5-6. Field Study on Prediction of Inland Large Earthquakes

 

To clarify how large earthquakes are generated, we should closely observe changing signals associated with their preparatory process underground. For the purpose of monitoring the preparation process of large earthquakes, various kinds of surveys and nearby observations have been being conducted. The main target area is the Hakuba Village region around the northern Fossa Magna. Affiliated organizations are Shinshu University, Toyama University, Tokyo Metropolitan University, Tokai University, Nagasaki University, and others. The main refined results are as follows:

1) GPS observations disclosed preceding anomalous change of strain of the crust about  a half year before the period of high sesimic activity in northen Fossa Magna region.

2) Changes of ground water and gasses underground observed, which are possible to be related with seismicity.

3) Anomalous rectangular electric current signals are observed, which are  detected as far as the whole area of Nagano Prefecture. The estimated current source was located at around the epicenter of M4.7 shock which occurred about 1 week later of the anomaly.

4) LANDSAT infrared image disclose the linearment of high ground temperature in the northern Niigata Prefecture. This is interpreted that pressurized hot water intruded up into near surface rocks from deep crust, which is considered to be a sign of preparation of high seismic activity including a severe shock of M5.5. 

Fig.1  Change in length across the east-west line across the Matsumoto basin(by Shinshu University).

Fig.2  Lineament of high ground temperature found in LANDSAT infrared image of Niigata area(by Nagasaki University).　X indicates the epicenter of M5.5 shock.