三浦半島北武断層の完新世における活動期と変位様式に関する考察

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The Kitatake Fault is one of the active right-lateral faults which dislocate hilly lands, marine terraces and Holocene lowland of the Miura Peninsula, south Kanto, running NWW to SEE. Stratigraphy and ^<14>C dates from Holocene deposits obtained by boring at seven localities on the eastern part of the Kitatake Fault are examined in order to reconstruct the age and style of faulting. At least three, probably four fault events during the last ca. 8000 years can be estimated as follows: Event I is a fault which resulted in the uplift of the northern side of the fault, expressed by the presense of the fault scarplet dislocating valley bottom plain. This event occurred after the deposition of Bed 1, probably ca. 1500～1000 yBP. Event II is estimated from the presence of very fine grained deposits which is thicker at the north side of the fault than the south, suggesting the southern side was uplifted prior to the deposition of Bed 1, and after the deposition of Bed 2, that is between ca. 2600 and 1800 yBP. Event III probably occurred at ca. 5000 yBP, that is after the deposition of Bed 3 and prior to that of Bed 2. Event IV could occurred before the deposition of Bed 3. North side of the fault was uplifted by these last two events. Recurrence interval is estimated to be between ca. 1000～1500 and 2500 years. Amount of vertical offset by these events is estimated to be 3～4m. Rate of right-later al offset of a stream due to the faulting is estimated to be 5m/1000 years at Yotsuda, judged by the radiocarbon date (ca. 3200 yBP from a peat bed on the beheaded valley bottom) and the amount of offset after the piracy.
横浜国立大学の論文
1991-10-31

三浦半島北武断層の完新世における活動期と変位様式に関する考察

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