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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Large-scale internal structure of the Sanbongi Fan-Towada Volcano, Japan: Putting the theory to the test, using GPR on volcaniclastic deposits
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Large-scale internal structure of the Sanbongi Fan-Towada Volcano, Japan: Putting the theory to the test, using GPR on volcaniclastic deposits

机译：日本Sanbongi Fan-Towada火山的大型内部结构：使用GPR对火山碎屑沉积物进行理论验证

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The Towada Caldera Volcano is located between the prefectures of Aomori and Akita - Northeast Honshu Island, Japan. The caldera, today filled by a lake, has produced 15,000 years ago a complex eruption emplacing an ignimbrite topped by the lake outburst flood deposit, through which the present Oirase River erodes. This flood deposit has shaped the geomorphologic feature named Sanbongi Fan, on which Towada City extends. This flood event hypothesis is mainly based on sedimentological and geomorphological evidences of floods mainly from outcrops retrieved from the Sanbongi Fan area. Because of the lack of extended outcrops - typical of the Japanese environment - the present paper has therefore put the theory to the test using GPR (Ground Penetrating Radar) radargram extending along a 640 m length. The GPR used for the survey was a Pulse-ekko-Pro with 50 MHz antennas, and the software Reflex was used to process the data. The radargrams have displayed a sole unit, which the GPR could not penetrate. It can be interpreted as the ignimbrite. On top of this deposit a series of subhorizontal layers, with the alternation between a backset and a foreset extends between 5 m and 3 m depth. Above 3 m, the units are regular and subhorizontal. The deposit is also characterized by the extensive presence of boulders, which are located along three bands: (1) on top of the ignimbrite; (2) in the units deposited by the outburst flood, between 3 and 5 m depths; (3) and in the units close to the surface, although part of these punctual elements are most certainly anthropogenic. Compared with the outcrops, the present research confirms that the material located above the ignimbrite material have been deposited by the outburst flood, creating large-sheet patterns, which have transported boulders. These sheets display backset and foreset patterns, depending on the position of the deposit, indicating flow pulsation or surges under a 'high-energy-flow' condition.
机译：十和田破火山口火山位于青森县和秋田县之间-日本东北本州岛。今天的火山口由一个湖泊充满，它在15,000年前产生了一种复杂的喷发，形成的火成岩顶着湖上的洪水冲积物，目前的奥入濑河正在侵蚀着它。该洪水沉积物塑造了十和田市延伸的名为Sanbongi Fan的地貌特征。该洪水事件假说主要基于洪水的沉积学和地貌学证据，这些证据主要来自从Sanbongi Fan地区获得的露头。由于缺乏伸出的露头（这是日本环境的典型特征），因此本论文使用沿640 m长度延伸的GPR（探地雷达）雷达图对这一理论进行了测试。用于调查的GPR是带有50 MHz天线的Pulse-ekko-Pro，并且使用Reflex软件处理数据。雷达图显示了GPR无法穿透的唯一单位。可以解释为易燃物。在该矿床的顶部，沉积了一系列的水平下层，后倾和前陆之间的交替延伸了5 m至3 m的深度。在3 m以上，单位是规则的和水平的。该矿床的特征还在于大量存在的巨石，它们沿着三个带分布：（1）在火成岩顶部； （2）在3至5 m深度的爆发洪水沉积的单位中； （3）和接近表面的单位中，尽管这些守时元素的一部分最肯定是人为的。与露头相比，目前的研究证实，位于爆发材料上方的物质是由于爆发洪水而沉积的，形成了大片状的图案，这些图案已经运送了巨石。这些薄片根据沉积物的位置显示反向和预兆模式，指示在“高能量流”条件下的流量脉动或波动。

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