DSpace collection: 期刊論文

Upper mantle seismic velocity anomaly beneath southern Taiwan as revealed by teleseismic relative arrival times

Tue, 27 Mar 2012 09:37:41 GMT

title: Upper mantle seismic velocity anomaly beneath southern Taiwan as revealed by teleseismic relative arrival times abstract: Probing the lateral heterogeneity of the upper mantle seismic velocity structure beneath southern and central Taiwan is critical to understanding the local tectonics and orogeny. A linear broadband array that transects southern Taiwan, together with carefully selected teleseismic sources with the right azimuth provides useful constraints. They are capable of differentiating the lateral heterogeneity along the profile with systematic coverage of ray paths. We implement a scheme based on the genetic algorithm to simultaneously determine the relative delayed times of the teleseismic first arrivals of array data. The resulting patterns of the delayed times systematically vary as a function of the incident angle. Ray tracing attributes the observed variations to a high velocity anomaly dipping east in the mantle beneath the southeast of Taiwan. Combining the ray tracing analysis and a pseudo-spectral method to solve the 2-D wave propagations, we determine the extent of the anomaly that best fits the observations via the forward grid search. The east-dipping fast anomaly in the upper mantle beneath the southeast of Taiwan agrees with the results from several previous studies and indicates that the nature of the local ongoing arc-continent collision is likely characterized by the thin-skinned style. (c) 2010 Elsevier B.V. All rights reserved.

Transition on the relationship between fractal dimension and Hurst exponent in the long-range connective sandpile models

Tue, 27 Mar 2012 09:37:38 GMT

title: Transition on the relationship between fractal dimension and Hurst exponent in the long-range connective sandpile models abstract: The relationships between the Hurst exponent H and the power-law scaling exponent B in a new modification of sandpile models, i.e. the long-range connective sandpile (LRCS) models, exhibit a strong dependence upon the system size L. As L decreases. the LRCS model can demonstrate a transition from the negative to positive correlations between H- and B-values. While the negative and null correlations are associated with the fractional Gaussian noise and generalized Cauchy processes, respectively, the regime with the positive correlation between the Hurst and power-law scaling exponents may suggest an unknown, interesting class of the stochastic processes. (C) 2010 Elsevier B.V. All rights reserved.

The landslide stage of the Hsiaolin catastrophe: Simulation and validation

Tue, 27 Mar 2012 09:37:36 GMT

title: The landslide stage of the Hsiaolin catastrophe: Simulation and validation abstract: Typhoon Morakot struck southern Taiwan in the summer of 2009, causing the most severe flooding since the 1950s. In the early morning of August 9, rainfall triggered the Hsiaolin landslide, and the resulting debris avalanche covered the township of Hsiaolin Village, Kaohsiung. Around five hundred people were buried alive. Reconstruction of the runout of the debris avalanche would increase understanding of the large-scale avalanches for future hazard mitigation purposes. Simulation of the debris avalanche runout can provide valuable information for this purpose. A new continuum shallow-water model is applied to flow over general topography. The Coulomb friction law is adopted; the friction coefficient is initially determined by high pressure rotary-shearing tests and subsequently fine-tuned by an iterative procedure to minimize the difference between the simulation and the measurement. The friction coefficients measured by laboratory tests are found to be in reasonable agreement with the best-fit result of the simulation. In addition, Voellmy rheology is applied, but it is found that the role of the fluid viscous drag is insignificant. The simulation result in the village area is further corroborated by near-surface magnetic surveys. These indicate that the northern part of the village is dislocated, while the artifact structures of the southern part are buried near their original locations. By comparing the landslide front and the flow direction of the simulation, we are able to confirm, as also described by survivors, that the landslide swept the northern part of the village into the Cishan River, while the southern part was flooded subsequently by the debris from a dam breach about 20 min after the landslide.

The influence of sediment cover variability on long-term river incision rates: An example from the Peikang River, central Taiwan

Tue, 27 Mar 2012 09:37:34 GMT

title: The influence of sediment cover variability on long-term river incision rates: An example from the Peikang River, central Taiwan abstract: This study explores the hypothesis that the relative frequency of rock exposure in the bed of an incising channel can have a first-order impact on the long-term average erosion rate. The 1999 Chi-Chi earthquake in central Taiwan generated thousands of landslides along the middle reach of the Peikang River. Sediment from these landslides produced widespread aggradation, such that much of the river's bed remains shielded from active bedrock incision. We present data that constrain the spatial and temporal variability of sediment cover for the Peikang River. Because the river is undergoing spatially variable Holocene bedrock incision (1-10 mm/yr), it offers a unique natural experiment to test the influence of intermittent sedimentation on long-term incision rates. Published electrical resistivity surveys at seven locations along the river reveal median sediment depth values ranging from 1.9 to 11.5 m. The sediment depth correlates inversely with long-term incision rate and sediment transport capacity. We interpret this as an indication that the frequency of bedrock exposure exerts a major influence on incision along the Peikang River.