Holocene Seismicity of the Northern San Andreas Fault Based on Precise Dating of the Turbidite Event Record

圣安德烈亚斯北部断层上一次破裂是在1906年摧毁旧金山的大地震中。陆地上确定这种地震的频率及其震级和破裂长度的努力受到了少数几个创建了地质记录的合适地点的阻碍。近海，新的核心数据显示，加利福尼亚州北部的大陆边缘航道记录了可能由圣安德烈亚斯大地震引发的地区性海底滑坡的全新历史。该项目利用2002年斯克里普斯R/V罗杰·雷弗尔号巡航期间收集的岩心，将海洋古地震技术应用于圣安德烈亚斯转换边缘北部的浊积岩历史。该项目的目标是测试圣安德烈亚斯断层北海岸段的完整边缘和分段破裂模型。正在利用近海浊积岩建立从旧金山到门多西诺角边缘的全新世事件年代学，并正在测试浊流事件是否同步(因此也就是地震)触发。这些方法包括直接测定每个浊积岩的年龄，生物地层学，以及使用密度、磁学、矿物学和可见光和X射线图像的直接物性对比，以构建沿断层的地层格架。使用放射性碳对断层沿线不同地点之间的事件进行对比，并使用每个事件的指纹来测试沿断层的沉积物之间的联系。直接的联系指向了地震的起源，因为海底滑坡的其他触发因素一次只在一个峡谷发生。利用这一信息，有可能确定圣安德烈亚斯北部过去地震的破裂长度和时间。这些信息将对分析旧金山的地震危险性很有价值，并有助于揭示目前尚不存在的大型断层系统的长期行为。

The Northern San Andreas Fault last ruptured in the great 1906 earthquake that destroyed San Francisco. Efforts on land to determine the frequency of such earthquake and their magnitudes and rupture lengths have been hampered by few suitable localities where a geologic record has been created. Offshore, new core data show that continental margin channels in Northern California have recorded a Holocene history of regional submarine landslides possibly triggered by San Andreas great earthquakes. This project is applying marine paleoseismologic techniques to the turbidite history along the Northern San Andreas transform margin using cores collected in 2002 during a cruise of the Scripps vessel R/V Roger Revelle.The goals of this project are to test models of full margin and segmented rupture along the North Coast segment of the San Andreas Fault. A Holocene event chronology along the margin from San Francisco to Cape Mendocino is being established using offshore turbidites and turbidite events are being tested for synchronous (and therefore earthquake) triggering. The methods include direct dating of each turbidite, biostratigraphy, and direct physical property correlation using density, magnetics, mineralogy and visible and X-ray imagery to construct a stratigraphic framework along the margin.Correlation of events between separate sites along the fault using radiocarbon, and fingerprints of each event are being used to test the linkages between deposits along the fault. Direct linkages point to an earthquake origin, since other triggers of submarine landslides happen in only one canyon at a time. Using this information, it may be possible to establish both rupture length and timing of past earthquakes along the Northern San Andreas. This information will be valuable for analysis of seismic hazards in San Francisco, as well as shed light on the long-term behavior of large fault systems that does not presently exist.