Precise Microearthquake Locations and Fluid Flow in the Geothermal Reservoir at Soultz-sous-Forêts, France
Precise Microearthquake Locations and Fluid Flow in the Geothermal Reservoir at Soultz-sous-Forêts, France
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法国 Soultz-sous-Forêts 地热库的精确微地震位置和流体流动
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发表时间：
2000
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通讯作者：
W. Phillips
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作者：
W. Phillips
我重新定位了两个微地震集群引起的水力刺激的干热岩地热水库在莱茵河地堑附近苏茨苏福雷，法国。这两个集群是从1993年获得的16，000个事件数据集中确定的集群集合中选择的。我手动确定P波和S波的到达时间，如果波形在给定的站点相似，则选择独特的峰值，或者如果波形是紧急的或节点的，则选择初至，并相应地判断权重。要求最少5个到达时间产生了226和355个事件的人口集群。在这两种情况下，重新定位显示了两个不同的平面活动补丁，100至200米宽，交叉和截断彼此沿着一个共同的边缘。直线段穿过平面斑块，并可能标记与地震不活跃的裂缝的交叉点。最早的活动发生在沿着这些段。因此，这些区段可以标记可能是流体流动网络的重要组成部分的渗透区。从流体流动建模研究中获得的路径尺寸约束和在取芯裂缝中发现的热液密封的预期限制效应支持将线性段解释为流动路径。通过与岩心和测井研究中发现的方向一致性，验证了平面特征的方向。此外，通过约束平行于活动平面的滑动面获得的震源机制表明垂直于右行走滑，与测得的应力场一致。震源机制表明，在内角的质量赤字，这意味着在断裂交叉点的活动的浓度可能会导致从一个断裂上的滑动导致扩展和由此产生的渗透率增加在其他。改进的定位精度的结果从一个十倍的改进的到达时间估计的精度相类似，估计从残差的标准偏差，分组的车站和相位，之前和之后重新挑选。对于相关性较差或节点阶段，仅观察到两倍的改善。对于这个数据集，手动相位拾取产生了更多的位置模式的可解释的细节，自动，互相关技术的结果相比。手动结果可用于指导自动技术的改进，以获得整个数据集的精确位置。
I relocated two microearthquake clusters induced by hydraulic stimulation of a hot-dry-rock geothermal reservoir in the Rhine Graben near Soultz-sous-Forets, France. The two clusters were chosen from a collection of clusters identified within a 16,000-event data set obtained in 1993. I determined P - and S -wave arrival times, manually, choosing distinctive peaks if waveforms were similar at a given station, or first breaks if waveforms were emergent or nodal, judging weights accordingly. Requiring a minimum of five arrival times yielded populous clusters of 226 and 355 events. In both cases, relocation revealed two distinct planar patches of activity, 100 to 200 m across, intersecting and truncating one another along a common edge. Linear segments traverse the planar patches and may mark intersections with seismically inactive fractures. The earliest activity occurred along these segments. These segments may therefore mark permeable zones that could be important components of the fluid-flow network. The interpretation of linear segments as flow paths is supported by path dimension constraints derived from fluid-flow modeling studies and by the expected confining effects of hydrothermal sealing found in cored fractures. Orientations of the planar features are verified through consistency with orientations found in core and logging studies. In addition, focal mechanisms obtained by constraining slip planes parallel to active planes indicate normal to right-lateral strike slip, consistent with the measured stress field. Focal mechanisms indicate mass deficits at inside corners, implying that the concentrations of activity at fracture intersections may result from slip on one fracture causing extension and a resulting permeability increase in the other. The improved location precision results from a ten-fold improvement in the precision of arrival-time estimation for phases that were similar, as estimated from the standard deviation of residuals, grouped by station and phase, before and after repicking. Only a two-fold improvement was noted for poorly correlated or nodal phases. For this data set, the manual phase picking yielded more interpretable detail in the location patterns, compared to results of an automatic, cross-correlation technique. The manual results could be used to guide improvements to automatic techniques to obtain precise locations of the entire data set.