Research on the deep structure of active faults in the North Anatolian fault zone, Turkey

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We have established a seismic observation network called IZINET and monitored seismic activity.In this network, the Izmit earthquake of magnitude 7.4 occurred on August 17, 1999 and hence we could determine its hypocenter very accurately. The seismic data set obtained from IZINET is very important and many seismologists over the world have used this data set. We also made temporary observations to investigate the aftershock activity and we found a zone of seismic activity along the earthquake faults which appeared on the Earth's surface. The distribution of aftershocks is inhomogeneous and some clustering activities were found. This aftershock data set is also important and has been used by many seismologists over the world. From several years before the Izmit earthquake, the seismic activity was high in the epicentral area. Finally we pointed out that the focal mechanism and the aftershock distribution can provide some important clues for the next future large earthquake in the vicinity of Istanbul. As for electric and magnetic observations, records before, during and after the Izmit earthquake could be obtained. Careful examination of the records shows that the electric and magnetic fields changed drastically with the seismic waves. We interpreted these changes in terms of the seismic dynamo effect. In order to confirm this hypothesis, we made simultaneous seismio and electromagnetic observations at the same site. The records immediately before the Izmit earthquake are important from the viewpoint of earthquake prediction, but so far we have been unable to detect any anomalous changes in the electric and magnetic fields. We also made resistivity survey along some segments of the active fault and found that high resistivity zones prevail in the vicinity of the fault. We then pointed out that the hypocenter of the Izmit earthquake is just located in the high resistivity zone. Also most aftershocks tend to occur in this high resistivity zone.