STUDY OF THE EVALUATION OF EARTHQUAKE OCCURRENCE POTENTIAL IN THE WESTERN PART OF THE NORTH ANATOLIAN FAULT ZONE

在该研究项目的每一年中，我们加强了地震观测并改进了分析系统，从而在土耳其西部的伊斯坦布尔地区建立了地震监测系统。目前，地震活动可以在网上监测，一些大地震的数据也可以在网上显示，以便这些数据可以用于地震生成机制的研究。我们将这些数据用于我们自己的地震层析成像研究，发现在伊兹米特震源区以西预计会发生大地震的震源区，地震活动变得更浅。通过对中等地震的波形反演，积累了地震孕育机制的信息，提高了对地壳应力分布的认识。就地震活动本身而言，在伊斯坦布尔以南可能发生大地震的震源区，地震活动并不十分活跃，但相当活跃 ...更多信息 住在附近。震源的年度数据显示，马尔马拉海下的东西向活动断层图像和预期的大地震图像已经出现。在电磁研究方面，我们进行了宽频带、长周期和短周期MT观测，弄清了包括伊兹米特震源区在内的广大区域的电阻率结构。结果发现，震源区一般是电阻性的，高电阻区对应于凹凸不平。在下地壳和上地幔中广泛存在的低阻带揭示了部分熔融带及其延伸。关于我们在伊兹米特地震中发现的地震发电机效应，我们进一步研究了与一些大地震有关的余震，例如最近在日本发生的新泻县地震。我们可以确认4.0级以上地震的影响，但在地震波到达之前无法检测到理论上预期的电磁信号，这仅仅是因为小地震的信噪比较低。少

In each year of this research project, we intensified seismic observations and advanced the analysis system, resulting in the establishment of an earthquake monitoring system in the Istanbul area, western Turkey. At present, seismic activity can be monitored on the web and also some data on major earthquakes are shown on the web, so that the data can be used for studies of earthquake generation mechanism. We have used the data for our own researches on seismic tomography and found that seismic activity becomes shallower in the earthquake source region of a big earthquake anticipated to the west of the Izmit earthquake source area. We also accumulated information on earthquake generation mechanism from waveform inversion for middle-size earthquakes, and increased our understanding of the distribution of crustal stress. As for seismicity itself, seismic activity is no very active in the earthquake source area for a big earthquake anticipated to the south of Istanbul, but it is rather act … More ive in its vicinity. Yearly data of hypocenters suggest an image of east-west active faults beneath the Marmara Sea and an image of the anticipated big earthquake has emerged. In electromagnetic studies, we made wide-band, long-period and short-period MT observations, and clarified the resistivity structure in a wide region including the Izmit earthquake source area. As a result, we found that earthquake source areas are resistive in general and highly resistive areas correspond to asperities. We also found a partial melting zone and its extension, as revealed by low resistivity zones widely existing in the lower crust and upper mantle. As for the seismic dynamo effect which we found during the Izmit earthquake, we made further studies for aftershocks associated with some major earthquakes, such as the Niigata Prefecture earthquake, which occurred recently in Japan. We could confirm the effect for earthquakes larger than magnitude 4.0, but could not detect electromagnetic signals anticipated theoretically before the arrival of seismic wave, simply because of low S/N for small earthquakes. Less