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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 JSW001 Oral Presentation 2396 Ancient subduction zone in the Sakhalin Island (the Sea of Okhotsk) Prof. Alexander Rodnikov Geophysical Center Russian Acadehy of Sciences IAVCEI In the Sea of Okhotsk in Eastern Sakhalin an ancient (Upper Cretaceous-Paleogene) subduction zone is distinguished. On the surface it is manifested by an ophiolite complex, which separates North Sakhalin oil and gas basin from Deryugin basin of the Sea of Okhotsk. This complex is represented with harzburgite, dunite, wehrlite, rodingite, gabbro and amphibolite forming ophiolite plates. It is supposed that 100 million years ago, the oceanic lithosphere of the Sea of Okhotsk subducted under Sakhalin, the eastern part of which was an andesite island arc. Behind andesite island arc, in western Sakhalin there was a back-arc basin where sandy clayey deposits accumulated in the Late Cretaceous- Paleogene, which subsequently formed the basement of Cenozoic North Sakhalin oil and gas basin. Approximately 10 15 million years ago subduction of the lithosphere of the Sea of Okhotsk apparently ceased. It is established that the Deryugin basin was formed at the place of ancient deep trench, and Sakhalin basin is located above the ancient (Late Cretaceous- Paleogene) subduction zone. So, the Late Cretaceous- Paleogene rocks of the North Sakhalin sedimentary basin formed in the conditions of back-arc basin may be favorable for generation, accumulation and conservation of hydrocarbons. Keywords: subduction zone, geodynamics, sakhalin
IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSW001 Oral Presentation 2397 Tomographic Inversion of Local P and S Data for Structure below the Toba Caldera Complex in North Sumatra Prof. Sri Widiyantoro Geophysics Bandung Institute of Technology IASPEI Wandono We have conducted a tomographic imaging for the Toba caldera, a 30 km x 90 km topographic depression, located in North Sumatra that represents one of the largest Quaternary calderas in the world. We estimate the 3D P- and S-wave velocity structures beneath the caldera complex using arrival time data of local earthquakes recorded by a 40-station seismic network which had been operated for 4 months (data by courtesy of a PASSCAL program) combined with data from a local network operated by BMG. The resulting tomographic images reveal the presence of pronounced low P and S velocity anomalies that are likely to map the distribution of magma within this subduction-related volcanic system. In the upper 10 km of crust the largest low-velocity region underlies a part of the great Sumatran fault and the southern part of the Toba depression and coincides with a gravity low centered over the regional uplift of a resurgent dome. The imaged low-velocity anomalies extending down to about 100 km depth may be related to the potency of a remaining supervolcano below the study region which will need further investigation. Keywords: toba caldera, tomography, supervolcano
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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 />
JSW001 Oral Presentation 2396<br />
Ancient subduction zone in the Sakhalin Island (the Sea of Okhotsk)<br />
Prof. Alexander Rodnikov<br />
Geophysical Center Russian Acadehy of Sciences IAVCEI<br />
In the Sea of Okhotsk in Eastern Sakhalin an ancient (Upper Cretaceous-Paleogene) subduction zone is<br />
distinguished. On the surface it is manifested by an ophiolite complex, which separates North Sakhalin<br />
oil and gas basin from Deryugin basin of the Sea of Okhotsk. This complex is represented with<br />
harzburgite, dunite, wehrlite, rodingite, gabbro and amphibolite forming ophiolite plates. It is supposed<br />
that 100 million years ago, the oceanic lithosphere of the Sea of Okhotsk subducted under Sakhalin, the<br />
eastern part of which was an andesite island arc. Behind andesite island arc, in western Sakhalin there<br />
was a back-arc basin where sandy clayey deposits accumulated in the Late Cretaceous- Paleogene,<br />
which subsequently formed the basement of Cenozoic North Sakhalin oil and gas basin. Approximately<br />
10 15 million years ago subduction of the lithosphere of the Sea of Okhotsk apparently ceased. It is<br />
established that the Deryugin basin was formed at the place of ancient deep trench, and Sakhalin basin<br />
is located above the ancient (Late Cretaceous- Paleogene) subduction zone. So, the Late Cretaceous-<br />
Paleogene rocks of the North Sakhalin sedimentary basin formed in the conditions of back-arc basin<br />
may be favorable for generation, accumulation and conservation of hydrocarbons.<br />
Keywords: subduction zone, geodynamics, sakhalin