Shin’ichi Miyazaki

Continuous GPS Array and Present-day Crustal Deformation of Japan

A GPS array with about 1,000 permanent stations is under operation in Japan. The GPS array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the Japanese islands. Based on daily coordinate data of the GPS stations, strain rate distribution is estimated. Most regions with a large strain rate are related to plate boundaries and active volcanoes. In addition, the Niigata-Kobe Tectonic Zone (NKTZ) is recognized as a region of large strain rate along the Japan Sea coast and in the northern Chubu and Kinki districts. This newly found tectonic zone may be related to a hypothetical boundary between the Eurasian (or Amurian) and the Okhotsk (or North America) plates. Precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities. Appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations.

A slow thrust slip event following the two 1996 Hyuganada Earthquakes beneath the Bungo Channel, southwest Japan

We report a “slow thrust slip event” that occurred beneath the Bungo Channel region, southwestern Japan. On Oct. and Dec., 1996, two Hyuganada earthquakes (both Mw = 6.7), followed by afterslips, occurred. In addition, a crustal movement characterized by an extremely slow rise was observed around the Bungo Channel, about 200 km north from the epicenters, and continued for about 300 days long. Assuming a slow slip on the plate boundary, we estimate its duration and surface displacements from GPS time series data by curve-fitting, and then, determine the fault slip distribution. We found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the Hyuganada earthquakes. Occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling.

Modeling the rupture process of the 2003 September 25 Tokachi‐Oki (Hokkaido) earthquake using 1‐Hz GPS data

Received 10 September 2004; accepted 3 October 2004; published 3 November 2004. [1] High-rateGPShasthepotentialtorecoverbothdynamic and static displacements accurately. We analyze 1-Hz GPS data recorded during the 2003 Tokachi-Oki earthquake. The 1-Hz GPS displacement waveforms show good agreement with integrated accelerometer records except for low frequency noise that are inherently present in integrated seismic records. The GPS waveforms were inverted to model the spatio-temporal evolution of the fault slip during the rupture. The slip is found to propagate downdip in the subduction zone with largest moment release 50 km northwest of the hypocenter. The region of largest slip agrees in general with traditional seismic studies, indicating that 1-Hz GPS can be used for finite fault studies. The 1-Hz GPS slip model shows clearer contrast with afterslip distributions than those inferred from strong motion data, possibly because 1-Hz GPS is more sensitive to cumulative slip distribution. INDEX TERMS: 1294 Geodesy and Gravity: Instruments and techniques; 7209 Seismology: Earthquake dynamics and mechanics; 7212 Seismology: Earthquake ground motions and engineering. Citation: Miyazaki, S., K. M. Larson, K. Choi, K. Hikima, K. Koketsu, P. Bodin, J. Haase, G. Emore, and A. Yamagiwa (2004), Modeling the rupture process of the 2003 September 25 Tokachi-Oki (Hokkaido) earthquake using 1-Hz GPS data, Geophys. Res. Lett., 31, L21603, doi:10.1029/ 2004GL021457.

Interplate coupling in northeast Japan deduced from inversion analysis of GPS data

Abstract The spatial distribution of the strength of interplate coupling between the subducting Pacific plate and the overlying continental plate in northeast Japan was investigated through an inversion analysis of GPS data, employing Akaike’s Bayesian Information Criterion. The GPS data used for the inversion analysis are rates of baseline length changes and vertical displacement rates of crustal movements during the period from April 6, 1996 to March 20, 1998, which were obtained at 161 continuous GPS observation stations operated by the Geographical Survey Institute of Japan. The result shows the average drag rates of the overriding plate on the model source regions off the Tohoku and Hokkaido districts are 6.7 cm/yr and 6.8 cm/yr, respectively, which are 0.85 and 0.87 as interplate coupling ratio. These values are much higher than those in previous studies. The average directions of drag rates are oriented N73°W±15° and N78°W±13° on the model source regions off the Tohoku and Hokkaido districts, respectively. These directions agree well with the direction of coseismic slip of the foot-wall side (N75°W) of the 1978 Miyagiken–Oki earthquake ( M 7.4), but differ slightly from the direction estimated from the plate motion model (N65°W) [Seno et al., J. Geophys. Res. 101 (1996) 11305–11315]. We also found afterslip of 5.5 cm/yr associated with the 1994 Sanriku–Haruka–Oki earthquake ( M 7.5) off Aomori prefecture. Interestingly enough, large afterslip occurred on the plate boundary even when more than a year had passed after the Sanriku–Haruka–Oki earthquake. The amount of drag rate becomes dramatically small at depths greater than about 50 km on the model source regions, indicating weak interplate coupling there.

Joint inversion of strong motion and geodetic data for the source process of the 2003 Tokachi-oki, Hokkaido, earthquake

The strong motion and geodetic data were individually inverted for the source process of the 2003 Tokachi-oki, Hokkaido, earthquake with a hypocenter 25 km deep and a fault plane above the subducting Pacific slab. Both the results show a simple slip distribution with a single major asperity, but the strong motion inversion may include a trade-off between slip location and rupture time and the geodetic inversion does not have sufficient resolution for far slips. We then carred out a joint inversion of the two datasets in order to overcome these weaknesses of the single dataset inversions. The resultant slip distribution still retains the simple pattern and has a seismic moment of 2.2 × 1021 N·m (Mw 8.2). The asperity, with a peak slip of 7.1 m, is located in the center of the fault plane 50 km away from the hypocenter in the down-dip direction. The slip rate functions on subfaults around the hypocenter and asperity indicate that the rupture propagated with a supershear speed on the upper part of the fault plane and slowed down to 100–90% of the S-wave velocity on the middle and lower parts. These simple slip patterns and near-supershear rupture may imply the maturity of the Hokkaido subduction zone around the source region.

Agrometeorological conditions of grassland vegetation in central Mongolia and their impact for leaf area growth

[1] The long-term observation of surface heat and water budget and hydrometeorological elements has been carried out over a grassland site at Arvaikheer (46.23� N, 102.82� E) in central Mongolia as the framework of the GEWEX Asian Monsoon Experiment-Asian Automatic Weather Station Network (GAME-AAN). The purpose of this study is to clarify the relationship between vegetation and climate using long-term data (1982–2000) of satellite-derived leaf area index (LAI) and climatic data observed at Arvaikheer. Furthermore, we aimed to reveal physical process by comparing soil moisture and heat and water budgets in 1999 and 2000 as a case study of good and poor vegetation growth. Significant positive correlations with 99% confidence levels were found for July precipitation (P) and the LAI in July (0.538), August (0.826), and September (0.564). Composite analysis for five highest (H5) and lowest (L5) LAI years showed the significant positive anomalies of P in July and LAI in July and August for H5. In June and July 1999, soil moisture and P values were higher than values in 2000; this pattern was reversed in August and September. The mean LAI during the 1999 growing season (1.0) was about twice that of 2000 (0.6). In 1999 the ratio of evapotranspiration (ET) to P (ET/P) and change of stored soil moisture (DW )t o P( DW/P) were 0.79 and 0.15, respectively. In 2000, ET/P and DW/P were 0.94 and 0.0, respectively. These results suggest that the P and DW before July had the most influent on grass growth in central Mongolia. INDEX TERMS: 1818 Hydrology: Evapotranspiration; 1866 Hydrology: Soil moisture; 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 3322 Meteorology and Atmospheric Dynamics: Land/ atmosphere interactions; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; KEYWORDS: Mongolia, grassland, leaf area index, soil moisture, rainfall, evapotranspiration

DJ-1-binding compounds prevent oxidative stress-induced cell death and movement defect in Parkinson’s disease model rats

Parkinson’s disease (PD) is caused by neuronal cell death. Although a precursor of dopamine and inhibitors of dopamine degradation have been used for PD therapy, cell death progresses during treatment. DJ‐1, a causative gene product of a familial form of PD, PARK7, plays roles in transcriptional regulation and anti‐oxidative stress, and loss of its function is thought to result in the onset of PD. Superfluous oxidation of cysteine at amino acid 106 (C106) of DJ‐1 renders DJ‐1 inactive, and such oxidized DJ‐1 has been observed in patients with the sporadic form of PD. In this study, we isolated compounds that bind to the region at C106 by a virtual screening. These compounds prevented oxidative stress‐induced death of SH‐SY5Y cells, embryonic stem cell‐derived dopaminergic cells and primary neuronal cells of the ventral mesencephalon, but not that of DJ‐1‐knockdown cells of SH‐SY5Y and NIH3T3 cells, indicating that the effect of the compounds is specific to DJ‐1. These compounds inhibited production of reactive oxygen species and restored activities of mitochondrial complex I and tyrosine hydroxylase that had been compromised by oxidative stress. These compounds prevented dopaminergic cell death in the substantia nigra and restored movement abnormality in 6‐hydroxyldopamine‐injected PD model rats. One mechanism of action of these compounds is prevention of superfluous oxidation of DJ‐1, and the compounds passed through the blood–brain barrier in vitro. Taken together, the results indicate that these compounds should become fundamental drugs for PD therapy.

Subsurface structure and faulting of the Median Tectonic Line, southwest Japan inferred from GPS velocity field

The Median Tectonic Line (MTL) is the longest arc-parallel fault system in southwest Japan whose right-lateral strike-slip is related to oblique subduction of the Philippine Sea plate (PH). We constructed a dense Global Positioning System network along a 200 km-long traverse line across the MTL in 1998 to estimate deep fault structure and slip distribution. Horizontal velocities were determined at 65 sites through campaign measurements and show crustal shortening in the direction of the plate convergence. Using multi-rectangular segments and depth-dependent coupling at the plate interface, we calculate and remove elastic deformation caused by the PH subduction. The residual velocity field shows right-lateral strike-slip block motion of about 5 mm/yr across the MTL, consistent with geological estimates. However, the block boundary does not coincide with the surface trace of the MTL, being displaced 20–30 km to the north. The residual velocity field is reproduced by a model with a 35–45° northwarddipping fault plane, full locking of the upper portion to a depth of 15 km, and steady slip of 5 mm/yr below. GPS results are supported by imaging of an inclined fault plane revealed by seismic profiling and currently low activity of shallow earthquakes.

Source processes of the 2005 West Off Fukuoka Prefecture earthquake and its largest aftershock inferred from strong motion and 1-Hz GPS data

We simultaneously inverted strong motion and 1-Hz GPS data recorded during the 2005 west off Fukuoka prefecture earthquake (MJMA 7.0) for its source process. The data at a GPS station near the source region provided strong constraint on the fault geometry and asperity area. The resultant slip distribution suggests a single asperity close to the Genkai island, where many houses were severely damaged. The maximum slip is 1.4 m, and the total seismic moment is 1.0 × 1019 Nm (MW 6.6). We also inverted strong motion data recorded during the largest aftershock (MJMA 5.8). The resultant slip distribution shows two asperities on the fault plane. The maximum slip in the major asperity is 0.12 m and the total seismic moment is 2.0 × 1017 Nm (MW 5.5). The main shock and largest aftershock may cause stress change on the Kego fault, which is a major fault running through the city of Fukuoka.

Resolving static offsets from high-rate GPS data: the 2003 Tokachi-oki earthquake

The Mw 8.0 2003 Tokachi-oki earthquake offshore Hokkaido is the largest earthquake observed to date by a dense GPS network (GEONET). These GPS data are important both for resolving the geodetic signature of the earthquake itself and studies of postseismic deformation. Because GPS positions are generally estimated by averaging 24 hours of observations, it can be difficult to separate the effects of the earthquake and early postseismic deformation. In order to address this difficulty, a Kalman filtering methodology is developed that allows the estimation of the static offsets for the mainshock, its largest aftershock, and postseismic deformation in the first 24 hours. The static offsets computed for this study can be used for earthquake rupture studies while the early postseismic data can be used to evaluate frictional properties of the fault.