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Attenuation of Rock Salt: Ultrasonic Lab Analysis of Gulf of Mexico Coastal Samples
Journal of Geophysical Research: Solid Earth ( IF 3.9 ) Pub Date : 2020-05-29 , DOI: 10.1029/2019jb019025
Jingjing Zong 1, 2 , Robert R. Stewart 1 , Nikolay Dyaur 1
Affiliation  

In an effort to achieve higher‐resolution imaging as well as detailed lithology descriptions, it is important to consider attenuation as an aid in compensating for seismic wave amplitude and phase distortions due to the viscoelastic properties of natural rocks. We have evaluated elastic‐wave attenuation on a variety of Gulf of Mexico (GoM) rock salt samples (>95% halite by weight) in the laboratory using the ultrasonic pulse‐transmission technique and the spectral ratio (SR) method. Under conditions of 297 K (75°F) and relative humidity of 46%, the estimated P‐ and S‐wave quality factors Q P and Q S range from 26 to 74 and 29 to 44 in the unjacketed core samples, respectively. Increasing triaxial pressure elevates Q (decreases attenuation), possibly due to the crack closure and rock frame compaction. For example, a 40 MPa confining pressure increases Q P to 275 at 297 K (75°F). Elevating temperature does not show a significant effect on Q values until raised from 339 to 366 K (150°F to 200°F), during which Q P drops sharply (attenuation increases). The attenuation mechanisms may include thermal cracking and grain boundary condition changes. We have determined well‐constrained empirical relationships between Q and velocity (V ) for both P‐ and S‐waves. These measurements and empirical relationships can further inform us about salt properties and assist with images of and through salt bodies.

中文翻译:

岩盐的衰减:墨西哥湾沿海样品的超声实验室分析

为了获得更高分辨率的成像以及详细的岩性描述,重要的是要考虑衰减,以补偿由于天然岩石的粘弹性而引起的地震波振幅和相位畸变。我们已经在实验室中使用超声脉冲传输技术和光谱比(SR)方法评估了各种墨西哥湾(GoM)岩盐样品(按重量计> 95%的岩盐)的弹性波衰减。在297 K(75 ° F)和相对湿度46%的条件下,无夹层岩心样品的估计P波和S波品质因数Q PQ S分别在26至74和29至44范围内。三轴压力增加会提高Q(减小衰减),可能是由于裂缝闭合和岩石框架压实。例如,在297 K(75 ° F)时,40 MPa的限制压力将Q P增加到275 。在从339 K升高到366 K(150 ° F到200 ° F)之前,升高的温度对Q值没有显着影响,在此期间Q P急剧下降(衰减增加)。衰减机制可以包括热裂纹和晶界条件变化。我们确定了Q和速度(V)用于P波和S波。这些测量值和经验关系可以进一步告知我们有关盐的性质,并帮助获得盐体以及通过盐体的图像。
更新日期:2020-07-01
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