2 0 0 0 丹沢山系渓流水質の経年変化と地震活動
神奈川県北西部丹沢山地の渓流水の溶存成分について2001-2008年にわたり調査・分析を行い、各溶存成分の経年変化と地殻変動の関係について評価した。地殻変動の指標として地震回数を用いた。2001-2008年の間、渓流水のpHは約4年周期で有意に変動していることが認められた。岩石・土壌起源と考えられる溶存成分間の相関を評価した。渓流水質は基盤地質を良く反映し、深成岩地域において、HCO3⁻とMg²⁺、Ca²⁺の間に有意の相関が、丹沢層群地域ではSO₄2-とanion当量との間に正の相関が、足柄層群地域ではHCO3-とSO₄2-とCa²⁺及びMg2+濃度間に正の相関が見られた。さらに、深成岩地域の断層にそって鉱泉水が認められ、その近傍の渓流水には、SO₄²⁻とCa²⁺、Mg2+間で正の有意の相関が見られた。2001-2008年に丹沢山地の地震観測点で得られた震度1以上の有感地震回数と渓流水質の相関を評価した。地震回数とpHとの間に良い相関が認められた。渓流水質のpHは、震源の位置に関わらず、地震動の回数に大きく影響されていると考えられる。さらに、地震回数と各溶存成分濃度との間にも有意の相関が認められた。堆積岩地域において、地震回数と渓流水のHCO3⁻およびMg²⁺との間に同位相で正の相関が見られた。一方、深成岩や丹沢層群地域では地震発生から半年遅れて地震回数と渓流水の多くの陽イオン及びHCO3⁻との間に正の相関が見られた。更にSO₄2-濃度の高い鉱泉水地点ではSO₄2-との間に良い正の相関が見られた。 このような、渓流水質と地震活動の間に認められた相関は、鉱泉水から渓流水へのフローが地震活動により変動したか、あるいは、基盤岩に存在する割れ目の風化面が地震活動により更新され、岩石に含まれる各種イオンの溶脱が活発になったことを示唆している。
- 著者
- 森 慎一 山下 浩之 有馬 眞 藤岡 換太郎
- 出版者
- 一般社団法人 日本鉱物科学会
- 雑誌
- 岩石鉱物科学 (ISSN:1345630X)
- 巻号頁・発行日
- vol.41, no.3, pp.67-86, 2012 (Released:2012-06-28)
- 参考文献数
- 185
- 被引用文献数
- 2 3
We determined K-Ar ages of the late Miocene to Pliocene andesitic to basaltic dykes and lavas distributed in the Tanzawa-Oiso area in the southern Fossa Magna region, central Japan. Our data indicate two distinct periods of volcanic activity in this region; one took place during the middle Miocene (about 15 Ma) and another during the late Miocene to Pliocene (7.5-4.2 Ma). Combined the present results with the age data reported previously from volcanic rocks in the southern Fossa Magna region, the present study suggests that the volcanic front in this region during 8 to 4 Ma was located at about 40 km east of the present-day volcanic front. The volcanic front began to migrate westward to the present-day location at about 4 Ma. The westward migration of volcanic front was probably associated with an abrupt change of lateral motion of the Philippine Sea Plate from north- northwestward to northwestward occurred between 4 and 2 Ma.
- 著者
- 平田 大二 山下 浩之 谷口 英嗣 菅 香世子 西川 正 青池 寛 有馬 眞 鈴井 正和
- 出版者
- 特定非営利活動法人日本火山学会
- 雑誌
- 日本火山学会講演予稿集
- 巻号頁・発行日
- vol.1996, no.2, 1996-11-05
1 0 0 0 OA 相模トラフ北部の海底地形と断層系の形成
- 著者
- 森 慎一 藤岡 換太郎 有馬 眞
- 出版者
- 公益社団法人 東京地学協会
- 雑誌
- 地学雑誌 (ISSN:0022135X)
- 巻号頁・発行日
- vol.119, no.4, pp.585-614, 2010-08-25 (Released:2010-11-08)
- 参考文献数
- 89
- 被引用文献数
- 2 6
This paper describes topographic and geologic features of the northern part of the Sagami Trough and surrounding areas, off central Japan, and discusses the role of the Philippine Sea plate in the development of the trough's topography and fault systems. In the study area, the Okinoyama Bank Chain, Miura Basin Chain, and several spurs are aligned NW-SE parallel to the axis of the Sagami Trough. We examine the lithological compositions of rock and piston-core samples collected from the R/V Hyper Dolphin during Japan Agency for Marine-Earth Science and Technology dives 906 and 907, and rock samples dredged during Ocean Research Institute of the University of Tokyo cruise KT88. These samples represent mainly volcaniclastic rocks derived from the volcanoes of the Izu arc and subordinate amounts of terrigenous sediment interpreted as derived from the Sagami and Sakawa Rivers. The topographic and geologic data define five fault systems in the eastern part of the northern Sagami Trough. We interpret the Okinoyama Bank Chain as an elevated outer-ridge belt developed at the landward slope of the plate boundary, which is represented by NW-SE trending right-lateral reverse faults (F1). At the northeast side of the Okinoyama Bank Chain, NW-SE trending normal faults (F2) formed and the Miura Basin Chain developed. The cutting relationship between these fault sets suggests that the collision of the Izu arc with the Honshu arc imposed a right-lateral shear stress field on the Okinoyama Bank and Miura Basin Chains. This shear stress may have led to clockwise rotation of these tectonic blocks formation of a set of NE-SW trending left-lateral reverse faults (F3). The initiation of the Izu block collision is interpreted as a turning point after which the northward motion of the Philippine Sea plate abruptly changed to NW and the Sagami Bay area came under a NW-SE compressional stress field, which resulted in the development of E-W trending right-lateral faults (F4) in the narrow shelf off the Miura Peninsula. A number of spurs subsequently developed along these faults. Finally, NNE-SSW trending right-lateral normal faults (F5) developed under an E-W extensional stress field, which caused the formation of N-S trending topographic depressions such as Tokyo Canyon and submarine highs such as Okinoyama and Oiso Spur.