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

在北安那托利亚断裂带西段存在一个地震缺口。该断层在地震断裂带内分为两条分支。北支为宽地堑式构造，南支为右旋走滑型活动断裂。我们称其南部分支为伊兹尼克-梅克斯断层。我们建立了局地地震观测网，进行了临时观测，发现伊兹尼克-梅克切断裂带地震活动非常少。这与北部分支的高地震活动性相反，那里间歇性地震群也很明显。Iznik-Mekece断裂目前可能处于第二类地震间隙的稳定状态。在那条短暂的小溪的沟渠处挖了沟，显示出大约四十米的右步偏移。表层土壤下的土层由崩积层组成，其下面是厚厚的泥石流层。上塌积层没有受到任何扰动，而下塌积层和泥流层则因伊兹尼克-梅切斯断层的断裂而受到扰动。从未受扰动的地层中采集的标本显示的年代约为B.P. 200年，表明自B.P. 200年以来没有发生过明显的断层活动。在受到断层活动干扰的崩积湖底附近发现了一个显示大约B.P. 500年的标本。由此得出结论，该断层最近的一次大地震一定发生在距今200-500年前。对于地震预测研究来说，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电位。地下水的化学成分和土壤气体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.