Episodes of intermittent uplift over periods of one month to a year have been observed by the Global Navigation Satellite System in the northeastern part of Chiba Prefecture, Kanto district, Japan. Uplift in the vicinity of Choshi in 2000 was accompanied by the earthquake near Choshi in June 2000 (M 6.1). Uplift of the northeastern part of Chiba Prefecture in 2005 was accompanied by the earthquakes near Choshi in April 2005 (M 6.1) and near Chiba city in July 2005 (M 6.0). Although our estimates of the source parameters for these uplifts were well explained by slips on the faults of these earthquakes, the amounts of slip we estimated for the uplifts were several times larger than we expected from the earthquakes. We attribute the above mentioned intermittent uplift events to aseismic slips on the faults of these earthquakes.
The way to have another look at earthquake prediction/forecast researches in Japan is discussed from a border between the seismology and the history and philosophy of science. Scientific revolution is often symbolically expressed as the shift of the paradigm, idea of which was introduced by Thomas Kuhn. In the field of earthquake prediction research, here we tentatively define its paradigm as a combination of the following ideas - though these would be too humble :1) plate tectonics, 2) asperity or distribution of frictional strength on a fault surface, 3) constitutive law of friction, 4) numerical simulations of precursory process, and 5) observation system of crustal deformation prior to a large earthquake. The case for the paradigm is that any of convincing precursors to a large earthquake has not been observed yet, and, the distribution of frictional strength on a fault surface, in particular, on the subducting plate boundary, is not precisely estimated. Our history of modern seismology is too short to resolve such observational problems. Given that essence of the progress in science is the repetition of proposal of hypotheses and its verification or its rejection, scientists are strongly obliged to propose new hypotheses based on new findings and discoveries to be tested and discussed. Even if the result does not occur along prediction/forecast, it should be appreciated as the science if their scientific context is acceptable. Progressive theory that prevails over degressive one, in the meaning of “research program” theorem proposed by Lakatos Imre, will stimulate the earthquake prediction research in Japan, for which the authors truly believe in. Individual researchers working on the prediction/forecast researches are responsible only for their scientific context. Administrative organizations of seismologists such as the Headquarters for Earthquake Research Promotion and the Coordinating Committee for Earthquake Prediction should take a responsibility for our society.
Strong seismic ground motions often make stone lanterns in temples and shrines collapse and suffer damages, and the stone lanterns tend to collapse in the direction of strong shaking in recent cases. In historic Japanese documents, descriptions of collapsed stone lanterns as results of strong earthquakes appear frequently, and are used in estimating and mapping the seismic intensity. In this report, we examine whether it is possible to further retrieve the characteristics of historic ground motions from the ages and damages of old stone lanterns at Zenkoji Temple, Nagano. We assume that severely damaged stone lanterns would be removed from the site after the earthquakes and be newly rebuilt thereafter, and this will distort the age distribution of stone lanterns. Less severely damaged lanterns would be rebuilt with the damaged parts, and the damages of stone lanterns could be the records of historical strong seismic ground motions at the site. If the directions of the damages caused by collapses are maintained, these could be used to estimate the direction of collapses, or of strong motion. Scarcity of the stone lanterns which were built before 1710s at Zenkoji Temple as well as the sudden increase of repairs and rebuilts in the mid 19th century are likely the results of strong earthquakes and resultant damages at Zenkoji Temple. Ratios between numbers of the damaged and undamaged stone lanterns do not correlate with the time series of historic earthquakes in Nagano. Damages of the stone lanterns are more often found in the rear of the stone lanterns, and we could not find that damages are concentrated into a particular cardinal direction. Stone lanterns at this site are likely to be so maintained that the damaged parts are rotated into the direction which makes the major damages less visible. On the contrary to the findings of the previously published report, we conclude that it is impossible to estimate the direction of historic strong motion from the statistics of damages of stone lanterns at Zenkoji Temple.
An earthquake cannot be observed near the hypocenter as it occurs at a significant depth underground. Accordingly, an earthquake is observed on the surface of the earth, where signals of the earthquake will be disturbed by artificial noises and other factors. Therefore, it is difficult to detect weak signals, including precursory movements. A possible solution to such problems lies in installing a monitoring instrument in the deep bedrock where S/N ratio is improved much better. Based on such an idea, we have been developing a multicomponent borehole instrument (a comprehensive crustal activity observation instrument) that is capable of observing crustal activity at significant depths for predicting earthquakes. This instrument can be equipped with highly sensitive stress meters, strain meters, tilt meters, seismographs, accelerometers, thermometers, and declinometers, and it is capable of observing multiple components of various types of signals. The stress meters were recently developed and can observe both stress and strain as reported in a previous paper about development of stress meters.
Stress and strain meters recorded seismic waveforms generated by the 2011 Tohoku earthquake (M9.0), which occurred on March 11, 2011, and provided useful data for research. In addition, favorable stress waveforms and strain waveforms of an earthquake that occurred in Chile (M8.7) on April 2, 2014 were also recorded．The epicentral distance is approximately 15000 km from the observation point. The tidal movements of the earth were also well recorded by the stress and strain meters.
This paper examined the reliability of the data observed by these instruments. We obtained invariants in elastic dynamics from earthquake waveforms and the earth tide recorded by the stress and strain meters and checked whether the invariants satisfy elastic invariant theory. The analysis revealed that the invariants obtained by the stress and strain meters were in good agreement with the theory. We concluded from these results that the developed stress and strain meters used for observation have been properly installed in the bedrock and have adequate accuracy and reliability.