Microseismicity at the North Anatolian Fault in the Sea of Marmara offshore Istanbul, NW Turkey
Microseismicity at the North Anatolian Fault in the Sea of Marmara offshore Istanbul, NW Turkey
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DOI：
10.1029/2008jb006244
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发表时间：
2009-09-03
影响因子：
3.9
通讯作者：
Dresen, Georg
中科院分区：
文献类型：
--
作者：
Bulut, Fatih;Bohnhoff, Marco;Dresen, Georg
马尔马拉海下方的北安纳托利亚断裂带(NAFZ)形成了一个“地震空隙”，预计在不久的将来会发生一场大地震。这段断层位于1912年的加诺斯和1999年的伊兹米特断裂之间，是自1766年以来唯一没有破裂的NAFZ段。为了监测C1arc1k盆地下方伊斯坦布尔近海主要断层分支的微震活动，在距离断层几公里的两个最外层的太子岛--亚西亚达和西夫里亚达安装了永久性地震台阵(PIRES)。此外，在整个C1narc1k盆地部署了一个临时海底地震仪网络。结合波形互相关和P波偏振确定慢度向量。我们联合反演方位角和旅行时观测来确定震源，并应用Bootstrap重采样技术来量化定位精度。我们观测了盆地沿线每月20次M<；2.5级地震的活动性。震源的空间分布表明，在C1narc1k盆地之下，围绕沉积中心的两个主要断裂分支在下方汇合成一个类似于17公里深的单一主断裂。在互相关技术的基础上，我们对密集分布的地震进行分组，并确定复合震源机制，实现对周围永久陆地台站的记录。断层面解具有以右旋走滑为主的机制，表明沿NAFZ这一段的正断层作用较小。在西面，我们观察到逆冲断层的分量越来越多。这支持了沿马尔马拉东海下方NAFZ的北部和主要分支的NW向右行走滑运动的模型。
The North Anatolian Fault Zone (NAFZ) below the Sea of Marmara forms a "seismic gap'' where a major earthquake is expected to occur in the near future. This segment of the fault lies between the 1912 Ganos and 1999 Izmit ruptures and is the only NAFZ segment that has not ruptured since 1766. To monitor the microseismic activity at the main fault branch offshore of Istanbul below the C1arc1k Basin, a permanent seismic array (PIRES) was installed on the two outermost Prince Islands, Yassiada and Sivriada, at a few kilometers distance to the fault. In addition, a temporary network of ocean bottom seismometers was deployed throughout the C1narc1k Basin. Slowness vectors are determined combining waveform cross correlation and P wave polarization. We jointly invert azimuth and traveltime observations for hypocenter determination and apply a bootstrap resampling technique to quantify the location precision. We observe seismicity rates of 20 events per month for M < 2.5 along the basin. The spatial distribution of hypocenters suggests that the two major fault branches bounding the depocenter below the C1narc1k Basin merge to one single master fault below similar to 17 km depth. On the basis of a cross-correlation technique we group closely spaced earthquakes and determine composite focal mechanisms implementing recordings of surrounding permanent land stations. Fault plane solutions have a predominant right-lateral strike-slip mechanism, indicating that normal faulting along this part of the NAFZ plays a minor role. Toward the west we observe increasing components of thrust faulting. This supports the model of NW trending, dextral strike-slip motion along the northern and main branch of the NAFZ below the eastern Sea of Marmara.