Abstract The shear-wave splitting parameters (i.e. fast axis orientation (ψ) and delay time (δt)) are measured at twelve broadband stations in the Kachchh rift zone (KRZ), Gujarat, India, using SKS/SKKS core phases. The average splitting parameters (ψ, δt) vary from (49.41 ± 5.88, 1.63 ± 0.28) at Bhachau (i.e., 4 km SE of the 2001 Bhuj mainshock location) to (103.78 ± 12.82, 1.91 ± 0.35) at Mandvi near the coast. The present study reveals a mean ψ of (76.91o ± 4.57o) with a mean δt of 1.84 ± 0.30 s, for the KRZ. The observed large mean delay 1.84 ± 0.30 s for the region suggests a combined anisotropic contribution from both the lithospheric frozen anisotropy as well as the asthenospheric flow induced anisotropy. Inferred thicknesses of the anisotropic layers from the estimated δt vary from 160 km (in the central KRZ) to 284 km (in the surrounding unrifted zones (SURZ)). The measured deviation of ψ from the absolute plate motion (APM) direction of the Indian plate varies from 5.93o (in the central KRZ) to 43.4° (in the SURZ). The large δt and large deviation of ψ from the APM (>35°) are found to be associated with those stations (e.g. MND, KNM, VGH, NGR, VJP, TPM), which lie near to the geological boundaries in the SURZ. The main finding of the present modeling study depicts a thick highly anisotropic upper mantle underlying the KRZ, where mantle anisotropy parallel to the Kachchh rift axis direction is caused by both frozen lithospheric anisotropy and asthenospheric flow-induced anisotropy. The geographical and azimuthal variations of the measured splitting parameters detect three different anisotropic continental fragments, which might have preserved an ENE-WSW trending fossilized olivine fabric, which was formed before the assemblage of these continental fragments.

中文翻译：

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剪切波分裂观测：对印度古吉拉特邦 Kachchh 裂谷带下方上地幔可变各向异性结构的影响

摘要 在印度古吉拉特邦 Kachchh 裂谷带 (KRZ) 的 12 个宽带台站使用 SKS/SKKS 核心相位测量了横波分裂参数（即快轴方向 (ψ) 和延迟时间 (δt)）。平均分裂参数 (ψ, δt) 从 Bhachau（即 2001 年 Bhuj 主震位置东南 4 公里）的 (49.41 ± 5.88, 1.63 ± 0.28) 到 Mand 附近海岸的 (103.78 ± 12.82, 1.91 ± 0.35) . 本研究揭示了 KRZ 的平均 ψ 为 (76.91o ± 4.57o)，平均 δt 为 1.84 ± 0.30 s。该地区观察到的大平均延迟 1.84 ± 0.30 s 表明岩石圈冻结各向异性和软流圈流动引起的各向异性的综合各向异性贡献。从估计的 δt 推断出的各向异性层的厚度从 160 公里（在 KRZ 中心）到 284 公里（在周围的非裂谷带（SURZ））不等。ψ 与印度板块绝对板块运动 (APM) 方向的测量偏差从 5.93o（在 KRZ 中心）变化到 43.4°（在 SURZ）。发现与 APM 的大 δt 和 ψ 大偏差 (>35°) 与位于 SURZ 地质边界附近的那些台站 (例如 MND、KNM、VGH、NGR、VJP、TPM) 相关。本模拟研究的主要发现描绘了位于 KRZ 下方的厚厚的高度各向异性上地幔，其中平行于 Kachchh 裂谷轴方向的地幔各向异性是由冻结的岩石圈各向异性和软流圈流动引起的各向异性引起的。