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ISSN 1069-3513, Izvestiya, Physics of the Solid Earth, 2019, Vol. 55, No. 4, pp. 600–615. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Fizika Zemli, 2019, No. 4.
The MW = 7.8 Earthquake of July 17, 2017 near the Commander
Islands: Tectonic Position and Geodynamic Setting
E. A. Rogozhina, b, A. I. Lutikova, b, *, G. Yu. Dontsovab, and V. N. Zhukovetsa
aSchmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, 123242 Russia
bFederal Research Center Geophysical Survey of the Russian Academy of Sciences, Obninsk, 249035 Russia
*e-mail: ail@ifz.ru
Received August 27, 2018; revised November 29, 2018; accepted December 3, 2018
Abstract—The tectonic position and overall geodynamic setting, as well as the seismological characteristics
and peculiarities of the aftershock process, are considered for the source of the strongest Near Aleutian earth-
qu a k e o f J u l y 17, 2 0 17, МW = 7.8, on the Commander Islands. It is shown that in contrast to the eastern seg-
ments of the Aleutian island arc, the subduction of the Pacific lithospheric plate beneath the Commander
block is not observed. The analysis has shown that, according to the distribution of the aftershock epicenters
in the form of a linear elongated narrow zone with a length of about 400 km, the seismic source occupied
almost entire northern slope of the Commander Island rise and spread in the Bering fault zone. It spanned
the whole of this seismogenic zone up to the transverse structure west of the Near Islands (Attu islands). The
focal mechanism solutions and the pattern of displacements in the sources of the main shock, as well as the
strongest foreshocks and aftershocks, suggest that the slip in the source was an almost pure right-lateral shear.
The aftershock process of the earthquake on July 17 developed quite feebly for an earthquake of this magni-
tude. Besides, it has two specific features distinguishing it from the aftershock processes of most of the Kuril-
Kamchatka earthquakes: (1) a low release of the cumulative scalar seismic moment (M0cum aft), which,
according to different estimates, made up from 0.75 to 1.0% of the main-event seismic moment (M0me); and
(2) a very slow growth of the deficit in the release of seismic moment (M0). At the same time, the duration of
the quasi-stationary phase of the M0cum release in the aftershocks, which is estimated at approximately half-
a-year and which took a considerable span of the total length of the aftershock process from this earthquake,
appears to be untypically long. These features of the aftershock process of the Near Island Aleutian earth-
quake of July 17, 2017 distinguish it from the aftershock processes peculiar to most of the strong Kuril–Kam-
chatka earthquakes. Overall, its source can be considered as a transform one between the two Benioff zones, the
Aleutian and Kuril–Kamchatka ones, rather than as a subduction source characteristic of the last two zones.
Keywords: earthquake, Bering Fault, Western segment of Aleutian Arc, focal mechanism, non-double-couple
seismic source, scalar seismic moment
DOI: 10.1134/S1069351319040086
INTRODUCTION
The earthquake of July 17, 2017, MW = 7.8 (ϕ =
54.52°, λ = 169.00°) near the Commander Islands,
called the Near Aleutian earthquake (NAE) (Chebrov
et al., 2017b), turned out to be the strongest seismic
event ever detected in the western segment of the
Aleutian island arc during the not particularly long
period of seismic observations in this region available
to us. The earthquake of December 17, 1929 in the
region of the Near Islands (United States) also with
MW = 7.8 (ϕ = 53.559°, λ = 171.972°) was the only
event comparable in magnitude with the NIAE. The
more-or-less systematic seismological observations in
the western segment of the Aleutian island arc encom-
passing the Commander and Near Islands began in
the 1920s. Before 1960, only the strongest seismic
events with magnitudes 6–7 were recorded. Detailed
catalogs for the region of Commander Islands have
only appeared since the 1960s after the re-equipment
of seismic stations of the reference seismic network
with modern SKD seismographs and the deployment
of a regional seismic network in Kamchatka. As can be
inferred from the degree of detail of the USGS NEIC
catalog (National Earthquake Information Center,
USGS, https://earthquake.usgs.gov), seismological
observations in the Near Islands also developed in a
similar way.
At present, the Aleutian island arc including its
western segment, have been on the whole studied quite
well in terms of seismology. The annual digests
“Earthquakes of Northern Eurasia” (until 1992,
“Earthquakes in the USSR”) publish the data on the
current seismic situation in the western segment of the
Aleutian island arc, including detailed descriptions of
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
THE MW = 7.8 EARTHQUAKE 601
the strongest seismic events; see, e.g., (Zobin et al.,
1991; Fedotov et al., 1996; Levina et al., 2002; 2009).
In particular, Levin et al. (2009) fairly thoroughly ana-
lyzed the strong earthquake of December 5, 2003 with
MS = 6.8 (MW = 6.6) and the instrumental epicenter
located approximately 250 km west-northwest of that
of the earthquake on July 17, 2017 considered in this
paper. This means that the source area of the earth-
quake of December 5, 2003 delineated by the after-
shocks was directly adjacent in the northwest to the
source of the earthquake of July 17. In the southeast,
the latter is adjoined by the MW = 6.4 source of
December 23, 2010 (ϕ = 53.127°, λ = 171.161°) on the
Near Islands. Besides the noted events of 2003 and
2010, no strong (MW ≥ 6.0) earthquakes were observed
in this region until the middle of 2017.
It is worth noting that in a number of recent works
addressing the seismicity of the Commander Islands,
e.g., (Lander et al., 2009; Gordeyev et al., 2015), the
opinion is expressed that the southern boundary of the
Commander block whose northeastern segment
accommodated the earthquake of July 17 is geody-
namically similar to the western boundary of the
Burma microplate where the Sumatra mega-earth-
quake MW ≈ 9.0 occurred on December 26, 2004. As a
result, it is concluded that a very strong (MW ∼ 9)
earthquake may hit the southern edge of the Com-
mander block in the foreseeable future.
This paper is devoted to the analysis of the seismic
history preceding the earthquake of July 17, 2017, as
well as the determination of the tectonic position of
this event and the overall geodynamic situation. In
particular, the similarities and distinctions between
the Commander block and the Burma microplate are
examined, and the possibility of a mega earthquake on
its boundaries are discussed.
When the paper was passing through the peer
review process, a new strong earthquake with MW = 7.2
hit the northwestern tip of Bering Island on Decem-
ber 20, 2018. We considered it reasonable to add a brief
review of this seismic event in this paper with as it is
directly related to the Near Island Aleutian earth-
quake of July 17, 2017.
ON THE SUBDUCTION PROCESS
IN THE WESTERN SEGMENT
OF THE ALEUTIAN ARC
At present, the western and eastern parts of the
Aleutian island arc have different geodynamic settings.
It is natural to expect these distinctions to also appear
in the characteristics of seismogenic movements in the
respective segments of the arc (Balakina and
Moskvina, 2010). This also concerns the phenomenon
of the subduction of the Pacific plate beneath the
Aleutian island arc and beneath the Bering litho-
spheric plate along different segments of the Aleutian
arc. The situation map of the MW ≥ 5.5 seismicity
within the entire Aleutian arc and the Alaska Penin-
sula is shown in Fig. 1.
Unlike the Central and Eastern segments of the arc
(Figs. 2–4), which bear clear seismological signs of
the existence of the Zavaritsky–Benioff seismic focal
zone and subduction of the Pacific Plate beneath the
Aleutian Arc, the Commander Islands’ archipelago
throughout its entire length, including its northern
and southern slopes, accommodates the earthquake
hypocenters that are confined within the depth inter-
val of 0 to 60 km with the peak concentration at 30–
40 km (Balakina and Moskvina, 2010) as illustrated in
Fig. 5.
From Figs. 2–4 it follows that the clearly pro-
nounced Zavaritsky-Benioff seismic focal zone plung-
Fig. 1. Site layout map showing seismicity (MW ≥ 5.5) of entire Aleutian arc and Alaska Peninsula. Solid cutting lines are lines of
cross sections through Aleutian arc shown in Figs. 2–5.
60
58
56
54
52
50
48
46
16 2 16 6 17 0 174 17 8 –178 –174 – 17 0 – 166 –162 – 15 8 –15 4 –15 0
Latitude, deg
Longitude, deg
Patton Ridge
Pribylova Islands
Kamchatka Peninsula
Shirshov Ridge
Bowers Ridge
Emperor Ridge
Kruzenstern
Trough
Emperor Fault
Obruchev Rise
Meiji Guyot
Detroit Seamount
AA
l
e
u
t
i
a
n
T
r
e
n
c
h
A
l
e
u
t
i
a
n
T
r
e
n
c
h
Commander Islands
Commander Islands
Commander Islands
Near IslandsNear Isla ndsNear Islands
Rat IslandsRat I slands
Rat Islands
Andreanof IslandsAndrean of IslandsAn dreanof Islands
Alaska PeninsulaA l a s k a P e n i n s u l aAlaska Peninsula
Fox IslandsF o x I s l a n d s
Fox Islands
0–70 km 70–150 km 150–250 km >250 km
602
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
ROGOZHIN et al.
ing in the northern azimuths exists at least in the
regions of the Rat Islands, Andreanof Islands, and Fox
Islands. This zone can be considered as the structure
of the subduction of the Pacific plate beneath the
Aleutian arc. The maximum depths of the subsiding
hypocenters vary from ~260–270 km in the region of
the Rat and Andreanof Islands to ~300 km in the
region of the Fox Islands. At the same time, the pene-
tration depth of the subsiding hypocenters across the
arc strike varies from ~150 km in the region of the Rat
Islands to ~200 km in the region of the Andreanof
Islands and to ~250 km in the region of the Fox
Islands. From Fig. 5b it follows that any signs suggest-
ing the existence of the subduction of the Pacific Plate
beneath the Commander Lithospheric Block are
absent, as noted, e.g., in (Balakina and Moskvina,
2010). The manifestation of Quaternary volcanism on
the Commander Islands are also missing. It is worth
noting, though, that traces of deep-focus seismicity
beneath the Commander Islands were revealed to a
depth of ~200 km based on the data of a more detailed
regional catalog of the Kamchatka earthquakes. How-
Fig. 2. (a) Cross section (heavy straight line) through ensemble of earthquake epicenters (Ml ≥ 2.5; MW ≤ 7.9) near Rat Islands
(top view) based on NEIC catalog (2000–2018). Horizontal mark on straight line shows origin point along section. (b) Vertical
cross section of earthquake hypocenters (Ml ≥ 2.5; MW ≤ 7.9) in Rat Islands region.
–50
–150
–250
–100
–200
–300
0100 200 300 400 500 600 700 800
55
54
53
52
51
50
49
48
175 17 6 177 178 179 –179180
Longitude, deg
Latitude, deg
Depth, km
Distance from point (178E, 48N), km
Rat IslandsR a t I s l a n d sRat Islands
Aleutian TrenchA l e u t i a n T r e n c hAleutian Trench
0–70 km
70–150 km
150–250 km
>250 km
0–70 km
70–150 km
150–250 km
>250 km
(a)
(b)
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
THE MW = 7.8 EARTHQUAKE 603
ever, the depth interval of 80 to 200 km contains only
0.8% of the total number of seismic events presented
in the catalog, which is probably within the statistically
acceptable level of errors.
In order to more accurately delineate the region of
deep-focus seismicity along the Aleutian island arc,
we constructed the cross sections cutting the Aleutian
arc from 175° E to 150.0° W with a step of 1.0° in lon-
gitude. Figure 5 shows the dependences of the maxi-
mum hypocentral depths of the earthquakes along the
Aleutian arc for the Eastern (Fig. 6a) and Western
(Fig. 6b) hemispheres obtained along the section cut-
ting the Aleutian arc (Figs. 2–5).
From Fig. 6 it can be seen that the largest hypocen-
tral depths (down to ~300 km) are observed in the cen-
tral and southeastern parts of the Aleutian island arc
where the latter is oriented at a steep angle to the direc-
tion of motion of the Pacific Plate. At the same time,
Fig. 3. (a) Cross section (heavy straight line) through ensemble of earthquake epicenters (Ml ≥ 2.5; MW ≤ 7.3) in region of Andre-
anof Islands (top view) based on NEIC catalog (2000–2018). Horizontal mark on straight line shows origin point along section.
(b) Vertical cross section of earthquake hypocenters (Ml ≥ 2.5; MW ≤ 7.3) in region of Andreanof Islands.
–50
–150
–250
–100
–200
–350
–300
0100 200 300 400 500 600 700 800
55
56
54
53
52
51
50
49
–179 –178 –177 –176 –175 –174 –173 –172 –171
Longitude, deg
Latitude, deg
Depth, km
Distance from point (173.5E, 49N), km
Andreanof Islands
A n d r e a n o f I s l a n d s
Andreanof Islands
Aleutian Trench
A l e u t i a n T r e n c h
Aleutian Trench
0–70 km
70–150 km
150–250 k
m
>250 km
0–70 km
70–150 km
150–250 k
m
>250 km
(a)
(b)
604
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
ROGOZHIN et al.
the northwestern edge of the plate partially sinks
beneath the Aleutian Arc. In the region of the Com-
mander Islands, the vector of motion of the Com-
mander block is almost parallel to the vector of motion
of the Pacific lithospheric plate and, therefore, the
subduction of the Pacific Plate beneath the Com-
mander block does not take place. In fact, that is what
the absence of the deep-focus seismicity in the region
of the Commander Islands testifies to. In Fig. 6a it can
be seen th at the f irs t ma nif est ation s of deep-f ocu s seis-
micity appear between 172° and 173° E, i.e., in the
region of the Near Islands, where the maximum hypo-
central depths sharply increase from 60 to 110 km. In
the vicinity of the Rat Islands (from 175° to 179° E),
the maximum hypocentral depths increase from 140 to
250 km. Further, from 180° to 163° W, the maximum
Fig. 4. (a) Cross section (heavy straight line) through ensemble of earthquake epicenters (Ml ≥ 2.5; MW ≤ 6.9) in region of Fox
Islands (top view) based on NEIC catalog (2000–2018). Horizontal mark on straight line shows origin point along section.
(b) Vertical cross section of earthquake hypocenters (Ml ≥ 2.5; MW ≤ 6.9) in region of Fox Islands.
–50
–150
–250
–100
–200
–350
–300
0100 200 300 400 500 600 700 800
55
56
57
58
54
53
52
51
50
–169 –168 –167 –166 –165 –164 –163
Longitude, deg
Latitude, deg
Depth, km
Distance from point (164 W, 50N), km
Fox Islands
F o x I s l a n d s
Fox Islands
Aleutian Trench
A l e u t i a n T r e n c h
Aleutian Trench
(a)
(b)
0–70 km
70–150 km
150–250 km
>250 km
0–70 km
70–150 km
150–250 km
>250 km
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
THE MW = 7.8 EARTHQUAKE 605
hypocentral depths vary from 230 to 300 km. The east-
ern part of the arc, including the Alaska Peninsula
from 163° to 150° W, is marked by a gradual shallowing
of the maximum depth of the hypocenters from ~240
to ~85 km. However, the overall pattern of deep-focus
seismicity in Alaska is fairly complicated: the mini-
mum of the subduction depths observed between 150°
and 145° W is followed further northeast by the new
growth in the number and maximum depths of the
intermediate earthquakes beneath continental Alaska.
However, this question is beyond the scope of this
paper. Thus, the deep-fo cus seismicity i s absent on the
northwestern flank of the Aleutian Arc (on the Com-
mander Islands) and becomes more complicated on its
northeastern flank (in the eastern Fox Islands, on the
Alaska Peninsula and then beneath the continental
Alaska).
TECTONIC POSITION
AND GEODYNAMIC SETTING
The epicenter of the main shock was located close
to the northeastern boundary of the Commander
block linearly stretching in the northwest direction.
The epicenter is localized about 200 km southeast of
the Bering Island (220 km from village Nikol’skoe), at
the foot of the shelf slope. Figure 7 shows the seismo-
tectonic map of the epicentral area of the Near Island
Aleutian earthquake of 2017. This map is based on Fig. 2
of (Lander et al., 2009). The Commander Block is an
independent seismotectonic zone located between two
large tectonic units: the Bering Plate in the north and
the vast Pacific Plate in the south (Mets et al., 1990).
A narrow, less than 100-km wide, Commander litho-
spheric block stretches for more than 500 km practi-
cally parallel to the vector of motion of the Pacific
plate and is separated from the latter by the transform
boundary running along the Aleutian oceanic trench
which has a depth of up to 7000 m. The steepness of
the submarine slopes reaches 30°–35°. Despite the
fact that the islands overall have a fairly long island
shelf, the edge of the escarpment at places is located
only 4–5 km off the coast (a traverse of the Poluden-
naya Bay on Bering Island).
We note that in contrast to the Commander Block,
the western boundary of the Burma microplate dis-
cussed in (Lander et al., 2009; Gordeev et al., 2015),
where the Sumatra mega-earthquake of 2004 occurred,
has a length of ~1200 km, whereas the width of the
microplate itself is at least 250–400 km. Therefore, in
contrast to the Burma microplate which can accom-
modate the source of the earthquake with MW ~ 9, the
Commander block is unlikely to be spacious enough to
host the source of such an earthquake. For example,
according to (Balakina and Moskvina, 2010, p. 31),
the magnitudes of the maximum earthquakes that can
occur in the archipelago of the Commander Islands
can barely be significantly above 7.5 because of the
limited size of the hosting tectonic structures. In fact,
Fig. 5. (a) Cross section (heavy straight line) through
ensemble of earthquake epicenters (Mb ≥ 3.1; MW ≤ 7.8 ) in
region of Commander Islands (top view) based on NEIC
catalog (2000–2018). Horizontal mark on straight line
shows origin point along section. (b) Vertical cross section
of earthquake hypocenters (Mb ≥ 3.1; MW ≤ 7.8) in region
of Commander Islands.
–10
–20
–30
–40
–50
–60
–70
0 50 100 200 300150 250 350
58.0
57.5
57.0
56.5
56.0
55.5
55.0
54.5
54.0
53.5
53.0
164.7 165.7 166.7 167.7 168.7 169.7
Longitude, deg
Latitude, deg
Depth, km
Distance from point (167 E, 53 N), km
Mednyi Island
Mednyi Island
Mednyi Island
Bering Island
Bering Island
Bering Island
Aleutian Trench
A l e u t i a n T r e n c h
Aleutian Trench
(a)
(b)
0–70 km
0–70 km
606
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
ROGOZHIN et al.
this is what we observe by the example of the Near
Island Aleutian earthquake of July 17, 2017.
Morphologically, the Commander Block is a
northwestern termination of the Aleutian island arc.
The band of seismic manifestations in the region
between longitudes λ = 169°–170° E, which passes
along the northern slope of the Aleutian trench, has
two branches, one along the southwestern foot of the
Fig. 6. (a) Maximum depths of earthquake hypocenters in cross sections cutting Aleutian arc (Eastern hemisphere). Abscissa axis
is longitude in degrees. (b) Maximum depths of earthquake hypocenters in cross sections cutting Aleutian Arc (Western hemi-
sphere).
0
–50
–150
–250
–100
–200
–300
166 168 17 0 17 2 174 176 178 180 0
–50
–150
–250
–100
–200
–350
–300
–180 –175 –165–170 –160 –155 –150
Maximum depth of hypocenters, km
Longitude, East Longitude, West
(a) (b)
Fig. 7. Seismotectonic map of epicentral region of Near Island Aleutian earthquake of 2017. 1, Commander block; 2, vector of
motion of Pacific plate relative to Kamchatka (Plate Motion Calculator, http://sps.unavco.org/crustal_motion/dxdt/model/);
3, vector of motion of Commander block relative to Kamchatka according to GPS data (Levin et al., 2002); 4, focal mechanism
of main event of July 17, 2017; 5, focal mechanism of aftershock of January 25, 2018 (MW = 6.2); 6, focal mechanism of foreshock
of July 17, 2017 near Mednyi Island (MW = 6.2); 7, focal mechanism of foreshock of June 2, 2017 in vicinity of Near Islands
(MW= 6.8); 8, focal mechanism of earthquake of December 20, 2018, MW = 7.2. All focal mechanisms are according to CMT
catalog (Global Centroid-Moment-Tensor (CMT) catalog Project, http://www.globalcmt.org/CMTsearch.html).
54°
56°
162°164 °166°168°17 0 °17 2 °
Shirshov
Ridge
Bering
Island
Aleutian Trench
Kamchatka Trench
Cape
Africa
Steller
Fault
Bering IslandBering IslandBering Island
8
6
5
4
7
1
5
2
6
3
7
4
8
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
THE MW = 7.8 EARTHQUAKE 607
island arc and another along the northeastern wall of
the Commander block on the boundary with the Ber-
ing lithospheric plate. Southeast of the Commander
Islands there is a topographic low which separates the
block from the rest of the Aleutian Arc in the present
tectonic structure of the region. As a result, the Com-
mander block is bounded from the northeast and
southwest by two narrow parallel seismic belts. The
seismicity of the block’s northeastern boundary is
concentrated along the Bering Fault (Mets et al.,
1990; Seliverstov, 2009) stretching in the oceanic
basement directly at the foot of the slope of the Com-
mander shelf. The earthquakes on the southwestern
boundary occur along the Aleutian Trench and along
the Steller Fault parallel to it (Mets et al., 1990;
Seliverstov, 2009). Over the century-long interval of
instrumental observations, seismic activity on the
northeastern boundary of the Commander litho-
spheric block has been slightly higher than of the
southwestern boundary. However, this can be proba-
bly associated with the incompleteness of the
acquired statistics and, inter alia, with the long qui-
escence observed on the southeastern segment of the
Aleutian Trench until 2017.
It seems that seismic manifestations along the
northeastern (Bering Fault) and southwestern bound-
aries (Steller Fault and Aleutian Trench) of the Com-
mander block are barely independent of each other
since they are primarily due to the same stresses
emerging in this narrow (~100 km wide) block. There-
fore, the earthquakes that occur along both of its
boundaries are likely to obey a common magnitude–
frequency relationship and a strong (M ≥ 7.5) earth-
quake along one boundary seems to exclude the possi-
bility of an event with a comparable magnitude to
occur along the other boundary. We note that the
described considerations can be regarded as a hypoth-
esis and need more solid substantiation, which can be
the subject of a separate work. Meanwhile, the differ-
ent seismic activity along the southeastern and north-
western boundaries of the block is probably associated
with the different velocities of the motion of the Com-
mander block relative to the Bering and Pacific litho-
spheric plates.
According to CMT catalog data, the sources of the
earthquakes on both parallel boundaries of the Com-
mander lithospheric block are predominantly right-
lateral strike-slip faults. This indicates that a narrow
linearly elongated block is sliding northwestwards par-
allel to the motion of the Pacific Plate and has a
slightly lower velocity compared to the latter. Indeed,
direct GPS measurements on the Bering Island reveal
a stable northwestward displacement of the Com-
mander Block and its convergence with Kamchatka at
a rate of about 5 cm/yr (Levin et al., 2002).
The study of the focal mechanisms of the earth-
quakes on the Near and Commander islands shows
that there are several different zones of seismotectonic
activity there (Newberry et al., 1986; Ruppert et al.,
2012). Figures 8a and 8b shows the maps of the focal
mechanisms for the earthquakes with МW ≥ 5.3 and
МW ≥ 6.0, respectively, on the western segment of the
Aleutian Arc based on the CMT catalog data
(http://www.globalcmt.org).
In the northwestern part of the selected region
close to Bering Island, one of the nodal planes of the
averaged (over the earthquakes with all magnitudes
МW ≥ 5.3) focal mechanisms strikes subparallel to the
islands. It is worth noting that in the western and east-
ern parts of this region, right-lateral strike slip dis-
placements are predominant; however, thrust type
displacements are present at places.
Farther east, near the Mednyi Island, one of the
nodal planes of the focal mechanisms of is also nearly
parallel to the strike of the island arc and is character-
ized by a mainly right-lateral strike-slip displacement
type. This focal mechanism is characteristic of the
earthquake of July 17, 2017.
Southeast of the Mednyi Island, the stress state
sharply changes in the vicinity of 170° E. Here, the
thrust and reverse faulting mechanisms become pre-
dominant.
The character of the focal mechanisms again
changes east of 170° E within the western segment of
the Aleutian arc in the region of the Attu Island and
northwest of it. Here, the epicenters of seismic
events are shifted slightly north compared to those
within the Commander Island arc. In the northeast,
the mechanisms of almost pure shear are observed
with one of the nodal planes oriented along the
island arc. The planes of this strike accommodate
right-lateral displacements, just as in the Com-
mander arc. The focal mechanisms on the south-
western slope of the Aleutian uplift pertain to the
oblique type (reverse fault with a strike-slip compo-
nent). On the nodal plane parallel to the arc, also the
reverse fault displacements with right-lateral com-
ponent take place.
With some deviations, this distribution of the com-
pression/extension regions is identical on the different
scale levels (Fig. 8).
Against this background, the seismological mani-
festations of the Near Aleutian earthquake of July 17,
2017 in the form of the location of the cloud of epicen-
ters of the main event, foreshocks, and aftershocks are
fairly consistent with the described pattern of the stress
field in the known sources of the earthquakes which
were previously detected in this region (Fig. 9). The
main, cloud of the epicenters of the aftershocks that
are linear in plan, just as the epicenter of the main
shock, are confined to the Bering fault zone. Here, in
the segment between 170° and 171° E, the field of the
epicenters of the repeated events is oriented trans-
versely to the general aftershock cloud. It is likely that
this segment coincides with the zone of the transverse
608
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
ROGOZHIN et al.
orientation of the nodal planes of the reverse fault type
focal mechanisms shown above (Fig. 8).
Thus, the source of the 2017 earthquake almost
completely (except for its extreme northwestern part)
occupied the northern slope of the rise of the Com-
mander island and spread in the Bering fault zone. It
covered this entire seismogenic zone up to the trans-
versal seafloor structure (which is geomorphologi-
cally expressed by the Stalemate Bank (Seliverstov,
2009)) west of the Near Islands (Attu Island) and
filled most of the “Commander seismic breach”
(Chebrov et al., 2017b). Therefore, it would be per-
haps more reasonable to refer to this earthquake as the
East Commander one.
Fig. 8. (a) Focal mechanism map for МW ≥ 5.3 earthquakes in Commander and western segments of Aleutian Arc, lower hemi-
sphere projections. White and dark fields are sectors of extension and compression, respectively. (b) Focal mechanism map for
МW ≥ 6.0 earthquakes in Commander and western segments of Aleutian Arc.
Bering Island
Mednyi Island
Attu Island
Agattu Island
Bering Island
Mednyi Island
Attu Island
Agattu Island
164°
56° N
54°
166°168°17 0°172 ° E
164°
56° N
54°
166°168°17 0°172 ° E
(a)
(b)
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
THE MW = 7.8 EARTHQUAKE 609
SEISMOLOGICAL MANIFESTATIONS
OF THE NEAR ALEUTIAN EARTHQUAKE
OF JULY 17, 2017
The information base for this study was composed of
the Unified catalog of the earthquakes of Northern Eur-
asia (UCENE) (Ulomov and Medvedeva, 2013), the
Regional Catalog of Kamchatka Earthquakes (RCKE)
of the Kamchatka Branch of the Federal Research Cen-
ter Geophysical Survey of the Russian Academy of Sci-
ences (KB FRC GS RAS) (http://www.emsd.ru/), the
Catalog of the Urgent Message Service (UMS) of KB
FRC GS RAS (http://www.ceme.gsras.ru/ceme/ssd_
news.htm), NEIC catalogs (http://earthquake.usgs.gov/
earthquakes/search/), and CMT catalog (http://www.
globalcmt.org/CMTsearch.html; (Dziewonski et al.,
1981; Ekström et al., 2012). In this work, the UCENE,
RCKE, and CMT catalogs were used for analyzing the
seismic history; the UMS, RCKE, NEIC, and CMT
catalogs were used for studying the aftershock
sequence of the earthquake of July 17, 2017 and a few
other strong earthquakes in the western segment of the
Aleutian island arc. The selected fragments of the
ECENE, RCKE, and UMS catalogs were prelimi-
narily unified in terms of the МW magnitude. Since
the CMT catalog is complete for the entire globe
starting with МW of ~5.5 (Kagan, 2003), the moment
magnitudes of all the large events were taken directly
from the CMT catalog. For the weaker shocks, we
used the correlation relations which are presented
below.
The earthquake of July 17, 2017 struck the Com-
mander Islands at 23:34 UTC in the region of Mednyi
Island. According to the UMS estimate, the magni-
tude of this event was MS = 7.5. Based on the data of
the other world seismic agencies, its moment magni-
tude is estimated at МW = 7.7 (NEIC) and МW = 7.8
(CMT). According to the data of the Kamchatka
Branch of the Russian Expert Council on earthquake
forecasting and assessment of seismic hazard and risk
(REC), the earthquake was felt with intensity 5–6 in
Nikolskoye (Bering Island) and with intensity 2 in
Petropavlovsk-Kamchatskii. This seismic event also
Fig. 9. Epicenters of 95 earthquakes including main shock epicenter of July 17, 2017, foreshocks and aftershocks recorded in region
of Commander Islands from May 24, 2017 to March 27, 2018 (according to FRC GS RAS data http://ceme.gsras.ru/cgi-bin/
new/mapCustom.pl?l=0&lat=55&lon=169&num=95&rad=300). Vertical and horizontal axes show North latitude and East lon-
gitude geographical coordinates, respectively.
57
56
55
54
53
16516616716816917 0 171 17 2 17 3
Bering IslandBering Island
Bering Island
Mednyi Island
Mednyi IslandMednyi Island
Stalemate
Bank
Stalemate
Bank
Stalemate
Bank Attu
Islands
Attu
Islands
Attu
Islands
610
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
ROGOZHIN et al.
caused a minor tsunami, of which a timely tsunami
warning was issued by the Regional Information and
Processing Center (RIOC) Petropavlovsk. The earth-
quake was preceded by a strong foreshock with MS = 6.2
(UMS) and МW = 6.2 (CMT), which occurred approxi-
mately 11 hours before the main event at 11:06 UTC and
had two aftershocks with mb = 5.1 (UMS), МW = 5.3
(CMT) and mb = 4.5 (UMS).
According to the UMS data, the July 17 earthquake
was accompanied by numerous aftershocks with rather
low magnitudes (4.2 ≤ mb ≤ 5.5) with allowance for the
magnitude of the main event. Overall, 36 aftershocks
with mb ≥ 4.2 were recorded during the first 6.5 days.
Figure 10 shows a scheme of the foreshocks and after-
shocks of the earthquake of July 17 for the period from
July 17 to 20 inclusive, i.e., three days after the main
event. By March 2018, the aftershock process
appeared to be almost finished. The aftershock that
occurred on January 25, 2018 northeast of the Bering
Island was the strongest; its magnitude was MS = 6.3
(UMS), МW = 6.2 (CMT).
The large circle northwest of the main shock epi-
center indicates the foreshock of July 17, 2017 at 11:06,
МW = 6.2. The July 17 earthquake had yet another
foreshock, even a stronger one, on June 2, 2017 with
МW = 6.8 in the region of the Near Islands. In turn, the
foreshock on June 2 was preceded by a strong fore-
shock with МW = 6.2 on March 27, 2017, which also
had a strike-slip mechanism.
The focal mechanisms of the foreshocks of June 2
and July 17, as well as the mechanism of the main
event according to the CMT catalog data, are pure
shears (Fig. 7). The practically identical similarity of
the mechanisms of the foreshocks of June 2 and July 17
(nos. 6 and 7 in Fig. 7) with the mechanism of the
main event (no. 4 in Fig. 7) provides an additional
argument that the seismic event of June 2, 2017 in the
Near Islands is a foreshock. The fact that the focal
mechanism of the main event is a pure right-lateral
shear without a vertical component probably explains
why the tsunami caused by this earthquake was insig-
nificant.
The aftershock Of January 25, 2018, МW = 6.2 (no. 5
in Fig. 7) has a source that does not satisfy the double-
couple model (the non-double-couple (NDC) source
type) (Frohlich, 1995; Lutikov et al., 2010), and its mech-
anism is a strike-slip with a significant reverse-fault com-
ponent. Indeed, the determinant of its seismic moment
tensor according to the CMT catalog data, with allow-
ance for the error matrix Mij = –0.354 ± 0.025 is guaran-
teed to be negative and characterizes the presence of a
significant component of uniaxial compression with a
predominantly shear type of the slip.
It can be seen that the region of the first-three-day
aftershocks (Fig. 10), tracing the source of the earth-
quakes of July 17, stretches from the Near Islands of
the Aleutian Arc in the southeast to Bering Island’s tip
closest to Kamchatka in the northwest.
Fig. 10. Sch eme of epice nter s for fore sho cks a nd af tersh ocks of Ju ly 17, 2017e arth qua ke, МW = 7.8 (main shock epicenter is shown
by square) for July 17 to 20 inclusive according to UMS data. Circles show foreshocks and aftershocks of Main Event, circle sizes
scale with magnitude (see legend right of figure). Strongest foreshocks of June 2, 2017, МW = 6.8 and July 17, 2017 at 11:06,
МW= 6.2 are labeled.
56°
55°
54°
53°
52°
166°167°168°169°17 0 °171 °17 2 °17 3 °
Bering IslandBering IslandBering Island
Mednyi IslandMednyi IslandMednyi Island
Aleutian TrenchA l e u t ian T r e n c hAleutian Trench
Attu IslandsAttu Islands
Attu Islands
June 2, 2017June 2, 2017June 2, 2017
July 17, 2017
July 17, 2017July 17, 2017
M. E.
MW = 6.0
MW = 4.5
MW = 5.0
MW = 5.5
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
THE MW = 7.8 EARTHQUAKE 611
The strong earthquake of December 20, 2018,
МW= 7.2 (CMT) with the coordinates 54.82° N,
164.84° E (FRC GS RAS) in a way concludes the seis-
mic activation period of the western segment of the
Aleutian arc in 2017–2018. Its instrumental epicenter
was located close to the southwestern boundary of the
Commander lithospheric block in the region of the
Aleutian Trench (Fig. 6), more than 4° (~260 km)
west of the epicenter of the considered earthquake of
July 17, 2017, beyond its cloud of aftershocks. There-
fore, the earthquake of December 20, 2018 near the
southern edge of the Commander block, which was
not an aftershock of the earthquake on July 17, 2018,
was probably initiated by the stress redistribution
caused by this event. It is likely that the strong earth-
quake of December 20, 2018 may demonstrate interre-
lated seismic manifestations along its northern and
southern flanks.
In terms of the release of M0, the earthquake of
December 20, 2018 contributed relatively little com-
pared to the earthquake of July 17, 2017. According to
the CMT catalog, its moment is M0 = 8.77 × 1019 N m
or only 16.2% of the M0 value for the event of July 17,
2017; thus, that this earthquake does not distort the
previous estimates of the release of M0.
Similarly to the aftershock of January 25, 2018 with
МW = 6.2, the event of December 20, 2018 with МW = 7.2
(no. 8 in Fig. 7) also has a source that does not satisfy
the double-couple model (an NDC type source)
(Frohlich, 1995; Lutikov et al., 2010), whereas its
mechanism is also strike-slip but with a significant
normal-fault component. Indeed, according to the
SMT catalog, the determinant of its seismic moment
tensor with the error matrix taken into account, det
Mij = 0.408 ± 0.019, is guaranteed positive and indi-
cates the presence of a significant component of uni-
axial tension.
A more detailed analysis of this seismic event is
beyond the scope of this paper.
SEISMIC HISTORY
We traced the entire available seismic history
during the release of the scalar seismic moment (M0)
in the source region of the July 17, 2017 earthquake
fr o m 174 2 to 2 017 in c l u s ive . We c o n s i der e d t h e a r e a
occupied by the aftershocks of this earthquake,
namely, that bounded between 53.0°, 56.0° N, and
165.0°, 173.0° E. For this analysis, we considered the
UCENE and RCKE earthquake catalogs. The
UCENE data were used for the period from 1742 to
2013 and the RCKE data, for 2013 to 2017 inclusive.
Due to the fact that the UCENE reports only separate
events during 1742 to 1920 for this territory, the time
behavior of the release of the cumulative (accumu-
lated) scalar seismic moment (M0cum) was traced from
1920 to 2017. Starting from 1976, the MW and M0 val-
ues for all more or less strong (MW ≥ 5.5) events were
taken directly from the Centroid Moment Tensor
(CMT) catalog. The conversion from the MLH mag-
nitude in UCENE to the moment magnitude MW was
done by the correlation formula obtained from 37 pair
values from UCENE and CMT:
(1)
The conversion from energy class KS currently used
in Kamchatka to M0 was conducted by the correlation
formula obtained from 60 pair values from RCKE and
CMT by linear orthogonal regression:
(2)
where Rc is the coefficient of linear regression.
The conversion from MW to M0 is conducted by the
Kanamori formula (Kanamori, 1978)
Figure 11 shows the time behavior of the release of
the cumulative scalar seismic moment M0cum in the
source (aftershock) area of the earthquake of July 17,
2017 from 1920 to 2017. The straight line is a linear
regression approximating the observed data on the
interval from 1924 to 1998 inclusive.
The regression is described by the following for-
mula:
(3)
It can be seen that approximately starting from
1990, the deficit in the release of M0 began to accumu-
late. By the time of the earthquake of July 17, 2017, the
deficit was ΔM0cum ≈ 1.78 × 1020 N m, which is equiv-
alent to the occurrence of an earthquake with MW ≈ 7.4,
a fairly close value to the actual observed magnitude of
the July 17 earthquake MW = 7.7–7.8. Thus, it can be
concluded that after the earthquake of July 17, 2017,
the deficit in the release of M0 that was accumulated in
this area since ~1990 was eliminated. Therefore, an
earthquake with a magnitude comparable to that of
the earthquake of July 17, 2017 (MW = 7.8) in the after-
shock region of this event in the nearest future is
unlikely.
ANALYSIS OF THE TIME BEHAVIOR
OF THE AFTERSHOCK PROCESS
The aftershock process of the event of July 17
developed rather feebly for an earthquake of this mag-
nitude. According to the UMS data, only 59 after-
shocks with magnitudes 4.1 ≤ mb ≤ 5.6 occurred there
during the first 75 days after the earthquake; according
to the RCKE data, 303 aftershocks with с 8.3 ≤ Ks ≤ 13 .0
(1.9 ≤ MW ≤ 5.5) were detected by September 25, 2017,
=+ ++
=
W
c
0.6125 0.027 MLH 2.385 0.186,
R 0.
()
968.
M
(
)
=± +±
=
0S
c
logM 1.017 0.064 K 4.416 0.906,
R 0.901,
=+
0W
log M 1.5 9.1
M
(
)
=± +±
=
0cum
c
log M 0.0082 0.0002 4.205 0.439,
R 0.983.
t
612
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
ROGOZHIN et al.
Here Ks is the regional energy class of the Kamchatka
earthquakes. The conversion to the moment magni-
tudes from the energy classes Ks was carried out by for-
mula (2). Practically all the events in the UMS catalog
are presented in terms of the mb magnitude. The mb
magnitudes were converted to MW magnitudes based
on the correlation dependence between mb and MW
obtained from 89 pairs of values in the form
According to both catalogs, 0.4 and 0.13% of the
scalar seismic moment of the main shock (M0me) was
released in the aftershocks during approximately 70 days
after the main event, respectively. This was anoma-
lously low and indicative of a new strong event there.
The estimates in the release of M0 in the aftershocks
based on the UMS and RCKE catalogs differ approx-
imately by a factor of three.
It is worth noting that the depth of the hypocenters
of all the aftershocks according to the UMS data
ranged from 10 to 40 km. At the same time, according
to the RCKE data, the hypocentral depths of all the
aftershocks lie within 2.3 km ≤ h ≤ 79.3 km and the
number of aftershocks with h > 50 km is less than 8%
of their total number. This means that the source was
located within the limits of the lithosphere.
In fact, the source of the July 17 earthquake is jux-
taposed in the southeast to the source of the strong
South Ozernovskoe earthquake of March 29, 2017,
04 h 09 m, МW = 6.6 in Kamchatka (56.98° N,
163.20°W) (Chebrov et al., 2017a). According to Fig. 9,
the linear size of the source estimated from the cloud
of the aftershocks is above 400 km, which is approxi-
mately thrice as large as the estimates of the linear size
=+ =
Wc
0.718 1.507, R 0.872.
Mmb
of the source with magnitude 7.7–7.8 (Lutikov and
Dontsova, 2002). In (Chebrov et al., 2017b), it is
noted, in particular, that a similar discrepancy
between the linear dimensions of the source and the
cloud of the aftershocks was also observed for the
other strongest earthquakes in the Aleutian Arc of
March 9, 1957 (MW = 8.6) and of February 4, 1965
(MW = 8.7) (Balakina and Moskvina, 2010). We also
note that this length of the source agrees closely with
the estimates of (Wells and Coppersmith, 1994) for the
linear seismic faults of the shear type. In the future, we
will use the RCKE catalog data, which are more com-
plete, and supplement them by the CMT data.
As noted above, the strongest aftershock with
МW= 6.2 occurred on January 25, 2018, i.e., more
than half-a-year after the main event. By the end of
February 2018, 83 aftershocks with mb ≥ 4.3 were
detected according to the UMS catalog and 559 after-
shocks with KS ≥ 8.3 (МW ≥ 1.9) were recorded accord-
ing to RCKE. Figure 12 shows the time history of the
release of M0cum/M0me in the aftershocks of the earth-
quake of July 17 in fractions of M0 of the main event for
the period from July 17, 2017 to February 27, 2018
inclusive. The graph is based on the RCKE data and
CMT catalog.
The linear regression conducted over the first 14 days
of the aftershock process development, when the
release of M0cum was approximately linear with time,
has the following form:
(4)
where time t after the main event (ME) is in days.
(
)
=±
+± =
0cum 0me
c
M M 0.00007 0.00001
0.0004 0.0001, R 0.919,
t
Fig. 11. Time dependence of M0cum release in aftershock region of earthquake of July 17 from 1920 to 2017 (left ordinate axis).
Straight line shows linear regression approximating observed data for 1924 to 1998 inclusive. Horizontal bars indicate 95% con-
fidence interval of regression in 2017. Triangles mark magnitudes (right ordinate axis) of strongest (МW ≥ 5.8) seismic events.
19.8
20.0
20.2
20.4
20.6
20.8
21.0
21.2
5.0
6.0
8.0
5.5
6.5
7.5
7.0
1920 1930 1940 1950 1960 1970 1980 2000 2010 2020199 0
T, years
logM0cum
MW max
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
THE MW = 7.8 EARTHQUAKE 613
As follows from Fig. 11, by February 27, 2018, the
aftershocks released the cumulative moment M0cum aft ≈
4.06 × 1018 N m or approximately 0.75% of M0me. The
deficit in the release of M0 (formula (4)) in the aftershocks
as of January 24, 2018 was ΔM0cum = 6.43 × 1018 N m,
which is equivalent to the occurrence of an earthquake
with MW ≈ 6.5, a slightly larger value than the magni-
tude of the aftershock of January 25, 2018. The fact
that ΔM0cum in the aftershocks estimated from the dif-
ference between the regression line and the actually
observed M0cum time series approximately corresponds
to the moment magnitude of the aftershock of January 25
means that the quasi-stationary phase of the M0cum
release in the aftershocks lasted about half-a-year. The
period from August 3, 2017 to January 24, 2018 (from
day 18 to day 186 in F ig. 12 ) can b e con sidered as the
phase of seismic quiescence within the aftershock
sequence before the strong aftershock of January 25,
2018.
According to Bath’s empirical law (Bath, 1965),
the difference between the main shock magnitude and
the magnitude of the strongest aftershock (ΔM) is
approximately constant and, as a rule, is 1.1–1.2 in the
units of moment magnitude. The analysis conducted
in (Kisslenger and Jones, 1991; Sherbakov and Tur-
cotte, 2004) has shown that the ΔM value varies con-
siderably, 0.6 ≤ ΔM ≤ 1.7. In the case of the Near Aleu-
tian earthquake of July 17, 2017 (МW = 7.8), with its
strongest aftershock of January 25, 2017 (МW = 6.2),
ΔM = 1.6, which lies within the probable variations in
ΔM cited above.
The aftershock process of the Near Aleutian
earthquake of July 17, 2017 has two distinguishing
features compared to the aftershock processes of the
most of the Kuril–Kamchatka earthquakes (Lutikov
and Rodina, 2013): (1) the low release of M0cum aft
(which, however, lies within the noted variations),
which, according to different estimates, made up
0.75% (RCKE) and 1.0% (UMS) of M0me; (2) the
very slow buildup of the deficit in the release of M0
(formula (4)).
CONCLUSIONS
Our analysis of the seismological and seismotec-
tonic data for the strongest earthquake of July 7, 2017
on the Commander Islands has shown that the seismic
source, according to the distribution of aftershock epi-
centers in the form of a linear 400-km long elongated
narrow zone, almost completely occupied the north-
ern slope of the Commander Island rise and settled in
the Bering fault zone. It covered this entire seismo-
genic zone up to the transverse structure west of the
Near Islands (Attu Island) and filled the “Com-
mander seismic breach” (Chebrov et al., 2017b). In
accordance with the focal mechanism solutions and
the pattern of displacements in the sources of the main
shock and strongest aftershocks, the slip in the source
was an almost pure right-lateral shear. The aftershock
process of the July 17 earthquake developed quite fee-
bly for an earthquake of this magnitude. Besides, it has
two distinctions compared to the aftershock processes
of most of the Kuril–Kamchatka earthquakes: (1) a
low release of the cumulative scalar seismic moment
(M0cum aft) which, according to different estimates,
makes up from 0.75 to 1.0% of the seismic moment of
the main shock (M0me); (2) a very slow buildup of the
Fig. 12. Time dependence of M0cum/M0me release in aftershocks of July 17 earthquake in fractions of M0 of main event for July 17,
2017 to February 27, 2018 inclusive. Graph is based on RCKE data and CMT catalog. Straight line shows regression (4). Horizontal
bars indicate 95% confidence interval of regression as of January 25, 2018.
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
2.5
3.5
3.0
4.0
4.5
5.0
6.0
7.0
8.0
5.5
6.5
7.5
0 20 40 60 80 100 120 140 160 180 200 220 240
T, days from M. E.
M
0cum
/M
0me
M
W max
614
IZVESTIYA, PHYSICS OF THE SOLID EARTH Vol. 55 No. 4 2019
ROGOZHIN et al.
deficit in the release of the seismic moment (M0). At
the same time, the duration of the quasi-stationary
phase of the M0cum release in the aftershocks, which
was estimated at about half-a-year and which covered
a significant part of the duration of the entire after-
shock process of this earthquake probably nearing its
completion as of March 2018, seems untypically long.
These peculiarities of the aftershock process of the
Near Island Aleutian earthquake of July 17, 2017 dis-
tinguish it from the aftershock processes characteristic
of most of the strong Kuril–Kamchatka earthquakes.
Overall, its source was confined to the zone of the nar-
row Commander block linearly elongated in the
northwestern direction which can be considered as a
transform structure between the two Zavaritsky–
Benioff zones (the Aleutian and Kuril–Kamchatka
ones) rather than subductional, characteristic of the
last two zones.
Compared to the Central segment of the Aleutian
Arc (the Rat and Andreanof islands) where the stron-
gest earthquakes with MW 8.6 (1957) and 8.7 (1965)
occurred in the XX century, the western segment (the
Commander and the Near islands) was not hit by the
earthquakes with MW > 7.8 at least during the past
250 years. Moreover, these segments markedly differ
in their internal structure: in the region of the Rat and
Adreanof islands, there is a clearly pronounced seis-
mic focal zone penetrating into the Earth almost down
to the bottom of the intermediate depths (Figs. 1, 2),
which suggests the existence of the subduction process
there. Between the Commander and Near Islands, the
phenomenon of the subduction ceases to exist so that
beneath the Commander Islands, only the litho-
spheric seismicity really exists with the maximum of
the hypocentral depth distribution at 10–50 km and a
rapid decrease of the number of hypocenters at large
depths.
FUNDING
The work was conducted as part of a state contract.
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Translated by M. Nazarenko
