Collaborative Research: Understanding the crustal link between the Columbia River flood basalts and lithospheric foundering.

S，地球上最大的火山事件是罕见的玄武岩洪水喷发，平均约4000万年一次。其中一些事件似乎导致了重大物种灭绝，总的来说，喷发的熔岩覆盖了地球的很大一部分；它们也代表了黄石公园等热点地区的开始。最近和暴露最好的洪水玄武岩事件发生在大约1600万年前，从俄勒冈州东部爆发。这是我们研究的目标。洪泛玄武岩喷发的基本驱动机制发生在岩石圈板块下方，该事件对板块的改造具有重要作用。然而，我们并不了解这些事件的基本面。就我们而言，有强有力的证据表明，受影响的岩石圈的大片下沉并沉入软流层，下沉的岩石圈的分布控制了火山活动的位置和分布。我们的研究将使用地震成像方法来成像这次地震在地壳以及下伏的岩石圈和软流层中创建和修改的结构，具体目标是找到原始岩浆室(S)并解决它们的形状。我们将部署大约60个地震仪，从俄勒冈州东北部主喷发中心中心向北延伸150公里，直到华盛顿州西南部，离开喷发区。我们将使用从世界各地发生的远距离地震向上传播的地震波。将采用的两种主要技术包括(1)当P波到达界面(例如我们正在研究的现已冻结的岩浆室(S)的边界)时发生的P波到S波的转换，以及(2)每条射线穿过感兴趣区域时发生的时间推进(或延迟)。这些延迟被用来制作由洪水玄武岩事件产生的地球主要体积的断层图像。

The Earth?s largest volcanic events are the rare flood-basalt eruptions that occur once every about 40 million years, on average. Some of these events appear to have caused major extinctions, and in net, the erupted lavas cover a significant portion of the Earth; they also represent the beginning of hotspots such as Yellowstone. The most recent and best-exposed flood basalt event erupted about 16 million years ago from eastern Oregon. This is the target of our study. The fundamental driving mechanism for flood basalt eruptions occurs below the lithospheric plate, and the event has a major effect on modifying the plate. Yet, we do not understand the fundamentals of these events. It our case, there is strong evidence that large pieces of the affected lithosphere foundered and sank into the asthenosphere, and that the distribution of the foundering lithosphere controlled the location and distribution of volcanism. Our study will use seismic imaging methods to image the structures created and modified by this event, both in the crust and in the underlying lithosphere and asthenosphere, with the specific goals of finding the primary magma chamber(s) and resolving their shape.We will deploy about 60 seismometers in a line extending north 150 km from the center of the main eruptive center in northeast Oregon into southwest Washington, out of the eruptive area. We will use seismic waves that propagate up from distant earthquakes that occur around the world. The two primary techniques to be employed involve (1) the conversion of P waves to S waves that occurs when the wave hits an interface (such as the boundaries of the now-frozen magma chamber(s) we are studying), and (2) the time advance (or delay) that occurs for each ray as it passes through the region of interest. These delays are used to make a tomographic image of the major volumes of Earth that have been created by the flood basalt event.