Variations in earthquake rupture properties along the Gofar transform fault, East Pacific Rise
Variations in earthquake rupture properties along the Gofar transform fault, East Pacific Rise
复制标题
东太平洋海隆戈法尔转换断层沿线地震破裂特性的变化
DOI：
10.1038/ngeo1454
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发表时间：
2012
影响因子：
18.3
通讯作者：
R. Hilst
中科院分区：
文献类型：
--
作者：
J. McGuire;J. Collins;P. Gouédard;E. Roland;D. Lizarralde;M. Boettcher;M. Behn;R. Hilst
洋中脊转换断层比大陆断层经历更多的前震，但主震很少使整个断层破裂。对东太平洋隆起Gofar转换断层地震数据的分析表明，前震区与主震区具有不同的材料特性，并充当破裂传播的屏障。在全球范围内，连接洋中脊段的海洋转换断层上的地震活动受到热控制1，2。然而，温度不是唯一的控制因素，因为海洋转换断层上的最大地震只破裂了热模型预测能够破裂的一小部分3，4，5。相反，大多数滑动发生时不会产生大地震3，4，6。当大地震确实发生时，它们经常准周期性地重复7，8。此外，海洋转换断层产生的前震数量级比大陆走滑断层多7，9。在这里，我们分析了一组约20,000前震，记录在海底地震仪阵列，发生在Gofar转换断层，东太平洋隆起6.0级地震之前。我们发现，长达一周的前震序列被限制在一个10公里长的区域，随后作为一个障碍，在主震破裂。前震区具有高孔隙度，主震前一周平均剪切波速度下降3%。我们的结论是，能够破裂的断层段在大地震中的材料特性不同的障碍区，可能是由于后者内的流体循环增强。我们认为，沿断层带材料性质的走向变化可以帮助解释前震的丰富性和相对缺乏的大地震发生在大洋中脊转换断层。
Mid-ocean ridge transform faults experience more foreshocks than continental faults, yet the mainshock rarely ruptures the entire fault. Analysis of seismic data from the Gofar transform fault at the East Pacific Rise indicates that the foreshock region has different material properties from the mainshock region, and acts as a barrier to rupture propagation. On a global scale, seismicity on oceanic transform faults that link mid-ocean ridge segments is thermally controlled1,2. However, temperature cannot be the only control because the largest earthquakes on oceanic transform faults rupture only a small fraction of the area that thermal models predict to be capable of rupture3,4,5. Instead, most slip occurs without producing large earthquakes3,4,6. When large earthquakes do occur, they often repeat quasiperiodically7,8. Moreover, oceanic transform faults produce an order of magnitude more foreshocks than continental strike-slip faults7,9. Here we analyse a swarm of about 20,000 foreshocks, recorded on an array of ocean-bottom seismometers, which occurred before a magnitude 6.0 earthquake on the Gofar transform fault, East Pacific Rise. We find that the week-long foreshock sequence was confined to a 10-km-long region that subsequently acted as a barrier to rupture during the mainshock. The foreshock zone is associated with a high porosity and undergoes a 3% decrease in average shear-wave speed during the week preceding the mainshock. We conclude that the material properties of fault segments capable of rupturing in large earthquakes differ from those of barrier regions, possibly as a result of enhanced fluid circulation within the latter. We suggest that along-strike variations in fault zone material properties can help explain the abundance of foreshocks and the relative lack of large earthquakes that occur on mid-ocean ridge transform faults.