FIRST RESULTS ON THE DIRECTION STATISTICS OF PAIRS OF EPICENTERS OF NEIGHBOR EARTHQUAKES ON KAMCHATKA

• Published in: Geodynamics & Tectonophysics
• Main Authors: A. A. Gusev, A. A. Palueva
• Format: Article in Journal/Newspaper
• Language: English; Russian
• Published: Russian Academy of Sciences, Siberian Branch, Institute of the Earth's crust 2016
• Subjects: epicenter; background seismicity; space-time; geometry; direction; lineament; en-echelon fault; migration; rose diagram; Science; Q; Kamchatka
• Online Access: https://doi.org/10.5800/GT-2016-7-4-0221; https://doaj.org/article/8d694124332d4e31a9c9bedb1243330d

Small earthquakes, often treated as “background seismicity”, are not distributed in space-time in a random manner. Often, space-time clustering is studied, that manifests itself as aftershock sequences and swarms. These phenomena can be described as a deviation (increase) of probability of short interevent distances and times as compared to the reference “pure random” or Poisson case; this tendency manifests itself in statistics of distances between epicenters. In the present work, we study the statistics of directions for vectors connecting pairs of epicenters of such small earthquakes which are close in space-time. Components of such pairs will be called “neighbors”, and the mentioned vectors will be called “link vectors”. A study of this kind is of interest from a number of viewpoints, such as: discovering new properties of statistical structure of observed fields of epicenters; establishing interactions between earthquake sources of small earthquakes, revealing geometrical properties of the pattern of active faults of a low rank. We will show that directions of link vectors clearly deviate from isotropy, and have instead non-uniform, often spiked, distribution of directions.Pairs of neighbors are extracted from the catalogue of small (ML=3.5–5.0) shallow earthquakes of the Kamchatka subduction zone. То define neighbors, bounds are set on the distance (10–60 km) and relative delay (0.5 day) between members of a pair. Before pair extraction, the work catalog was decimated to reduce space-time event density within dense clusters. With the catalog of pairs at hand, we constructed distributions of azimuths of link vectors (rose diagrams of directions). In Fig. 3 one can see example histograms and corresponding rose diagrams for two 10-year periods (see Table 1 for definitions and labels of the periods); processing was done using two variants of maximum delay: 0.5 and 5 days. Angles (modified azimuths, n) in all histograms and rose-diagrams are counted off from the direction with azimuth of 37° that represents the ...