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

在本研究项目的每一年，我们都加强了地震观测并推进了分析系统，从而在土耳其西部伊斯坦布尔地区建立了地震监测系统。目前，可以在网上监测地震活动，还可以在网上显示一些关于大地震的数据，以便这些数据可以用于研究地震的孕育机制。我们利用这些数据进行了地震层析成像研究，发现在伊兹米特震源区以西预计发生的一次大地震的震源区，地震活动变浅。我们还通过对中等规模地震的波形反演，积累了地震孕育机制的信息，加深了对地应力分布的了解。至于地震活动本身，由于伊斯坦布尔以南预计会发生一次大地震，震源区的地震活动不是很活跃，但它相当于…更多的人生活在它的附近。每年的震中数据表明，马尔马拉海下东西向活动断层的图像和预期的大地震图像已经浮出水面。在电磁研究方面，我们进行了宽频带、长周期和短周期的大地电磁观测，弄清了包括伊兹米特震源区在内的大范围的电阻率结构。结果发现，震源区总体上是阻性的，高阻性区对应于凹凸体。我们还发现了部分熔融带及其延伸，低电阻带广泛存在于下地壳和上地幔中。至于我们在伊兹米特地震中发现的地震发电机效应，我们对与一些大地震有关的余震进行了进一步的研究，例如最近发生在日本的新泻县地震。对于4级以上的地震，我们可以证实这种影响，但由于小震的S/N较低，在地震波到达之前，我们无法从理论上检测到预期的电磁信号。较少

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