Oscillatory tendency of interevent direction in earthquake sequences

The epicenter motion direction carries important information about the seismogenic dynamics but, to our knowledge, lacks systematic study. In this work, we studied the earthquake process from this perspective. To grasp the feature in directional information, we proposed a new descriptor, i.e., the direction of motion change defined as the difference in azimuths between two consecutive earthquake events. For the aftershock sequences of the Landers and the Northridge Earthquakes, the regional earthquake catalogs of south China, southern California, and New Zealand, and the corresponding aftershock depleted catalogs, we studied the distribution and long-range correlation of the direction of motion change. Similar results are found for the aftershock and regional earthquake process even if aftershocks depleted from the catalogs: Both of them hold a tendency for successive events to migrate in opposite directions along fault zones and show no long-range correlation, rendering plausibly a fundamental characteristic governed by seismogenic dynamics. For aftershocks, the phenomenon is conjectured to be the alternate release of residual stress at both ends of the fissures. With regard to regional earthquakes, the underlying physics and mechanisms are not very clear. It should be something related to the seismodynamic process, such as stress configuration modified by earthquakes. The study from this new perspective of directional information is believed to benefit a better understanding of the earthquake process.