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

我们建议在北美西部和位于会聚板块边界后面的其他隆起大陆地区，如西藏、土耳其-乌拉尼亚和高原-普纳高原之下，以与主要构造省相当的比例尺，详细绘制地幔Pn速度图。这一测绘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正在进行的关于大盆地下的“双重”莫霍面的争论。我们建议以一种简单而有效的方式使用大量的ISC数字数据来获得数千个Pn速度确定，这将基于北美西部数百个地震台记录的大约1万个事件的Pn到达时间报告。我们计划使用两台站方法，其中震源位于震中距离，Pn是第一个到达，震源位于或非常接近两台站对的方位。站对被选择为在可定义的构造省内。一项绘制科罗拉多高原下的Pn速度图的试点研究产生了非常令人鼓舞的结果，大约有1000个Pn速度测定。我们计划将我们的努力扩展到北美西部的其他省份，以及位于会聚板块边界后面的其他高架大陆地区。我们还建议使用所有可用的PN速度以及震源和台站延迟，使用赫恩和克莱顿的程序。由于台站和震源的空间分布有很大的差异，这种方法的分辨率可能会因省而异。两站和层析成像方法的综合结果将提供最高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.