Scattered-Wave Imaging Algorithms for Regional and Local Arrays

标题：区域和局部阵列的散射波成像算法参考文献：J. Revenaugh， UC Santa crus地球上的非均质性对弹性波的散射是高频波形复杂性的一个明显和主要来源，产生缓慢衰减的能量序列，在主要（几何）到达后的几分钟内可以在记录中看到。传统上，试图描述散射性质的研究要么将其视为区域平稳的统计过程，要么将注意力限制在地壳分层产生的散射波场的相干部分。这两种方法都产生了有价值的结果，并将继续这样做，但每种方法都对散射的本质做出了限制性假设，最终限制了它们的效用。我们开发了一种替代方法，利用石油行业开发的一种算法的变体，利用区域阵列（孔径为100公里）远震地震记录，对地壳和上地幔的散射结构进行成像。该方法已应用于南加州地震台网和夏威夷火山观测台阵列的数据。这两个阵列的结果揭示了散射强度与背景和余震的密度之间有趣且可能非常重要的地理相关性。更重要的是，这些结果提供了一个非常重要的“概念证明”，即可以在小于平均站距的尺度长度下提取可靠的结构信息。在我们的提案中，我们记录了一项工作计划，通过更好地处理弹性散射物理，更精确的波场求和，结合三分量记录和正则化反演，来改进我们当前方法（称为Kirchhoff尾da偏移或KCM）所采用的成像范式。在这样做的过程中，我们将继续尊重区域和本地地震阵列记录的通常紧急情况：不规则的仪器部署、数据丢失、扩展的震源特征（由于地震破裂过程和近震源结构造成的波形复杂性）、台站效应和有限的照明反向方位角。我们的目标是为pascal社区和永久密集的局部和区域阵列数据用户提供广泛应用于地壳和上地幔散射结构成像的“罐装”算法。我们将把算法应用于南加州和夏威夷岛的手头数据。

Abstract for proposal EAR0106836 (PH #36x)Title: Scattered-wave imaging algorithms for regional and local arraysPI's: J. Revenaugh, UC Santa CruzThe scattering of elastic waves by heterogeneities in the Earth is an obvious and dominant source of waveform complexity at high frequencies, producing slowly decaying trains of energy that are visible in records for several minutes following primary (geometrical) arrivals. Studies attempting to characterize the nature of scattering traditionally have treated it either as a regionally stationary statistical process, or have restricted attention to the coherent portion of the scattered wavefield produced by crustal layering. Both approaches have yielded valuable results and will continue to do so, but each makes restrictive assumptions about the nature of scattering that ultimately limit their utility. We have developed an alternative approach, utilizing a variant of an algorithm developed by the oil industry to image scattering structures in the crust and upper mantle using regional array (aperture of order 100 km) recordings of teleseismic earthquakes. The method has been applied to data from the Southern California Seismic Network and the Hawaiian Volcano Observatory array. The results from both arrays reveal an intriguing and potentially very important geographic correlation of the strength of scattering with the density of background and aftershock earthquakes. More importantly, these results provide an all-important "proof of concept"that it is possible to extract reliable structural information at scale-lengths less than average station separation. In our proposal, we document a work plan to improve upon the imaging paradigm employed by our current method (referred to as Kirchhoff coda migration, or KCM) through better treatment of the physics of elastic scattering, more accurate wavefield summation, the incorporation of three-component recordings, and a regularized inversion. In so doing, we will continue to honor the usual exigencies of regional and local array recordings of earthquakes: irregular instrument deployment, data dropouts, extended source signatures (waveform complexities due to the earthquake rupture process and near-source structure), station-site effects and limited illumination back azimuths. Our goal is the production of "canned" algorithms of broad-spread application to the imaging of crustal and uppermost mantle scattering structures by both the PASSCAL community and to users of permanent dense local and regional array data. We will apply the algorithms to data in hand from Southern California and the island of Hawaii.