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Study on Dating of Active Faults by means of Background Dosimetry and Paleomagnetic Measurement

背景剂量和古地磁测量活断层测年研究

基本信息

批准号：
60460053
负责人：
TAKEUCHI A.
金额：
$ 3.78万
依托单位：
Toyama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1986
项目状态：
已结题

项目摘要

On the purpose of establishing a geophysical method for age determination of the most recent activity of Quaternary faults, we chose gackground (very low energy) dosimetry and archaeo-magnetic technique as dating tools because at least several times of stick-slip activity occurred within an archaeological time span. Since the Atotsugawa fault in central Japan was already recorded by some historic documentations in Yedo dinasty, that is, the latest activity was occurred in 1858; it was used as one of the most suitable test site for the fault age determination.In the first phase of the project, the fossil earthquake along the Atotsugawa fault were successfully detected from liquified sand beds near the main slip plane using paleomagnetic measurement. In the second phase, the paleomagnetic method has been applied to the other active faults such as Atera fault, the Itoigawa-Shizuoka tectonic line (3 sites), Tan'na fault, Gohmura-yamada fault and so on. The result succeeded to date paleoearthquakes along many of them.The second phase was focused mainly into the dosimetric dating of fault gouges along the earthquake fault, since the method can give more dirtect informations for the fault activity. Here, both thermoluminescense (TL) and elctron spin resonance (ESR) techniques were used. TL glow curves showed that the 1585 event did not completely erase paleodose responsible for the TL output more than 240゜C. Finally, more probable ages of 300-350 years b.p. could be estimated using a initial value for residual dosage because of incompleteness at the time of the slip event, while conventional calculation give rather old ages ranging from 2000-3000 years b.p.

为了建立第四纪断裂最新活动的地球物理定年方法，我们选择了地面（甚低能量）剂量学和古磁技术作为定年工具，因为在一个考古时间跨度内至少发生过几次粘滑活动。由于日本中部的Atotsugawa断层在江户时代的一些历史文献中已经有记载，即最新的活动发生在1858年;在第一期工程中，利用古地磁测量方法，在近主滑动面的液化砂层中成功地探测到了沿Atotsugawa断层沿着的化石地震。在第二阶段，对Atera断层、Itoigawa-Shizuoka构造线（3处）、Tan'na断层、Gohmura-yamada断层等活动断层进行了古地磁测年，成功地测定了多处活动断层的古地震年龄。因为该方法能提供断层活动性的更直接信息。在这里，热释光（TL）和电子自旋共振（ESR）技术被使用。热释光发光曲线表明，1585年事件并没有完全消除造成240 ℃以上热释光输出的古剂量。最后，由于滑脱事件发生时的不完整性，用剩余剂量的初始值可以估算出300-350年的可能年龄，而传统的计算给出的年龄范围为2000-3000年。