Yaolin Shi

Two-dimensional modeling of the P-T-t paths of regional metamorphism in simple overthrust terrains

Quantitative modeling of metamorphic P - T - t paths in thrust belts has so far been limited to one-dimensional simplification. We have developed a two-dimensional time-dependent finite-element procedure, capable of tracing and updating fault and strata boundaries during faulting, for modeling thermal evolution of overthrust terrains. We show that the two-dimensionality of an overthrust and the speed and duration of thrusting have significant effects on the P - T - t paths of rocks in orogenic belts. The results suggest that petrological studies of P - T paths of rocks from different lateral positions in an orogenic belt, along with two-dimensional modeling procedure, can put strong constraints on models of regional tectonic processes.

Thermal modeling of the Southern Alps, New Zealand

Finite-element modeling of the thermal regime across the Southern Alps of New Zealand has been carried out along two profiles situated near the Franz Josef and Haast valleys. The modeling involves viscous deformation beneath the Southern Alps, including both uplift and erosion, and crustal/lithospheric thickening, as a result of crustal shortening extending to 20 mm/y of a 25-km thick crust. Published uplift rates and crustal thickness variations along the two profiles are used to constrain the modeled advection of crustal material, and results are compared with the recent heat flow determinations, 190±50 mW/m2 in the Franz Josef valley and 90±25 mW/m2 in the Haast valley. Comparisons of the model with published K−Ar and fission track ages, show that the observed heat flow in the Franz Josef valley is consistent with observed zircon fission track ages of around 1 Ma, if the present-day uplift rate is close to 10 mm/y. Major thermal differences between the Franz Josef and Haast profiles appear to be due to different uplift and erosion rates. There is weak evidence that frictional heating close to the Alpine fault zone is not significant. The modeling provides explanations for the distribution of seismicity beneath the Southern Alps, and predicts a low surface heat flow over the eastern foothills due to the dominant thermal effect of crustal thickening beneath this region. Predicted temperatures at mid-crustal depth beneath the zone of maximum uplift rate are 50–100°C cooler than those indicated in previously published models, which implies that thermal weakening of the crust may not be the main factor causing the aseismicity of the central Southern Alps. The results of the modeling demonstrate that the different types of reset age data in the region within 25 km of the Alpine fault are critical for constraining models of the deformation and the thermal regime beneath the Southern Alps.

Lithosphere Effective Viscosity of Continental China

Abstract The rheological structure of the continental lithosphere is a very important issue in the study of lithosphere dynamics. Evaluation of lithosphere viscosity is the primary task. On the basis of the new research achievements of Chinese continental temperature and strain rate, the authors have extrapolated the results of laboratory rock experiments to field geological deformation, and uncertainties such as, lithology, temperature, strain rate, and extrapolation are carefully investigated. The effective viscosity of crust and upper mantle in continental China are calculated. The effective viscosity of the middle and lower crust are usually in the range of 10 21 –10 24 Pa·s and 10 21 –10 22 Pa·s, respectively. The lower crust of the Tibetan plateau has a low viscosity of 10 19 –10 20 Pa·s, which is in agreement with the previous conclusion that there is ductile lower crustal flow in the Tibetan plateau.

Three‐dimensional crustal structure in central Taiwan from gravity inversion with a parallel genetic algorithm

The genetic algorithm method is combined with the finite-element method for the first time as an alternative method to invert gravity anomaly data for reconstructing the 3D density structure in the subsurface. The method provides a global search in the model space for all acceptable models. The computational efficiency is significantly improved by storing the coefficient matrix and using it in all forward calculations, then by dividing the region of interest into many subregions and applying parallel processing to the subregions. Central Taiwan, a geologically complex region, is used as an example to demonstrate the utility of the method. A crustal block 120£ 150 km 2 in area and 34 km in thickness is represented by a finiteelement model of 76 500 cubic elements, each 2£ 2£ 2 km 3 in size. An initial density model is reconstructed from the regional 3D tomographic seismic velocity using an empirical relation between velocity and density. The difference between the calculated and the observed gravity anomaly (i.e., the residual anomaly) shows an elongated minimum of large magnitude that extends along the axis of the Taiwan mountain belt. Among the interpretive models tested, the best model shows a crustal root extending to depths of 50 to 60 km beneath the axis of the Western Central and Eastern Central Ranges with a density contrast of 400 or 500 kg/m 3 across the Moho. Both predictions appear to be supported by independent seismological and laboratory evidence.

GPU Solutions to Multi-scale Problems in Science and Engineering

This book covers the new topic of GPU computing with many applications involved, taken from diverse fields such as networking, seismology, fluid mechanics, nano-materials, data-mining , earthquakes ,mantle convection, visualization. It will show the public why GPU computing is important and easy to use. It will offer a reason why GPU computing is useful and how to implement codes in an everyday situation.

Hydrogeological modeling of porous flow in the Oregon accretionary prism

Venting of pore fluid was recently reported near the front of the Oregon accretionary prism and was directly measured at one of the venting sites during Alvin dives. In this study, the authors model the flow of pore fluid in the Oregon accretionaly prism. They use seismic reflection sections to constrain subsurface structures, drill-hole results from Deep Sea Drilling Project Leg 18 to constrain sediment properties, and regional tectonic information to constrain the timing and the rate of plate convergence and sediment imbrication and thickening. The results of two-dimensional, time-element, finite-element modeling show that high pore pressures are generated beneath the decollement due to the load of imbricated and thickened sediments. Diffusive flow at a rate of several millimetres per year is predicted within the accretionary prism if fault zone permeability is discounted. The presence of a decollement or permeable fault penetrating the accretionary prism, as imaged on the seismic reflection section, can drastically alter the patterns of fluid flow and produce focused venting of fluid, as observed. On the other hand, fluid venting along faults may not significantly alter the high pore pressures below the decollement.

Stochastic dynamic model of SARS spreading

Based upon the simulation of the stochastic process of infection, onset and spreading of each SARS patient, a system dynamic model of SRAS spreading is constructed. Data from Vietnam is taken as an example for Monte Carlo test. The preliminary results indicate that the time-dependent infection rate is the most inportant control factor for SARS spreading. The model can be applied to prediction of the course with fluctuations of the epidemics, if the previous history of the epidemics and the future infection rate under control measures are known.

Depth variations of P-wave azimuthal anisotropy beneath Mainland China

A high-resolution model of P-wave anisotropic tomography beneath Mainland China and surrounding regions is determined using a large number of arrival-time data recorded by the China seismic network, the International Seismological Centre (ISC) and temporary seismic arrays deployed on the Tibetan Plateau. Our results provide important new insights into the subducted Indian plate and mantle dynamics in East Asia. Our tomographic images show that the northern limit of the subducting Indian plate has reached the Jinsha River suture in eastern Tibet. A striking variation of P-wave azimuthal anisotropy is revealed in the Indian lithosphere: the fast velocity direction (FVD) is NE-SW beneath the Indian continent, whereas the FVD is arc parallel beneath the Himalaya and Tibetan Plateau, which may reflect re-orientation of minerals due to lithospheric extension, in response to the India-Eurasia collision. There are multiple anisotropic layers with variable FVDs in some parts of the Tibetan Plateau, which may be the cause of the dominant null splitting measurements in these regions. A circular pattern of FVDs is revealed around the Philippine Sea slab beneath SE China, which reflects asthenospheric strain caused by toroidal mantle flow around the edge of the subducting slab.

Some thermotectonic aspects of the Tibetan plateau

Abstract Advective heat transfer plays a prominent role in the thermal evolution of tectonically active regions, such as the Tibetan plateau. Different tectonic histories lead to different thermal evolutions, so that a study of the present and ancient thermal signatures can improve our understanding of thermotectonic histories. We use an “upwind” finite-element method to calculate the thermal consequences of two tectonic models suggested by previous studies, and compare the calculated results with observations. Many factors that may affect the thermal structure are investigated, including advection, frictional/shear heating, latent heat of melting, and heat refraction. An imbricated thrust model yields a thermal structure that agrees best with observations of heat flow, crustal low-velocity zones, leucogranites and inverted metamorphism. We suggest that a heterogeneous thermal structure exists beneath Tibet. Southern Tibet has a relatively hot mid-crust and cold mantle resulting from frictional/ shear heating and advective cooling that are due to active thrusting, whereas northern Tibet has a relatively cool crust and hot mantle resulting from thermal relaxation in a region of thickened crust after the cessation of thrusting.

Heat flow across the toe of accretionary prisms — The role of fluid flux

Compaction-driven fluid flow in accretionary prisms is ineffective in changing heat flow across the lower slope, even when the rate of fluid flow is greatly enhanced by hydrofracturing, as results of numerical analysis show. For most faults which are long relative to their thickness, conductive heat loss to the wall rock is much more effective in heat transport than advective transport along the faults.