No abstract

The damaging earthquake (M=6.8) on September 14, 1984 was a strike-slip faulting trending ENE-WSW across an area of earthquake swarm near Ontake volcano, central Japan. The rupture was 12 km long, about 10 km wide and very shallow, though there was no break on the surface. The earthquake occurred near the boundary of crustal blocks between two adjacent earthquake swarms that have been markedly active since 1976. The expansion of aftershock activity to the west and to the east was obvious, though the rupture pattern was complicated. The largest aftershock of M=6.2 to the west of the main shock was conjugated with the main fault. The largest to the east was a reverse faulting. However the pressure axes of these faultings were the same as that of the main shock. The difference between these fault types might be controlled by block boundaries with different directions around the volcano.

No abstract

The disturbed pattern of mineralization of developing enamel of the rat incisor after the oral administration of SrCl2 and NaF was investigated in an attempt to disclose possible mechanisms which might not be readily detectable under normal conditions, but which may control the progressive mineralization of developing enamel, especially during the maturation stage. Undemineralized ground sections of upper incisors were examined by contact microradiography, tetracycline labeling, and electron microprobe analysis. It was clear that Sr and F disturb the pattern of mineralization during the maturation stage in a characteristic fashion. Sr inhibits the early stage of maturation in which mineralization progresses from the surface toward the middle layer, whereas F accelerates the same stage prominently. At the late stage of maturation, the pattern of hypomineralization is different in the enamel of Sr- and F-treated rats. Mineralization in the inner and innermost layers of the Sr-treated rats and that in the outer layer of the F-treated rats ceases earlier than that in the controls, although the enamel is still hypomineralized. At the latest stage of maturation, Fe penetrates more deeply into the hypomineralized enamel of the Sr- and F-treated rats, because of the higher porosity of the matrix. These results suggest that the maturation stage is not a simple, continuous process, but rather is composed of substages (phases) which have different control mechanisms and in which mineralization progresses in different modes and rates.

A series of large earthquakes occurred off east coast of Honshu, Japan, during the period of October to November 1989. Mechanisms were studied for the foreshock (M=6.5), the mainshock (M=7.1) and the two aftershocks (M=5.2 and 5.3) using the STS‐I broadband records at station INU about 700km away from the epicenters. The lowpass filtered seismograms of these earthquakes show mutually very similar waveforms, in good agreement with those calculated for a known mechanism by an extended reflectivity method. The mainshock is 10 times as large as the foreshock and 2000 times as large as the aftershocks in terms of seismic moment. Assuming that the mainshock (or foreshock) is a collection of some elementary sources at a focal point and that aftershock seismograms represent the responses to such elementary sources, the broadband seismogram of the mainshock (or foreshock) for the first 60s was deconvolved with that of an aftershock to obtain the moment rate function. The moment rate functions of the mainshock and foreshock are both triangle‐like with durations of 14 and 9s respectively. Their rising slopes are mutually very different, a greater slope is associated with the greater shock. This and the similar results for other pairs of earthquakes suggest that the rising slope of moment rate function is causaly related to the eventual size of seismic rupture.