## 1 Introduction
It was noted in [33] that the cusp is a versatile and very compact area for study, because all geomagnetic lines reaching the magnetopause converge into the cusp region. Consequently, all processes on the magnetopause, including magnetic reconnection, leave their signatures in the precipitating charged particle profile. The Cluster mission, composed of four identical spacecraft flying around the Earth [34], has one of the primary science objectives--to investigate the penetration through the polar cusps of the shocked solar wind. The Cluster data revealed [35] that the polar cusps are very dynamic regions. Their locations are ruled by the orientation of the interplanetary magnetic field, the dynamic pressure of the solar wind at the magnetopause, and the length of the reconnection line (X-line) at the magnetopause. Figure 3, reprinted from [35], shows that, most of the time, the cusp is located at invariant magnetic latitudes 75\({}^{\circ}\)-80\({}^{\circ}\) and in a longitudinal region of 10 h-14 h magnetic local time (MLT). However, sometimes, its longitudinal extension may be more comprehensive, depending, for example, on the reconnection X-line length [36]. Also, it was noticed in [32] that the Cluster satellites, which data are presented in Figure 3, due to the geometry of their orbits, do not allow to determine the entire longitudinal extent of the cusp correctly, and to do so, the spacecrafts should have been placed in more or less parallel orbits, so that they fly at the same latitude, though at different longitudes or local times, which could be realized in subsequent magnetosphere missions. As shown in [37], using data from the satellite Polar, the polar cusp may be between 08 h and 16 h MLT. After extreme solar events penetrated the polar cusp, solar wind plasma became denser. Therefore, the geomagnetic field lines under the cusps became more conductive during these times. Suppose a high conductivity along geomagnetic lines helps generate earthquakes in their footprints in the crust. In that case, one may suggest that seismic activity could be increased in those longitudinal regions in which their high latitudinal areas were located under the polar cusp when the shocked solar wind arrived and the geomagnetic storms started. In the present paper, we are checking up on this suggestion. According to [38], adequate solar wind magnetosphere coupling time should constantly change with time and season due to Earth's rotation and its motion along the orbit (Russell-McPherron mechanism). Therefore, to obtain a more reliable result, it was advisable to analyze the response of seismic activity to geomagnetic storms with reasonably  
Figure 3: Magnetic local time (MLT) and invariant latitude (ILAT) for cusp crossings by the Clusters. Black and red symbols mark the crossings in the Northern and Southern Hemispheres, respectively (reprinted from [35]). Figure 2: A picture of the Earth’s magnetosphere reprinted from [[http://english.igg.cas.cn/NC/RN/](http://english.igg.cas.cn/NC/RN/)]([http://english.igg.cas.cn/NC/RN/](http://english.igg.cas.cn/NC/RN/)) 201504/t20150413_146311.html, accessed on 1 April 2024.  
similar characteristics. For this purpose, we chose two geomagnetic storms that occurred on the same day, 17 March 2013 and 2015 (St. Patrick's Day geomagnetic storms). These magnetic storm onset times were also relatively identical: 06:04 UTC for the storm on 17 March 2013 and 04:48 UTC on 17 March 2015. This means that, at the time of the shocked solar wind's arrival at the magnetopause, under the cusp were located the high-latitudinal areas, which were almost the same longitudinal region (there was no difference in tectonics). These two geomagnetic storms have been analyzed in many papers [39; 40; 41; 42] (and references herein) and discussed at many conference sessions. In a unique collection of _Journal Geophysical Research_ (June 2017, Issue 6), there are more than 30 papers by researchers worldwide investigating the storm-time geospace behavior during the St. Patrick's Day geomagnetic storms of 2013 and 2015.