Deep-water turbidites as Holocene earthquake proxies: the Cascadia subduction zone and Northern San Andreas Fault systems
Deep-water turbidites as Holocene earthquake proxies: the Cascadia subduction zone and Northern San Andreas Fault systems
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DOI：
10.4401/ag-3452
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发表时间：
2003-12
影响因子：
1
通讯作者：
C. Goldfinger;C. Nelson;Joel E. Johnson
中科院分区：
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作者：
C. Goldfinger;C. Nelson;Joel E. Johnson
卡斯卡迪亚边缘的新地层学证据表明，在马扎马火山灾难性喷发之后，13次地震使从温哥华岛到至少加州边界的边缘破裂。这13起事件发生的平均重复时间为？？自第一次后马扎马事件以来的600年？？7500年前最年轻的事件？300年前，卡斯卡迪亚海岸沿着被掩埋的沼泽地可能出现了海岸沉降和海啸淹没的广泛证据。我们可以将全新世记录延长到至少9850年，在此期间，沿着同一地区发生了18个事件。重复次数的模式与大多数（但不是所有）陆上地点观察到的模式一致，加强了两者都是由板块范围内地震产生的论点。我们还观察到，卡斯卡迪亚全新世事件的序列可能包含一个重复的模式，一个诱人的看看什么可能是一个主要的断层系统的长期行为。在过去的？？7500年，这种模式似乎至少重复了三次，最近的一次是公元1700年的事件，这是三次事件中的第三次，事件T4和T5之间间隔了845年。这一长间隔在许多海岸记录中也得到了承认，并可作为近海和陆上记录之间的锚点。在靠近北方圣安德烈亚斯断层的Noyo海峡的两个活塞岩心和一个箱形岩心中发现了类似的地层记录，显示了浊积岩层的循环记录，在全新世/更新世动物群"基准面"之上有31个浊积岩层。到目前为止，我们已经确定了20个事件的年龄，其中包括最高的5个事件。最重要的事件返回到“现代”时代，我们解释可能是1906年的圣安德烈亚斯地震。倒数第二个事件返回的截距年龄为公元1664年（2？范围1505 - 1822）。第三个事件和第四个事件被集中在一起，因为它们之间没有半远洋沉积物。这一事件的年龄是公元1524年（1445 - 1664年），虽然我们不确定这一事件是代表一个事件还是两个事件。第五个事件的年龄是公元1204年（1057 - 1319年），第六个事件的年龄是公元1049年（981 - 1188年）。这些结果与迄今为止的陆上工作相吻合，表明倒数第二个事件的年龄在17世纪中期，最有可能是第三个事件的年龄？？1500 - 1600，第四个事件？1300.我们目前没有测试北方圣安德烈亚斯事件沿着同步性所需的空间采样，因此无法有信心地确定观察到的浊流记录是地震产生的。然而，陆上和海上记录之间事件数量的良好一致性表明，与卡斯卡迪亚一样，除了地震以外的浊流触发似乎没有显著增加沿着最北端圣安德烈亚斯边缘的浊流记录。两千年
New stratigraphic evidence from the Cascadia margin demonstrates that 13 earthquakes ruptured the margin from Vancouver Island to at least the California border following the catastrophic eruption of Mount Mazama. These 13 events have occurred with an average repeat time of ?? 600 years since the first post-Mazama event ?? 7500 years ago. The youngest event ?? 300 years ago probably coincides with widespread evidence of coastal subsidence and tsunami inundation in buried marshes along the Cascadia coast. We can extend the Holocene record to at least 9850 years, during which 18 events correlate along the same region. The pattern of repeat times is consistent with the pattern observed at most (but not all) localities onshore, strengthening the contention that both were produced by plate-wide earthquakes. We also observe that the sequence of Holocene events in Cascadia may contain a repeating pattern, a tantalizing look at what may be the long-term behavior of a major fault system. Over the last ?? 7500 years, the pattern appears to have repeated at least three times, with the most recent A.D. 1700 event being the third of three events following a long interval of 845 years between events T4 and T5. This long interval is one that is also recognized in many of the coastal records, and may serve as an anchor point between the offshore and onshore records. Similar stratigraphic records are found in two piston cores and one box core from Noyo Channel, adjacent to the Northern San Andreas Fault, which show a cyclic record of turbidite beds, with thirty- one turbidite beds above a Holocene/.Pleistocene faunal «datum». Thus far, we have determined ages for 20 events including the uppermost 5 events from these cores. The uppermost event returns a «modern» age, which we interpret is likely the 1906 San Andreas earthquake. The penultimate event returns an intercept age of A.D. 1664 (2 ?? range 1505- 1822). The third event and fourth event are lumped together, as there is no hemipelagic sediment between them. The age of this event is A.D. 1524 (1445-1664), though we are not certain whether this event represents one event or two. The fifth event age is A.D. 1204 (1057-1319), and the sixth event age is A.D. 1049 (981-1188). These results are in relatively good agreement with the onshore work to date, which indicates an age for the penultimate event in the mid-1600 s, the most likely age for the third event of ?? 1500-1600, and a fourth event ?? 1300. We presently do not have the spatial sampling needed to test for synchroneity of events along the Northern San Andreas, and thus cannot determine with confidence that the observed turbidite record is earthquake generated. However, the good agreement in number of events between the onshore and offshore records suggests that, as in Cascadia, turbidite triggers other than earthquakes appear not to have added significantly to the turbidite record along the northernmost San Andreas margin during the last ?? 2000 years.