Estimation of motion of subsurface fracture by using proximity AE doublets analysis

邻近声发射（AE）偶波分析用于地下裂缝测量。声发射是一种微地震事件。根据声发射源的分布估计地下裂缝的位置和形状。地下裂缝的测量在与地球有关的人类活动的许多领域都很重要。地热能是从地下裂缝储层中提取的，裂缝储层中储存着蒸汽和热水。二氧化碳被储存在地下裂缝的微小空间中。邻近声发射双波分析是一种既能估计地下断裂精细结构又能估计其运动的新方法。邻近声发射偶波具有相似的波形，它们以小于1秒的间隔连续发生。由于声发射波传播的介质在间隔内不发生变化，因此可以实现声发射源之间的精确相对定位。在倒谱分析中检测了相邻声发射偶波之间的纵波和横波间隔。邻近声发射双峰在其倒谱的内部有一个或两个峰。在邻近的AE双波中，在第一个事件衰减之前，会出现具有相似波形的第二个事件。通常，很难估计两种波形及其间隔之间的相似性。我做了时间-频率分析，当倒谱中间隔有两个峰时，可以确定p波的间隔。在时频分析中，将第二次横波到达后的数据替换为零，表示横波间隔的峰值减小。这种分析可以显示相邻声发射偶波之间的纵波间隔。本文估计了Soultz地热田邻近声发射偶波源之间的相对位置。

Proximity Acoustic Emission (AE) doublets analysis is used for subsurface fracture measurement. AE is a microseismic event. Location and shape of subsurface fracture is estimated from distribution of AE sources. Measurement of subsurface fracture is important in many areas of human activities associating with the Earth. Geothermal energy is extracted from subsurface fracture reservoirs in which steam and hot water are stored. Carbon dioxide is stored in tiny spaces of subsurface fracture.Proximity AE doublet analysis is a new method in which both fine structures of subsurface fracture and their motion can be estimated. Proximity AE doublets have a similar waveform, and they occur in a succession with an interval that is less than 1 s. Accurate relative location between AE sources can be realized because a medium, in which AE waves propagate, does not change during the interval. Intervals of P-wave and S-wave between proximity AE doublets are detected in cepstrum analysis. Proximity AE doublets have one or two peaks at their internals in their cepstrum. In proximity AE doublets, a second event with a similar waveform arrives before attenuation of the first event. Conventionally, it is difficult to estimate similarity between the two waveforms and their interval. I made time-quefrency analysis that can determine interval of P-wave when there are two peaks of the interval in the cepstrum. Data after the second S-wave arrival are replaced with zeros and the peak that represents S-wave interval decrease in the time-quefrency analysis. This analysis can show the interval of P-wave between proximity AE doublets. I estimated relative locations between AE sources of proximity AE doublets, which were measured in Soultz geothermal field.