MULTIDISCIPLINARY RESEARCH ON FAULT ACTIVITY IN THE WESTERN PART OF THE NORTH ANATOLIAN FAULT ZONE

北安纳托利亚断裂带西段存在一条咸水空区。该断裂在地震空区分为两支。北支以宽阔的地块状构造为特征，南支为右旋走滑型活动断裂，我们称南支为Iznik-Mekess断裂。我们建立了当地的地震观测网，并进行了临时观测，发现Iznik-Mekess断裂的地震活跃度很低。这与北支的强震活动相反，那里也有明显的间歇性震群。Iznik-Mekess断裂目前可能处于第二类地震空区的稳定处。Iznik-Mekess断裂在小溪的航道上发生了拉裂，表现出约40米的右阶分叉被厚厚的泥石流沉积覆盖的堆积层。上部堆积层没有受到任何干扰，而下层堆积层和泥石流层则是与Iznik-Mekess断裂的断裂活动有关而受到扰动的。未受干扰层的样品显示距今约200a B.P.，表明自200a B.P.以来没有发生过重大的断裂活动。在因断层扰动而遭受扰动的崩积层底部附近发现了一件距今约500年的标本。由此推断，该断裂最近一次大地震发生在距今200-500年的B.P.。持续监测可能的前兆变化是很重要的。我们开始连续测量地磁总强度和自然电位。地下水的化学成分和土壤气中的氡浓度也进行了常规测量。

There exists a saismic gap in the western part of the North Anatolian Fault Zone.This fault is separated into two branches in the seismic gap area.The northern branch is characterized by a wide,graben-like structure, while the southern branch shows an active fault of right-lateral strike-slip type.We call the southern branch the Iznik-Mekece fault.We established a local seimsmic observation network and made temporary observations found that seismic activiry is very low at the Iznik-Mekece fault.This is wuite contrary to high seismicity at the northern branch where intermittent earthquake swarms are also notable.The Iznik-Mekece fault may currently be at the stabe of seismic gap of the second kind.Trenching was made at the channel of the small ephemeral stream showing a right-step defiection of about forty meters.The layer below surface soil is composed of colluvium deposits which are underlain by thick mud-flow deposits.The upper colluvium layer has not suffered any disturbances, whereas the lower colluvium layer and the mud-flow layer were disturbed in association with faulting on the Iznik-Mekece fault.The spcimens taken from the umdisturbed layer show the date of about 200 years B.P., indicating that no significant faulting has taken place since 200 years B.P. One specimen specimen showing about 500 years B.P. was found near the bottom of the colluvium laver which suffered disturbances due to faulting.It is concluded that the latest large earthquake at this fault must have taken place 200-500 years B.P.For earthquake prediction studies,continuous monitoring of possible precursoy changes is important.We started continuous measurements of geomagnetic total intensiry and self-potential.Chemical components of groundwater and radon concentration in soil gas have also been measured routinely.