光波側距による大気境界層の日周・年周変動およびフィリピン海プレートによる有度地塊傾動機構の解明

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Automatic laser ranging is being carried out to monitor the activity of the tilting Udo Block along the laser paths from the Crustal Activity Observatory of Shizuoka University to Yatsuyama and Yambara. The air temperatures of the laser paths are calculated from ranged distances under the assumption of constant distance. The rangers monitor also re-fraction of the laser paths caused by the air temperature structure and intensity profile of the reflected laser using a computer controlled step motor. The atmospheric temperature distributions and their daily and seasonal changes have been explained by the solar heating in the daytime and radial cooling in the night , resulting in lifting of warmer air masses and sinking of cooler air masses. Systematic offsets have been detected from the calculated air temperature, and compared with the surface air temperature at the Shizuoka Station of the Japan Meteorological Agency. The offsets relate to the changes in the distance of the laser paths, caused by the crustal movement. The amount of the changes is more than several em in laser path distance. The maximum distance occurred in the middle of April 1998 just before the earthquakes to the east off Izu Peninsula, and the minimum distance occurred in the early January 2000 after the Taiwan Earthquake of September 1999. The changes in distance were correlated with tilt records of the Crustal Activity Observatory. The Udo Block is tilting northwestward by large-scale gravity collapse along the active Kusanagi and Asabata Faults. The basal part of the collapsed Udo Block is riding on the subducting Philippine Sea Plate along the Suruga Trough The detected crustal movements have been explained by changes in the tilt of the Udo Block, controlled by the subduction of the Philippine Sea Plate under the Udo Block. The stress in the Philippine Sea Plate is sensitively related to earthquakes along the eastern and western margins of the Philippine Sea Plate. The earthquakes on the eastern margin release the compressional stress of the westward Pacific Plate motion and the stress field changes from compressional to tensional before the earthquakes in the east off Izu Peninsula related to magma intrusion. The earthquakes on the western margin in Taiwan decrease the resistivity to subduction along the western margin, and induce the subduction. The simulated stress condition of the Philippine Sea Plate is well correlated with the detected crustal movements with reasonable a time lag.
静岡大学の論文

光波側距による大気境界層の日周・年周変動およびフィリピン海プレートによる有度地塊傾動機構の解明

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