Larger earthquakes recur more periodically: New insights in the megathrust earthquake cycle from lacustrine turbidite records in south-central Chile
Larger earthquakes recur more periodically: New insights in the megathrust earthquake cycle from lacustrine turbidite records in south-central Chile
复制标题
DOI：
10.1016/j.epsl.2017.10.016
复制
发表时间：
2018
影响因子：
5.3
通讯作者：
J. Moernaut;M. Daele;K. Fontijn;K. Heirman;P. Kempf;Mario Pino;G. Valdebenito;R. Urrutia;M. Strasser;M. Batist
中科院分区：
文献类型：
--
作者：
J. Moernaut;M. Daele;K. Fontijn;K. Heirman;P. Kempf;Mario Pino;G. Valdebenito;R. Urrutia;M. Strasser;M. Batist
智利中南部的历史和古地震记录表明，俯冲巨型逆冲断层上的大地震--例如AD 1960（MW 9.5）--平均每1300年就会发生一次。根据自AD 1960年以来的地震间矩积累的大地测量计算，假定该地区已经具有发生Mw 8地震的可能性。然而，要估计这种大地震在短期内发生的可能性，需要在智利中南部大型逆冲断层地震的长期复发模式中构建这一假设。在这里，我们提出了两个长期的湖泊记录，包括35地震触发浊积岩在过去的4800年。浊积岩范围与历史地震烈度的校准揭示了不同的宏观地震烈度阈值（≥ VII 1/2与≥ VI 1/2），用于在取心点生成浊积岩。最强地震（≥ VII 1/2）的重现期（292±93年）比≥ VII 1/2地震的重现期（139±69年）长。此外，分布拟合和事件间隔时间的变异系数（CoV）表明，更强的地震以更周期的方式重复（CoV：0.32 vs.0.5）。我们的多阈值震动记录与海岸古地震数据的互补性质（海啸，同震沉降）的区域相关性表明，强度≥ VII 1/2的事件重复破裂的同一部分的巨型逆冲断层超过至少10300公里的距离，可以被分配到Mw ≥ 8.6。我们假设，一个高板块锁定区-确定的大地测量研究和大的滑动在公元1960年-作为一个占主导地位的区域凹凸，弹性应变建立了几个世纪以来，大多数被释放在准周期性的大地震和巨地震。我们的古记录表明，泊松复发模型是不足以描述大规模逆冲断层地震复发在智利中南部。此外，它们还表明，在未来110年内，发生Mw 7.7-8.5地震的可能性增加，而发生Mw ≥ 8.6（类AD 1960）地震的可能性仍然很低。
Historical and paleoseismic records in south-central Chile indicate that giant earthquakes on the subduction megathrust–such as in AD1960 (M w 9.5)–reoccur on average every∼ 300 yr. Based on geodetic calculations of the interseismic moment accumulation since AD1960, it was postulated that the area already has the potential for a M w 8 earthquake. However, to estimate the probability of such a great earthquake to take place in the short term, one needs to frame this hypothesis within the long-term recurrence pattern of megathrust earthquakes in south-central Chile. Here we present two long lacustrine records, comprising up to 35 earthquake-triggered turbidites over the last 4800 yr. Calibration of turbidite extent with historical earthquake intensity reveals a different macroseismic intensity threshold (≥ VII1/2 vs.≥ VI1/2) for the generation of turbidites at the coring sites. The strongest earthquakes (≥ VII1/2) have longer recurrence intervals (292±93 yrs) than earthquakes with intensity of≥ VI1/2 (139±69 yr). Moreover, distribution fitting and the coefficient of variation (CoV) of inter-event times indicate that the stronger earthquakes recur in a more periodic way (CoV: 0.32 vs. 0.5). Regional correlation of our multi-threshold shaking records with coastal paleoseismic data of complementary nature (tsunami, coseismic subsidence) suggests that the intensity≥ VII1/2 events repeatedly ruptured the same part of the megathrust over a distance of at least∼ 300 km and can be assigned to M w≥ 8.6. We hypothesize that a zone of high plate locking–identified by geodetic studies and large slip in AD 1960–acts as a dominant regional asperity, on which elastic strain builds up over several centuries and mostly gets released in quasi-periodic great and giant earthquakes. Our paleo-records indicate that Poissonian recurrence models are inadequate to describe large megathrust earthquake recurrence in south-central Chile. Moreover, they show an enhanced probability for a M w 7.7–8.5 earthquake during the next 110 years whereas the probability for a M w≥ 8.6 (AD1960-like) earthquake remains low in this period.