Spatiotemporal Sequences of Earthquake Epicenters as a Subspecies of Grouped Seismic Evens

Linear sequences of earthquake epicenters (“chains”) related in space and time are studied. A new approach to understanding earthquake chains as a special kind of group (clustered) events is proposed. It is believed that clusters of group earthquakes with pronounced spatial anisotropy potentially represent the desired chains. Such chains are given the physical meaning of markers of activated tectonic faults. A formalized algorithm for the allocation of linear sequences of earthquake epicenters based on the proposed approach has been developed. The search for chains is conducted in the catalog of group earthquakes. Previously, single earthquakes (i.e., not included in clusters) are removed from seismicity. For this, a previously developed algorithm was used, focused on the selection of any interrelated events, and not only (mainly) aftershock and/or foreshock series (Descherevsky et al., 2016a). The proposed method of isolating earthquake chains has been successfully tested on earthquake catalogs of Garm, Iran and central Turkey. Chain maps are provided, and summary statistics of the chain field are discussed. As a rule, these chains can be compared with various tectonic disturbances, but a significant part of them are not tied to known structures. For the Garm district, the continuity of the results obtained with previously performed studies is shown. Like almost any method of analyzing seismic data, the earthquake chain algorithm has a significant number of configurable parameters. Within certain limits, you can vary the criteria for allocating group events, the minimum number of events in the chain and its minimum length, as well as the required level of straightness of the chain. However, all these settings primarily affect the total number of chains found in the catalog, and their location and orientation (azimuths) they almost do not depend on the algorithm settings. This allows us to consider the proposed analysis method as a fundamentally new way of extracting and visualizing information about the spatial and temporal organization of seismicity. A more detailed study of both the structure of earthquake chains and its changes over time in various seismically active regions of the world can contribute to a better understanding of the dynamics of the seismotectonic process.