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致读者本报告的动机在2003年7月召开的PBO常务委员会上,提出了很多有关现有钻孔应变仪的性能问题,我们可以在PBO的网页上看到。这些问题由许多委员提出,反映了人们有兴趣来确保作为PBO的一部分所安装的钻孔应变仪能够提供可靠的、而且是可以根据地壳应变来标定的数据。本报告将尝试根据2003年8月至2004年2月对钻孔应变观测数据的分析来回答这些问题。分析所利用的时间受限于为第一和第二两年的部署必须作出选择钻孔应变仪类型的决定。我们不可能在有限的时间内对所有的钻孔应变数据进行分析,所以只选择了一部分仪器的观测数据进行分析,且某些类型的分析只用在有疑问的仪器的数据上。本报告的观点尽管在报告中没有保密的材料,但是读者应该认识到这篇报告主要是在PBO常务委员会内部使用,而从未打算对钻孔应变仪的性能进行全面的描述。因为PBO白皮书和《地球透镜》(The Earthscope)项目建议书已经总结了根据钻孔应变仪的测量得到的科学结果,关于这些结果在本报告的第8部分比其他部分要简略一些。本报告的现况由于本报告具有较高的意义,所以正准备在USGS(美国地质调查局)上评审、批准和在线发表。经USGS批准不是为了得到和现在不一样的结论,而是为了能使所有的钻孔应变仪得到全面的评估。例如,我们要尽力完全填好第7部分的表格。本报告草稿在美国地质调查局评审和批准之前在网上发表,因此其结论应当是初步的。本报告草稿包含对2004年2月以后分发给PBO常务委员会的报告所进行的修正。只有一处修正影响了这篇报告的结论:利用Frolich体应变仪资料绘制的长期变化图是不正确的,并且导致该仪器的三分量尺度因素不同于大多数仪器这一结论也是错误的。在当前的版本中已对这一错误进行了改正;重标了功率谱的垂直坐标,对尺度的错误也作了改正。这些修正不会影响报告的结论。其他方面的修正很小。
The Readers’ Motivation for this Report At the PBO Standing Committee held in July 2003, a lot of questions about the performance of existing borehole strain gauges were put forward on the PBO’s website. These questions were raised by many members and reflect the interest that people are interested in ensuring that borehole strain gauges installed as part of a PBO can provide reliable and data that can be calibrated to crustal strain. This report will attempt to answer these questions based on the analysis of borehole strain observations from August 2003 to February 2004. The time taken for the analysis is limited by the decision that the type of borehole strain gauge must be chosen for the first and second two-year deployment. We can not analyze all borehole strain data for a limited time, so we select only part of the instrument’s observation data for analysis, and some types of analysis are only used on the data of the instrument in question. Although the report does not contain confidential material, readers should recognize that this report was primarily intended for internal use within the PBO Standing Committee and never intended to provide a comprehensive picture of the performance of a borehole strain gauge. Because the PBO White Paper and The Earthscope project proposals have summarized the scientific results from borehole strain gage measurements, these results are somewhat less detailed than the rest of the report in section 8. STATUS OF THE REPORT As this report is of high significance, it is being prepared for review, approval and online publication at the USGS. Approved by the USGS is not intended to give a different conclusion than it is now, but to enable a complete assessment of all borehole strain gauges. For example, we will try our best to complete the form in Part 7. The draft report was posted online before the United States Geological Survey assessed and approved it, so its conclusion should be preliminary. The draft report contains amendments to the report circulated to the PBO Standing Committee since February 2004. There is only one correction affecting the conclusion of this report: the long-term change plot using Frolich body strain gauge data is incorrect and the conclusion that the three-component scale factor of this instrument differs from most instruments is also wrong. This error has been corrected in the current version; the vertical coordinate of the power spectrum has been re-calibrated and the error of the scale has also been corrected. These amendments will not affect the conclusions of the report. Other amendments are small.