Magnitude Of Uplift Research Articles

Effects of Vertical Motion on Uplift of Underground Structure Induced by Soil Liquefaction

The uplift of underground structures induced by soil liquefaction can damage underground structure systems. Numerical simulations have shown that uplift is positively correlated with the energy of horizontal input motion. However, the effects of vertical input motion on uplift have not been studied comprehensively in the past. Previous studies on the vertical motion concluded that the effects of vertical motion on uplift depend on the overall characteristics of earthquake motion. These motion characteristics have only been studied separately in previous studies. A comprehensive study to explore the interactions and overall effects of these characteristics on the uplift of underground structures is essential. In this study, the FLAC program with the PM4Sand model was used as a numerical tool to explore the effects of vertical input motion on the uplift of underground structures. The numerical model was calibrated using centrifuge test results, and 48 earthquake motions were selected as input motions to study the effects of the overall characteristics of earthquake motions on the uplift of underground structures. The simulation results show that the frequency content characteristics of horizontal and vertical motion are the major factors affecting the uplift magnitude and the responses of liquefiable soils. However, most simulation cases show that the inclusion of vertical motion causes a 10% difference in the tunnel uplift, compared to cases without vertical motion.

An improved analytical solution for solving the shield tunnel uplift problem

The problem of shield tunnel uplift is a common issue in tunnel construction. Due to the decrease in shear stiffness at the joints between the rings, uplift is typically observed as bending and dislocation deformation at these joints. Existing modeling methods typically rely on the Euler-Bernoulli beam theory, only considering the bending effect while disregarding shear deformation. Furthermore, the constraints on the shield tail are often neglected in existing models. In this study, an improved theoretical model of tunnel floating is proposed. The constraint effect of the shield machine shell on the tunnel structure is considered using the structural forms of two finite long beams and one semi-infinite long beam. Furthermore, the Timoshenko beam theory is adopted, providing a more accurate description of tunnel deformation, including both the bending effect and shear deformation, than existing models. Meanwhile, the buoyancy force and stratum resistance are calculated in a nonlinear manner. A reliable method for calculating the shear stiffness correction factor is proposed to better determination of the calculation parameters. The proposed theoretical model is validated through five cases using site-monitored data. Its applicability and effectiveness are demonstrated. Furthermore, the influences of soil type, buried depth, and buoyancy force on the three key indicators of tunnel floating (i.e. the maximum uplift magnitude, the ring position with the fastest uplift race, and the ring position with the maximum uplift magnitude) are analyzed. The results indicate that the proposed model can provide a better understanding of the floating characteristics of the tunnel structure during construction.

Post-rifting uplift and inversion of an intra-plate basin: The Doseo basin, Central Africa

There is a growing recognition that the post-rifting phase of basin evolution is far from being tectonically quiescent, as it can involve episodic uplift. However, the dynamic mechanisms responsible for this phenomenon remain a subject of controversy, particularly for intra-plate basins situated distant from active plate boundaries. Accurately determining the timing and magnitude of uplift is essential for elucidating the driving model behind these processes. In this study, we document the thermal history of the Doseo basin within the West and Central Africa Rift System (WCARS) using a combination of apatite fission track analysis and vitrinite reflectance data. Our findings reveal a period of accelerated exhumation during the late Eocene to Miocene epoch (∼45-20 Ma), characterized by kilometer-scale uplift, which corresponds to the formation of angular unconformities, folds, and fault-related anticlines. This specific time interval appears to be critical for the Cenozoic petroleum system, coinciding with the peak maturation of source rocks and the simultaneous formation of compressional traps. When integrated with the seismic data and previously published thermochronological data, our research reveals two significant cooling and uplift events in WCARS: a Santonian extrusion event and a late Eocene exhumation event. Both of these events have the potential to impact the entire tectonic plate, and Tethys realm. Furthermore, this two-stage exhumation event aligns closely with the timing of the Africa-Europe convergence collision. Consequently, we come to conclude that far-field lateral compression emerges as the dominant driving mechanism for intra-plate uplift, outweighing the influence of the mantle model.

Geological and biotic context of the Plio-Pleistocene evolution of the Caucasus-Caspian Region (Akchagylian transgression)

We discuss geological and biotic aspects of the extensive Akchagylian transgression that occurred in the Caspian region of Eurasia near the Plio-Pleistocene transition, in Piacenzian and Gelasian. It is shown that the onset of the Akchagylian marine sedimentation in Western Turkmenistan (ca. 3.2 Ma) preceded that in the Kura Basin (ca. 3.0 Ma). The position of the upper boundary of the Akchagylian remains uncertain (ca. 2.1 or 1.8 Ma). The analyzed biotic content of the Akchagylian includes molluscs, microfossils (pollen, dinocysts, foraminifers), and mammals. It is noted that specific forms of the Akchagylian aquatic biota co-occur with microfossils that clearly indicate a connection with the World Ocean or related seas. The palynology of the Akchagylian time signals a directed cooling in the Pliocene and Early Pleistocene with several warm and humid epochs. The Akchagylian transgression was preceded by a change of a structural-sedimentary pattern of the region. In the latest Miocene and Early Pliocene, a pre-existed longitudinal tectonic zonation of the Caucasian-Caspian segment of the Paratethys gradually changed into clearly transverse tectonic zonation. The latter was manifested in the tectonic uplift of the Greater Caucasus, its northern piedmonts and the Lesser Caucasus, and in the subsidence of the western parts of the South and Middle Caspian basins. The interplay of longitudinal and transverse tectonic features shaped the configuration of the Akchagylian brackish-water basin and controlled thickness of its deposits. It was the transverse zonation that dominated in the thickness pattern. The increasing role of the transverse zonation in the post-Akchagylian time is manifested in the magnitudes and rates of the Quaternary tectonic uplift. These parameters were calculated based on current heights of the top of the Akchagylian marine deposits in different parts of the basin. The highest magnitudes of uplift are found in the Eastern Caucasus (up to 1980 m on the NE slope and about 2500 m in the axial part) and in the west of the Lesser Caucasus in eastern Turkey (up to 1750 m). The maximum level of the Akchagylian transgression is estimated at 40–50 m above the present level of the World Ocean. We show a low probability of connection of the Akchagylian basin with the Mediterranean Sea or the Persian Gulf, and a high probability of its connection with the Arctic Ocean through the northern tributaries of the Kama River and the Pechora Basin in the NE of East European Plain.

Flexural Response to Erosional Unloading of Continental Margins: An Example From the Bering Sea, USA

AbstractThe geodynamic response of continental margins to erosion may reveal current and past changes in the location of the continental slope. We model the three‐dimensional isostatic response to erosion along the retreating Beringian Margin to test the hypothesis that the margin and its canyons were dominantly eroded during the Pleistocene. Our results predict 900 m of flexural uplift, though evidence for this magnitude of uplift is not observed in Pleistocene and younger deposits, suggesting a substantial amount of margin erosion occurred pre‐Pleistocene. Uplift of this magnitude may be represented by a Late Miocene unconformity across the Bering Shelf and upwarped subsurface units at the base of the Beringian Margin. The distribution of uplift from varying canyon incision and margin retreat scenarios has implications for the extent of geodynamic response during erosional periods.

Reconstruction of the Meso-Cenozoic tectono-geomorphological evolution of the Keguqin mountain in the Central Tian Shan based on geomorphological analysis and low-temperature thermochronology

Forming the northwestern branch of the Chinese Tian Shan, the Keguqin mountain located north of the Yili basin is characterized by Mesozoic relict landscapes and active faults, which recorded abundant information of long term tectono-geomorphologic evolution of the Tian Shan mountain range. However, the post-Jurassic deformation history of the Keguqin mountain is unclear. In this study, we applied apatite fission track, apatite (UTh)/He and geomorphologic analyses to reconstruct the landscape evolution of the Keguqin mountain and the northern Yili basin. Our results suggest that this region underwent three stages of accelerated cooling/exhumation in the Permian, Late Triassic-Jurassic and Cretaceous. The Permian cooling event likely reflects post magmatic cooling related to the Paleozoic orogeny of the Tian Shan. Late Triassic-Jurassic exhumation is possibly a far field response of the Qiangtang collision. The Cretaceous differential exhumation in the study area was controlled by activation of the Kashihe fault zone and secondary faults. As the Cretaceous cooling is widely observed in the vast Central Asia region, northern Tibet and Southern Pamir, and coeval with the Mongol-Okhotsk orogeny, Qiangtang collision and Karakorum collision. It is difficult to decipher the tectonic drive of the Cretaceous activation of the Kashihe fault zone. Relict landscapes in the Keguqin mountain were firstly established after the Paleozoic, slightly exhumed during the Cretaceous, and were uplifted and tilted by Late Cenozoic deformation. The latest uplift magnitude of the Keguqin mountain is estimated to be ∼250–500 m and ∼ 380–430 m of the hanging wall of the Kashihe fault zone and the Keguqin fault, respectively.

A meta-analysis of the impact of rail stations on property values: Applying a transit planning lens

• Introduction of 10 new variables to the rail access uplift meta-analysis literature. • Transit expenditure share and network expanse positively impact rail access premiums. • Rent control policies and ethno-racial dynamics affect rail access premiums. • Tests effects of Global Financial Crisis (2007–2009) on rail access premiums. • Expansion of geo-scope of rail access premium comparisons; includes Global South. Access to transit infrastructure is valuable. In areas surrounding rail stations, some of that value gets absorbed by property markets. Since 1970, over 200 case studies worldwide have explored the extent to which transit access impacts property value uplift. However, findings from this body of research vary widely. In an attempt to explain this variation, previous meta-analytic studies have focused on testing the roles that built environment elements, temporal factors, and modelling techniques play in shaping the observed relationship between proximate positioning from rail stations and property pricing. This study expands on these meta-analyses by introducing the first examination of how transit service elements – e.g. frequency, fare, reliability – impact rail-induced residential property value uplift. It further contributes to the literature by expanding the range of geo-comparability of uplift findings across four continents, examining the potential effects of the Global Financial Crisis of the late 2000s, and adding 10 new variables of potential influence not only under the banner of ‘transit service’, but pertaining to neighborhood socio-demographics and housing policy as well. Findings reveal that factors of geography, housing data type, race and ethnicity, rent control policies, rail type, transit cost, and transit network expanse all significantly affect rail access uplift magnitude ranging from depreciating effects of 7.4 percentage points to appreciating effects of 9.6 percentage points. Beyond helping to explain variation across the literature, these findings can be a useful tool for policymakers combatting trends of increasing market-driven displacement from transit-rich areas, those pursuing financing mechanisms for transit infrastructure, and to transit planners concerned with how their decisions may affect matters of housing equity for the communities they serve.

Characterization of Wind Gusts: A Study Based on Meteorological Tower Observations

Accurate information on wind gusts is of critical importance to various practical problems. In this study, observational wind data from high-frequency response (i.e., at a sampling rate of 10 Hz), ultrasonic anemometers instrumented at four different heights (i.e., 10 m, 40 m, 160 m, 320 m) on a weather tower were collected. The observation site featured a typical suburban condition, with no significant obstacles in the immediate proximity. The data were analyzed to identify a total of twelve descriptors of wind gusts, and to find the parent distributions that estimate these parameters well via regression analysis. The results show that the gust parameters in the context of gust magnitude and amplitude with units are best fit by the Weibull model, while non-dimensional parameters in terms of gust factor and peak factor are reasonably assessed by the log-logistic distribution. The uplift time and gust nonsymmetric factor generally exhibit a lognormal distribution, while the Gamma distribution can describe the gust length scale, uplift magnitude and passage time. It is also shown that gust factors increase linearly along with turbulence intensity. Nevertheless, empirical linear formulas given in previous studies tend to over-predict. For the vertical structure of gust descriptors, it is found that the average wind speed, gust amplitude and gust length scale in 10 min monotonically increase with height, whereas the function relationship of gust amplitude, peak factor, gust factor, turbulence intensity, rise amplitude and falling amplitude tends to decrease with height.

Re-Os Geochronology of the Liuchapo Formation across the Ediacaran-Cambrian Boundary of the Yangtze Block (South China)

The Ediacaran-Cambrian (E-C) succession in South China records remarkable oceanic, biological and geochemical variations, but it was not well defined geochronologically, which hinders the interpretation of the spatio-temporal seawater chemical architecture during the time E-C interval. This study presents two Re-Os isochron ages of 520.2 ± 6.1 and 561.7 ± 8.5 Ma for the barite-rich black shales from the top Liuchapo and Doushantuo formations respectively in Tianzhu County, Guizhou Province. In combination with existing age data, the two new Re-Os isochron ages suggest that the Liuchapo Formation was deposited between 550 and 520 Ma. Moreover, like the polymetallic Ni-Mo-PGE layers of shelf margin (or platform) facies and V-rich horizons of transitional (or shelf slope) to deep-water facies, the barite deposits were likely formed due to differential mineralization. The timing offset likely resulted from differential elemental concentration related to certain local factors (i.e., hydrothermal fluids, seawater redox and biological activity). The isochron-derived initial 187Os/188Os ratios of the top Liuchapo Formation (0.902 ± 0.048) and the Doushantuo Formation (0.740 ± 0.042) fall within the range of continental weathering flux (1.54) and oceanic crust (0.126), implying the involvement of marine hydrothermal fluids. Moreover, their difference of initial 187Os/188Os ratios may reflect variations of continental weathering intensity and uplift magnitude.

INSAR-BASED LOS SURFACE DEFORMATION COMPARISON OF METRO MANILA BEFORE AND AFTER THE JANUARY 2020 TAAL VOLCANO ERUPTION

Abstract. The city of Metro Manila has been constantly battered by several hazards on an annual basis. On January 2020, the Taal Volcano erupted with multiple recorded earthquakes. Previous literatures have found that Metro Manila is experiencing a steady subsidence. Determination of land uplift or subsidence is crucial in planning and mitigating the effects of flooding in the area. The study aims to determine whether an uplift occurred in Metro Manila after the eruption or is the study area still experiencing subsidence This study uses a pair L1 SLC Sentinel 1 Images. Radar Interferometry is used to generate Interferograms and Satellite Line of Sight (LOS) deformation was determined between the 2 dates of image acquisition. It was found that the Metro Manila area generally experienced an uplift except for some areas in Caloocan which shows subsidence. The uplift magnitude gradually decreases going from the South to North with a max value of 9.6 cm.

Cenozoic structural evolution of the Catalina metamorphic core complex and reassembly of Laramide reverse faults, southeastern Arizona, USA

AbstractThis study investigates the Late Cretaceous through mid-Cenozoic structural evolution of the Catalina core complex and adjacent areas by integrating new geologic mapping, structural analysis, and geochronologic data. Multiple generations of normal faults associated with mid-Cenozoic extensional deformation cut across older reverse faults that formed during the Laramide orogeny. A proposed stepwise, cross-sectional structural reconstruction of mid-Cenozoic extension satisfies surface geologic and reflection seismologic constraints, balances, and indicates that detachment faults played no role in the formation of the core complex and Laramide reverse faults represent major thick-skinned structures.The orientations of the oldest synextensional strata, pre-shortening normal faults, and pre-Cenozoic strata unaffected by Laramide compression indicate that rocks across most of the study area were steeply tilted east since the mid-Cenozoic. Crosscutting relations between faults and synextensional strata reveal that sequential generations of primarily down-to-the-west, mid-Cenozoic normal faults produced the net eastward tilting of ∼60°. Restorations of the balanced cross section demonstrate that Cenozoic normal faults were originally steeply dipping and resulted in an estimated 59 km or 120% extension across the study area. Representative segments of those gently dipping faults are exposed at shallow, intermediate (∼5–10 km), and deep structural levels (∼10–20 km), as distinguished by the nature of deformation in the exhumed footwall, and these segments all restore to high angles, which indicates that they were not listric. Offset on major normal faults does not exceed 11 km, as opposed to tens of kilometers of offset commonly ascribed to “detachment” faults in most interpretations of this and other Cordilleran metamorphic core complexes. Once mid-Cenozoic extension is restored, reverse faults with moderate to steep original dips bound basement-cored uplifts that exhibit significant involvement of basement rocks. Net vertical uplift from all reverse faults is estimated to be 9.4 km, and estimated total shortening was 12 km or 20%. This magnitude of uplift is consistent with the vast exposure of metamorphosed and foliated cover strata in the northeastern and eastern Santa Catalina and Rincon Mountains and with the distribution of subsequently dismembered mid-Cenozoic erosion surfaces along the San Pedro Valley. New and existing geochronologic data constrain the timing of offset on local reverse faults to ca. 75–54 Ma.The thick-skinned style of Laramide shortening in the area is consistent with the structure of surrounding locales. Because detachment faults do not appear to have resulted in the formation of the Catalina core complex, other extensional systems that have been interpreted within the context of detachments may require further structural analyses including identification of crosscutting relations between generations of normal faults and palinspastic reconstructions.

Pasternak Model-Based Tunnel Segment Uplift Model of Subway Shield Tunnel during Construction

Segment uplift is a frequent problem during the construction of shield tunnels. The phenomenon of segment uplift in Xuzhou Metro Line 1 is investigated. The segment uplift magnitude in the shale layer is quite smaller than that in the clay layer. A tunnel segment uplift calculation model based on the Pasternak foundation beam model is proposed, which considers the hardening process of the grouted body with time. The finite difference method is adopted to calculate the magnitude of segment uplift during different tunnel construction stages, and a numerical solution of segment uplift on the longitudinal direction is obtained. The applicability of the numerical solution is studied by comparing with the field test results and parametric analyses are also performed to investigate the effects of different factors on segment uplifting. The results show that the coefficient of subgrade modulus, shear stiffness of the shear layer, and grout pressure all influence the segment uplifting of the tunnel. The influence of the coefficient of subgrade modulus and grout pressure on segment uplift is more significant.

Thermal history reconstruction from apatite fission-track analysis and vitrinite reflectance data of the Bongor Basin, the Republic of Chad

The Bongor Basin in southern Chad is one of the Cretaceous–Paleogene rift basins developed on the Precambrian crystalline basement and has been confirmed as a petroliferous basin in the last decade. Less than 400 m of Cenozoic unconsolidated sediments are separated by an unconformity from an underlying section of Lower Cretaceous units, in turn separated by another unconformity from underlying Precambrian basement. In addition, there is a locally low-angle unconformity within the Cenozoic section. A synthesis of apatite fission-track analysis data in four wells from the basin reveals two cooling episodes from Late Cretaceous to early Paleocene (beginning between 75 and 60 Ma) and mid-Miocene, respectively. The results suggest that regionally synchronous cooling is a likely scenario. The first exhumation between 75 and 60 Ma affected the whole basin, and the magnitude of uplift and erosion was approximately 1100–1250 m across the whole basin. In contrast, the second exhumation during the Miocene affected mainly the northern part of the basin while the magnitude was weak and could not be detected in the southeast of the basin. Potential trapping structures, for example, fault blocks and synsedimentary anticlines, formed prior to and inverted anticlines as a result of the first cooling phase of exhumation (strong compressional inversion) and were available for hydrocarbon migration and accumulation during the main phase of hydrocarbon generation. The Miocene exhumation was less pronounced and had weak or no impact on the hydrocarbon generation and accumulation.

Seismic methods for fluid discrimination in areas with complex geologic history — A case example from the Barents Sea

We have developed a new scheme for calculation of density ratio, an attribute that can be directly linked to hydrocarbon saturation, and applied it to seismic amplitude variation with offset (AVO) data from the Hoop area in the Barents Sea. The approach is based on the inversion of Zoeppritz’s equation for PP-wave. Furthermore, by using interval velocities, we quantified uplift magnitude for a given interval beneath Base Cretaceous unconformity (BCU) horizon in the Hoop area. Depending on the temperature gradient, the maximum burial depth can be estimated, a crucial factor affecting the elastic properties of the rocks. Coupling uplift map with temperature history for key stratigraphic units from basin modeling enabled us to extend the training data away from well control. By doing so, we created nonstationary AVO probability density functions (PDFs) for calibration and classification of seismic attributes in the test area. This decreases the likelihood of misclassification of pore fluid type as opposed to the case where the training data are created based only on sparse well-log data. We tested and compared the methods on the Barents Sea seismic data set, and the results were validated at four well locations. Finally, maps of fluid distribution obtained from stochastic rock-physics modeling honoring burial history were compared against the density ratio map. Four maps revealed the same anomalous zones, the major difference being the detection of the down-flank presence of oil associated with some of the predicted gas anomalies in the prospect area, in the case of density ratio map. Possible gas caps were detected/predicted only for certain temperature constraints during the AVO classifications and were most obvious in the density ratio map.

Laramide Uplift near the Ray and Resolution Porphyry Copper Deposits, Southeastern Arizona: Insights into Regional Shortening Style, Magnitude of Uplift, and Implications for Exploration

AbstractThis study integrates new geologic mapping and structural analysis with previous work near Walnut Canyon and Telegraph Canyon to address the style and magnitude of shortening and the relationship between contractional structures and porphyry preservation and localization between the Ray and Resolution porphyry copper deposits. Cenozoic extensional structures were superimposed on earlier contractional structures formed during the Laramide orogeny, which dates from ~80 to 50 Ma. This superposition requires that Cenozoic normal faults be restored prior to analysis of Laramide contractional structures and their relationship to nearby porphyry copper deposits. Five distinct sets of normal faults within the study area progressively tilted the region 65° east. The amount of extension was 10.3 km or 276%. Using key constraints such as offset strata, cutoff angles between faults and various units, and Laramide fault geometries, the study area was structurally reconstructed and verified using 2-D kinematic modeling of reverse fault offset and related folding. Total shortening is 7.2 km or 98%. Laramide reverse faults are interpreted as thick-skinned basement-cored uplifts, because they restore to moderate angles, have related fault-propagation folds, and involve significant crystalline basement rock. The Telegraph Canyon reverse fault has at least 5.3 km of offset, and the Walnut Canyon reverse fault has 3.2 km. The preferred estimate of the total vertical uplift for the fault system is 5.2 km but could be several kilometers greater. The restored strike direction of these faults combined with mid-Cenozoic erosion surfaces throughout the region suggests that this fault system may be responsible for the Laramide uplift of the Tortilla Mountains and Black Hills. In addition, most major porphyry centers appear to have been intruded into the footwall of this large uplift, with local examples including Ray and Resolution, suggesting that topography generated from this uplift may have been critical to preservation of these ore systems. Though definitive crosscutting relationships do not exist in the immediate map area, geologic relationships in a broader area suggest that shortening here began after 74 Ma and, in the Ray area, had ended by ~69 Ma and that porphyry formation postdated reverse faulting by as much as 5 m.y. to as little as <1 m.y.

Results from the first geologic traverse on the topographic rim of a complex impact crater, Endeavour Crater, Mars

AbstractA geologic traverse along the rim of the 22-km-diameter Endeavour Crater by the Opportunity Mars rover has provided the first field geologic observations of outcrop-scale structure and stratigraphy at a complex impact crater, characteristics that were previously undocumented due to erosion of similar-size craters on Earth. Two findings of note are (1) the attitude of sheets, foliations, and contacts between rim impact breccias and pre-impact substrate is antiformal, the limbs dipping inward toward the center of the crater inside the crater rim and outward exterior to the crater rim; and (2) coherent blocks of crust segment the rim topographically and structurally into a series of right- and left-stepping elongate rises of variable size and orientation. These segments experienced differing magnitudes of uplift during crater formation along identified vertical scissors faults. Brecciation along the faults bounding rim segments created zones of enhanced subsurface fluid transport through the crater rim, potentially responsible for localized areas of aqueous alteration identified in outcrops near segment boundaries.

Landscape and Tectonic Evolution of Bayin River Watershed, Northeastern Qaidam Basin, Northern Tibetan Plateau: Implications for the Role of River Morphology in Source Analysis and Low‐Temperature Thermochronology

AbstractThe Bayin River, the largest river in the northeastern Qaidam basin, plays an important role in the source‐to‐sink system and landscape evolution at the basin‐mountain boundary between the Qilian Mountains and the Qaidam basin in the northern Tibetan Plateau. In this study, we conduct field observation, topographic analysis, zircon U–Pb dating, and apatite (U–Th)/He dating to constrain the landscape and tectonic evolution of the Bayin River watershed. Bedrock zircon U–Pb dating indicates the age group of 420–450 Ma for far‐source sediments and the age group of >1,700 Ma for near‐source sediments in the Bayin River watershed. Detrital zircon U–Pb dating results from the Mesozoic and Cenozoic strata in the Bayin River watershed reveal that the most important source transition occurred during the Cretaceous. The Zongwulong Mountains gradually uplifted throughout the Cenozoic, along with decreasing far source and increasing near source based on detrital zircon U–Pb dating. Rapid uplift occurred across the Qilian Mountains during the late Cenozoic, leading to high normalized steepness indices, young apatite (U–Th)/He ages, and deep incised valleys at the basin‐mountain transition zone. The knickpoints caused by the latest headward erosion just reach an elevation of ~3,800 m on the river longitudinal profiles, indicating that the latest uplift magnitude is ~300–400 m relative to the basin surface of the Qaidam basin. Elevation distribution and apatite (U–Th)/He ages reveal that river incision leads to high relief in the Zongwulong Mountains and influences its tectonic evolution.

Late Cenozoic uplift of the Sierra Nevada, California? A critical analysis of the geomorphic evidence

From the earliest days of California geology, the ramp-like profile of the northern half of the Sierra Nevada mountains and putative signs of recent incision have been interpreted as evidence that the range was formed by the tilting of a rigid block in the late Cenozoic. Over the years, various geomorphic analyses have been used to quantify the magnitude of uplift and to establish its timing, such as analyzing the gradients of ancient channels, examining the tilt of sedimentary beds, and reconstructing the incisional history of rivers. Most studies that have used these methods have supported substantial (>500 m) recent uplift of the Sierra. In contrast, investigations based on other sources of paleotopographic information, such as isotope records, thermochronology, and detrital zircon geochronology, have found that the Sierra have been at high elevations for much of the Cenozoic. This set of contradictory results motivates a re-examination of the geomorphic evidence for late Cenozoic uplift. A critical assessment of these geomorphic studies, based on new topographic analyses and field investigations, reveals that their conclusions are not well supported. For example, several studies based their results on reconstructions of ancient channels that would have flowed up and over bedrock ridges as high as 190 m, a physical impossibility. Other weaknesses include unjustified assumptions regarding the original tilt of fluvial deposits, misinterpretations of stratigraphic relationships, and inadequate recognition of the effect of lithology on channel profiles. The studies supporting recent tilting in the northern Sierra Nevada are inconclusive and rely on observations not unique to tectonic forcing. Indeed, much of the evidence based on the paleogradients of the Tertiary channels is consistent with an early trellis drainage network formed across alternating bands of resistant and weak lithologies. In addition, analyses are presented to demonstrate that deep northern Sierran canyons thought to have been recently incised were, instead, cut as early as the Eocene-Oligocene. Two geomorphic studies from the southern Sierra are consistent with late Cenozoic tilting and uplift although ongoing tectonic activity may be insignificant. Finally, I present a conceptual model of the evolution of the Sierran landscape, applicable primarily to the northern half of the range, illustrating the development of three different drainage networks since the late Jurassic.

Exponentially decreasing erosion rates protect the high-elevation crests of the Himalaya

Glacierised mountains erode rapidly due to efficient glacial erosion around the long-term equilibrium line altitude (ELA), as well as by intense frost-cracking action. This ‘glacial buzzsaw’ is hypothesised to limit mountain heights globally to within about 1.5 km of the local ELA. However, we show that the high Himalaya contrasts this picture with a precipitous decline in the erosion rate at its high-elevation crests. We obtain headwall-erosion rates at eight Himalayan debris-covered glaciers from estimates of the corresponding supraglacial debris flux. The data reveal large variation of erosion rates in the range of 0.04–1.0 mm/yr. We establish that this variability is controlled by an exponential decrease in erosion rate with decreasing mean annual temperature of the headwall due to a decline in frost-cracking intensity at low temperatures. The implied order of magnitude decline of erosion rate at the high altitude of the Himalaya, apart from the pattern and magnitude of uplift, may be crucial for generating relief, and for protecting the spectacularly high crests from the action of ‘glacial buzzsaw’.

Earth surface deformation in the North China Plain detected by joint analysis of GRACE and GPS data.

Mass redistribution of the Earth causes variable loading that deforms the solid Earth. While most recent studies using geodetic techniques focus on regions (such as the Amazon basin and the Nepal Himalayas) with large seasonal deformation amplitudes on the order of 1–4 cm due to hydrologic loading, few such studies have been conducted on the regions where the seasonal deformation amplitude is half as large. Here, we use joint GPS and GRACE data to investigate the vertical deformation due to hydrologic loading in the North China Plain, where significant groundwater depletion has been reported. We found that the GPS- and GRACE-derived secular trends and seasonal signals are in good agreement, with an uplift magnitude of 1–2 mm/year and a correlation of 85.0%–98.5%, respectively. This uplift rate is consistent with groundwater depletion rate estimated from GRACE data and in-situ groundwater measurements from earlier report studies; whereas the seasonal hydrologic variation reflects human behavior of groundwater pumping for agriculture irrigation in spring, leading to less water storage in summer than that in the winter season. However, less than 20% of weighted root-mean-squared (WRMS) reductions were detected for all the selected GPS stations when GRACE-derived seasonal deformations were removed from detrended GPS height time series. This discrepancy is probably because the GRACE-derived seasonal signals are large-scale, while the GPS-derived signals are local point measurements.