USArray FlexArray augmentation of a seismic study of the extension paradox at the northwest margin of the Basin-&-Range Province

内华达州的地形很高--即使是山脉之间的山谷也有几千英尺的海拔。 由于这个平均海拔在俄勒冈州边界和内华达州中部之间没有显著变化，我们认为地壳（通俗地说，是漂浮在地幔上的冰山）在这一地区的厚度一定是相同的。 然而，值得注意的是，我们已经发现，当我们向南穿过同一地区时，伸展的量--山脉和山谷之间边界处的断层作用导致的地壳拉伸量--增加了大约5倍。 当地壳被拉伸时，它会变薄，那么为什么内华达州中部的地壳没有变薄，海拔也没有降低呢？ 这就是我们正在研究的“外延悖论”。我们认为，答案可能是地壳的下部足够脆弱，可以在地质时间尺度上流动，而北方内华达州下方的下地壳正在向南流向内华达州中部，有助于均衡地壳厚度并平衡整个地区的海拔。 我们正在通过收集一个新的地震剖面来测试这一假设，该剖面将非常详细地测量内华达州西北部的地壳厚度和结构，该地区过去没有用这种方法进行过很好的研究。 我们正在利用NSF的Earthscope计划最近为国家科学企业开发和收购的最新技术和设备。Earthscope通过其一个部门“US-Array”资助开发了一个“FlexArray”，这是一个大型的易于运输的地震仪库。 我们将使用这种新设备来研究地壳，比以前更详细-我们预计将放置1000多个地震仪来记录我们将在精确控制的时间和地点引爆的6次爆炸所产生的声波。 通过测量地震波从每次爆炸到每个地震仪穿过地壳所需的时间，我们可以准确地了解地震波穿过地球的速度，这反过来又可以让我们绘制出不同的岩石类型和结构。在我们的项目中，我们正在培训一群斯坦福大学的本科生，学习了解大陆所需的地质和地球物理技术。 通过将课堂从校园扩展到内华达沙漠和山脉，并将理论扩展到实践，我们正在丰富下一代科学领导人的教育。 我们还与土地管理局和国家森林管理人员合作，进行一项安全的实验，对环境没有持久的影响，我们希望通过这样做，扩大公众对科学方法的理解，并提高公众对当地地质的认识。 我们所有的数据都将通过地球镜数据中心存档并公开发布;最终，我们对内华达州北方地壳的新了解将有助于我们和其他科学家更好地了解该地区的地震危险。

Nevada has high topography - even the valleys between the mountain ranges are at elevations of several thousand feet. Because this average elevation does not change significantly between the Oregon border and central Nevada, we believe that the Earth's crust (colloquially, the iceberg floating on the mantle) must be the same thickness across this region. What is remarkable, however, is that we have discovered that the amount of extension - the amount of stretching of the crust by faulting at the borders between the mountains and the valleys - increases by a factor of about 5 as we go south across this same region. When the crust is stretched it thins, so why then is the crust not thinner, and the elevation lower, in central Nevada? This is the "extension paradox" that we are studying. We believe the answer may be that the lower part of the crust is weak enough that it can flow over geological timescales, and that the lower crust beneath northern Nevada is flowing south to central Nevada, helping to equalize the crustal thickness and balance the elevations across this region. We are testing this hypothesis by collecting a new seismic profile that will measure the crustal thickness and structure in great detail across northwestern Nevada, a region that has not been well-studied by this method in the past. We are making use of the latest technology and equipment that has recently been developed and acquired for the national scientific enterprise by NSF's Earthscope program. Earthscope, through one of its divisions "US-Array", has funded the development of a "FlexArray", a large pool of easily transportable seismographs. We will use this new equipment to study the Earth's crust in more detail than has previously been possible - we expect to lay out over 1000 seismographs to record the sound waves created by 6 explosions that we will detonate at precisely controlled times and locations. By measuring the time it takes for the seismic waves to travel through the Earth's crust from each explosion to each seismograph, we can build up an accurate picture of the seismic wave-speed through the Earth, which in turn lets us map out the different rock types and structures present at depth. During our project we are training a group of Stanford undergraduates in the combination geologic and geophysical techniques required to understand the continents. By extending the classroom from campus to the Nevadan deserts and mountains, and by extending theory to practice, we are enriching the education of the next generation of scientific leaders. We are also working with Bureau of Land Management and National Forest managers to carry out a safe experiment with no lasting environmental impact, and in so doing we expect to enlarge public understanding of scientific methodologies, and public appreciation of local geology. All our data will be archived with and publicly released through an Earthscope Data Center; ultimately our new understanding of the crust beneath northern Nevada will help us and other scientists better understand earthquake hazard in this region.