Pattern Of Uplift Research Articles

Exhumation and topographic evolution of the Chiapas Massif Complex (southern Mexico) constrained by thermochronologic data modeling along vertical profiles

Thermochronometry is used to better understand the processes responsible for Cenozoic magmatism and exhumation of the Chiapas Massif Complex that spans a diffuse triple junction between the Caribbean, North American and Cocos plates. A combination of zircon U-Pb, apatite fission tracks, (U-Th)/He as well as numerical modeling show contrasting histories. Exhumation started earlier in the south (~16 Ma) relative to the north (~9 Ma). Northern exhumation is related to activity on the Tonalá fault system, while to the south it may be correlated with transpressive deformation in Chiapas fold-and-thrust belt. The southern block also experienced significant topographic growth from ~5 Ma to ~1 Ma followed by intense erosion. Overall, the pattern of uplift is in agreement with the ‘closing zipper’ model in which a forearc sliver is progressively incorporated to the North American plate. Thermal models also support a Pleistocene decrease in topography consistent with independent paleoenvironmental and geomorphologic evidences.

Detection of time variable gravity signals using terrestrial clock networks

The relativistic redshift between two earth-bound clocks can be interpreted in terms of gravity potential variation between the clock locations. A clock with a fractional frequency uncertainty of 10-18 is sensitive to a gravity potential variation of 0.1 m2/s2 or a height difference of 1 cm. Case studies for four regions affected by different mass change processes - Himalaya, Amazon, Greenland, and Fennoscandia - have been carried out. As the clocks rest on the deformable Earth’s surface, clock observations do not only include potential variations due to mass changes but also associated variations due to the vertical deformation of the land. For the simulations, vertical displacements were derived from real GNSS (Global Navigation Satellite Systems) measurements, and mass variations were computed from GRACE (Gravity Recovery And Climate Experiment) solutions. In the Himalayan region, seasonal variations with a maximum range of -0.20.2 m2/s2 were obtained. There, early and long-lasting precipitation patterns in North-East India and the gradual spreading towards the West can be observed by a dedicated clock network. For the Amazon region, seasonal variations with a maximum range of -0.50.5 m2/s2 observed by clocks also reveals the Amazon’s seasonal properties of annual rainfall variability at the North and South of the equator. The rainy season in the North of the equator is during the summer season from June to August, but from November to April in the South of the equator. The long-term trend of the ice mass loss in Greenland between 2004 and 2015 causes signals of potential variations of 1 m2/s2 that again can clearly be observed by clock measurements. Especially, the higher rates of mass variations in the west and south parts of Greenland can well be observed. The land uplift pattern of Fennoscandia due to the GIA (Glacial Isostatic Adjustment) can also be detected using optical clocks, however, the vertical deformations dominate the signal and not the mass changes. These examples illustrate that terrestrial clock networks can be used in the future as a modern tool for detecting various time-variable gravity signals for understanding the regional/local patterns of the variations and for providing complementary information to other geodetic techniques.

Rock-uplift history of the Central Pontides from river-profile inversions and implications for development of the North Anatolian Fault

Major strike-slip fault systems on Earth, like the North Anatolian Fault (NAF), play an important role in accommodating plate motion, but surprisingly little is known about how such structures evolve through space and time. Along the central sector of the NAF in the Central Pontides, transpression and crustal thickening along the northward restraining bend of the fault are thought to have generated rock-uplift rates of 0.2–0.3 km/Myr since at least 400 ka based on Quaternary marine and river terraces, while data from low-temperature thermochronology suggest that an enhanced exhumation phase occurred within the last 11 Myr. However, the precise onset of this faster uplift phase, which likely reflects deformation associated with the development of the central sector of the NAF, is poorly constrained.Here we define the spatiotemporal pattern of rock-uplift rates within the Central Pontides over the last ∼10 Myr by performing linear inversions of 19 river profiles that drain the northern margin of the Central Pontides, from the Sinop Range to the Black Sea. We use 21 new 10Be-derived basin-average denudation rates to calibrate an erodibility parameter, which we use to convert our χ-transformed river profiles into rock-uplift histories. Our results document an increase in rock-uplift rates after 10 Ma, with peak rates of ∼0.15–0.25 km/Myr occurring between 4 and 2 Ma. Moreover, the spatiotemporal pattern of uplift suggests that faster rock uplift started in the eastern part of the Sinop Range and migrated westward over a period of ca. 2 to 2.5 Myr, which we relate to the westward propagation of the NAF through this sector at a rate of 74 ± 13 km/Myr. In the context of previously published constraints on the westward propagation of the NAF starting in eastern Turkey at ∼12 Ma, our results suggest differences in fault-propagation rates that coincide with differences in the orientation of the NAF relative to plate-convergence velocity vectors. Fault segments with higher obliquity appear to have propagated at rates up to 2-fold slower than those oriented more parallel to the plate-convergence vector.

Active Deformation Pattern in the Western Flank of the Central Taurides, Southern Margin of the Central Anatolian Plateau: Inferences From Geomorphic Markers and Kinematic Indicators

AbstractThe southwestern margin of the Central Anatolian Plateau corresponds to the upper crust of the subduction between African and Anatolian plates, with a high relief of up to 2 km. This mountainous region has distinctive geomorphological features and presents a unique setting to investigate the mechanism of orogenic plateau margin development related to subduction and topographic evolution around the Eastern Mediterranean. We present new kinematic data from exposed fault planes and tectonic landforms from high‐resolution digital elevation models to elucidate the deformation pattern and its relation with the crustal deformation. We evaluate the deformation pattern based on the spatial distribution of kinematic analyses and geomorphic markers like low relief upland surfaces, disrupted karst basins, knickpoints, and deep bedrock incisions from watershed to shoreline. Our geomorphic analysis reveals a post‐orogenic transient actively deforming topography. The geomorphic markers constrain long‐term surface uplift pattern with a mean cumulative surface uplift of 1,710 ± 50 m and shows an increasing trend from west to east, from 1,600 ± 50 to 1,800 ± 50 m. Our results suggest a dome‐like uplift pattern in the west‐east direction across the southern margin that reaches up to maximum cumulative uplift values in the quadrangle of Alanya‐Başyayla‐Ermenek‐Gazipaşa. Our kinematic measurements along the youngest generation of faults revealed an active NE‐SW extensional deformation across a broad 200 km zone in the north of the subduction. Our findings have significant implications for understanding the morphotectonic evolution and post‐orogenic deformation in the plateau margins and geodynamic evolution of the Eastern Mediterranean.

Northeastward expansion of the Tibetan Plateau: Topographic evidence from the North Qinling Mts.–Weihe Graben Coupling system, Central China

Mountain-Basin Coupling systems form during late stages of the collisional orogeny when mountains rise compared to the adjacent sedimentary basins. In this study, we focus on the spatial and temporal pattern of uplift, subsidence and related topographic features of the transtensional Weihe Graben–North Qinling Mountain Coupling system, at the northeastern extension of the Tibetan Plateau. The opening of the Weihe Graben and the ongoing high seismicity in the Weihe Graben result from the lateral extrusion of the Qinling Block away from the Tibetan Plateau. We quantify the influence of uplift gradients on topography and drainage divides by (a) carrying out field surveys, (b) conducting a digital elevation model-based analysis of topographic properties, and (c) compiling and integrating data on exhumation, uplift, subsidence, and denudation of numerous previous studies. Together, these morphological analyses show that the influence of the uplift of the Tibetan Plateau on the study area gradually decreases from the westernmost Taibai Mts. to the easternmost Huashan Mts. We found large χ gradients across the drainage divide of the Huashan Mts. and river piracy implying a southward migration of the drainage divide in the Huashan Mts. We conclude that the initial exhumation of the North Qinling Mts. occurred during the Lower Eocene to Oligocene (cycle 1). As peneplanation surfaces formed, this implies discontinuous exhumation and surface uplift. A second stage of uplift occurred in the Oligocene to Middle Miocene (cycle 2), followed by the third stage from Middle to Upper Miocene (cycle 3). The final period of uplift occurred from latest Miocene to Holocene times (cycle 4). The uppermost Miocene to Holocene geomorphological features imply surface uplift within the westernmost North Qinling Mts. and are controlled by the inflation of a mid-crustal magma layer, prograding from the eastern Tibetan Plateau towards the Taibai Mts., associated with lateral extrusion of the Qinling Block away from the rising Tibetan Plateau. The high seismicity of the Weihe Graben implies ongoing tectonic activity influenced by deep-seated lithospheric motion.

Plan‐Form Evolution of Drainage Basins in Response to Tectonic Changes: Insights From Experimental and Numerical Landscapes

AbstractSpatial gradients in rock uplift control the relief and slope distribution in uplifted terrains. Relief and slopes, in turn, promote channelization and fluvial incision. Consequently, the geometry of drainage basins is linked to the spatial pattern of uplift. When the uplift pattern changes, basin geometry is expected to change by migrating water divides. However, the relations between drainage pattern and changing uplift patterns remain elusive. The current study investigates the plan‐view evolution of drainage basins and the reorganization of drainage networks in response to changes in the spatial pattern of uplift, focusing on basin interactions that produce globally observed geometrical scaling relations. We combine landscape evolution experiments and simulations to explore a double‐stage scenario: the emergence of a fluvial network under block uplift conditions followed by tilting that forces drainage reorganization. We find that the globally observed basin spacing ratio and Hack's parameters emerge early in the basin formation and are maintained by differential basin growth. In response to the tilting, main divide migration induces basin size changes. However, basins' scaling relations are mostly preserved within a narrow range of values, assisted by incorporation and disconnection of basins to and from the migrating main divide. Lastly, owing to similarities in landscape dynamics and response rate to uplift pattern changes between experiments and simulations, we conclude that the stream power incision model can represent fluvial erosion processes operating in experimental settings.

3D Evolution of Detachment Fault Systems in Necking Domains: Insights From the Klakk Fault Complex and the Frøya High, Mid‐Norwegian Rifted Margin

AbstractDetachment fault systems typically record displacements in the order of 10s of kilometers. The principles that control the growth of smaller magnitude normal faults are not fully applicable to the evolution of detachment fault systems. We use interpretation of 2D and 3D seismic reflection data from the mid‐Norwegian rifted margin to investigate how the structural evolution of a detachment fault interacted with the effects of isostatic footwall rollback to produce complex 3D geometries and control the configuration of associated supradetachment basins. We further investigate the effects of lateral interaction and linkage of extensional detachment faults on the necking domain configuration. In our study area, the domain‐bounding Klakk Fault Complex demonstrates how successive incision may induce a complex structural relief in response to faulting and fault plane folding. We interpret the previously proposed metamorphic core complex within its footwall as an extension‐parallel turtleback‐structure. The now eroded turtleback is flanked by a major supradetachment basin, connecting two main basin segments. We attribute footwall‐ and turtleback exhumation to Middle Jurassic‐Early Cretaceous rifting. The study area further demonstrates how detachment fault geometries can change during rifting and lead to the formation of younger, successively incising fault splays. Lateral linkage between the original detachment fault plane and these fault splays enables displacement along a detachment fault system consisting of fault segments generated at different stages in time. Implicitly, detachment faults are complex 3D systems that change configuration during their evolution, perpetually controlling associated basin formation, footwall configuration, subsidence and uplift patterns.

Deciphering complexity of block-faulted topography – Insights from morphometric variables, drainage patterns and river profiles (Orlickie-Bystrzyckie Mountains Block, Central Europe)

The Orlickie-Bystrzyckie Mountains Block (OBMB) is a medium-size, transboundary morphostructure within the Sudetes range in Central Europe, subject to non-uniform uplift in the late Cenozoic. Geologically, it consists of Variscan basement and Permian to Cretaceous sedimentary cover. This paper attempts to unravel its morphotectonic history and decipher the spatial pattern of uplift and erosional response, using several complementary, quantitative approaches to characterize topography. The focus is on: (1) general relief properties captured by selected topographic variables; (2) fault-generated escarpments, which define the eastern and northern limits of the study area; (3) drainage patterns and its peculiarities; (4) diversity of longitudinal river profiles and valley morphology. A LiDAR-based high-resolution digital terrain model was the primary source of elevation data. An important component of the study was examination of the role of lithological diversity on relief properties. A statistical approach generally revealed a secondary role of the rock factor and provided a foundation to interpret the macro-topography of the OBMB in terms of tectonic controls. Based on geomorphometric characteristics and information about the distribution of sedimentary rocks, which can be used as marker horizons to identify vertical displacements, four major and one secondary centres of surface uplift have been recognized. They are all asymmetric, being bounded by distinct fault-generated escarpments on one side and sloping gently in the opposite direction. Erosional response to uplift has been variable and includes, apart from simple incision into rising crustal blocks, the origin of epigenetic-antecedent water gaps, drainage diversions, headward erosion, and captures. This study also reveals that morphometric indices routinely used to extract the tectonic signal from landform patterns do not necessarily provide consistent information.

Isolating climatic, tectonic, and lithologic controls on mountain landscape evolution.

Establishing that climate exerts an important general influence on topography in tectonically active settings has proven an elusive goal. Here, we show that climates ranging from arid to humid consistently influence fluvial erosional efficiency and thus topography, and this effect is captured by a simple metric that combines channel steepness and mean annual rainfall, ksnQ. Accounting for spatial rainfall variability additionally increases the sensitivity of channel steepness to lithologic and tectonic controls on topography, enhancing predictions of erosion and rock uplift rates, and supports the common assumption of a reference concavity near 0.5. In contrast, the standard channel steepness metric, ksn, intrinsically assumes that climate is uniform. Consequently, its use where rainfall varies spatially undermines efforts to distinguish climate from tectonic and lithologic effects, can bias reference concavity estimates, and may ultimately lead to false impressions about rock uplift patterns and other environmental influences. Capturing climate is therefore a precondition to understanding mountain landscape evolution.

Recent Uplift Characteristics of the Southeast Tibetan Plateau, an Analysis Based on Fluvial Indices

The southeastern Tibetan Plateau (SETP) is well known for its large strike–slip faults with high slip rates and a high potential for seismic hazards. However, little is known about its thrust faults and associated seismic hazards, even though they can produce devastating earthquakes despite their relatively low slip rate. Here we investigated the thrust faults and the recent tectonic uplift pattern in the SETP on a regional scale by combining geomorphic analysis and geodetic data. We quantify the potential differential uplift in the SETP recorded in the long-term landscape evolution with geomorphic indices and compare them with differential uplift derived from decadal leveling data and millennial-scale fluvial terrace incision rates. The results show that the northwest of the SETP underwent higher uplift rates compared to its southeast areas, which is in agreement with the GPS-based leveling. Essentially, the geomorphic indices build two value ranges that are spatially clustered and separated by the Muli thrust fault system, a transverse fault system, which is orientated oblique/perpendicular to the large strike–slip fault. The geomorphic indices indicating rapid uplift rates spatially correspond with high rates derived from leveling data on the northwest side of the Muli thrust fault. The Muli thrust fault, therefore, acted as an important topographic and tectonic boundary absorbing partial southeast crustal movement. Hence, further detailed studies, such as seismological investigations, are suggested to be conducted on the Muli fault for seismic hazards evaluation.

Old orogen – young topography: Evidence for relief rejuvenation in the Bohemian Massif

Abstract The Bohemian Massif is the relic of a major Paleozoic mountain range that is known to have exhumed and its surface levelled in the Permian, but its Neogene landscape evolution is largely unconstrained. The landscape is characterized by rolling hills and extended planation surfaces above an elevation of about 500 m. However, at lower elevations deeply incised gorges confined by steep hillslopes are abundant and contrast impressively with the low relief landscapes above. Rivers with a bimodal morphology (i.e. steep at lower elevations and gentle at higher elevations) drain either to the north into the Vltava (Moldau) River or to the south into the Danube River. Hence, a continental drainage divide runs through the Bohemian Massif. Here, we quantify spatial characteristics of the Bohemian Massif landforms by computing landscape metrics like steepness index or geophysical relief derived from digital elevation models. From this we infer temporal change of the landscape in the past and predict them for the future evolution of the region. We show that the landscape is characterized by out-of-equilibrium river profiles with knickpoints abundantly at elevations between 450 m and 550 m separating steep channel segments at lower elevations from less steep channels at higher elevations. Hypsometric maxima at or close above knickpoint elevations, along with high and low values in geophysical relief as indicator for the degree of fluvial landscape dissection downstream and upstream of major knickpoints, support the idea of landscape bimodality. Furthermore, we find a distinct drainage divide asymmetry, which causes the reorganization of the drainage network of the region. Across-divide gradients in channel steepness predict the northward migration of the Danube-Vltava drainage divide including growth and shrinkage of tributary catchments, thus controlling changes in the Central European drainage pattern. All aspects suggest that the region experienced relief rejuvenation during the last few million years. We suggest that this relief rejuvenation is related to the inversion of the Molasse basin with a long wavelength rock uplift pattern and low uplift rates. Vertical motion of crustal blocks at discrete faults may locally affect the uplift pattern. However, the contrasting bedrock properties between the sedimentary cover (Molasse sediments) and the crystalline basement (Bohemian Massif) cause substantial differences in erosion rate and are thus the superior control on the topographic variations of the entire region.

Orogenic-orographic feedback and the rise of the Central Andes

The rise of large mountain ranges is considered to be driven by tectonics potentially coupled with climate driven-erosion, although the role of this coupling remains uncertain. The arid climate of the Central Andes allows us to strengthen our understanding of the relative roles of these processes in mountain range development globally. Here we compile estimates of exhumation, sedimentation, aridity and surface uplift across the Central Andes for the last 50 Ma. We aim to place constraints on the relative timing of rock uplift (displacement of rocks with respect to the geoid), exhumation (displacement of rocks with respect to the surface) and surface uplift (displacement of the earth's surface with respect to the geoid). We show that initial rock uplift of the Andes extends back at least 50 Myr. This rock uplift generated orographically driven precipitation on windward slopes leading to increased exhumation but limited preservation of surface uplift. Eastward propagation of the mountain range resulted in increasingly extreme orographic effects on the leeward side amplifying aridity, reducing exhumation and increasing preservation of surface uplift. Essentially, surface uplift shows a ∼5-10 Myr lag behind initial rock uplift as the Andes grow asymmetrically through time. We suggest that an eastward propagating pattern of exhumation, aridity and surface uplift with time, reconciles previous contradictory models of Andean uplift. One Sentence SummaryUplift of the Central Andes is reconstructed over the last 50 Myr and the precise relationship between roles of tectonics and climate established.

Seismic Induced Ground Deformation and Ionospheric Perturbations of the 29 July 2021, Mw 8.2 Chignik Earthquake, Alaska

AbstractThe subsurface, surface, and ionospheric characteristics associated with the 29 July 2021 Mw 8.2 Chignik Earthquake are studied in detail using continuous Global Positioning System (cGPS) data over Alaska. The cGPS‐inverted coseismic displacements demonstrate that the slip is distributed along the rupture area northeast of the epicenter with a maximum coseismic slip of ∼3.85 m occurring at a depth of ∼24.25 km. The vertical surface displacement estimated from the coseismic slip exhibits a similar deformation pattern with a maximum uplift of ∼1.0 m over the highly slip area. The ionospheric electron density perturbations associated with the Chignik earthquake were investigated using cGPS‐derived Total Electron Content (TEC) data. Unlike the northeast‐directed coseismic rupture and surface uplift, the ionospheric imprints of this event are more dominant southwest of the epicenter. This study reveals that the Earth's magnetic field and the ionospheric background electron density significantly controlled the TEC perturbation orientation and amplitudes rather than the rupture propagation and coseismic uplift pattern.

Long-term uplift pattern recorded by rivers across contrasting lithology: Insights into earthquake recurrence in the epicentral area of the 2016 Kumamoto earthquake, Japan

Topography results from the interplay between rock uplift and erosion, and studying river responses to active tectonics may enable the rates and spatial distribution of rock uplift to be inferred. Normalized channel steepness index (ksn) is widely used to infer rock uplift rates, and rock erodibility plays a significant role in determining the variation of channel steepness in response to external forces. Various measures may be applied to evaluate rock erodibility; however, since they are essentially qualitative, it is difficult to quantify relationships between rock mass strength and channel forms. In this study, we inferred long-term rock uplift rates along the Futagawa fault, an active normal-dextral fault, and the Idenokuchi fault, an active normal fault, in southwestern Japan, based on morphological characteristics of rivers across substrates with contrasting erodibility. The widely used detachment-limited model predicts that, when the rock uplift rate is spatially uniform, the ratio of erodibility of different rock types can be written by an inverse ratio of their ksn values. We employed this theoretical prediction to quantitatively calibrate the effects of rock mass strength on channel steepness. Within the study area, channel steepness was larger in the eastern part where volcanic rocks were exposed than in the western part where less resistant sedimentary rocks predominated. We calculated ratios of substrate erodibility using drainage basins close to the Futagawa fault that experienced similar rock uplift. Calibrated ksn exhibited a clear difference between the eastern and the western part of the fault, suggesting that contrasting erodibility alone cannot explain the observed channel steepness. We also confirmed that the observed channel steepness could not be explained without differential rock uplift, even when considering the combined effects of channel width, precipitation, and erosion process. The distribution of long-term rock uplift rates inferred from calibrated ksn and vertical slip rates of the fault compiled from published papers agree with the distribution of vertical displacement of the earthquake that occurred on the fault in 2016, suggesting that earthquakes similar to the 2016 event have occurred repeatedly in the study area.

Three-dimensional control of alluvial fans by rock uplift in an extensional regime: Aydın Range, Aegean extensional province

Tectonics imparts a first-order control on the overall morphology of alluvial fan systems in extensional settings by influencing sediment flux and accommodation space, while other factors such as climate, catchment lithology, and fault footwall characteristics are secondary. Previous alluvial fan modeling studies have focused on the link between the three-dimensional development of alluvial fans and rock uplift, however, despite the potential influence of tectonics on the overall three-dimensional morphology of alluvial fans, the controlling mechanisms, as well as their relative importance, remain largely unquantified in a natural setting with a targeted source-to-sink approach. Here, we examine 45 alluvial fans and their catchments along the southern mountain front of the Aydın Range, delimited by segmented normal faults in the western Anatolia Extensional Province, to quantify the role of rock uplift. We quantify river incision rates and catchment-wide erosion rates together with a series of topographic analyses across the southern flank of the Aydın Range as a proxy for rock uplift. Our results indicate that the spatial distribution of thicker and steeper alluvial fans fit well with higher rock uplift rates along the strike of the mountain front. In contrast, a lower uplift rate is responsible for prograding alluvial fans with decreasing thickness and gradients. Also, our data shows that alluvial fan thickness compared to other alluvial fan metrics strongly associated with the pattern of the rock uplift. This study demonstrates a field-based, quantitative linkage between three-dimensional alluvial fan morphology and rock uplift which has significant implications for improving alluvial fan models and understanding how alluvial fans respond to tectonics in extensional regions.

Out of phase Quaternary uplift-rate changes reveal normal fault interaction, implied by deformed marine palaeoshorelines

We have mapped and constrained the timing of tectonically deformed uplifted Late Quaternary palaeoshorelines in the Messina Strait, southern Italy, an area above a subduction zone containing active normal faults. The palaeoshorelines are preserved from up to thirteen Late Quaternary sea-level highstands, providing a record of the deformation over this timescale (~500 ka) for the Messina-Taormina Fault, the Reggio Calabria Fault and the Armo Fault. The palaeoshorelines reveal spatial patterns of uplift through time along the strike of these normal faults, and, given the across strike arrangement of the faults, also reveal how the contribution of each fault to the regional strain-rate progressed through time. The results reveal that the uplift rates mapped within the fault hangingwalls and footwalls were not constant through time, with a marked change in the location of strain accumulation at ~50 ka. The uplift rates, once converted into throw-rates, imply that the three faults comprised similar throw-rates prior to ~50 ka (in the range 0.77–0.96 mm/yr), with the Armo and Reggio Calabria faults then switching to lower rates (0.32 mm/yr and 0.33 mm/yr respectively), whilst the Messina-Taormina Fault accelerated to 2.34 mm/yr. The regional extension rate, gained by summing the implied heave rates across the three faults, was maintained through time despite this re-organisation of local strain accumulation at ~50 ka. We explain these out-of-phase fault throw-rate changes during the constant-rate regional extension conditions as due to interactions between these upper plate normal faults. We finally discuss how fault throw-rates changing through time may affect a long-term seismic hazard assessment within active normal fault systems.

3D geodynamic-geomorphologic modelling of deformation and exhumation at curved plate boundaries: Implications for the southern Alaskan plate corner

Plate corners with extreme exhumation rates are important because they offer a perspective for understanding the interactions between tectonics and surface processes. The southern Alaskan margin with its curved convergent plate boundary and associated zones of localized uplift is a prime location to study active orogeny. Here, we present the results of fully-coupled thermo-mechanical (geodynamic) and geomorphologic numerical modelling, the design of which captures the key features of the studied area: subduction of oceanic lithosphere (Pacific plate) is adjacent to a pronounced asymmetric indenter dipping at a shallow angle (Yakutat microplate), which in turn is bounded to the east by a dextral strike-slip shear zone (Fairweather fault). The resulting first-order deformation/rock uplift patterns show strong similarities with observations. In particular, relatively young thermochronological ages are reproduced along the plate-bounding (Fairweather) transform fault and in the area of its transition to convergence (the St. Elias syntaxis). The focused exhumation of the Chugach Core also finds its equivalent in model predicted zones of high rock uplift rates in an isolated region above the indenter. From these results, we suggest that the general exhumation patterns observed in southern Alaska are controlled by mutually reinforcing effects of tectonic deformation and surface erosion processes.

Tectonic segmentation by N-S-trending cona cross structure in the Eastern Himalaya: Evidence from thermochronology and thermokinematic modeling

The Main Himalayan Thrust (MHT), the most prominent tectonic boundary between the subducting Indian crust and the overthrusting Himalaya, occurs as a key structure dominating the active tectonics of the Himalaya. Previous studies indicate that the MHT forms a major buried ramp in the mid-crust, which with varying geometry and kinematics leads to a distinctive pattern of uplift along the Himalaya. However, it is unknown if and how these along-strike variations are correlated with the well-known active N-S-trending normal faults across the Himalaya and Tibetan Plateau. In this study, we report 39 new apatite and zircon fission track ages in the Cona area (~92°E) in the eastern Himalaya, coinciding with the easternmost N-S-trending extensional system in southern Tibet, the Cona Cross Structure (CCS). Spatial patterns of surface cooling ages are consistent with an overthrusting of the Himalayan wedge above a mid-crustal ramp in the MHT. Thermokinematic inverse modeling yields contrasting geometries and kinematics for the mid-crustal ramp on both sides of the CCS. Specifically, to the west of the CCS, the MHT developed a major ramp (with a dip angle of 20.4 ± 2.9°) spanning 50–70 km, which initiated at ~11.7 ± 0.6 Ma. To the east, thermokinematic inversion suggests a much less developed ramp spanning only ~10–15 km, initiated at ~6.8 ± 0.3 Ma. These results imply an ~14-km deeper depth of the MHT to the west of the CCS than to the east. Our modeling also suggests distinctive and evolving ramp-thrusting rates for the MHT on both sides of the CCS. This suggests an independent deformation accommodation by the MHT ramp thrusting in segments divided by the CCS along strike. Our study highlights a genetic correlation between the active orogenic-parallel ramp evolution and the N-S-trending faulting across the Himalaya, which divides the orogenic-parallel tectonics into independent structural segments.

Role of Poroelasticity During the Early Postseismic Deformation of the 2010 Maule Megathrust Earthquake

AbstractMegathrust earthquakes impose changes of differential stress and pore pressure in the lithosphere‐asthenosphere system that are transiently relaxed during the postseismic period primarily due to afterslip, viscoelastic and poroelastic processes. Especially during the early postseismic phase, however, the relative contribution of these processes to the observed surface deformation is unclear. To investigate this, we use geodetic data collected in the first 48 days following the 2010 Maule earthquake and a poro‐viscoelastic forward model combined with an afterslip inversion. This model approach fits the geodetic data 14% better than a pure elastic model. Particularly near the region of maximum coseismic slip, the predicted surface poroelastic uplift pattern explains well the observations. If poroelasticity is neglected, the spatial afterslip distribution is locally altered by up to ±40%. Moreover, we find that shallow crustal aftershocks mostly occur in regions of increased postseismic pore‐pressure changes, indicating that both processes might be mechanically coupled.

Seismically-induced changes in sea-level markers: Jolly Buoy Island, South Andaman

Sea-level markers like coastlines, landforms, tidal notches and coral reefs can unveil the seismic behaviour of subduction processes. Jolly Buoy Island, South Andaman, has undergone a remarkable change in shape and orientation due to rising sea levels and active tectonics. Involving integrated field, remote sensing and GIS techniques, we systematically estimated shoreline change rate, reef uplift and morphometry of tidal notches to track inter-, co- and postseismic periods. We quantified higher subsidence rates in the SW coast (−0.227m) than in the NE coast (−0.128m) during the coseismic period from geomorphology and biological resource mapping. The uplift was evident during the postseismic period in the NE and Eastern part of the Island compared to the SW and Western coast. The shoreline change analysis corroborates the results of the seaward migration of the northeast coastline. A gradual fading of uplift towards the southwest coast cause erosion in that part. The tidal notches identified during fieldwork also suggest similar subsidence and uplift patterns. Finally, here we proposed a model of geomorphological evolution of Jolly Buoy with possible local tectonic connections. More seismic data and geomorphic evidence from other islands can reveal regional significance.