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 2309 Tectonophysical model of Tersko-Sunja segment of East Ciscaucasia based on seismostomography and lineament analysis. Mrs. Galina Ivanchenko Institute of Geospheres Dynamics Researcher IASPEI The geodynamic situation in East Ciscaucasia in a fragment of the Scythian plate between Pericaspian rigid lithospheric inclusion and collision zone of the Great Caucasus is determined by horizontal compression. The area is in high tectonic stress condition and is deformed actively enough. Along the Caucasian ridge in a sedimentary cover the thrust series of N -Q age are developed. Reversed fault thrust character is established for Karpinsky Range (inversion structure at southern edge of the East Europe platform) tectonic boundaries. Intensity and style of deformations appreciably differ in the different strips of north - northeast (antiCaucasian) trend differentiated by elongated fracture zones. Usually it is activated fracture zones of the basement. The fragments of these zones are well fixed by geophysics. Many modern fractures, zones of localization of deformations and structural lines are established automated space image interpretation on technology LESSA. The area between the Caucasian ridge and Karpinsky Range is in a condition of strong compression and proceeding folds and thrust deformations of a sedimentary cover. The analysis and new interpretation of seismic records have allowed allocating in area Tersko-Sunja zone the set of earthquakes with deep the centers more than 70 kms [Godzikovskaja A.A. 1988]. Presence of such earthquakes, alongside with mantle earthquakes under the central part of Caspian sea, will be coordinated well to geodynamic model according to which deep shift or embryonic subduction zone, probably is formed here. We shall note, that it is cut in the west by an extended cross-Caucasian fracture zone of the north - northeast trend being also border of blocks with a various seismic mode. Seismotomographic analysis of Tersko-Sunja zone has shown a presence of structural heterogeneity in a transverse section, interpretive as a underthrust fault under the Caucasian ridge or thrust of a ridge on the Scythian plate, and heterogeneity of other type in a section along a ridge, interpretive as segmentation of underthrust fault zone. The presence of highvelocity anomaly under the Caucasian ridge on depths of 40-70 kms in a zone of the greatest gradients of a relief also does not contradict the given assumption. A set of thrusts, reversed faults and folds compensate in a sedimentary cover above the surface of detachment the movement of Transcaucasian- South-Caspian block (subplate) to Eurasia which is probably realized in depth by embryonic subduction zone. At least, under the Scythian plate the thickening of the crust compensating to deformation in a sedimentary cover is not fixed, though subduction or underthrust fault mechanism in continental conditions is limited enough and cannot accept scales of normal subduction of oceanic crust. Keywords: seismotomography, lineament, subduction
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 2310 Spatial variation of the crustal stress field in Taiwan Region Mr. Wen-Nan Wu Institute of Geophysics National Central Universit Ph.D Candidate IASPEI Taiwan is located along a strongly oblique convergent zone, where the Philippine Sea Plate (PSP) subducts northward beneath the Ryukyu Arc while the Eurasian Plate (EP) eastward beneath the Luzon Arc. In order to provide insight into the collision process and mountain-building for Taiwan, we applied a damped stress inversion technique (Hardebeck and Michael, 2006), which minimized the weighted sum of the data misfit and the model length, to the fault plane solutions which are shallower than 35 km from the Broadband Array in Taiwan for Seismology data center from 1995 July to 2006 December. region was gridded with 0.1 degree space grid and each earthquake was assigned to the nearest grid node. We next simultaneously inverted for stress in all grid nodes included all events within a 0.3 degree x 0.3 degree rectangle centered at the grid node, but the grid node with less than 8 earthquakes was abandoned. For the damped inversion, we chose the value of the damping parameter near the corner of the trade-off curve, in the lower left, where both the model length and data variance are relatively small, and stress orientation uncertainty was estimated using 2000 bootstrap resamplings of the entire data set. The 95% confidence region of the stress model is defined by the 95% of bootstrap solutions closet to the preferred solution. The result of the damped stress inversion indicates that in general the direction of compression is consistent with the relative plate motion direction of the PSP and EP but varies with the tectonic units. The direction of compression shows a significant clockwise rotation around the Lukang Magnetization High in mid-west , and the direction of extension is related to the rifting of the Okinawa Trough in northeastern . On the other hand, theHuatung Faultseems to dominate the crustal stress field in southeastern . Moreover, the spatial variation of the crustal filed shows a significant stress boundary which is corresponding to the location of a possible tear fault at the northwestern tip of the subducting PSP. Keywords: stressinversion, taiwan, focalmechanism
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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 2310<br />
Spatial variation of the crustal stress field in Taiwan Region<br />
Mr. Wen-Nan Wu<br />
Institute of Geophysics National Central Universit Ph.D Candidate <strong>IASPEI</strong><br />
Taiwan is located along a strongly oblique convergent zone, where the Philippine Sea Plate (PSP)<br />
subducts northward beneath the Ryukyu Arc while the Eurasian Plate (EP) eastward beneath the Luzon<br />
Arc. In order to provide insight into the collision process and mountain-building for Taiwan, we applied a<br />
damped stress inversion technique (Hardebeck and Michael, 2006), which minimized the weighted sum<br />
of the data misfit and the model length, to the fault plane solutions which are shallower than 35 km<br />
from the Broadband Array in Taiwan for Seismology data center from 1995 July to 2006 December.<br />
region was gridded with 0.1 degree space grid and each earthquake was assigned to the nearest grid<br />
node. We next simultaneously inverted for stress in all grid nodes included all events within a 0.3<br />
degree x 0.3 degree rectangle centered at the grid node, but the grid node with less than 8 earthquakes<br />
was abandoned. For the damped inversion, we chose the value of the damping parameter near the<br />
corner of the trade-off curve, in the lower left, where both the model length and data variance are<br />
relatively small, and stress orientation uncertainty was estimated using 2000 bootstrap resamplings of<br />
the entire data set. The 95% confidence region of the stress model is defined by the 95% of bootstrap<br />
solutions closet to the preferred solution. The result of the damped stress inversion indicates that in<br />
general the direction of compression is consistent with the relative plate motion direction of the PSP and<br />
EP but varies with the tectonic units. The direction of compression shows a significant clockwise rotation<br />
around the Lukang Magnetization High in mid-west , and the direction of extension is related to the<br />
rifting of the Okinawa Trough in northeastern . On the other hand, theHuatung Faultseems to dominate<br />
the crustal stress field in southeastern . Moreover, the spatial variation of the crustal filed shows a<br />
significant stress boundary which is corresponding to the location of a possible tear fault at the<br />
northwestern tip of the subducting PSP.<br />
Keywords: stressinversion, taiwan, focalmechanism
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