Research for Non-volcanic Deep Tremors by ushig Seismic Array and Electromapetic Active Monitoring

ACROSS（精确控制常规操作信号系统）的一个要点是通过连续传输非常精确控制的地震波和电磁波正弦信号来获取一对信号源和接收器之间的传递函数的噪声鲁棒观测系统。目前，正在操作两台电磁发射机；一个在北海道的堀边，一组电偶极子为180mx10A，连续2年以上；另一个在静冈县，偶极子矩较大，为600mx20A，用于长距离传输。为了确定传递函数和估计信号传播的延迟时间，本文介绍了静冈传输实验的最新结果。该观测系统的关键是能够获得东海地区俯冲板块边界上方约20 km处反射回来的电磁扩散波的震源和接收点之间的高信噪比传递函数数据。所需的观测系统包括(a)具有10^6 Am的大偶极矩的精确控制的信号发射机，(b)精确同步和敏感的传感器阵列，以及(c)在数据管理的各个方面进行降噪的技术系统。(c)最重要的目标是浅层的空间噪声及其由环境干扰（如降雨导致电导率分布的变化）引起的时间变化。作为我们实现东海地区地震和火山场实际监测方法的第一步，我们在静冈大学校园安装了一个大型测试发射机（偶极矩=560mx20A）来解决问题（a,b,c）。在0.1 ~ 20hz频率范围内的试验观测中，对距离发射机20km的先进观测系统采集的数据进行1周的叠加，传递函数的信噪比达到-5。虽然已经进行了一些技术革新，并将在介绍中加以说明，但结果令人鼓舞，似乎是朝着积极监测我们的目标的常规方法迈出的重要里程碑。此外，我们对即将到来的东海地震的“水”监测进行了展望，该地震位于静冈县菲律宾海板块和亚洲板块之间接触的深处。当然，我们需要更强大的发射机和专门为我们的探测设计的观测网络。相对于EM ACROSS中信号是衰减和色散较大的扩散波，地震ACROSS在波传播几何光学中的射线路径概念更容易掌握。此外，Toki地震信号源已连续运行近5年，积累了大量包含深部岩石圈时间变化信息的数据。通过对多个Hi-net台站的地震资料分析，我们发现爱知县Horai Hi-net台站（HOUH）周围具有较好的信噪比，并且在HOUH周围的小型地震阵列观测的初步研究表明，相对强的后期阶段明显存在明显的非均质性。最近的一个话题是在森町（与静冈大学合作）启动一个新的地震发射机（MRI/JMA），就在东海地震的预期焦平面上方。少

An essential point of ACROSS (Accurately Controlled Routinely Operated Signal System), is a noise-robust observation system of acquiring the transfer function between a pair of signal source and receiver by means of continuous transmission of very accurately controlled sinusoidal signals of both seismic and electromagnetic waves. At present, two EM transmitters are being operated ; one at Horonobe in Hokkaido with a set of electric dipoles of 180mx10A continuously for more than 2 years, and another at Shizuoka with a larger dipole moment of 600mx20A for long distance transmission. In this report, the recent results obtained by Shizuoka transmission experiments are presented in order to determine the transfer function and to estimate the delay time of signal propagation.The essential factor for the observation system is to enable us to the acquire the high S/N transfer function data between the source and the receiving site of electromagnetic diffusion waves which are reflected back fro … More m the depth of-20 km just above the subducting plate boundary beneath the Tokai region. The observation system demanded is consistedof (a) the accurately controlled signal transmitters with a large dipole moment of-10^6 Am, (b) the accurately synchronized and sensitive sensor array, and (c) such a technology system that makes noise reduction at every aspect of data management. The most important targets of (c) are the spatial noise in the shallow layers and its temporal change originated from the environmental disturbances (e.g. rain falls leading to the change in conductivity distribution).As the first step of our approach towards realization of the actual monitoring the earthquake and volcanic fields in Tokai region, we have installed a large test transmitter (dipole moment=560mx20A) in Shizuoka University campus to work on the problems (a,b,c). In the trial observation in the frequency range 0.1-20Hz, the S/N of -5 for the transfer functions has been reached by one week stacking of the data acquired at the advanced observation system located up to 20 km from the transmitter. Whereas a number of technical innovations were made and are demanded further as will be shown in the presentation, the results were encouraging and appear as a substantial milestone towards the routine methodology for the active monitoring of our targets. Further we present a prospect towards the monitoring of 'water' in the coming Tokai Earthquake field located deep in the vicinity of contact between the Philippine Sea Plates and Asian Plates in Shizuoka prefecture. ^s a matter of course, we need more powerful transmitters and also an observation network designed specially for our approa.In contrast to EM ACROSS, in which the signal is diffusion wave with large attenuation and dispersion, seismic ACROSS appears easy to grasp the approach by ray-path concept in geometric optics of wave propagation. In addition, the seismic signal source at Toki has been operated already for almost 5 years continuously to accumulate a large amount of data containing the information on the temporal variation in the deep lithospheres. By analyzing seismic data from several Hi-net stations, we found around the Horai Hi-net station)HOUH) in Aichi prefecture shows fairly good S/N and preliminary studies of small seismic array observations around the HOUH indicate relatively strong later phases are clearly observed with slignificant heterogeneities. One of the latest topics is the start of a new seismic transmitter at morimachi(MRI/JMA) in cooperation with Shizuoka Univ.) just above the expected focal plane of Tokai Earthquake. Less