Total Electron Content (TEC) derived from satellite-based measurements has been widely used for the detection of ionospheric perturbations associated with earthquakes. In this paper, we analyze Pre-Earthquake Ionospheric Anomalies (PEIAs) with TEC data from Global Positioning System (GPS) stations in two Pakistani regions, Islamabad (33.74°N, 73.16°E) and Multan (30.26°N, 71.50°E). These stations operate within seismogenic zones of three earthquakes in Pakistan and Tajikistan. We implement a statistical technique on daily TEC for the detection of PEIA. The results show that PEIAs appear in the form of enhancement during 08:00–12:00 UT (LT = UT+5 h) within 5–10 days before the mainshock. Global Ionospheric Maps (GIMs) over the epicentre are examined on abnormal TEC days. Dense electron enhancements occur during 08:00−12:00 UT, i.e. before three M_w> 5.0 earthquakes. Diurnal mean TEC deviates on the suspected days. It supports the anomalous signatures observed in the temporal and spatial distributions during the particular days. The geomagnetic and solar indices show no activity. These results endorse the existence of Lithosphere Atmosphere Ionospheric Coupling (LAIC) mechanism within the earthquake preparation period associated with the Pakistan and Tajikistan earthquakes.

来自卫星测量的总电子含量 (TEC) 已广泛用于检测与地震相关的电离层扰动。在本文中，我们使用来自巴基斯坦两个地区全球定位系统 (GPS) 站的 TEC 数据分析震前电离层异常 (PEIA)，伊斯兰堡 (33.74°N, 73.16°E) 和木尔坦 (30.26°N, 71.50°E) ）。这些台站在巴基斯坦和塔吉克斯坦的三场地震的发震区内运行。我们在日常 TEC 上实施统计技术来检测 PEIA。结果表明，在主震前5-10天内的08:00-12:00 UT（LT = UT+5 h），PEIAs以增强的形式出现。在异常 TEC 天检查震中上的全球电离层图 (GIM)。密集电子增强发生在 08:00-12:00 UT 期间，即在三个 M 之前_w > 5.0 地震。昼夜平均 TEC 在可疑天数上有偏差。它支持在特定日子里在时间和空间分布中观察到的异常特征。地磁和太阳指数显示没有活动。这些结果证实了在与巴基斯坦和塔吉克斯坦地震相关的地震准备期间岩石圈大气电离层耦合（LAIC）机制的存在。