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Regional variation of coda wave attenuation in Northeast India: An understanding of the physical state of the medium
Physics of the Earth and Planetary Interiors ( IF 2.3 ) Pub Date : 2020-02-01 , DOI: 10.1016/j.pepi.2019.106404
Rabin Das , Sagarika Mukhopadhyay

Abstract In this study an attempt has been made to estimate spatial variation in attenuation characteristics in Northeast India using coda Q. The entire study region is divided into three sub-regions for this purpose. Estimated average frequency dependencies of coda wave attenuation for 30 s window length are Qc(f) = 135 ± 7f0.99±0.03, Qc(f) = 109 ± 7f1.10±0.03 and Qc(f) = 90 ± 2f1.04±0.02 for Shillong Plateau, Mikir hills and surrounding River valley, and Indo-Burma Ranges respectively. It is observed that Q0 is greater for the Shillong Plateau than the other sub-regions. This indicates lower attenuation due to more rigid high-density material present in this area than the other sub-regions. The depth variations of the Qc, Q0 and n values were also examined. It is observed that the rate of increase of Q0 with depth is not uniform for all the sub-regions. Indo-Burma Ranges has the smallest Q0 and the largest n values at all depth levels among the three sub-regions. These results indicate that central part of Indo-Burma Ranges is the most attenuative, seismically active and heterogeneous in nature. However, this region has smaller Qc values than the other two sub-regions for all window lengths up to the 6 Hz. This means at lower frequencies the subsurface beneath this area is more attenuative compared to the other two sub-regions. Similar trends are observed at 8, 10 and 12 Hz, up to 45 s window lengths. For window lengths ≥55 s, central part of Indo-Burma Ranges has higher Qc values at 10 and 12 Hz compared to Shillong plateau. Qc values are lower for Shillong Plateau compared to the other two regions for window length ≥ 55 s at 10 and 12 Hz, which corresponds to depth levels ≥90 km. Such a complicated variation in Qc values is a manifestation of complex nature of tectonic regime in Northeast India.

中文翻译:

印度东北部尾波衰减的区域变化:对介质物理状态的理解

摘要 本研究尝试使用尾波 Q 估计印度东北部衰减特征的空间变化。为此,整个研究区域分为三个子区域。30 s 窗口长度的尾波衰减的估计平均频率依赖性为 Qc(f) = 135 ± 7f0.99±0.03、Qc(f) = 109 ± 7f1.10±0.03 和 Qc(f) = 90 ± 2f1.04西隆高原、米基尔山和周围河谷以及印缅山脉分别为 ±0.02。据观察,西龙高原的 Q0 大于其他子区域。这表明由于该区域中存在比其他子区域更坚硬的高密度材料,因此衰减较低。还检查了 Qc、Q0 和 n 值的深度变化。可以看出,所有子区域的 Q0 随深度增加的速率并不均匀。Indo-Burma Ranges 在三个子区域中的所有深度级别都具有最小的 Q0 和最大的 n 值。这些结果表明,印缅山脉的中心部分在性质上是最衰减、地震活跃和非均质的。然而,对于高达 6 Hz 的所有窗口长度,该区域具有比其他两个子区域更小的 Qc 值。这意味着在较低频率下,与其他两个子区域相比,该区域下方的地下更衰减。在 8、10 和 12 Hz,最多 45 秒的窗口长度下观察到类似的趋势。对于窗口长度 ≥ 55 s,与西隆高原相比,印缅山脉的中心部分在 10 和 12 Hz 时具有更高的 Qc 值。与其他两个区域相比,西隆高原的 Qc 值在 10 和 12 Hz 时窗口长度 ≥ 55 s 时较低,这对应于深度水平 ≥ 90 km。Qc 值如此复杂的变化是印度东北部构造体制复杂性的体现。
更新日期:2020-02-01
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