Although additional cases and a randomized, controlled study with another cholangioscope are needed, diagnostic and therapeutic procedures using SPY-DS appear to be feasible and safe.

The stepwise protonation constants of two linear triphosphate ligand anions, triphosphate, and di-imidotriphosphate, , were investigated by potentiometric titration, and the intrinsic chemical shifts of the stepwise protonated species of these anions were determined from the pH-dependence of the 31P NMR chemical shifts. All stepwise protonation constants of were found to be larger than those of , and the 31P NMR signals due to P3O8(NH)2 always appeared at a lower magnetic field compared to the signals due to P3O10. These results indicate higher basicity of the P3O8(NH)2 ligand, because it contains two imino groups in the ligand molecule. The 31P NMR signals for the end phosphate groups appear at a lower magnetic field than those for the middle phosphate groups, indicating that the basicity of the end phosphate group is higher than that of the middle phosphate group. It can be expected that the high basicity of the P3O8(NH)2 ligand brings about the formation of high stability complexes with various metal ions. Furthermore, the only 31P NMR signal due to the middle phosphate group of P3O8(NH)2 ligand molecule clearly showed a low-field shift in the range of pH < 2.5. The reason for this peculiar low-field shift should be the change of the localization of imino protons around the nitrogen atom in P3O8(NH)2.Graphical Abstract

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The area of the Japan Trench, about 40"N off the T6hoku District of north-eastern Honshu, Japan, was for the first time extensively covered by an ocean bottom seismograph (OBS) array. Seven OBSs were available for analyses of natural earthquakes and the observation period lasted two weeks during 1980 July and August. During this period, each OBS registered between 300 and 600 earthquakes. About 100 events were simultaneously recorded by at least three OBSs. Hypocentres were calculated by using a generalized inversion technique. Sixty-five events, mostly with magnitudes (M) from 1.5 to 3.0, which were not located by a land network, were determined to be within or near the area covered by the OBS array. The OBS array had nearly uniform detectability for earthquakes with M over 2.0 within the latitude range of 39.S0-41.5"N and the longitude range of 143"-146.5"E. Within this area there is a highly active region of microseismicity beneath the seaward wall of the Japan Trench. The seaward activity is concentrated within 100 km of the trench axis and is low beneath the Northwest Pacific Basin. A seismicity gap was found just westward of the trench axis, beneath the landward wall of the trench at a water depth of between 6000 and 4000m. Seismic activity continues landward from the region west of the gap.The OBS array enabled us to determine the focal depth of microearthquake activity with better resolution than was previously possible. The results show that the microearthquake activity is concentrated within the upper part of the oceanic lithosphere. On the seaward side, most events occur at a depth of less than 30 km beneath the trench wall, while the activity on the landward side starts to deepen westward exactly at the trench axis.This paper reports the first direct observations to clarify the spatial distribution of microearthquakes associated with the bending and/or subducting of the oceanic plate just beneath the Japan Trench axis. 654 N. Hirata et al.