A Detailed Mapping of Uppermost Mantle Pn Velocities in Western North America and Other Continental Regions Located Behind Convergent Plate Boundaries

我们建议在与主要构造省相当的尺度上绘制北美西部和其他位于会聚板块边界后面的高架大陆区域（如西藏、土耳其-乌拉尼亚和Altiplano-Puna高原）下的上地幔Pn速度图。这种制图将对大陆高原的结构和起源提供关键的限制。这样的结果可以用来回答关于大盆地下“双重”莫霍的争论。我们建议使用大量的数字ISC数据，以一种简单而有效的方式获得数千个Pn速度的确定，这将基于北美西部数百个地震台站记录的大约10,000个事件的Pn到达时间报告。我们计划使用双站方法，其中源位于震中距离，其中Pn是第一个到达，并且源处于或非常接近双站对的方位角。台站对选择在可确定的构造省内。一项在科罗拉多高原下绘制Pn速度的初步研究产生了非常令人鼓舞的结果，大约有1000个Pn速度测定。我们计划将我们的工作扩展到北美西部的其他省份，以及位于汇聚板块边界后面的其他高地大陆地区。我们还建议使用所有可用的Pn速度和源和站延迟，使用赫恩和克莱顿的程序。由于台站和震源的空间分布差异很大，这种方法的分辨率可能因省而异。双站和层析成像方法的综合结果将提供上地幔速度的详细地图。

We propose to map in detail uppermost mantle Pn velocities beneath western North America and other elevated continental regions located behind convergent plate boundaries, such as the Tibetan, Turkish-Uranian, and the Altiplano-Puna plateaus on a scale comparable to the major tectonic provinces. This mapping will provide critical constraints on the structure and origin of continental plateaus. Such results can be used to answer an ongoing debate over the "double" Moho beneath the Great Basin. We propose to use the massive digital ISC data in a simple but effective way to obtain thousands of Pn velocity determinations, which will be based on the reports of Pn arrival times from about ten thousand events recorded at hundreds of seismic stations in western North America. We plan to use the two- station method in which the source is located at epicentral distances where Pn is the first arrival and the source is in, or very near, the azimuth of the two-station pair. The station pairs are selected to be within definable tectonic provinces. A pilot study to map Pn velocity beneath the Colorado plateau produced very encouraging results with about a thousand Pn velocity determinations. We plan to extend our efforts to the rest of the provinces in western North America, and to other elevated continental regions located behind convergent plate boundaries. We also propose to use all available Pn velocities and source and station delays, using the procedure of Hearn and Clayton. Because of the large variations in the spatial distribution of stations and sources, the resolution of this method may vary from one province to another. The combined results of the two-station and tomography methods will provide a detailed map of uppermost mantle velocities.