Abstract An earthquake of small magnitude (ML3.5) occurred on 12 April 2020 near the east district boundary of NCT, Delhi with maximum PGA for the event observed to be 14.13 gals. A few smaller aftershocks also occurred in the area. The estimated fault plane solution of the mainshock suggests normal faulting with some strike slip component. The focal mechanism corroborates with the NE - SW orienting lineaments mapped in the region near the epicenter. The source parameters of the event, namely, seismic moment, stress drop, corner frequency, and source radius are estimated to be 1.15 x 1014 N-m, 25.7 bars, 5.7 Hz and 300 m, respectively. The decay rate of acceleration with epicentral distance suggests a regression relation PGA = 474 D −1.347, which may be useful for understanding the ground motion in the region. A noise analyses at NDI rock and UJWA soil sites clearly suggest a significant reduction in ambient noise by ∼10 dB in the frequency band (1.0–10.0) Hz at the respective sites, during the COVID-19 lockdown situation. The reductions of the noise level improve the signal to noise ratio substantially at all the seismic stations located in the urban agglomerations, which enabled the recording of clear phases of the event and hence improved the analysis.

中文翻译：

---

在 COVID-19 大流行封锁的背景下，2020 年 4 月 12 日在德里 NCT 及其周边地区普遍感受到的震颤（ML 3.5）：分析和观察

摘要 2020 年 4 月 12 日在德里 NCT 东区边界附近发生了小震级 (ML3.5) 地震，观测到该事件的最大 PGA 为 14.13 加仑。该地区还发生了几次较小的余震。估计的主震断层面解表明存在一些走滑分量的正常断层。震源机制证实了在震中附近区域绘制的 NE - SW 定向线条。该事件的震源参数，即地震矩、应力降、角频率和震源半径估计分别为 1.15 x 1014 Nm、25.7 条、5.7 Hz 和 300 m。加速度随震中距离的衰减率表明回归关系 PGA = 474 D -1.347，这可能有助于理解该地区的地面运动。NDI 岩石和 UJWA 土壤站点的噪声分析清楚地表明，在 COVID-19 锁定情况下，相应站点的频带 (1.0–10.0) Hz 中的环境噪声显着降低了约 10 dB。噪声水平的降低显着提高了位于城市群中的所有地震台站的信噪比，从而能够记录事件的清晰阶段，从而改进分析。