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在30.1°E和30.8°E之间的北安纳托利亚断层系,从平直段到释放弯曲段,其b值从1.1上升到1.7。GPS资料对这个弯曲段的扩张特性给予了证实,观测到的扩张速率为0.3μ应变/a。在该区域断层面解从大量右旋走滑变为弯曲段中部的带法向分量的斜向滑动,这与拉张盆地构造相吻合。我们认为,由于切向和法向断层运动的叠加,地壳体高度破碎,相当于一个短的平均裂纹长度。由于现存裂纹上的低正应力,摩擦滑动被认为是地震活动产生的主要机制,引起b值升高。研究区中的最低b值(b～0.8)是在断层弯曲段和毗连段之间的交汇处发现的,这个地段恰好穿过1999年伊兹米特地震的震中。沿几何障碍体的地震活动数值模拟预示着,在这个交汇处有局部应力集中。因此,b值最低的场地被认为是大地震最容易发生的地方,这个结论被伊兹米特地震所证实,震中离预测位置约13km。在1992年年初,沿断层弯曲段的中部和西北部空间平均b值开始上升,并且对应一个强烈的水平拉张期。由于1992年没有记录到任何大地震,因此假定这种异常拉张和应力的相关变化是由无震断层滑动引起的。根据可使用的地震构造信息,计算出了因深处缓慢位错而造成的地表位移。GPS资料通过深度为10km、等效震级M_W=5.9的正断层震源而得到很好的解释。不同孕震深度的应力变化也计算了出来,基于的假设是偏应力和平均应力下降而库伦应力变化为正的地段最容易观测到b值上升,也就是说,断层已接近破裂。对于右旋走滑断层,满足这种应力条件的地点是b值上升最大的地方。伊兹米特地震的地表破裂仅同研究区西部和东部的已知断层迹线有关。沿断层弯曲部分,地表破裂从地图上标示出的断层迹线脱离出来,贯穿推测的1992年慢地震引起的正库伦应力变化区域。最大地表滑动(5m)是在最大库伦应力变化(～3bar)场地附近观测到的,这表明1992年的慢地震可能已部分地松开了其后发生的伊兹米特地震的破裂面。我们认为,沿复杂断层弯曲部分观测到b值的明显变化可用来描述构造形变在时空上的不同状态。
In the North Anatolian fault system between 30.1 ° E and 30.8 ° E, the b-value increases from 1.1 to 1.7 from the straight section to the bend-releasing section. The GPS data validates the expansion characteristics of this bend, with an observed rate of expansion of 0.3μ strain / a. In this region, the fault solution from the large amount of dextral strike-slip to the diagonal slip of the normal component of the middle of the bend coincides with the structure of the pull-out basin. In our opinion, due to the superposition of tangential and normal fault movements, the crust is highly fragmented and corresponds to a short average crack length. Due to the low normal stress on existing fractures, frictional sliding is considered as the main mechanism of seismic activity, causing the b value to increase. The lowest b-value (b ~ 0.8) in the study area was found at the intersection between the bend and adjacent sections of the fault, just across the epicenter of the 1999 Izmit earthquake. Numerical simulation of seismic activity along a geometric obstacle indicates that there is local stress concentration at this juncture. Therefore, the site with the lowest b value is considered to be the most prone to major earthquakes. This conclusion was confirmed by the Izmit earthquake, which was about 13 km away from the predicted location. At the beginning of 1992, the average b-value in the central and north-western parts of the bend along the fault began to rise and corresponded to a strong horizontal pull-out period. Since no major earthquakes were recorded in 1992, it is assumed that the associated changes in stress anomalies and stresses are caused by slipless seismogenic faults. Based on the available seismic structure information, surface displacements due to slow dislocations at depth are calculated. GPS data are well interpreted by normal-fault sources with a depth of 10 km and an equivalent magnitude of M_W = 5.9. The stress changes at different seismogenic depths are also calculated based on the assumption that the b-value rise is most likely to be observed in the sections where the deviatoric stress and mean stress drop and the change in Coulomb stress is positive, that is, the fault is nearing rupture. For dextral strike-slip faults, the location that satisfies this stress condition is where b increases most. The surface rupture of the Izmit earthquake is only related to the known fault traces in the west and east of the study area. Along the curvature of the fault, the surface rupture detaches from the fault traces indicated on the map and runs through the presumed area of normal coulomb stress changes caused by the 1992 slow earthquakes. Maximum surface slip (5 m) was observed near the maximum Coulomb stress change (~ 3 bar), indicating that the slow earthquake of 1992 may have partially loosened the rupture of the Izmit earthquake that followed. In our opinion, the significant change in b observed along the curvature of a complex fault can be used to describe the different states of tectonic deformation in time and space.