Inversion of P-wave velocity anisotropy

Summary. We examine the way in which measurements of velocity anisotropy can add to our understanding of upper mantle structure. Measurements of P -wave velocity anisotropy in a single plane contain very little direct information about the anisotropic structure. A promising technique is to fit the observed velocity variation with a mixture of an assumed anisotropic constituent and a proportion of isotropic material. Using this technique, mixtures of orthorhombic and transversely isotropic olivine are obtained, which are in excellent agreement with observed velocity variations in the Pacific.     

Surface-wave propagation in an ocean basin with an anisotropic upper mantle: observations of polarization anomalies

Summary. Observations of surface waves crossing ocean basins indicate that, at least in some cases, a better interpretation of what was previously considered to be the simultaneous arrival of fundamental Love and second Rayleigh modes, with similar group velocities, is the coupled motion of the second-generalized mode surface wave propagating in an anisotropic upper-mantle. This mode displays the polarization anomalies expected from anisotropic alignments caused by syntectonic recrystallization of olivine in a zone of horizontal shear. The polarity of the pattern of anomalies, found in waves crossing the Pacific Basin, suggests that the lithosphere is dragging the asthenosphere.     

剪切波分裂与地震预测

地震剪切波分裂（SWS）可用来监测饱和流体微裂纹岩石的细微形变。本文报告了由小地震记录到的剪切波分裂系统性变化的证据,通过监测震前的应力积累可预测即将发生的大震的时间和震级。通过对冰岛西南部的M1．7级震群事件到台湾Ms7．7级集集地震等15个震例（其中包括成功预测的冰岛西南部的M5．0地震）的剪切波分裂研究,可以看到预测效果。大地震发生前观测到剪切波分裂时间延迟会明显增加,而临震前短时间内时间延迟会突然下降。研究表明,震级与临震前这种时间延迟增加的持续时间和减小的持续时间的对数都具有线性相关。然而,作为日常应力预测常缺乏适当的持续小震群。可靠的地震预测需要应力监测站（简称SMS）中采用毗邻钻孔中的可控源井间地震技术。利用应力监测站的全球网络实时应力预测世界范围破坏性地震是非常可能的。     

Controlled sources for shear-wave surveys in mines

The ability to analyse shear-wave anisotropy in a mine environment is greatly aided by using multiple source orientations of a reproducible, impulsive shear-wave source. The analysis of what is probably the first controlled source shear-wave experiment in a mine environment demonstrates clearly that shear-wave polarizations and time delays between split shear-wave arrivals are reliably measured because of the use of multiple source orientations rather than a single shear-wave source. Reliability is further aided by modelling the shear-wave source radiation pattern, which allows for the unequivocal discrimination between seismic raypaths where shear-wave splitting did and did not occur. The analysis also demonstrates the great importance of high reproducibility of the seismic source for the use of shear waves in time-lapse surveys to monitor changes in a rockmass.