In Chu-Chie, Taiwan, tidal strain observation with a borehole strainmeter system has been carried out since 2001. The Chu-Chie station (N23°31′39″, E120°35′59″, h=300m) is located in the central part of Taiwan and is about 40km distant from the epicenter of the destructive Chi-Chi earthquake (ML=7.3) which occurred on September 21, 1999. The strainmeter system detects three components of horizontal strains in 82°, 202° and 322° measured from the North in clockwise directions using differential transformers. We analyzed tidal strains and determined amplitudes and phase lags of 13 major constituents by applying the tidal-analysis program BAYTAP-G to 1-year strain data of 2003. The “observed” tidal strain amplitudes were compared with the “theoretically expected” amplitudes that were obtained from the GOTIC2 program. As a result, the ratio of the observed amplitudes and the theoretically expected amplitudes ranges between 0.7 and 3.3. Some parts of these discrepancies may be caused by uncertainty of determination of scale factors of instruments. Other reasons to be considered are complicated geological and topographic effects around the observation site.

We carried out precise crustal strain observation using a laser strainmeter system at the Rokko-Takao station in Kobe, Japan from 1989 to 1997. The long-term strain record is characterized by remarkable annual changes of the order of 2–3×10−6 and linear strain accumulation of −4.4×10−7/year (in contraction). The annual strain changes are inversely proportional to temperature changes that precede the strain changes by about 1 month. The apparent annual strain changes were mainly caused by refractive-index changes in the light path due to the ambient temperature changes. After eliminating the annual temperature effect, linear strain accumulation is corrected to be −6.3∼−6.7×10−7/year. Residual strains show the oscillating behavior, in which the oscillating cycle seems to become shorter and shorter as time goes by. During the period, a destructive earthquake of M=7.2 occurred near the Kobe City on 17 January 1995. We investigated the oscillating behavior in secular variations of ground-strains by introducing the deterministic approach of earthquake prediction to search for the “critical point” of the occurrence of an earthquake in the extended power law equation. However, we could not obtain a unique solution to determine eight unknown parameters including the “critical point”. This may be mainly due to lack of data for 4 months from August to November in 1994 by the failure of the laser source before the occurrence of earthquake on 17 January 1995. After removing environmental effects and tidal components, we carefully re-examined strain changes in 7 days and 1 day before the occurrence of the earthquake, but we could not detect anomalous strain changes exceeding 1×10−8 before the earthquake.

In order to make geophysical and geological investigations of the Nojima Fault on Awaji Island, Japan, three boreholes measuring 1800 m, 800 m and 500 m deep were drilled into the fault zone. The fault is one of the seismic source faults of the 1995 Hyogo-ken Nanbu earthquake of M7.2. A new multicomponent borehole instrument was installed at the bottom of the 800 m borehole and continuous observations of crustal strain and tilt have been made using this instrument since May 1996. A high-pressure water injection experiment within the 1800 m borehole was done in February and March 1997 to study the geophysical response, behavior, permeability, and other aspects of the fault zone. The injection site was located approximately 140 m horizontally and 800 m vertically from the instrument. Associated with the water injection, contraction of approximately 0.7 x 10(-7) str (almost parallel to the fault) and tilt of approximately 1 x 10(-7) rad in the sense of upheaval toward the injection site were observed. In addition to these controlled experiments, the strainmeter and tiltmeter also recorded daily variations. We interpret strain and tilt changes to be related to groundwater discharge and increased ultra-micro seismicity induced by the injected water.

Three long series of tidal gravity observations, totalizing approximately 24 years and recorded with three superconducting gravimeters, T004, T008, and T009, at stations Wuhan (China) and Kyoto (Japan), are studied. The tidal amplitude factors and phase differences are determined precisely using Eterna and Nsv techniques. The precision of the main tidal amplitudes is at the same level of 0.01 μGal. The atmospheric gravity signals are corrected using the coefficients determined with a regression method between tidal gravity residual and station air pressure. The oceanic gravity signals are modeled based on five global oceanic models. It is found that the oceanic models developed by the analysis of measurements from Topex/Poseidon altimeters have the best fit to the superconducting gravimeter measurements, since the observed residuals and the discrepancies between the amplitude factors and the theoretical tidal models are reduced more significantly. The long-period gravity variations are dominated by the non-linear drift phenomena of the instruments, and the short-term variations in gravity are due to the background noise at the stations.

An 800 m borehole was drilled near the Nojima Fault, on which a strike-slip larger then 1 m occurred during the 1995 Hyogo-ken Nanbu earthquake (M = 7.2). Crustal activity near the fault has been observed since May 1996 using a multicomponent instrument installed at the bottom of the borehole. Data of three components of strain, two components of tilt and temperature observed from May 1996 to December 1998 were analyzed. Long-term changes of strain and tilt show a north-east-south-west extension and southwards subsidence. As for the Earth tides and atmospheric effect, orientation of the principal axis of strain was mainly east-west and orientation of the maximum subsidence was mainly north-south. The observational data of strain had variations corresponding to a change in temperature at a depth of 800 m. The thermal expansion coefficient of the crust was calculated to be approximately 2.0 x 10(-6)/degreesK.

Atmospheric effects on gravity observations at Kyoto were estimated by using meteorological data sets at an interval of 12 h during a 4 month period from July to October in 1993. The effects owing to the air mass near the gravity station were evaluated by numerical integrals, and those distant from the station were calculated by using spherical harmonic expansions of meteorological data. The error in the calculated atmospheric effects was of the order of 0.1 μgal at most, except for the error related to the response of the oceans near the station based on the inverted barometric loading mode. About 90% of the atmospheric effects were attributed to local atmospheric variations within 50 km of the station. The remaining effects owing to the air mass outside this zone were of the order of 1 μgal, in which different features were recognized as compared with the effects owing to the regional air mass around Kyoto. The atmospheric effects thus estimated were compared with gravity data obtained by a superconducting gravity meter at Kyoto. The residuals showed gravity changes of a few microgals, a part of which might be caused by sources such as variations of the ground water level around the station.