1997年伊朗中东部加恩-比尔兼德(GheanBirjiand)Zirkuh余震序列分析

分析了由当地地震台网记录的1997年伊朗加恩-比尔兼德(Ghean-Birjiand)Zirkuh余震序列. 基于余震的分布，可以判断出一垂直的北西南东走向的断层，其长度90 km. 加恩比尔兼德Zirkun地震的断层破裂明显地表现为起始于震中区，单方向地向东南方向传播. 沿断层的余震分布剖面显示，余震分布的深度范围可达20 km. 表明地震活动发生在上地壳，这一地区地震发生层的厚度20 km. 余震的分布表明，在主震的震源过程中块体西部是断层的上盘. 余震的时空分布表现出两个显著的空区，与地表断裂中所见到的间断一致. 可以得出这样的结论: 在主震和余震过程中第一个空区起着障碍体的作用，而第二个空区较深的部位在主震或余震的过程中发生了破裂. 地震后的前10天, 其余震的时间频次衰减图象遵循修正的大森关系，而此后的余震序列非常好地遵循大森模型. 

ANALYSIS OF THE 1997 ZIRKUH (GHEAN-BIRJAND) AFTERSHOCK SEQUENCE IN EAST-CENTRAL IRAN

In this study, the 1997 Zirkuh (Ghaen-Birjand) locally recorded aftershock sequ ence was analyzed. On the basis of the distribution of aftershocks, a NW-SE tre nd vertical faulting with an extension of at least 90 km could be estimated. The fault rupture causing the Zirkuh earthquake apparently initiated in the epicent ral area and propagated unilaterally to southeast. The cross-section of aftersh ocks along the fault suggests that the aftershocks had a depth range deep to 20 km, indicating that the seismic activity was taking place within the upper crust and the seismogenic layer, in this region, had a thickness not greater than 20 km. The distribution of aftershocks suggested that the western block acted as ha nging wall during the source process of the main shock. The time-space distribu tion of aftershocks showed two distinguished gaps coincided with the observed ga ps on the surface faulting. It was concluded that the first gap acted as a barri er during the main shock and aftershocks, while the deeper part of second gap wa s ruptured either during the main shock or the aftershocks. The time-frequency pattern of aftershocks decay followed the Modified Omori relations for the first 10 days while the Omori model was best fitted for the later stage of the afters hock sequence.