Summary
The possibility of delayed strain release by aseismic faulting following a main shock is studied in relation to the recent earthquake off Nemuro peninsula, Hokkaido, Japan 17 June, 1973. The main purpose of this paper is to obtain a comprehensive view of the land movement in eastern Hokkaido with respect to the seismic cycle there This region, particularly the Nemuro peninsula area, has been subject to extensive land subsidence in the past several decades. At Hanasaki, for example, it amounted to −60 cm in the past 70 years. The long-term accumulation of subsidence in the same area, as read from remaining marks of the ancient sea level, is only −2 m in the past 5000–6000 years. There-fore, the rate of the recent land movement is twenty times or more as high as the long-tern one, which is known from the geomorphological evidence. Such disagreement between the two kinds of rates leads us to expect a future uplift phase which will compensate the previous subsidence.
Delayed strain release by aseismic faulting is suggested in order to account for the former Nemurooki earthquake (1894) as inferred from the tidal record at Hanasaki. The model is basically a compound fault system with brittle-ductile transition at a certain depth in the plate boundary. If this were the case, the tide-gauge at Hanasaki would record a significant land uplift following the 1973 earthquake for 40 cm or more in the forthcoming several years. The slip mode in the ductile part is a matter of concern from the viewpoint of earthquake prediction, as a secondary shock may occur if the fault should slip quickly. The recent sea-level change at Hanasaki seems to suggest slow propagation of fracture in the down-dip direction. A brief discussion is added on the rheological properties of the plate boundary to estimate the viscosity coefficient for future reference.
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Kasahara, K. Aseismic faulting following the 1973 Nemuro-Oki earthquake, Hokkaido, Japan (a possibility). PAGEOPH 113, 127–139 (1975). https://doi.org/10.1007/BF01592905
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DOI: https://doi.org/10.1007/BF01592905