Fenglin Niu, Paul G. Silver, Thomas M. Daley, Xin Cheng Ernest L. Majer ，在 《 Nature 》杂志上发表了一篇题为“ Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site ”的文章，先看看其研究有没有价值。 It is well known from laboratory experiments that seismic velocities vary with the level of applied stress 3–5 . Such dependence is attributed to the opening and closing of microcracks due to changes in the stress normal to the crack surface 6–8 . In principle, this dependence constitutes a stress meter, provided that the induced velocity changes can be measured precisely and continuously. Indeed, there were several attempts in the 1970s to accomplish this goal using either explosive or non-explosive surface sources 9–11 . The source repeatability and the precision in travel-time measurement appeared to be the main challenges in making conclusive observations. 点评：地震波速度确实能反映地下结构或裂隙张开闭合的变化，会随加载应力的变化而变化。但如用波速预测地震就很困难，这要求：（ 1 ）打多个较深的、靠近震源的钻孔，在孔内布设传感器，这意味着需要知道震源体的精确位置，而震源又不是一个小尺度的岩体，因此不具有实际可操作性。（ 2 ）在大震前，中小地震在一个地震区会发生多次，假如每个地震前都能探测到波速变化，波速变化多大才能预测大震呢？（ 3 ）如何根据波速变化预测大震的三要素呢？这些又是“此路不通”的难题。 其实每个大震前的中小破裂事件比波速变化更能反映岩石的破裂程度，为何愿“舍近求远”呢？纯属多此一举。 It is not clear to us why the larger M= 2.6 event is not observed while the smaller M = 1 event shows clearly in the delay time data. But we noticed that data collected in the second period had a better SNR than those of the first period. The associated stress change of the M = 2.6 event thus might be below the resolution of the first-month data. 这句话的中文意思是：尚不清楚为何较大的 M=2.6 地震未观测到时间延迟，而较小的 M=1.0 地震却显示出清楚的时间延迟。但我们注意到第二期试验比第一期试验具有更高的数据信噪比，与 2.6 级地震相关的应力变化有可能湮没于第一期资料的噪声中。 点评：这句话说明了作者的方法即使对小震预测也无完全的对应性。 We put forward the hypothesis that there is a change in effective elastic moduli before rupture, such as a sudden increase in microcrack density, which is a phenomenon related to dilatancy and observed in many laboratory studies 1,2 . As such, further continuous seismic monitoring might provide an effective tool for understanding the stress changes that accompany and perhaps precede seismic activity. 点评：假定如微破裂密度的增加与 与诸多实验研究中观测到的岩石膨胀相关， 这句话更有问题了。实际上在岩石膨胀开始前，还有一个稳定破裂阶段，稳定破裂也会导致密度增加。在该文中，作者在 2005 年 10 月 29 日 至 2006 年 1 月 10 日， 只是根据波速变化探测到了一个 1.0 和 3.0 级的地震，不可能是膨胀开始后的地震事件（预震或前震事件），因期待已久的 Parkfield 6.0 级地震发生在 2004 年 9 月 28 日 ，公认为一次主震事件，其后一定时间范围的地震为余震事件。 读完这篇文章后感觉莫名其妙，真不知审稿人是如何审稿的。如某个作者在 CNS 杂志上发表 10 篇这样低水准的论文，你会认为该人是“大牛”吗？你觉得该人可以评选为院士吗？呵呵，不误人子弟就不错了。 原文见： Preseismic velocity changes observed from active.pdf
标签: 学术价值
