During 2014–16, a semi-permanent network of four 3-component broadband seismographs was operational in the Rajasthan craton and Aravalli mobile belt in the NW Indian shield. The reliable and accurate broadband data from 16 selected regional Indian earthquakes of Mw 5.5–7.8 from this seismic network enabled to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of northern India, covering the region below north India between the entire Himalaya (from the Pakistan Himalaya in west to the Burmese arc in the east) and Rajasthan (including Aravalli mobile belt). First, Rayleigh- (at 7–87s) and Love- (at 7–82s) wave group velocity dispersion curves were measured and then these curves were inverted to estimate the crustal and upper mantle structure below north India. It is observed that group velocities are of variable nature within the region. This could be attributed to the complex crust-mantle structure in the study region resulted from the magmatism episodes associated with the Proterozoic collision, 65 Ma Deccan volcanism and the Himalayan collision. The best model in the study region reveals a two-layered crust, with a 15-km thick upper-crust (UC) of average shear velocity (Vs) of 3.12 km/s and a 25-km thick lower-crust(LC) of average Vs of 3.44 km/sec. The modeling detects a drop in Vs (∼1-2%) at 79–120 km depths, underlying north India, representing the probable seismic lithosphere-asthenosphere boundary (LAB) at 79 km depth. A geothermal gradient extrapolated from the surface heat flow (∼74 mW/m2) shows that such a gradient would intercept CO2-bearing mantle peridotite solidus at 100 km depth, and thus could signal the presence of small amounts of partially melted magma below 100 km depth. Therefore, this 1–2% drop in Vs could be attributed to the presence of carbonatite melts in the upper mantle related to magmatic episode of 65 Ma Deccan plume activity as also suggested by existing geological and seismological evidence.

中文翻译：

---

通过表面波色散研究描绘北印度下方的平均一维剪切速度结构

在 2014-16 年期间，一个由四个 3 分量宽带地震仪组成的半永久性网络在拉贾斯坦克拉通和印度西北地盾的阿拉瓦利移动带中运行。来自该地震台网的 16 个选定的 5.5-7.8 级印度区域地震的可靠和准确的宽带数据能够估计印度北部的群速度频散特征和一维区域剪切速度结构，覆盖整个印度北部以下地区。喜马拉雅山（西起巴基斯坦喜马拉雅山，东至缅甸弧）和拉贾斯坦邦（包括阿拉瓦利移动带）。首先，测量Rayleigh-（7-87s）和Love-（7-82s）波群速度频散曲线，然后将这些曲线倒置以估计印度北部以下的地壳和上地幔结构。据观察，群速度在该区域内具有可变性质。这可能是由于与元古代碰撞、65 Ma 德干火山活动和喜马拉雅碰撞相关的岩浆活动导致研究区的壳幔结构复杂。研究区的最佳模型揭示了两层地壳，15 公里厚的上地壳 (UC) 平均剪切速度 (Vs) 为 3.12 公里/秒，下地壳 (LC) 厚 25 公里3.44 公里/秒的平均 Vs。该建模检测到印度北部 79-120 公里深度处的 Vs 下降（~1-2%），代表 79 公里深度处可能的地震岩石圈-软流圈边界（LAB）。从地表热流外推的地温梯度 (~74 mW/m2) 表明，这样的梯度将在 100 公里深度拦截含 CO2 的地幔橄榄岩固相线，因此可以表示在 100 公里深度以下存在少量部分熔化的岩浆。因此，Vs 下降 1-2% 可归因于上地幔中碳酸岩熔体的存在，这与 65 Ma 德干羽流活动的岩浆事件有关，现有地质和地震学证据也表明这一点。