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4次破坏性地震所伴随的震磁变化用压磁效应作了解释,这些变化是在日本中部伊豆半岛东部观察到的。大部分数据由重复测量获得。虽然这些数据受到电力火车噪音的影响,但在靠近地震断裂的测点上观测到了有意义的地磁变化。1978年伊豆半岛附近地震(M7.0)与1980年伊豆半岛东部近海地震(M6.7)的同震变化都可由压磁模型得到很好的解释。在靠近1976年河津地震(M5.4)震中的一个测点上观测到高达5nT的总强度变化。该变化不能由单断裂模型解释,由此提出了一个双断裂模型。对于1978年东伊豆地震(M4.9),在KWZ台观察到显著前兆性的与同震的总强度变化。KWZ台很靠近伊豆大岛附近地震(M7.0)的隐伏分支断裂,M7.0地震发生时此断裂存在无震移动。M4.9地震的前兆磁变化被描述为是这条隐伏断层的无震断裂。而M4.9地震的同震回弹扩大了断层滑动面。这意味着我们通过磁场观察到了地震成核带的形成过程。
The seismic magnetic changes associated with the four devastating earthquakes are explained by the piezomagnetic effect observed in the eastern part of the Izu Peninsula in central Japan. Most of the data is obtained by repeated measurements. Although these data are affected by the power train noise, meaningful geomagnetic changes have been observed at measuring points near the seismic break. The coseismic changes of the earthquakes around the Izu Peninsula in 1978 (M7.0) and the M8.7 in the eastern Izu Peninsula in 1980 can all be well explained by the piezomagnetic model. A total intensity change of up to 5 nT was observed at a point near the epicenter of the 1976 Hojin earthquake (M5.4). This change can not be explained by a single fracture model, thus a double fracture model is proposed. For the 1978 East Izu Earthquake (M4.9), significant precursory and coseismic total intensity changes were observed at the KWZ station. The KWZ station is very close to the hidden branch fault of the M7.0 earthquake near Izu Oshima. There was no earthquake-induced movement of this fault during the M7.0 earthquake. The precursor magnetic change of the M4.9 earthquake is described as a seismic-free fault of this buried fault. The coseismic rebound of the M4.9 earthquake widens the fault slip surface. This means that we have observed the formation of the seismic nucleation zone through the magnetic field.