Earthquake july 17, 2017, Mw = 7.8 near the Komandorsky islands and strong seismic manifestations in the western segment of Aleut island arc

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Abstract

The tectonic position, seismological characteristics and features of the aftershock process of the source of the strongest Near-Aleutian earthquake on July 17, 2017 on the Commander Islands with Мw = 7.8 are considered. The analysis showed that the seismic source according to the distribution of aftershock epicenters in the form of a linearly elongated narrow zone with a length of about 400 km almost completely occupied the northern slope of the Commander island elevation and was located in the Bering fault zone. It covered the whole of this seismic-generating zone up to the transverse structure to the west of the Near Islands (Attu is.). In accordance with the focal mechanisms solution and the nature of the displacements in the foci of the main shock, the strongest foreshocks and aftershocks, the shift in the source was an almost pure right-sided shift. The aftershock process of the July 17 earthquake developed quite enough inertly for an earthquake of such strength. In addition, it has two features in comparison with the aftershock processes of most of the Kuril-Kamchatka earthquakes: 1) low release of the cumulative scalar seismic moment (M0cum aft), which according to various estimates was from 0.75% to 1.0% of the seismic moment of the main shock (M0me); 2) a very slow increase in the deficit in the release of the seismic moment (M0). At the same time, the duration of the quasi-stationary phase of M0cum release in aftershocks, estimated at about ½ year and covering a significant part of the duration of the entire aftershock process of this earthquake, seems unusually long. These features of the aftershock process of the Middle Aleutian earthquake on July 17, 2017 distinguish it from the aftershock processes characteristic of most strong Kuril-Kamchatka earthquakes. In general, its source can be considered as a transform between the two Benioff zones – Aleutian and Kuril-Kamchatka, and not subduction, that is characterise the last two.

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About the authors

A. I. Lutikov

Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences; Unified Geophysical Survey of the Russian Academy of Sciences

Author for correspondence.
Email: ail@ifz.ru
Russian Federation, Bol’shaya Gruzinskaya str. 10, building 1, Moscow, 123242 Russia; Lenin Ave. 189, Obninsk, Kaluga Region, 249035 Russia

E. A. Rogozhin

Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences; Unified Geophysical Survey of the Russian Academy of Sciences

Email: ail@ifz.ru
Russian Federation, Bol’shaya Gruzinskaya str. 10, building 1, Moscow, 123242 Russia; Lenin Ave. 189, Obninsk, Kaluga Region, 249035 Russia

G. Yu. Donzova

Unified Geophysical Survey of the Russian Academy of Sciences

Email: donzova@ifz.ru
Russian Federation, Lenin Ave. 189, Obninsk, Kaluga Region, 249035 Russia

V. N. Zhukovez

Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences

Email: ail@ifz.ru
Russian Federation, Bol’shaya Gruzinskaya str. 10, building 1, Moscow, 123242 Russia

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Supplementary files

Supplementary Files
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2. Fig. 1. Seismotectonic map of the epicentral region of the Middle Aleutian earthquake of 2017 1 - Commander block; 2 - the motion vector of the Pacific plate relative to Kamchatka [Plate Motion Calculator, http://sps.unavco.org/crustal_motion/dxdt/model/]; 3 - movement vector of the Commander block relative to Kamchatka according to GPS data [Levin et al., 2002]; 4 - the focal mechanism of the main event 07/17/2017; 5 - the focal mechanism of the aftershock on 01/25/2018 (Mw = 6.2); 6 - the foreshock focal mechanism July 17, 2017 (Mw = 6.2); 7 - the focal mechanism of the foreshock on 06/02/2017 near the Near Islands (Mw = 6.8). All focal mechanisms are given according to [Global CMT catalog].

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3. Fig. 2. Map of the foci of earthquakes of the Commander and western segment of the Aleutian Arc (5.3 ≤ Mw <6.0) (a) and (Mw ≥ 6.0) (b). The projections on the lower hemisphere are given. White field - stretching sector, dark - compression. The black dot on the stereograms of the focal mechanisms is the stretching axis T.

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4. Fig. 3. The epicenters of 95 earthquakes, including the epicenters of the main shock on July 17, 2017, foreshocks and aftershocks recorded in the Commander Islands region from May 24, 2017 to March 27, 2018

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5. Fig. 4. Scheme of foreshocks and aftershocks of the earthquake of July 17, 2017, Mw = 7.8 (indicated by a large square), for the period from July 17 to 20 inclusive, according to the data of the SJS GS RAS. The largest circles are marked foreshocks 02.06.2017, Mw = 6.8 and 07/17/2017 at 11:06, Mw = 6.2.

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6. Fig. 5. The time course of the release of M0cum in the aftershock region of the earthquake on July 17 from 1920 to 2017. The straight line shows linear regression, approximating the observed data for the period from 1924 to 1998. inclusive. The horizontal bars indicate the 95% confidence interval of the regression in 2017. Triangles show the magnitudes (right axis of ordinates) of the strongest (Mw ≥ 5.8) seismic events.

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7. Fig. 6. Map of aftershocks (2.3 ≤ Mw ≤ 6.2) earthquakes of July 17, 2017 (Mw = 7.8) for the entire period, from July 17, 2017 to February 27, 2017, a total of 378 aftershocks. The main event is indicated by a large diamond; aftershocks are shown filled circles, the diameter of which is proportional to the magnitude.

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8. Fig. 7. The graph of repeatability of aftershocks in the range of magnitudes 2.5 ≤ Mw ≤ 6.0, constructed according to the table. 1. Straight lines indicate orthogonal regressions, carried out in the ranges of magnitudes 2.5–4.0 and 4.0–6.0.

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9. Fig. 8. The course of the release of the scalar seismic moment (M0cum) in aftershocks as a share of the main event M0 according to the data of the catalog of the SDC EGS RAS (a) and according to the catalog of the RKZK KF EGS RAS (b). Triangles indicate maximum aftershock magnitudes (second axis of ordinates). The straight line shows the regression on the initial part of the graph.

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10. Fig. 9. The time course of the release of M0cum / M0me in aftershocks of the earthquake of July 17, in fractions of the main event M0 for the period from July 17, 2017, to February 27, 2018, inclusive. The graph is constructed according to the RCLC KF EGS RAS and the catalog of the CMT [Global Centroid-Moment-Tensor (CMT) catalog]. The straight line shows the regression (6). The horizontal bars indicate the 95% confidence interval of the regression on 01/25/2018.

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11. Fig. 10. Earthquakes of the Commander and Near Aleutian Islands (1988–2010), together with their aftershock sequences.

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