Geology topics

X. Zhang

Publications and source records attributed to X. Zhang.

10 recordsLinked to original sources

USGS2022

Earthquake early warning: Toward modeling optimal protective actions

Over the past few years early earthquake warning systems have been incorporated into earthquake preparation efforts in many locations around the globe. These systems provide an excellent opportunity for advanced warning of ground shaking and other hazards associated with earthquakes. This study aims to optimize this advanced warning for individuals inside a building when the alert is received. A conceptual framework is presented for modeling optimal protective actions during earthquakes when an earthquake early warning system is available to the individual. Various factors impacting the ability of an individual to take protective action are considered for the modeling process.

Conference Paper↗

USGS2011

Modeling the spatial-temporal dynamics of net primary production in Yangtze River Basin using IBIS model

The climate change has significantly affected the carbon cycling in Yangtze River Basin. To better understand the alternation pattern for the relationship between carbon cycling and climate change, the net primary production (NPP) were simulated in the study area from 1956 to 2006 by using the Integrated Biosphere Simulator (IBIS). The results showed that the average annual NPP per square meter was about 0.518 kg C in Yangtze River Basin. The high NPP levels were mainly distributed in the southeast area of Sichuan, and the highest value reached 1.05 kg C/m 2 . The NPP increased based on the simulated temporal trends. The spatiotemporal variability of the NPP in the vegetation types was obvious, and it was depended on the climate and soil condition. We found the drought climate was one of critical factor that impacts the alterations of the NPP in the area by the simulation.

Yangtze River↗

USGS2009

Models of pure CO 2 and pure CH 4 adsorption on the late paleozoic coals from the Kailuan Coalfield, Hebei, China

Isothermal adsorption experiments of pure CO 2 and CH 4 on different coals in rank (the No. 11 Coal from the Linnancang Mine and the No. 9 Coal from the Majiagou Mine) from the Kailuan Coalfield of Hebei Province, China, have been studied. Four different models (Langmuir, BET, D-R, and D-A) were used to fit the experimental data of CO 2 and CH 4 adsorption and their fitting degree were investigated. The results showed that the adsorption capacity of the Majiagou coal(R o, ran = 1. 21%) is higher than that of the Linnancang coal (R o, ran = 0. 58%). The adsorption capacity of CO 2 is higher than that of CH 4 on the same coal under the same pressure. The adsorption isotherms of pure CO 2 and pure CH 4 on the Majiagou coal can be classified as Type I and their fitting errors of curves are very weak; thus the experimental data can be presented using the Langmuir isotherm. However, the adsorption of Linnancang coal is more complicated, and can be presented using D-A model because of its minimum error. Monolayer adsorption occurs during the adsorption of pure CO 2 and pure CH 4 on the No. 11 Coal and that of pure CH 4 on the No. 9 Coal.

Acta Geologica Sinica↗

USGS2006

Scaling uncertainties in estimating canopy foliar maintenance respiration for black spruce ecosystems in Alaska

A major challenge confronting the scientific community is to understand both patterns of and controls over spatial and temporal variability of carbon exchange between boreal forest ecosystems and the atmosphere. An understanding of the sources of variability of carbon processes at fine scales and how these contribute to uncertainties in estimating carbon fluxes is relevant to representing these processes at coarse scales. To explore some of the challenges and uncertainties in estimating carbon fluxes at fine to coarse scales, we conducted a modeling analysis of canopy foliar maintenance respiration for black spruce ecosystems of Alaska by scaling empirical hourly models of foliar maintenance respiration (Rm) to estimate canopy foliar Rm for individual stands. We used variation in foliar N concentration among stands to develop hourly stand-specific models and then developed an hourly pooled model. An uncertainty analysis identified that the most important parameter affecting estimates of canopy foliar Rm was one that describes R m at 0??C per g N, which explained more than 55% of variance in annual estimates of canopy foliar Rm. The comparison of simulated annual canopy foliar Rm identified significant differences between stand-specific and pooled models for each stand. This result indicates that control over foliar N concentration should be considered in models that estimate canopy foliar Rm of black spruce stands across the landscape. In this study, we also temporally scaled the hourly stand-level models to estimate canopy foliar Rm of black spruce stands using mean monthly temperature data. Comparisons of monthly Rm between the hourly and monthly versions of the models indicated that there was very little difference between the estimates of hourly and monthly models, suggesting that hourly models can be aggregated to use monthly input data with little loss of precision. We conclude that uncertainties in the use of a coarse-scale model for estimating canopy foliar Rm at regional scales depend on uncertainties in representing needle-level respiration and on uncertainties in representing the spatial variability of canopy foliar N across a region. The development of spatial data sets of canopy foliar N represents a major challenge in estimating canopy foliar maintenance respiration at regional scales. ?? Springer 2006.

Mitigation and Adaptation Strategies for Global Ch↗

USGS2006

Crustal structure across the Altyn Tagh Range at the northern margin of the Tibetan Plateau and tectonic implications

We present new seismic refraction/wide-angle-reflection data across the Altyn Tagh Range and its adjacent basins. We find that the crustal velocity structure, and by inference, the composition of the crust changes abruptly beneath the Cherchen fault, i.e., ∼100 km north of the northern margin of the Tibetan plateau. North of the Cherchen fault, beneath the Tarim basin, a platform-type crust is evident. In contrast, south the Cherchen fault the crust is characterized by a missing high-velocity lower-crustal layer. Our seismic model indicates that the high topography (∼3 km) of the Altyn Tagh Range is supported by a wedge-shaped region with a seismic velocity of 7.6–7.8 km/s that we interpret as a zone of crust–mantle mix. We infer that the Altyn Tagh Range formed by crustal-scale strike-slip motion along the North Altyn Tagh fault and northeast–southwest contraction over the range. The contraction is accommodated by (1) crustal thickening via upper-crustal thrusting and lower-crustal flow (i.e., creep), and (2) slip-parallel (SW-directed) underthrusting of only the lower crust and mantle of the eastern Tarim basin beneath the Altyn Tagh Range.

Earth and Planetary Science Letters↗

USGS2004

Ship Shoal as a prospective borrow site for barrier island restoration, coastal south-central Louisiana, Usa: Numerical wave modeling and field measurements of hydrodynamics and sediment transport

Ship Shoal, a transgressive sand body located at the 10 m isobath off south-central Louisiana, is deemed a potential sand source for restoration along the rapidly eroding Isles Dernieres barrier chain and possibly other sites in Louisiana. Through numerical wave modeling we evaluate the potential response of mining Ship Shoal on the wave field. During severe and strong storms, waves break seaward of the western flank of Ship Shoal. Therefore, removal of Ship Shoal (approximately 1.1 billion m 3 ) causes a maximum increase of the significant wave height by 90%–100% and 40%–50% over the shoal and directly adjacent to the lee of the complex for two strong storm scenarios. During weak storms and fair weather conditions, waves do not break over Ship Shoal. The degree of increase in significant wave height due to shoal removal is considerably smaller, only 10%–20% on the west part of the shoal. Within the context of increasing nearshore wave energy levels, removal of the shoal is not significant enough to cause increased erosion along the Isles Dernieres. Wave approach direction exerts significant control on the wave climate leeward of Ship Shoal for stronger storms, but not weak storms or fairweather. Instrumentation deployed at the shoal allowed comparison of measured wave heights with numerically derived wave heights using STWAVE. Correlation coefficients are high in virtually all comparisons indicating the capability of the model to simulate wave behavior satisfactorily at the shoal. Directional waves, currents and sediment transport were measured during winter storms associated with frontal passages using three bottom-mounted arrays deployed on the seaward and landward sides of Ship Shoal (November, 1998–January, 1999). Episodic increases in wave height, mean and oscillatory current speed, shear velocity, and sediment transport rates, associated with recurrent cold front passages, were measured. Dissipation mechanisms included both breaking and bottom friction due to variable depths across the shoal crest and variable wave amplitudes during storms and fair-weather. Arctic surge fronts were associated with southerly storm waves, and southwesterly to westerly currents and sediment transport. Migrating cyclonic fronts generated northerly swell that transformed into southerly sea, and currents and sediment transport that were southeasterly overall. Waves were 36% higher and 9% longer on the seaward side of the shoal, whereas mean currents were 10% stronger landward, where they were directed onshore, in contrast to the offshore site, where seaward currents predominated. Sediment transport initiated by cold fronts was generally directed southeasterly to south-westerly at the offshore site, and southerly to westerly at the nearshore site. The data suggest that both cold fronts and the shoal, exert significant influences on regional hydrodynamics and sediment transport.

Journal of Coastal Research↗

USGS2003

Geology and timing of mineralization at the Cangshang gold deposit, north-western Jiaodong Peninsula, China

The Cangshang gold deposit of the north-western Jiaodong Peninsula contains reserves of greater than 50 tonnes (t) and is developed by the largest open pit gold mine in China. This deposit is a Jiaojia-style (i.e. disseminated-and-veinlet) deposit. It is controlled by the San-Cang fault zone, which trends ~040° and dips 40–75°SE at the mine site. The main (no. 1) orebody lies between a hanging wall of Precambrian metamorphic rocks (mainly amphibolite) of the Fenzishan Group and a footwall composed of the Mesozoic Linglong granitoid. The ore zone is mainly composed of pyritized, sericitized and silicified granitoid, which has undergone variable degrees of cataclasis. SHRIMP U–Pb dating of zircon indicates that the protolith of the hanging wall amphibolite was formed at 2530±17 Ma and underwent metamorphism at 1852±37 Ma. The footwall granodiorite has been dated at 166±4 Ma, whereas zircons from the ore zone yield a younger age of 154±5 Ma. Cathodoluminescence images of zircons from the granodiorite and ore zone show oscillatory zonation indicative of an igneous origin for both and the ages of these zircons, therefore, are all interpreted to be representative of magmatic crystallization. Dating of sericite by 40 Ar– 39 Ar has been used to directly determine the timing of formation of the Cangshang deposit, providing the first time absolute age on formation of the Jiaojia-style gold deposits. The well-defined age of 121.3±0.2 Ma provides the precise timing of gold mineralization at the Cangshang deposit. This age is consistent with those of Linglong-style (vein type) gold mineralization, also from the north-western Jiaodong Peninsula, at between 126 and 120 Ma. Therefore, our work indicates that both styles of gold deposits in the Jiaodong Peninsula were formed during the same mineralization event.

Jiaodong Peninsula↗

USGS2002

Historical and projected carbon balance of mature black spruce ecosystems across north america: The role of carbon-nitrogen interactions

The role of carbon (C) and nitrogen (N) interactions on sequestration of atmospheric CO2 in black spruce ecosystems across North America was evaluated with the Terrestrial Ecosystem Model (TEM) by applying parameterizations of the model in which C-N dynamics were either coupled or uncoupled. First, the performance of the parameterizations, which were developed for the dynamics of black spruce ecosystems at the Bonanza Creek Long-Term Ecological Research site in Alaska, were evaluated by simulating C dynamics at eddy correlation tower sites in the Boreal Ecosystem Atmosphere Study (BOREAS) for black spruce ecosystems in the northern study area (northern site) and the southern study area (southern site) with local climate data. We compared simulated monthly growing season (May to September) estimates of gross primary production (GPP), total ecosystem respiration (RESP), and net ecosystem production (NEP) from 1994 to 1997 to available field-based estimates at both sites. At the northern site, monthly growing season estimates of GPP and RESP for the coupled and uncoupled simulations were highly correlated with the field-based estimates (coupled: R2= 0.77, 0.88 for GPP and RESP; uncoupled: R2 = 0.67, 0.92 for GPP and RESP). Although the simulated seasonal pattern of NEP generally matched the field-based data, the correlations between field-based and simulated monthly growing season NEP were lower (R2 = 0.40, 0.00 for coupled and uncoupled simulations, respectively) in comparison to the correlations between field-based and simulated GPP and RESP. The annual NEP simulated by the coupled parameterization fell within the uncertainty of field-based estimates in two of three years. On the other hand, annual NEP simulated by the uncoupled parameterization only fell within the field-based uncertainty in one of three years. At the southern site, simulated NEP generally matched field-based NEP estimates, and the correlation between monthly growing season field-based and simulated NEP (R2 = 0.36, 0.20 for coupled and uncoupled simulations, respectively) was similar to the correlations at the northern site. To evaluate the role of N dynamics in C balance of black spruce ecosystems across North America, we simulated historical and projected C dynamics from 1900 to 2100 with a global-based climatology at 0.5?? resolution (latitude ?? longitude) with both the coupled and uncoupled parameterizations of TEM. From analyses at the northern site, several consistent patterns emerge. There was greater inter-annual variability in net primary production (NPP) simulated by the uncoupled parameterization as compared to the coupled parameterization, which led to substantial differences in inter-annual variability in NEP between the parameterizations. The divergence between NPP and heterotrophic respiration was greater in the uncoupled simulation, resulting in more C sequestration during the projected period. These responses were the result of fundamentally different responses of the coupled and uncoupled parameterizations to changes in CO2 and climate. Across North American black spruce ecosystems, the range of simulated decadal changes in C storage was substantially greater for the uncoupled parameterization than for the coupled parameterization. Analysis of the spatial variability in decadal responses of C dynamics revealed that C fluxes simulated by the coupled and uncoupled parameterizations have different sensitivities to climate and that the climate sensitivities of the fluxes change over the temporal scope of the simulations. The results of this study suggest that uncertainties can be reduced through (1) factorial studies focused on elucidating the role of C and N interactions in the response of mature black spruce ecosystems to manipulations of atmospheric CO2 and climate, (2) establishment of a network of continuous, long-term measurements of C dynamics across the range of mature black spruce ecosystems in North America, and (3) ancillary measureme

Conference Paper↗

USGS2002

A preliminary study on fine structures of Jiashi earthquake region and earthquake generating fault

It is very unusual that nine large earthquakes of similar magnitudes (M = 6.1-6.8) occured within a very small area and a very short period of time (1997-1998) in Jiashi of Xinjiang Province, Northwest China. This paper analyzes the observed data of the aftershocks in the Jiashi earthquake region for studying the generating mechanism and deep structural background of the Jiashi strong earthquake swarm. The simultaneous inversion method was used to calculate the hypocenter positions and 3-D velocity structure of this region. The results show that the aftershocks concentrated in a NNE-trending belt, which roughly coincides with the NE-trending belt of the two strong earthquake belts. Velocity structure obtained from 3-D inversion suggests that there exist two low velocity zones, one trending NNE and the other NNW, below the depth of 12 km. These low velocity zones are almost consistent with the two strong earthquake belts. The preliminary results lead to the conclusion that the low velocity zones correspond to two deep crustal faults. At the time of our observation, microearthquakes took place on the NNE-trending fault, while the NNW-trending fault was relatively quiescent.

Acta Geophysica Sinica↗

USGS2001

Economic development and conservation of biological and cultural diversity in Yunnan Province, China

Chinese and American scientists are co-operating to develop concepts, strategies, agreements, and proposals in support of an economic development and sustainable ecosystems project in Yunnan Province, People's Republic of China. Yunnan's Provincial Government has initiated a major programme to develop and further utilise its biological resources to help improve economic conditions for its citizens. They are co-operating with the US Geological Survey (USGS) on evaluation and management of biological resources so economic development will be compatible with sustainable ecological systems. Scientists from the USGS and co-operating universities will provide expertise on synthesising biological data, conducting a Gap Analysis for the Province, evaluating innovative economic opportunities, and designing an effective education, training, and outreach programme.

Environmental Development and Sustainability↗