Investigating the Presence of Preseismic Velocity Changes

研究地震速度变化的存在

• 批准号: 0910535
• 负责人: David Schaff
• 金额: $ 21.12万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0910535&HistoricalAwards=false
• 关键词: Investigating; Presence; Preseismic; Velocity; Changes

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Earthquakes strike without warning and are some of the most destructive and devastating forces of nature in terms of loss of life. In May, 2008 the Wenchuan earthquake in China killed 80,000 people with 20,000 still missing. The 2004 Sumatra earthquake generated a giant tsunami that left 225,000 casualties in its wake, affecting eleven countries. In 1976 the Tangshan earthquake in China again, killed 240,000 people, the deadliest in recorded history. Statistics compiled at Columbia University indicate that of all natural disasters world-wide including floods, droughts, hurricanes, tornadoes, and fires?earthquakes rank the highest for total number of casualties. Many of the other natural disasters provide some type of warning so that at least lives can be saved even if property damage is extensive. Understandably people have diligently sought for some clues to foretell of impending great earthquakes in hopes of alleviating some of this loss and suffering. But earthquake prediction remains an extremely challenging problem. Most of the evidence of precursors is anecdotal and has not been scientifically verified in a rigorously controlled setting that produces reproducible results.Professional seismologists have been doing their best to contribute what they could to the challenge of earthquake prediction. There has been a long history of looking for precursory variations in the velocity of seismic waves or other waveform attributes preceding large earthquakes. The search for preseismic velocity changes has been called the holy grail of seismology. This project will continue taking small steps in that pursuit. Progress has been made. It is now scientifically well-documented that coseismic and postseismic velocity changes have been measured by a variety of means for several large earthquakes all demonstrating consistent behavior. The data in these studies, however, do not have the temporal sampling required to confirm the existence or non-existence of a preseismic velocity change. The findings are inconclusive simply because of a lack of data. We present in this proposal three different strategies designed to greatly improve the insufficient temporal sampling in the preseismic period. They involve new data and new technologies that are state-of-the-art and have recently come on the scene. The first approach is to do a comprehensive analysis of new repeating event sequences that have become available as a source for repeatable waves in the same location. The abundant new data sources for the repeating events substantially improves the temporal sampling for this now standard method for measuring velocity variations. The second approach takes advantage of the hot, new field of ambient seismic noise correlations which just recently has been applied for velocity change monitoring. The technique utilizes continuous data streams from permanent stations and so is able to finely sample velocity variations in the days leading up to large earthquakes. We propose enhancements to this method from our correlation detector research to better be able to extract the signal from the noise. The third strategy is to develop a prototype time-dependent double-difference tomography code to invert for where the changes are occurring spatially and to be able to use the majority of the microseismicity.Both laboratory experiments and theories have concluded that there should be measureable velocity changes in the crust preceding large earthquakes. They have yet to be consistently and reliably measured in the field. The reason for this may be due to lack of high quality data since we don?t know where and when the next earthquake will strike. However, an extremely well controlled experiment at Parkfield has recently observed velocity changes preceding two earthquakes presenting the most convincing evidence to date that these predicted changes do occur in the field. But conducting many more of these types of experiments is economically infeasible and so alternative strategies are needed to confirm the existence of preseismic velocity changes before other large earthquakes.The question that seismologists are most often asked by the lay public is, "Can we predict earthquakes yet?" The answer is not currently. While it is a far off goal, the general population clearly cares about this issue and desires that a portion of the resources they provide would be allocated towards that end. Engineers can build safer buildings to reduce the loss of life substantially, but in many of the poorer countries which also happen to be the ones that suffer the greatest number of casualties, this is economically prohibitive and so they would benefit the most from better earthquake forecasting.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。地震袭击没有警告，是自然界中最具破坏性和毁灭性的力量，造成生命损失。 2008年5月，中国汶川地震造成8万人死亡，2万人失踪。 2004年苏门答腊地震引发了一场巨大的海啸，造成225，000人伤亡，影响了11个国家。 1976年，中国唐山再次发生地震，造成24万人死亡，这是有史以来死亡人数最多的一次。 哥伦比亚大学的统计数据表明，在全世界所有的自然灾害中，包括洪水、干旱、飓风、龙卷风和火灾？地震是伤亡人数最多的地区。 许多其他自然灾害提供了某种类型的警告，以便即使财产损失很大，至少可以挽救生命。 可以理解的是，人们一直在努力寻找一些线索来预测即将发生的大地震，希望减轻一些损失和痛苦。 但地震预测仍然是一个极具挑战性的问题。 大多数前兆的证据都是传闻，没有在严格控制的环境中进行科学验证，产生可重复的结果。专业地震学家一直在尽最大努力为地震预测的挑战做出贡献。 在大地震前寻找地震波速度或其他波形属性的随机变化已经有很长的历史了。 寻找震前速度变化被称为地震学的圣杯。 该项目将继续在这方面迈出小步。 已经取得了进展。 现在，科学上有充分的文献证明，对于几次大地震，同震和震后的速度变化已经通过各种手段测量出来，所有这些都表现出一致的行为。 然而，这些研究中的数据并不具有确认存在或不存在前沉降速度变化所需的时间采样。 由于缺乏数据，调查结果是不确定的。 我们在这个建议中提出了三种不同的策略，旨在大大改善在presea期间的时间采样不足。 它们涉及新的数据和新的技术，这些技术是最先进的，最近才出现。 第一种方法是对新的重复事件序列进行综合分析，这些事件序列已成为同一位置可重复波的来源。 重复事件的丰富的新数据源大大改进了用于测量速度变化的这种现在标准方法的时间采样。 第二种方法利用了最近才被应用于速度变化监测的环境地震噪声相关性的热点新领域。 该技术利用来自永久台站的连续数据流，因此能够对大地震前几天的速度变化进行精细采样。 我们从我们的相关检测器研究中提出了对这种方法的增强，以便能够更好地从噪声中提取信号。 第三个策略是开发一个原型的时间相关的双差层析成像代码，以反转的变化发生的空间，并能够使用大多数的microseismic activity.Both实验室实验和理论得出的结论是，应该有可测量的速度变化，在地壳前大地震。 在实地，这些指标尚未得到一致和可靠的衡量。 其原因可能是由于缺乏高质量的数据，因为我们不？I don’我不知道下一次地震会在何时何地发生。 然而，最近在帕克菲尔德进行的一项控制非常好的实验观察到了两次地震前的速度变化，这提供了迄今为止最令人信服的证据，证明这些预测的变化确实发生在现场。 但进行更多此类实验在经济上是不可行的，因此需要替代策略来确认其他大地震之前存在震前速度变化。地震学家最常被普通公众问到的问题是：“我们能预测地震吗？“答案不是现在。 虽然这是一个遥远的目标，但普通民众显然关心这个问题，并希望将他们提供的一部分资源用于这一目的。 工程师可以建造更安全的建筑物，以大幅减少生命损失，但在许多贫穷的国家，也恰好是那些遭受伤亡人数最多的国家，这在经济上是不允许的，所以他们将从更好的地震预报中受益最多。