HR: 1330h
AN: T52B-0271    [PDF]
TI: A Magmatic System as an Indicator of Tectonic Stresses around Plate Boundary; Crustal Deformation in and around Izu-Oshima Japan Derived from Continuous GPS Measurments
AU: * Murakami, M
EM: mccopy@gsi.go.jp
AF: The Geographical Survey Institute, 1-Kitasato, Tsukuba, Ibaraki, 305-0811 Japan
AB: The area around Izu peninsula Japan is situated in a boundary region between the Philippine Sea plate and a continental plate. There are a number of things that bring a complexity to the tectonic setting of the region; the proximity to a triple junction of a continental and two oceanic plates and a volcanic front running through being accompanied by a line of volcanic islands and several major volcanoes on land. There still remain a number of questions yet to be solved. The crustal deformation data set provided by continuous GPS measurements is one of the key pieces of information to understand the ongoing complex tectonic processes in the region. Among the results, an interesting and even intriguing finding from GPS is that a large horizontal strain is not seen in and around the northern part of Izu peninsula which is thought to be the plate boundary. A high rate of shear strain accumulation is found between the peninsula and Izu-Oshima, which is a volcanic island located in further south of the plate. Even in the historical period several earthquakes as large as M7.0 and a number of eruptions of the volcano were recorded. A simple estimation of the accumulated strain suggests that there is an enough energy to produce at least M6 earthquake in the area. As a first step to understand the tectonic situation we are interested in the temporal and spatial change of strain field in the region. We find an interesting interaction between the magmatic system of the volcano and surrounding tectonic situation. We detected an inflation of the island suggesting a swell of a magma chamber located at about 5 km depth beneath the caldera. The trend of the inflation changed when Miyakejima, which is another island volcano about 70 km to the south of Izuoshima, erupted in 2000. The eruption was associated with a huge dike intrusion which deformed the crust within a distance of about 200 km. Another interesting finding is the episodicity of the inflation which is correlated with the occurrence of earthquake swarm. The focal mechanism of the swarms is accordant with the surrounding tectonic situation. Those suggest a multi-layered interaction between the magmatic system and the tectonic stresses around it. In the presentation we will discuss the details of the relationship between crustal deformation and seismicity in Izu-Oshima volcano revealed by multidisciplinary geophysical monitoring.
DE: 1208 Crustal movements--intraplate (8110)
DE: 1243 Space geodetic surveys
DE: 7223 Seismic hazard assessment and prediction
DE: 8123 Dynamics, seismotectonics
DE: 8434 Magma migration
SC: Tectonophysics [T]
MN: 2003 Fall Meeting