[Japanese]

The background of the research:

Immediately after occurrence of a big earthquake in an ocean, Japan Meteorological Agency forecasts arrival time and height of tsunami, and issue tsunami warning or advisory, if necessary. However tsunami prediction by the present database system, which is based on the rapid determination of a focus and size of an earthquake from seismograms, accompanies some errors. The forecast system needs to be improved, because, for example, it underestimates a tsunami size caused by a "tsunami earthquake"(*1).

Research themes of the first laboratory:

Our research sub-themes are as follows.

(1) Developing methods of tsunami forecasts based on observation by offshore tsunami observation systems.

(2) Developing methods to determine mechanisms of earthquakes using waveforms by strainmeter or broadband seismograph.

(3) Quantitative analysis of error factors in the database for tsunami forecasts.

(4) In case of occurrence of a tsunami, an urgent field survey is performed in order to understand and record tsunami phenomena in cooperation with other institutes concerned. The survey results are utilized as basic data and open to the public.

*1: A "tsunami earthquake" generates extremely large tsunami than one expected from its seismic magnitude.

Rupture regions or source processes in large earthquakes of Japan are analyzed, and the structure of the earthfs crust is investigated in details by seismic waves.

Various type crustal deformation like the slow slip, the pre-slip, the after-slip, etc. in an earthquake cycle is made clear by observation and data analysis

The positioning data of GPS at volcanic regions by Japan Meteorological Agency shows large annual variations and differences. The cause of these errors is considered as insufficiency of meteorological correction because the altitudes of observation sites are largely different from each other and vapor amount in troposphere cannot be neglected. We are developing a method to improve accuracy of volcano observation data by using meteorological data given by numerical weather prediction model.

In order to realize more accurate seismic information, to evaluate seismic activity or to extend studies on earthquake forcast, improvement in analyzing techniques for hypocenter parameters and seismicity parameters are highly requested.

In this study, introduction of effects of crustal ihomoginiety on analyzing these parameters, with using data obtained from high-resolution and high-density seisimic observing network, are studied. Three dimensional seismic wave structure is calculated as a base of this study. Utilization of these improved parameters for analysis of seismic activity will be also studied.

Since an occurrence of the great earthquake of magnitude 8 class of Richter scale is anticipated on the Tokai and the surrounding areas, the seismic activity and the crustal deformation are monitored by the Japan Meteorological Agency, based on the Large-Scale Earthquake Countermeasures Act. Moreover, along the Nankai Trough neighboring the source region of the Tokai earthquake, the To-nankai and the Nankai earthquakes are considered to occur with a high probability in the first half of this century.

For this reason, in the seismology and volcanology research division, the following researches are advanced not only for raising the prediction accuracy of the Tokai earthquake, but also for developing monitoring capability concerning the future To-nankai and the Nankai earthquakes:

1) Prediction of earthquake generating process by three dimensional numerical simulation taking the mechanical interaction among the Tokai earthquake, the To-nankai and the Nankai earthquakes into consideration,

2) Investigation of the crust and plate structure beneath the To-nankai and the Nankai areas to provide a precise dynamics model for the numerical simulation,

3) Analysis of underground physical-properties using the signal from the Accurately Controlled Routinely Operated Signal System (ACROSS), and development of the technique for monitoring the crust activity,

4) Improvement of the accuracy of estimating the vertical displacement by using GPS and tidal gages,

5) Development of the long range facility for measuring displacement in order to observe precisely a phenomenon like the slow slip event being observed in the Tokai and the surrounding areas.

By application of effective geodetic observation techniques and numerical simulation techniques with the Finite Element Method, we are going to evaluate ground deformation and detect magma activity. From these developments, quick and precise evaluation of high volcanic activity levels will be possible for disaster mitigation. 1. Development of evaluation method of volcanic activity levels from geodetic observation We selected Izu-Oshima as a main field where we will carry out many kinds of geodetic observation as GPS, EDM, tilt, gravity, SAR and seismic observations. Our goal is establishment of an evaluation method of volcanic activity level. We also investigate evaluation methods of volcanic activity level at other active volcanoes. 2. Development of evaluation method of volcanic activity levels from scenario of magma ascend From development of assumption of magma supply rate, we will make scenarios of magma ascend at volcanoes where few historical data are available. For the purpose, we are carrying out gravity survey at Kirishima-yama volcano to determine the structure under the volcano.