The Influence of Seismometer Coverage on the Earthquake Focal Mechanism Solution (Case Study: Toba Swarm Earthquake)

Abstract The focal mechanism of an earthquake is necessary to describe the plane and characteristics of the fault. In the case of local earthquakes, the focal mechanism is often determined based on the first polarity of the primary wave. Therefore, the quality of the earthquake focal mechanism depends on the station coverage and the number of first polarities of primary waves. This study aims to investigate the variation in solution and quality of earthquake focal mechanisms with different station coverage. We conducted experiments on Toba swarm earthquake data for the May-June 2021 period with different gap angles of 90°, 180°, and 220°. The location of the earthquake was determined using the HYPO71 program. The earthquake’s focal mechanism was determined with the HASH program based on the first polarity of the primary wave. The results show that the focal mechanisms with different station coverage have different focal mechanism solutions. High variations in focal mechanism solutions (uncertainty) can lead to fatal errors in determining fault planes and characteristics. Therefore, paying attention to station coverage when installing seismometer stations is crucial to properly identify the fault characteristics that cause earthquakes.