IASPEI - Picture Gallery
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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS014 Poster presentation 2315 The mechanical role of the Philippine Sea Plate in Taiwan orogeny Mrs. Yu-Yeh Lin Institute of Applied Geophysics National Chung Cheng University IASPEI Wei-Hau Wang We use the finite element software ADELI to simulate the collision between the Eurasian and the Philippine Sea Plates in central Taiwan. The Taiwan mountain belt is characterized by an asymmetric wedge in E-W cross section, which is believed to be the result from an indention of a strong backstop. However, the formation of this backstop is still unclear. We attempt to solve this puzzle by simulating the Taiwan mountain building with a thermomechanical model. Our simulation result shows that no distinct strength contrast between the Eurasian and the Philippine Sea plates can be found at depths shallower than 18 km. In depths of 18 to 42 km, the quartzo-feldsparic continental crust abruptly loses its strength while the colliding olivine-dominated Philippine Sea Plate remains strong. It is at this place the backstop effect appears. As a result, a highly deformed lower continental crust stands in front of a relatively undeformed Philippine Sea plate. By contrast, the upper continental crust above the toe of the Philippine Sea plate, where the Central Range is located, has been elevated by the deformed underlying lower crust but remains little deformation This is consistent with recent observations that the Central Range has few earthquakes but with a moderate uplift rate. At both sides of the Central Range, stress accumulates in the upper crust. This results in two thrust belts in Western Foothills and Coastal Range respectively. Our model also suggests that the fastest uplift rate appears at eastern Central Range despite that its topography is not the highest. This implies that significant erosion must have been carrying on in this area, which has been supported by recent geochronological studies. Keywords: taiwan, orogeny, backstop
IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS014 Poster presentation 2316 Shallow crustal geological signatures in electrical Prof. Kalyan Kumar Roy Dept. Geol.Sci.Jadavpur University,Kolkata.India Emeritus Scientist IAGA N, Sri Rama Murthy, Lakshi Kanta Das, Kajal Kumar Mukherjee Collinear dipole-dipole traversing across the Singhbhum shear zone,an Archean-Proterozoic contact, across the geological boundary of two Archaean granite bodies of different ages and chemical compositions, across a Proterozoic volcanic body and across an Archean iron ore basin clearly depict shallow crustal inhomogeneity upto two kms from the surface.Scintrex 10 kilowatt transmitter and IPR-8 and 10 receivers were used to conduct this survey.8 to 10 amperes of current could be sent through the ground and upto 500microvolt potential could be measured in the potential dipole reliably.Both current and potential dipoles were of length 500 meters and dipole separation were varied from n=1 to 8.Global optimization tools,viz,Genetic Algorithm (GA) and Very Fast Simulated Annealing(VFSA) gave better convergence than convensional linearised least squares inversion,viz.,weighted ridge regression approach for 2D resistivity modeling. Singhbhum shear zone could be clearly demarcated between the Archean Singhbhum craton and the Proterozoic North Singhbhum Fold Belt. The depth extent of an iron ore body in the Archean Noamundi iron ore basin on the western side of the Singhbhum craton could be mapped.The contact of two separate granite bodies of different geological ages could be deciphered.Signature of a vocanic body also could be seen in the electrical conductivity models below the Proterozoic Dhanjori volcanic basin.Advent of global positioning system(GPS) and easily available long distance communication system(cell phones) improved significantly the practical feasibility of use of high power DC resistivity set up for shallow crustal studies where magnetotelluric method fails because of very high cultural noise. Keywords: electricalconductivity, precambrians, singhbhum
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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy<br />
(S) - <strong>IASPEI</strong> - International Association of Seismology and Physics of the Earth's<br />
Interior<br />
JSS014 Poster presentation 2315<br />
The mechanical role of the Philippine Sea Plate in Taiwan orogeny<br />
Mrs. Yu-Yeh Lin<br />
Institute of Applied Geophysics National Chung Cheng University <strong>IASPEI</strong><br />
Wei-Hau Wang<br />
We use the finite element software ADELI to simulate the collision between the Eurasian and the<br />
Philippine Sea Plates in central Taiwan. The Taiwan mountain belt is characterized by an asymmetric<br />
wedge in E-W cross section, which is believed to be the result from an indention of a strong backstop.<br />
However, the formation of this backstop is still unclear. We attempt to solve this puzzle by simulating<br />
the Taiwan mountain building with a thermomechanical model. Our simulation result shows that no<br />
distinct strength contrast between the Eurasian and the Philippine Sea plates can be found at depths<br />
shallower than 18 km. In depths of 18 to 42 km, the quartzo-feldsparic continental crust abruptly loses<br />
its strength while the colliding olivine-dominated Philippine Sea Plate remains strong. It is at this place<br />
the backstop effect appears. As a result, a highly deformed lower continental crust stands in front of a<br />
relatively undeformed Philippine Sea plate. By contrast, the upper continental crust above the toe of the<br />
Philippine Sea plate, where the Central Range is located, has been elevated by the deformed underlying<br />
lower crust but remains little deformation This is consistent with recent observations that the Central<br />
Range has few earthquakes but with a moderate uplift rate. At both sides of the Central Range, stress<br />
accumulates in the upper crust. This results in two thrust belts in Western Foothills and Coastal Range<br />
respectively. Our model also suggests that the fastest uplift rate appears at eastern Central Range<br />
despite that its topography is not the highest. This implies that significant erosion must have been<br />
carrying on in this area, which has been supported by recent geochronological studies.<br />
Keywords: taiwan, orogeny, backstop
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