Automatic travel time determination from a frequency-domain transfer function; The Sompi event analysis

Hasada, Yoko*; Kumazawa, Mineo; Tsuruga, Kayoko*; Kunitomo, Takahiro; Kasahara, Junzo*

Handbook of Geophysical Exploration; Seismic Exploration, Vol.40, p.381 - 395, 2010/03

Mapping non-asperities and continuous, active monitoring of the interior of the earth's crust

Tsuruga, Kayoko; Kasahara, Junzo; Mikada, Hitoshi*; Yamaoka, Koshun; Fujii, Naoyuki

Chigaku Zasshi, 115(1), p.51 - 71, 2006/02

https://doi.org/10.5026/jgeography.115.51

This paper proposes the idea (Exploration of Asperities-Reflectors System, EARS) for getting to know the occurrence of large - huge earthquakes which take place along a subduction plate boundary. A large earthquake along the subducting plate boundary is considered to occur repeatedly in the particular asperity, which is the region of strongly coupled zone of two plates. The regions other than asperities along the plate boundary are considered as stable - quasi-stable region in which slow-slip may release the strain energy caused by the oceanic plate subduction. The intensity of coupling and the heterogeneities in a particular large asperity is not possible to know at present. The strong seismic reflections from the subducting plate boundary were found in the aseismic forearc region in the Japan Trench. Similar strong PP reflections were also observed in the NE region of the Hamana Lake and the same region has also showed large aseismic slip detected by GPS. When we map the asperities-reflectors system, the continuous monitoring of seismic reflection intensity may give the change of the physical state at the subducting plate boundary. The rapid change may trigger a large earthquake at an adjacent asperity. We introduce the innovative measurement system, ACROSS, which has been developed for active monitoring by continuous sinusoidal elastic waves and also describe the recent submarine OBS system. To obtain real-time monitor of the transmission signals from ACROSS at the potential regions near the trenches can be done by use of submarine cables. A newly built system planned in the Tonankaki region should consider this requirement.

A Report of the 1st international workshop on 'Active Monitoring in the Solid Earth Geophysics'

Tsuruga, Kayoko; Ogawa, Katsuro*; Nagao, Hiromichi; Hasada, Yoko; Fujii, Naoyuki*; Kasahara, Junzo; Kumazawa, Mineo

Chigaku Zasshi, 114(4), p.659 - 664, 2005/04

https://doi.org/10.5026/jgeography.114.4_659

The 1st International Workshop on 'Active Monitoring in the Solid Earth Geophysics' was held in Mizunami city, Gifu, from June 30, 2004 to July 2. This paper discusses the significance of the active monitoring of the earth, and reports the summary of the workshop.

Evaluation of a dense seismic array for the acquisition of high quality data in the ACROSS observation

Tsuruga, Kayoko; Kunitomo, Takahiro; Hasada, Yoko; Kumazawa, Mineo; Shigeta, Naotaka; Kasahara, Junzo

2004 AGU Fall Meeting Program and Abstract, S31C-05, 0 Pages, 2004/00

We are developing an active monitoring methodology named ACROSS (Accurately Controlled Routinely Operated Signal System) to detect any subtle temporal change of physical properties in the Earth's interiors (Kumazawa et al., 2000). ACROSS is a comprehensive measurement system to determine continuously the transfer function of a linear system by means of the coherent signals. The combination of ACROSS transmission and array observation allow us to obtain the transfer function with high S/N (ratio of signal to noise) and S/B (ratio of signal to bias) in space and time. In this paper, we briefly review the specifications of our seismic array and report the latest results of the data analyses.

Travel time estimation from a transfer function in frequency domain: The revised Sompi event analysis

Hasada, Yoko; Kumazawa, Mineo; Tsuruga, Kayoko; Kunitomo, Takahiro

AGU 2004 Fall Meeting, 0 Pages, 2004/00

We have developed a method to extract "events" localized in time domain from a transfer function in frequency domain, which is a basic analysis method of ACROSS(Accurately Controlled Routinely Operated Signal System)and referred to as the Sompi event analysis. Though the validity of the Sompi event analysis is confirmed through various numerical tests especially for analysis of dispersive wave, there are some problems in practical application. Here we introduce a revised procedure by means of weighted least squares fitting, which is based on maximum likehood estimation.

A Dense Seismic Array for Acquisition of High Quality Data in ACROSS Observation

Tsuruga, Kayoko; Kunitomo, Takahiro; Hasada, Yoko; Kumazawa, Mineo; Shigeta, Naotaka;

Gekkan Chikyu Gogai, (47), 95 Pages, 2004/00

There is a problem of vibration in a diagnosis system of helical evaporator tubes installed in a nuclear power station. Numerical simulations are implemented on the assumption that the vibration is caused by the Coulomb's friction. An analytical model is derived as a large scale nonlinear vibration system and a lot of computational cost would be required to carry out the simulations. The Transfer Influence Coefficient Method, which has high accuracy and efficiency in numerical computations, is applied and efficiently implements the simulations. The vibrations are qualitatively reproduced by the simulations. It enables us to make a pre-evaluation of several means to suppress the vibrations are qualitatively reproduced by the simulations. It enables us to make a pre-evaluation of several means to suppreess the vibration and the most effective devise is expected through the simulation.