan Plateau, which shows a strong resistance to NE extrusion of the weak plateau material, leading to clockwise rotation.

A Novel Approach to the Analysis of the Soil Consolidation Problem by Using Non-Classical Rheological Schemes

The paper presents classical and non-classical rheological schemes used to formulate constitutive models of the one-dimensional consolidation problem. The authors paid special attention to the secondary consolidation effects in organic soils as well as the soil over-consolidation phenomenon. The systems of partial differential equations were formulated for every model and solved numerically to obtain settlement curves. Selected numerical results were compared with standard oedometer laboratory test data carried out by the authors on organic soil samples. Additionally, plasticity phenomenon and non-classical rheological elements were included in order to take into account soil over-consolidation behaviour in the one-dimensional settlement model. A new way of formulating constitutive equations for the soil skeleton and predicting the relationship between the effective stress and strain or void ratio was presented. Rheological structures provide a flexible tool for creating complex constitutive relationships of soil.

Seismicity and Pn Velocity Structure of Central West Antarctica

AbstractWe have located 117 previously undetected seismic events mainly occurring between 2015 and 2017 that originated from glacial, tectonic, and volcanic processes in central West Antarctica using data recorded on Polar Earth Observing Network (POLENET/ANET) and UK Antarctic Network (UKANET) seismic stations. The seismic events, with local magnitudes (ML) ranging from 1.1 to 3.5, are predominantly clustered in four geographic regions; the Ellsworth Mountains, Thwaites Glacier, Pine Island Glacier, and Mount Takahe. Eighteen of the events are in the Ellsworth Mountains and can be attributed to a mixture of glacial and tectonic processes. The largest event noted in this study was a mid‐crustal (∼19 km focal depth; ML 3.5) normal mechanism earthquake beneath Thwaites Glacier. We also located 91 glacial events near the grounding zones of Thwaites Glacier and Pine Island Glacier that are predominantly associated with time periods of significant calving activity. Eight events, likely arising from volcano‐tectonic processes, occurred beneath Mount Takahe. Using Pn travel times from the seismic events, we find laterally variable uppermost mantle structure in central West Antarctica. On average, the Ellsworth Mountains are underlain by a faster mantle lid (VPn = ∼8.4 km/s) compared to the Amundsen Sea Embayment region (VPn = ∼8.1 km/s). Within the Amundsen Sea Embayment itself, we find mantle lid velocities ranging from ∼8.05 to 8.18 km/s. Laterally heterogeneous uppermost mantle structure, indicative of variable thermal and rheological structure, likely influences both geothermal heat flux and glacial isostatic adjustment spatial patterns and rates within central West Antarctica.

Postseismic Deformation due to the 2012 Mw 7.8 Haida Gwaii and 2013 Mw 7.5 Craig Earthquakes and its Implications for Regional Rheological Structure

AbstractObservations of ∼7 years of postseismic deformation following the 2012 M w 7.8 Haida Gwaii and 2013 M w 7.5 Craig earthquakes in western British Columbia and southeastern Alaska provides insight into the regional rheologic structure and seismological hazards. A stress‐driven afterslip‐only model cannot alone explain rates or spatial patterns of the far field and later stage postseismic deformation measured by Global Positioning System (GPS). We thus develop an integrated model that fits the observations by combining afterslip on the deeper extension of the faults and distributed viscous flow in the asthenosphere. The best‐fit integrated model has a 60‐km thick lithosphere overlying a Burgers body asthenosphere with a Maxwell viscosity of 2 × 1019 Pa s (0.8–3 × 1019 Pa s at 95% confidence), with a Kelvin viscosity assumed equal to 10% of that value. These values are in good agreement with rheological models derived from glacial isostatic adjustment data. The early, near‐field postseismic deformation from both events is dominated by their corresponding afterslip, however, throughout the Craig postseismic period, the dominant mechanism in the far field is viscoelastic relaxation. For the intermediate region between the two earthquakes, both events contribute to the observed postseismic displacements. Because there was no obvious afterslip following the Haida Gwaii event or known large historical earthquakes on the southernmost part of the QCF, this region continues to have great potential to suffer a large earthquake in the future.

Morphological analysis of fibrous webs electrospun from Polycaprolactone, polylactic acid and their blends in chloroform based solvent systems

In this study, polycaprolactone (PCL), polylactic acid (PLA), and PLA/PCL blend electrospun fibrous webs are prepared using chloroform based solvent systems at different concentrations. The solvents to be used with chloroform are selected in accordance with the morphological and rheological structures of the polymers. While the morphology of the produced networks is observed under a scanning electron microscope, fiber diameter measurements and pore analysis are performed with Image J Software System. Although bead-free webs could not be achieved for neat PCL samples, neat PLA samples and PCL/PLA blends result in smooth fiber surfaces with homogeneous fiber diameter distributions. The results show that the increase in PLA concentration does not cause much change in fiber diameter but induces an increase in the area of pores. Furthermore, in the PLA/PCL blend, it is determined that as the ratio of PCL in the mixture increases, the fiber diameter decreases even if there is an acceptable reduction in the average pore area.

Swelling behaviour, rheological property and drug release profile of the anti-inflammatory drug metamizole sodium from xanthan gum–ZnO nanoparticles

In this study, our aim was to determine the effect of the polymer matrix on the drug delivery system; active-drug-loaded xanthan-gum (XaG)-based ZnO nanoparticles were synthesized under the ultrasonic irritation method. We characterized the structure using UV–Vis, SEM–EDX, FTIR and XRD techniques. The morphology of the nanoparticles has been carried out using SEM, and the results revealed that hexagonal disc structures were prepared with a size below 100 nm. The consideration of theoretical error analysis in estimating kinetic model parameters for simulating the drug release profile was incurred, to find a general model applicable to multimechanistic release. Five error analysis methods for identifying the kinetic model parameters have been calculated and their comparison based on goodness of fit. Results showed that drug-loaded XaG/ZnO nanoparticles released the drug with the Higuchi model (R2 = 0.97–0.99). We compared the viscosities of nanostructures obtained by using different synthesis methods such as magnetic stirring and ultrasonic irradiation at different times (10–20 min) to illuminate the rheological structure. Comparing Krigbaum and Wall parameters (Δb) for all samples, XaG/ZnO nanoparticles synthesized by ultrasonic irritation method proved to be an optimal miscible formulation. From the results, XaG/ZnO nanoparticles can potentially be recommended as a reliable nanocarrier with the release of metamizole sodium (MS) drug.

Meso‐Cenozoic rheological structure of the Linqing Depression: Implications for cratonic destruction

The evolution of the lithospheric rheological structure can reveal geodynamic processes of cratonic destruction. Using data of palaeo‐heat flow, crustal structure, and rheological parameters, we studied the rheological structure of the Linqing Depression. The results show that the lithosphere of the Linqing Depression experienced two stages of weakening, one in the Cretaceous and the other in the Palaeogene, with lithospheric strengths of approximately 2.09 and 1.67 × 1012 N/m and effective elastic thicknesses (Te) of approximately 24 and 20 km, respectively. The Meso‐Cenozoic rheological structures correspond to the ‘jelly sandwich’, ‘crème brûlée’, and ‘banana split’ models. The transformation of these models is closely related to the thermal regime, stress environment, and mantle water content of the Linqing Depression. The rheological structure evolution of the Linqing Depression is correlated with the cratonic destruction of the North China Craton. The geodynamic mechanism of lithospheric weakening in the late Early Cretaceous is related to the subduction and retreat of the Pacific Plate, and the lithospheric weakening in the late Early Palaeogene was a combined effect of the Indo‐Asian collision and subductions of the Pacific and Philippine Sea plates.

Strength variations of the Australian continent: Effects of temperature, strain rate, and rheological changes

The Australian continent is composed of several geologic provinces, showing a general age progression from Archean in the west to Phanerozoic in the east. The lithospheric heterogeneity and complex tectonic history of this region make it a key area for studying the thermal and rheological structure of the geological provinces and testing the influence of different conditions, such as temperature, rheology, and strain rate on the plate strength. In a previous study, temperature and compositional variations of the Australian upper mantle have been determined based on a joint interpretation of the seismic tomography and gravity data. In this study, we further implement a thermal model of the crust, based on available surface heat flow data from regional and global database. The crustal and upper mantle thermal models show different anomalies distribution, indicating a significant variation of the thermal conditions with depth. The new thermal models are used to estimate strength and effective elastic thickness ( Te ) distribution in the lithosphere. For this aim, we assigned the rheology of the crust based on the seismic velocities provided by the AuSREM model and used the strain rate values obtained from a global mantle flow model, constrained by seismic and gravity data. The maximal strength and Te are found in the West Australian Craton, on account of the low temperatures in the lithospheric mantle. We found that locations of the intraplate earthquakes attend to sharp changes in the lithospheric strength. Comparison of the results with those obtained for uniform rheology and strain rate, indicate that in the Officer basin the variations of the crustal rheology enhance the effect of temperature changes, while in the Yilgarn craton they reduce it. On the other hand, the lower values of the strain rate in the cratons than in the Phanerozoic regions influence the strength/ Te in the opposite way with respect to temperatures. Integrated strength (Pa m) and strength (Pa) variations along three cross-sections. Horizontal and vertical axes of the cross-sections display the distance and depth (both in km), respectively. (a) Integrated strength of the lithosphere. The three black lines show the location of the cross-sections; (b) Integrated strength of the crust. White circles show the earthquakes location, occurred from 1990 to present-day, with moment magnitudes (Mw) >2.5, taken from the USGS seismic catalogue ( https://earthquake.usgs.gov/earthquakes/search/ ); (c) Integrated strength of the mantle lithosphere; (d) Percentage of crustal strength; (e) Strength variations along three cross-sections (A-A′, B-B′, and C-C′, respectively). • A crustal themal and rheological model of the Australian continent is set up. • Crustal thermal anomalies correlate with surface heat flow variations. • Upper mantle thermal anomalies correlate with age of the tectonic features. • The strength distribution is strongly influenced by the temperature variations.

Seismic evidence for the crustal deformation and kinematic evolution of the Nansha Block, South China Sea

To understand the crustal deformation of the Nansha Block (NB), this study presents an interpretation of a recently acquired multichannel seismic profile that traverses the Southwest Subbasin (SWSB), the NB, and the Nansha Trough (NT). A total of six Cenozoic unconformities and three stratigraphic sequences are identified. On the basis of tectonic, structural and stratigraphic features, the NB is divided from northwest to southeast into two structural domains, namely, the Hyper-stretched and Forebulge Domains. Based on the interpretation of the seismic profile, the fault-derived and whole crustal extension factors (βf and βc, respectively) for the NB are calculated. The calculation results show that βc is greater than βf in a limited space of appr. 200 km, where the crust underwent depth-dependent extension. We suggest that the crustal extensional pattern of the NB may be a combination of distal limited depth-dependent extension and proximal uniform extension. The interpretation of the unconformities is also used to calculated the fault-derived crustal extension at various stages. The two main extension stages, the syn-rift and syn-drift, account for appr. 70% and 25% of the total extension, respectively. A comparison with the seismic profiles of the eastern NB shows that the crustal extension along the continental margin of the NB is heterogeneous, with more significant crustal deformation on the west side of the NB. The heterogeneity of the crustal extension along the depth and margin may be related to the thermal condition and rheological structure of the crust or lithosphere.

Thermal and Orbital Evolution of Low-mass Exoplanets

Abstract The thermal, orbital, and rotational dynamics of tidally loaded exoplanets are interconnected by intricate feedback. The rheological structure of the planet determines its susceptibility to tidal deformation and, as a consequence, participates in shaping its orbit. The orbital parameters and the spin state, conversely, control the rate of tidal dissipation and may lead to substantial changes in the interior. We investigate the coupled thermal–orbital evolution of differentiated rocky exoplanets governed by the Andrade viscoelastic rheology. The coupled evolution is treated by a semianalytical model, 1D parameterized heat transfer, and self-consistently calculated tidal dissipation. First, we conduct several parametric studies, exploring the effect of the rheological properties, the planet size, and the orbital eccentricity on tidal locking and dissipation. These tests show that the role of tidal locking into high spin–orbit resonances is most prominent on low eccentric orbits, where it results in substantially higher tidal heating than synchronous rotation. Second, we calculate the long-term evolution of three currently known low-mass exoplanets with nonzero orbital eccentricity and absent or yet-unknown eccentricity forcing (namely GJ 625 b, GJ 411 b, and Proxima Centauri b). The tidal model incorporates the formation of a stable magma ocean and a consistently evolving spin rate. We find that the thermal state is strongly affected by the evolution of eccentricity and spin state and proceeds as a sequence of thermal equilibria. Final despinning into synchronous rotation slows down the orbital evolution and helps to maintain long-term stable orbital eccentricity.

Lithospheric thermal regime under the Qinling Orogenic Belt and the Weihe Basin: A transect across the Yangtze and the North China cratons in central China

The thermal regime of the lithosphere could be a clue for the processes of geodynamics. Based on the Yuquan-Yulin seismic reflection transect along the Sichuan Basin (Yangtze Craton)–Qinling Orogenic Belt (QOB)–Weihe Basin–Ordos Basin (North China Craton), we modified crustal and mantle lithospheric structures to fit the observed data such as elevation, gravity, geoid height, and heat flow. Then we studied thermal structure, lithospheric thermal thickness and rheological structure of this area. The results suggest that the Moho temperature along the transect ranges from 580 to 740 °C; the thickness of the thermal lithosphere varies from 70 to 190 km. The rheological strength is characterized by the rheological characteristics of “weak crust-strong mantle” in the Sichuan Basin, the south QOB and the Ordos Basin, and “strong crust–weak mantle” in the north QOB and Weihe Basin. The Sichuan Basin has the lowest heat flow, the thickest lithosphere, and the strongest lithospheric strength, while the north QOB and Weihe Basin have the highest heat flow, the thinnest lithosphere, and the weakest lithosphere. The thermal regime of the Sichuan and Ordos basins is affected by the stability of the craton. The thermal regime of the QOB and Weihe Basin respond to the thermal effect of extensional/rifting tectonics. The thermal regime along the transect indicates that this area is mainly affected by the convergence caused by the continental collision of the Indian Plate.

Essential Nanostructure Parameters to Govern Reinforcement and Functionality of Poly(lactic) Acid Nanocomposites with Graphene and Carbon Nanotubes for 3D Printing Application.

Poly(lactic) acid nanocomposites filled with graphene nanoplatelets (GNPs) and multiwall carbon nanotubes (MWCNTs) are studied, varying the filler size, shape, and content within 1.5–12 wt.%. The effects of the intrinsic characteristics of nanofillers and structural organization of nanocomposites on mechanical, electrical, thermal, and electromagnetic properties enhancement are investigated. Three essential rheological parameters are identified, which determine rheology–structure–property relations in nanocomposites: the degree of dispersion, percolation threshold, and interfacial interactions. Above the percolation threshold, depending on the degree of dispersion, three structural organizations are observed in nanocomposites: homogeneous network (MWCNTs), segregated network (MWCNTs), and aggregated structure (GNPs). The rheological and structural parameters depend strongly on the type, size, shape, specific surface area, and functionalization of the fillers. Consequently, the homogeneous and segregated network structures resulted in a significant enhancement of tensile mechanical properties and a very low electrical percolation threshold, in contrast to the aggregated structure. The high filler density in the polymer and the low number of graphite walls in MWCNTs are found to be determinant for the remarkable shielding efficiency (close to 100%) of nanocomposites. Moreover, the 2D shaped GNPs predominantly enhance the thermal conductivity compared to the 1D shaped MWCNTs. The proposed essential structural parameters may be successfully used for the design of polymer nanocomposites with enhanced multifunctional properties for 3D printing applications.

Thermo-rheological structure of the northern margin of the South China Sea: Structural and geodynamic implications

Rheological properties of continental lithosphere are key controls on the behavior of continental deformation. Using thermal structure, constrained by surface heat flow data and measured thermal properties of rocks, the present study calculates different thermo-rheological structure scenarios for the ocean–continent transition (OCT) at the northern margin of the South China Sea, using two different models: a conventional model, taking into account frictional sliding and power-law creep, and a model that additionally includes a high-pressure brittle-fracture mechanism. Two compositions of the lower part of the lithosphere are considered: a soft case with felsic granulite lower crust and wet peridotite lithospheric mantle, and a hard case with mafic granulite lower crust and dry peridotite lithospheric mantle. The former scenario shows a major rheological change from a “jelly sandwich” to a “Christmas tree” type of rheology from north to south along the margin. This complex rheological structure explains lateral changes in earthquake distribution and geometries of extensional faults of the OCT at the northern margin of the South China Sea. Further, our analyses indicate that the initial lithospheric rheology profile probably has only one ductile layer in the lower part of upper crust. Such an initial lithospheric rheology model predicts focused extension to form asymmetric margins, which is the case for the SCS.

Mapping the Four‐Dimensional Viscosity Field of an Experimental Lava Flow

AbstractViscosity is a critical rheological property that determines the behavior, evolution, and final morphology of lava flows. Determining the viscosity of an active lava flow, however, is nontrivial. The rheological structure of lava is complex, and during active flow conditions, viscosity can change by orders of magnitude through space and time. This makes viscosity one of the most elusive properties of flowing lava. After almost a century of research on lava viscosity, it is still common practice to reduce the viscosity of a flow to a single value, generalizing an immense field of deviations and complexities. Considering lava viscosity as a one‐dimensional variable may be sufficient for characterizing some aspects of flows, but it does not allow for solving higher‐order rheological problems, such as depth structure, spatial variability, or rates of change. This study presents, for the first time, the four‐dimensional viscosity field of an actively flowing experimental lava. Results from this experiment include time‐series thickness, surface velocity, and temperature maps that are used to solve for the 4‐D viscosity of the lava flow with a spatial resolution of 2 cm. Additionally, the approach used in this study allows for an analysis of vertical rheological structure, specifically, crust and core viscosity layers. Although this study was performed in an experimental setting with crystal‐ and bubble‐free lava, the basic data collection techniques applied are common in field volcanology and thus could be applicable in certain natural settings.

Modeling Deformation and Stress States in the Island-arc Crust Considering Heterogeneous Rheological Structure

Modeling Deformation and Stress States in the Island-arc Crust Considering Heterogeneous Rheological Structure

Sensitivity of elastic thickness to water in the Martian lithosphere

Ancient Mars likely hosted oceans similar to those on Earth; however, such water is not presently observed on Mars. One possible explanation for the lack of present-day oceans is that surface water was transported into and stored within the interior of Mars throughout the geological history. As water can influence the rheological structure of the Martian lithosphere, we investigated the sensitivity of the elastic thickness of the lithosphere to water using recent laboratory data. Calculations indicate that the presence of water results in a significant decrease in elastic thickness relative to dry conditions at a given thermal structure. Gravity and topographic data acquired by the Mars Global Surveyor and other orbiters indicate a temporal change in elastic thickness during the geological history of Mars. The extremely thin elastic layer during the planet’s early history can be explained by a water-rich rheological model, whereas a dry rheology can account for the relatively thick elastic layer inferred during the later evolution of Mars. Although thermal evolution of Mars has a large uncertainty, the strong sensitivity of elastic lithospheric thickness to water suggests possible sequestered water into deeper levels during the early history of Mars.

Response of a Rheologically Stratified Lithosphere to Subduction of an Indenter‐Shaped Plate: Insights Into Localized Exhumation at Orogen Syntaxes

AbstractThis study investigates the influence of the 3‐D geometry of a down‐going plate, the rheological structure of the upper plate, and the migration of the overriding plate toward the trench in relation to the overall subduction velocity on the exhumation pattern in orogen syntaxes. Using a thermomechanical numerical code (DOUAR), we analyze the strain localization, rock uplift, and exhumation response of a rheologically stratified continental lithosphere to subduction of a convex‐upward‐shaped indenter. The models consider three thermorheological lithospheric profiles that determine the degree of mechanical coupling between the upper crust and lithospheric mantle. These models include a strong, cratonic lithosphere; a weaker, younger (and hotter) continental plate; and an intermediate case. The strongly coupled case predicts a localization of high rock uplift rates along narrow linear bands crossing the entire model domain parallel to the trench. In contrast, in a weakly coupled lithosphere, rock uplift is concentrated within a curved ellipse region of anomalously high exhumation rates located above the indenter apex. The aspect ratio of the localized area of rapid rock uplift is controlled by the initial width of the rigid indenter and the relationship between boundary velocities. In particular, the combination of little or no upper plate migration with a narrow indenter causes a nearly circular region (~100‐km diameter) of rapid exhumation that resembles the pattern of thermochronometer ages observed in orogen syntaxes such as the Southeast Alaska and the Olympic Mountains of the Cascadia subduction zone (western USA).

Tidally induced lateral variations of Io's interior

Satellite and recent Earth-based observations of Io's surface reveal a specific spatial pattern of persisting hotspots and sudden high-intensity events. Io's major heat producing mechanism is tidal dissipation, which is thought to be non-uniformly distributed within Io's mantle and asthenosphere. The question arises to what extent Io's non-homogeneous heat production can cause long-wavelength variations in the interior and volcanic activity at the surface. We investigate dissipation patterns resulting from two different initially spherical symmetric visco-elastic rheological structures, which are consistent with geodetic observations. The spatial distributions of the time-averaged tidal heat production are computed by a finite element model. Whereas for the first rheological structure heat is produced only in the upper viscous layer (asthenosphere-heating model), the second rheological structure results in a more evenly distributed dissipation pattern (mixed-heating model) with tidal heating occurring in the deep mantle and the asthenosphere. To relate the heat production to the interior temperature and melt distribution, we use steady-state scaling laws of mantle convection and a simple melt migration model. The resulting long-wavelength thermal heterogeneities strongly depend on the initial tidal dissipation pattern, the thickness of the convective layer, the mantle viscosity, and the ratio between magmatic and convective heat transport. While for the asthenosphere-heating model a strong lateral temperature signal with up to 190 K peak-to-peak difference can remain, convection within a thick convective layer, as for the mixed-heating model, can reduce the lateral temperature variation to <1 K, if the mantle viscosity is sufficiently low. Models with a dominating magma heat transport preserve the long-wavelength pattern of tidal dissipation much better and are favoured, because they are better to explain Io's thick crust. The approach presented here can also be applied to investigate the effect of an arbitrary interior heating pattern on Io's volcanic activity pattern.

Channel flow and fault segmentation with implications for the generation of earthquakes in the Longmenshan fault zone, eastern Tibetan Plateau

The Ms 8.0 Wenchuan earthquake occurred in the Longmenshan fault zone (LFZ) of the eastern margin of the Tibetan Plateau (TP). The tectonic activities in this region have been a focus of extensive studies in the past two decades. Two different models involving oblique stepwise rise and channel flow, respectively, are proposed and can be used to explain the generation of earthquakes. The oblique stepwise rise model emphasizes more about the fault of the upper crust, whereas the channel flow model concerns more about the different crustal rheological structures. Currently, because of the confirmation of geophysical data on the rheological structure of the TP, more researchers agree with the channel flow model. To investigate the generation of earthquakes in the LFZ, this study establishes a three-dimensional viscoelastic model based on the heterogeneity of the lithospheric structure and the segmentation of faults. Using ANSYS finite element software to simulate the evolution of stress and strain, the calculated results are consistent with focal mechanism solutions, fault striations, and topography. The best-fit stress field suggests that stress localization in the Longmenshan range is mainly controlled by the channel flow and fault segmentation. The differing viscosities and relative movement between the channel flow and the Sichuan Basin induce a concentration of stress in the LFZ. The stress was most concentrated in segment II, closest to the leading edge of the channel flow, and wherein the Wenchuan earthquake occurred. Additionally, the higher locking degree of segment II found before the Wenchuan earthquake induced higher stress levels at shallow depths, corresponding to higher seismic activity in segment II. Thus, the combined action of the channel flow and fault segmentation controls the distribution of stress and causes the generation of earthquakes in the LFZ.