This study presents an analysis of the spatial and temporal distribution of the two large destructive earthquakes that occurred in Lake Van area on October 23, and November 9, 2011, together with the azimuth-dependent distribution of the seismic activity and microseismicity clusters after the mainshocks, associated with the complex rupture processes of their aftershock sequence. The sequence began with the magnitude Mw 7.1 earthquake of 23 October and a second destructive earthquake of Mw 5.6. The aftershock sequences of the two mainshocks were linked to the local crustal faults beneath Lake Van area, followed successively and produced unusually intense activity and significant damage in the area. The main purposes of this study are to document the spatial and temporal distribution and evolution of the October 23, 2011 aftershock hypocenters and the azimuth-dependent distribution of seismic activity, and to understand the spatial and temporal character of the aftershock sequence using the distributional and evolutional patterns of the aftershock hypocenters. A total of 10,000 aftershocks were obtained from seismic data with a high signal-to-noise ratio over collected over three years from October 23, 2011 to March 2014. These aftershocks were plotted for the time periods from November 2011 through March 2012 to March 2014 and ≈ 5000 aftershocks were retained in the depth versus distance cross-sections to detect the clusters in the first step of study (November 2011–March 2012). The focal depth distribution of the aftershock clusters, the migration of hypocenter activity and microseismicity clusters were analyzed and the distributional patterns of the detected clusters were assessed using the geometric distribution of the aftershock hypocenters. The spatial and temporal distribution of aftershocks reveal interesting key features of the deep rupture complexity of the Van earthquake: (1) most prominent aftershocks have been located in the upper crust at depths shallower than 10 km beneath ruptured area, indicating that the upper crust is brittle and seismogenic; (2) two spatial clusters have been detected at 8-10 km depths and the upward extrapolation of these clusters intersects with faults; the main cluster (60 km wide) bounded by inferred reverse faults (f3 and f4) and the central cluster (25–30 km wide) bounded by faults (f1 and f2); (3) these spatial clusters form the largest volumetric pattern of the conical-shaped cluster at depths of about 25–30 km of the azimuth-dependent rotational projections, suggesting azimuthal distributions of deep rupture characteristics; and (4) the strongest temporal cluster of microseismicity derived from temporal distribution of aftershocks has been detected within an area of about 2.5–3.0 km² and it is spatially observed at 20 km depth within the central cluster, suggesting progressive failure of the adjacent patches of possible fault.

Launched on 2 February 2018, CSES is the first constellation in China to advance our understanding of seismo-ionospheric influence and lithosphere-atmosphere-ionosphere coupling process in electromagnetic environment during earthquake prediction practice. For this purpose, a software platform developed for automatically searching ionospheric perturbations from the CSES plasma data had been put into service immediately after the Wushi MS 7.1 earthquake occurred on 23 January 2024 to weekly detect possible precursory information before impending aftershocks. Effective ionospheric variations were successfully detected two times during more than four weeks. An ionospheric perturbation with an enhanced magnitude 38.3% was primarily detected on electron density but none on ion density on 24 January 2024 at night orbit 33175 and the corresponding variations in different parameters recorded at the same orbit presented a complex features. There irregularities possibly combined with influence both from three following strong aftershocks with magnitudes over 5.0 during 25–30, January and magnetic storm disturbance due to Kp value once up to 3.7 on 24 January. An electron perturbation with an amplitude 24.6%, as well as an ion one with 27.3%, was successfully searched automatically at the same revisiting orbit 33251 occurred on the revisiting date of 3 February 2024 in a magnetic quiet period. These two plasma variations, as well as ones on other ionospheric parameters, were characterized by highly similar properties, which increases the availability as seismic precursors. However, no obvious variations had been observed at other revisiting orbits or other orbits near the aftershock areas during this period till the occurrence of a magnitude 5.3 earthquake on 24 February and the strongest one 5.8 on 25 February, respectively, 20 days after and 1000 km away.