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A Possible Mechanism for the Ferromanganese Nodules “Floating” in the Near Equatorial Part of the Pacific Ocean

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Abstract

In this paper we apply the mechanism of a near-bottom tsunami in the open ocean to explain the paradoxical location of massive ferromanganese nodules at the surface of sediments of different ages. These tsunamis are generated by the strongest (M > 7.5) earthquakes in the Central American seismic zone and propagate in the near-bottom water layer (3000-5000 m). Their amplitudes are equal to 0.8-3.0 cm, while the velocities reach 180 m/s. Such perturbations of the water layer are able to cause not only the erosion of the sediments but also the transport (rolling, overturning) of ferromanganese nodules over the ocean bottom. As a result, they can be located at the surface of sediments of various ages. This confirms our supposition about the mechanism of “floating” of massive ferromanganese nodules. Previously, in order to solve the problem mentioned above, we used the mechanism of the Raylpigh waves, which are excited by the strongest (M > 7.5) earthquakes in Central America. However, an analysis of the amplitudes of the Rayleigh waves showed that, at distances of 3300-5400 km from the seismic zone, these amplitudes are very small (about 0.5 mm). Therefore, they are able to cause erosion at a rate up to 50 m/My by mechanical forcing on the sediments. However, the Rayleigh waves are not able to move ferromanganese nodules because of their small scale (0.5 mm) as compared to the size of the nodules (5-10 cm). Hence, the mechanism of a near-bottom tsunami is preferable for explaining the effect of nodule “floating.”
Oceanology; Vol. 42, No. 5, 2002, pp. 677-681. Translated from Okeanologiya, Vol. 42, No. 5, 2002, pp. 709-713.
Original Russian Text Copyright © 2002 by Kuzin, Barash.
English Translation Copyright © 2002 by MAIK "Nauka /Interperiodica " (Russia).
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A Possible Mechanism for the Ferromanganese Nodules
“Floating” in the Near Equatorial Part of the Pacific Ocean
I. P. Kuzin and M. S. Barash
Shirshov Institute o f Oceanology, Russian Academy of Sciences, Moscow, Russia
Received July 4, 2001
AbstractIn this paper we apply the mechanism of a near-bottom tsunami in the open ocean to explain the
paradoxical location of massive ferromanganese nodules at the surface of sediments of different ages. These
tsunamis are generated by the strongest (M > 7.5) earthquakes in the Central American seismic zone and prop
agate in the near-bottom water layer (3000-5000 m). Their amplitudes are equal to 0.8-3.0 cm, while the veloc
ities reach 180 m/s. Such perturbations of the water layer are able to cause not only the erosion of the sediments
but also the transport (rolling, overturning) of ferromanganese nodules over the ocean bottom. As a result, they
can be located at the surface of sediments of various ages. This confirms our supposition about the mechanism
of “floating” of massive ferromanganese nodules. Previously, in order to solve the problem mentioned above,
we used the mechanism of the Raylpigh waves, which are excited by the strongest (M > 7.5) earthquakes in
Central America. However, an analysis of the amplitudes of the Rayleigh waves showed that, at distances of
3300-5400 km from the seismic zone, these amplitudes are very small (about 0.5 mm). Therefore, they are able
to cause erosion at a rate up to 50 m/My by mechanical forcing on the sediments. However, the Rayleigh waves
are not able to move ferromanganese nodules because of their small scale (0.5 mm) as compared to the size of
the nodules (5-10 cm). Hence, the mechanism of a near-bottom tsunami is preferable for explaining the effect
of nodule “floating.”
INTRODUCTION
In our previous article [13], we considered a possi
ble mechanism of the influence of the Rayleigh surface
waves in the Central American zone on the bottom sed
iments in the Clarion-Clipperton province during the
strongest earthquakes (M > 7.5). This formulation of
the problem was conditioned, first of all, by the impos
sibility to explain the existing correlation between the
unconsolidated sediments and ferromanganese nodules
(erosional cut and “floating” of the nodules) using the
previously considered mechanisms. They include
(a) long-term periods when no sediments are accumu
lated; (b) regional erosion of the Tertiary sediments and
accumulation of ferromanganese nodules as residual
elements; (c) the effect of the bottom shaking under the
forcing of the seismic waves from the strongest earth
quakes; (d) microflux of geogases; (e) bioturbation and
extrusion of nodules to the surface of the floor by
benthic organisms; (f) rheological properties of the sed
iments; and (g) hydrodynamics of the density-stratified
bottom water layers [2, 4, 19]. All these mechanisms
cannot explain the facts of erosion of Tertiary sedi
ments 34—80 m thick and the location of the denser
ancient (mainly Oligocene) ferromanganese nodules
(density about 2.0 g/cm3) [11] at the surface of the sed
iments of different ages up to recent ones (the density
of the consolidated sediments is about 1.2 g/cm3 [12]).
In the solution of the problem on the relations
between the sediments and ferromanganese nodules,
we focused, first of all, on the data of sufficiently strong
shocks of the earth’s surface under the influence of
the Rayleigh waves during the strongest earthquakes
(M ~ 8.5). It is known that during the Lisbon (1775),
Assam (1950), and Alaska (1964) earthquakes, notable
vibrations of the ground were observed at distances of
4000 to 8000 km [6, 18] during the propagation of the
Rayleigh waves. It is natural to suppose that similar
shocks are manifested at the ocean bottom in the Clar
ion-Clipperton province during the strongest earth
quakes in Central America at distances from 3300 to
4300 km from the closest experimental study area and
4300-5400 from the most remote one (see Fig. 3 in [13]).
In order to study the possible amplitudes of the
ocean bottom vibrations, we used the records of
200 earthquakes at seismic stations in Petropavlovsk-
Kamchatskii and Severo-Kurilsk with M = 6.0-8.2
from different seismically active zones in the Pacific
Ocean at distances from 580 to 9200 km [13]. It was
found that at distances of 3300-4300 km and
4300-5400 km the amplitude of the vertical oscilla
tions in the Rayleigh waves during earthquakes with
M = 7.5-8.2 reaches 0.4-0.5 mm. This means that,
when a benthic storm begins under the influence of the
Rayleigh waves caused by one of those earthquakes,
the surface layer of unconsolidated sediment, accumu
lated over a period of 200-250 to 400-500 years, could
be washed out [2, 19].
An estimate of the recurrence of the earthquakes of
the magnitude groups 7.5-7.9, 8.0-8.4, and greater
than 8.5 on the basis of the data available [17,24] leads
678 KUZIN, BARASH
Fig. 1. Schematic of a near-bottom tsunami recording dur
ing the earthquake on March 14, 1979, near the Mexican
coast (according to [20]). (a) Position of the pressure gauge
(P) and the epicentral гопе of the earthquake with a magni
tude M = 7.6 (hatched area); (b) sea level record of the near
bottom tsunami generated by the earthquake on March 14,
1979. E is the moment of arrival of the body waves; T is the
moment of arrival of the tsunami wave. The amplitude of
the record equal to 1 cm corresponds to a pressure change
of 100 Pa. TTie high-frequency component of the oscilla
tions with a period of 2-4 min and amplitude of 0.1 cm cor
responds to the Rayleigh surface waves.
as to the conclusion that over 1000 years about
20 earthquakes with such amplitudes can occur. By
decreasing the possible amplitude 1.6-2.0 times (to
increase the probability of such vibrations), we obtain
in estimate of the sediment erosion of about 5 mm for
1000 years. If we assume that the beginning of the ero
sion started 17 My BP, the erosional cut should be equal
to 85 m. At a rate of the sediment accumulation equal
to 1.5 mm in one thousand years, the layer of the sedi
ments accumulated during this period would be equal
to 25 m. In this case, the erosion would be equal to
60 m. This is comparable with the mean estimate of the
jrosional cut [2, 19]. In the latter paper it is shown,
however, that it is likely that the period of erosion of the
Tertiary sediments in the Clarion-Clipperton study
areas does not exceed 1 My (more precisely,
0.9-0.7 My). In this case, the mechanism of the sedi
ment erosion gives a value of the erosional cut that is
underestimated 7-16 times. It should be added that the
small (up to 0.5 mm) amplitudes of the ocean bottom
vibrations during the propagation of the Rayleigh
waves cannot explain the displacement of massive
ferromanganese nodules to the surface of the uncon
solidated sediments of different ages up to the recent
ones.
Taking into account that the Rayleigh surface waves
mechanism cannot be used for the explanation of the
erosional cut of unconsolidated sediments and, even
more, it cannot be used to explain the problem of the
ferromanganese nodules, we applied for the first time
the mechanism of a near-bottom tsunami to solve this
problem. We are analyzing the tsunamis generated by
strong earthquakes and propagating in the bottom layer
in the open ocean.
ANALYSIS OF THE TSUNAMI DATA
It is known that the majority of the tsunamis (up to
80%) are excited by the strongest earthquakes with
M > 7; that is, they have a seismic origin [8]. According
to the data available over the past 450 years
(1537-1979), about 55 events of the tsunami type and
similar ones (high tidal waves, storm flooding, etc.)
occurred during such earthquakes in the Central Amer
ican seismic active zone [15, 16]. According to the data
from [22], the possible magnitudes values M of 7.0-8.3
were determined for half of the known earthquakes.
However, we cannot use this information directly
because it is related to the manifestation of tsunamis
near the coast and, using these data, it is difficult to esti
mate the motion of the near-bottom layer in the open
ocean. Only after near-bottom tsunamis were recorded
in the 1970s-1980s far from the coastline using the
pressure gauges did it become possible to use this infor
mation in the solution of the problem of the interaction
between the sediments and ferromanganese nodules on
the basis of observations in the Clarion-Clipperton
province.
At present, at least four records of near-bottom tsu
namis are known to be related to the following earth
quakes: (a) in the Central American seismically active
zone near the Mexican coast on March 14,1979, M = 7.6;
(b) in the south Kuril zone near Shikotan Island on Feb
ruary 23, 1980, M = 7.0; (c) and (d) in the Gulf of
Alaska on November 14, 1987, and March 6, 1988,
M = 7.6 in both cases.
The first record was obtained at a point south of the
California Peninsula during an earthquake in the Petat-
lan town region (Mexico) with a focal depth equal to
20 km. The pressure gauge was located at a depth of
3210 m at a distance of 980 km (8.8°) from the epicen
ter. The tsunami record had a multiphase character.
Along with the main maximum 8 mm (double ampli
tude 1.6 cm), four other maxima can be distinguished
with amplitudes from 6.5 to 3 mm and periods of oscil
lations from 15 to 45 min (figure) [20]. The time of the
tsunami wave propagation is 1 h 28 min, which corre
sponds to a velocity of 670Jcm/h or 186 m/s. This value
OCEANOLOGY Vol. 42 No. 5 2002
A POSSIBLE MECHANISM FOR THE FERROMANGANESE NODULES “FLOATING” 679
is close to the estimate 638 km/h or 177 m/s obtained
from the relation V = JgH, where g = 9.79 m/s2 is the
acceleration due to gravity at a latitude of 22° N and H
is the ocean depth in meters. Taking into account the
periods of the oscillations and the velocity of the tsu
nami wave propagation, its length can be estimated as
170-500 km.
The second record of a near-bottom tsunami was
made by a group of researchers headed by
S.L. Solov’ev over the shelf of Shikotan Island (depth
133 m) during an earthquake with M = 7.0 and a focus
located 30-40 km under the upper part of the continen
tal slope of the Kuril-Kamchatka Trench, depth con
tour 800 m [9]. The amplitude of the first, the greatest
wave, was equal to 3.5 cm (double amplitude 7 cm); its
period was 18 min. Over approximately 10 h after the
arrival of the first wave, about 11 maxima with a
decreasing amplitude from 2-3 to 1.75-1.50 cm and
periods of 11-24 min (most frequently 17 min) were
observed. In 15 min, the wave covered a distance of
33 km from the epicenter, which corresponds to a
velocity greater than 130 km/h or about 37 m/s (wave
lengths 24-52 km).
Near-bottom tsunamis from the earthquakes in the
Gulf of Alaska with focal depths of 10 km were
recorded at two points: (a) south of Kodiak Island at a
depth of 5 km; (b) southwest of Vancouver Island,
ocean depth 3 km. In 1987, during the earthquake at the
point closest to the epicenter south of Kodiak Island
(A ~ 970 km or 8.7°), the amplitude of the tsunami
reached 1 cm, while in a more remote one southwest of
Vancouver Island (A ~ 1730 km or 15.6°), the amplitude
reached 1.7 cm [21]. During the earthquake in 1988, the
amplitudes of the tsunamis at the same points were
equal to 2.6 cm (A ~ 900 km or 8.1°) and 2.9 cm
(A ~ 1520 km or 13.7°), respectively. In the latter case,
the tsunami records both in the California and South
Kuril regions had a multiphase character (five maxima
with amplitudes from 2.9 to 2.0 cm) [23]. Unfortu
nately, the lack of a time reference on the tsunami
record in 1988 (the tsunami record of 1987 is not pub
lished) does not allow us to determine the velocity of
the wave propagation and the periods of the main and
subsequent tsunami pulses.
Thus, concluding the discussion of the data on near
bottom tsunami, we have to note the following. First,
unlike the surface waves generating vibrations of the
bottom and indirectly influencing the near-bottom
water layer, the perturbation during a tsunami is gener
ated in the boundary water layer. As this takes place, the
perturbations related to the same magnitude of the
earthquake at comparable distances from the source
exceed the amplitude of oscillations in the surface
waves by at least one order of magnitude (8 mm as
opposed to 0.8 mm, according to [13]). This excess can
be as high as 20-40 times at distances about 15°
(according to [ 13], the displacement associated with the
Rayleigh waves at M = 7.5-7.9 is equal to approxi
mately 0.75 mm, while in the records during the earth
quakes in the Gulf of Alaska they were equal to
1.7-2.9 cm).
Second, in the case of a tsunami, the perturbations in
the bottom water layer propagate at a very high speed
as compared to the usual currents, not less than
650-750 km/h (see above and also [6]) or 180-210 m/s.
Both factors should facilitate an intensive influence of
the bottom tsunami on the sediment^ and ferromanga
nese nodules on the ocean bottom.
From the consideration of the previous information
it follows that to solve this problem we can take the tsu
nami records during the earthquakes in the Gulf of
Alaska at a point southwest of Vancouver Island
(13.7°-15.6°) as a first approximation of the initial data,
extrapolating them to the distances corresponding to the
remoteness of the study areas 2 (3-3) and 1 (4-49°)
in the Clarion-Clipperton province from the Central
American seismically active zone. We assume that the
minimum amplitude of a tsunami oscillation is 8 mm
taking into account the wave decay due to the respec
tive 2.0- to 2.7- and 2.8- to 3.4-fold excess in the epi-
central distances to study areas 2 and 1 compared to
those observed during the recording of these waves.
This possibility is taken into account by the choice of
the initial amplitude of the tsunami, which is
2.1-3.6 times smaller than that observed in the experi
ment (8 mm as opposed to 1.7-2.9 cm as shown above).
It is noteworthy that, according to the available data,
tsunami waves are characterized by a weak decay as the
coefficient of turbulent viscosity in the bottom bound
ary layer is constant. Only in a more complex model of
turbulence should the decay of a tsunami increase [10].
Another important factor in the choice of the bottom
tsunami as the source conditioning the observed ero
sion of the sediments and transport of ferromanganese
nodules to the surface of the present sediments is the
estimate of the tsunami recurrence. It is known that not
every earthquake with a magnitude M > 7 is accompa
nied by a tsunami. For example, as follows from the
above-mentioned data, of 55 events of tsunami type in
Central America that occurred during the last 450 years
(1537-1979) [15, 16], only about 17 events fit the pro
portion of clearly manifested tsunamis after a thorough
analysis. According to [22], from 27 determinations of
the earthquake magnitudes, the overwhelming majority
falls in the M ranges 7.0-7.4 and 7.5-7.9 (11 determi
nations in each range). Only two clearly manifested tsu
namis are related to the first group. It is noted in many
publications dedicated to the study of tsunamis that
many factors influence the generation of a tsunami dur
ing a strong earthquake: the mechanism of the focus
(the most effective is the displacement with an upward
motion— the piston mechanism); the depth of the focus
(the maximum amplitudes of tsunamis correspond to a
depth of the source equal to 10 km) [1, 8, 14, and oth
ers]; and the depth of the basin where tsunami is gener
ated (approximately 1300 m) [7].
680 KUZIN, BARASH
However, up to the present, the reason why during
earthquakes of the same magnitude tsunamis are gener
ated in some cases and are not generated in others is
still not known. The solution of this problem goes
beyond the scope of this study; however, it is necessary
to note the following. As mentioned above, at the earth
quakes with M > 7.5, tsunamis are generated in 80% of
the cases [8]. We can assume 50% as the lower limit.
Then, based on the recurrence of the earthquakes with
M = 7.5-8.5 considered above, we can expect that over
1000 years, 10 tsunamis (but not 20) with an amplitude
of at least 8 mm can be generated. In this case, the total
erosion of the sediments over 1000 years will be
80 mm. Extrapolating this estimate over 1 My, we get
an erosional cut of the sediment layer equal to 80 m. It
follows from this that the observed erosional cut in the
study areas 1 and 2 in the Clarion-Clipperton province
could appear within 0.42-1 My. This conclusion agrees
with the results of [19].
As for the problem of the location of ancient ferro
manganese nodules over the recent sediments, their
“floating” or maintenance at the surface of the bottom
is possible when they are displaced (overturned, rolled)
under the influence of a near-bottom tsunami with
amplitudes at least the sizes of the nodules (5-10 cm).
In the light of the data considered above, this possibility
seems quite feasible.
Thus, from the example of study areas in the Clar
ion-Clipperton province, we can conclude that near
bottom tsunamis caused by the earthquakes with
M = 7.5-8.5 from the Central American seismically
active zone are the most applicable mechanism explain
ing the features of the interaction between the sedimen
tary layer and ferromanganese nodules. We have to
admit that there is an uncertainty with the generation
and recurrence of tsunamis for earthquakes with
M = 7.5-8.5 which can cause doubt about the reliabil
ity of the estimates of the washout of the bottom sedi
ments in the study areas mentioned above. However,
the influence of near-bottom tsunamis on the relations
between the sediments and ferromanganese nodules is
beyond doubt. A similar conclusion can be reached for
other ferromanganese nodule provinces in the Pacific
Ocean taking into account the high seismicity of its
margins. At the same time, we cannot neglect the influ
ence of strong benthic currents in certain regions, for
example, in the province near Antarctica where seismic
activity is low (see Fig. 1 in [13]).
DISCUSSION OF THE RESULTS
In the case of a near-bottom tsunami in the open
ocean generated by an earthquake with M > 7.5, the
intensity of the influence in the water column near the
bottom of an individual event at comparable distances
increases from 10 to 20-40 times (the amplitude of the
perturbation is equal to 8-29 mm as opposed to 0.5 mm
in the Rayleigh waves).
If we assume that the recurrence of the tsunamis is
two times smaller than the recurrence of the earth
quakes with M = 7.5-8.5 and the minimum washout
during each near-bottom tsunami is equal to 8 mm
(which is 32 times or 1.5 order of magnitude greater
than under the influence of the Rayleigh waves), the
total erosional cut would be equal to 80 mm after
1000 years or 80 m after 1 My. Then, the washout of the
unconsolidated Tertiary sediments in the study areas
mentioned above could be formed during the last
0.42-1 My. This estimate agrees with the estimate
made from the stratigraphic data in [19].
In the case when we choose a tsunami to solve this
problem, besides the differences in the value of the per
turbation compared to the Rayleigh surface waves,
there are differences in the origin of forcing. In the
former case, the bottom water layer plays a passive role.
The perturbations propagate at a very high velocity of
about 3.6 km/s in a solid medium covered by unconsol
idated sediments. The forcing has a short-wave charac
ter (the period is about 18 s on average, the wavelength
is 65 km) and relatively short duration (about 5 min;
see, for example, [5]). In the case of a tsunami, the per
turbation spreads in the water layer with an amplitude
that is 10-40 times greater than the displacement of the
bottom under the Rayleigh wave forcing. The velocity
of the tsunami wave propagation is approximately
20 times smaller than that of a Rayleigh wave, but it is,
however, much greater than the velocities of the usual
oceanic currents (180 m/s and greater). The forcing has
a long-wave character (the periods are 15-45 min, the
wavelength is 170-500 km) and significantly greater
duration, from two and more hours, according to [20],
to 11 h, according to [9]. The significant amplitude of
perturbations, a velocity greater than the velocity of the
usual oceanic currents, and the long duration of forcing
should facilitate not only the washout of the sediments
but also the transportation (overturning, rolling) of fer
romanganese nodules. As a result, they can be located
over sediments of different ages including the recent
ones.
It is noteworthy that the estimate of the erosional cut
of the Tertiary sediments based on the data on natural
tsunamis is not indisputable due to the uncertainty
related to the recurrence of tsunamis. However, the
influence of a near-bottom tsunami on the sediment
layer and ferromanganese nodules is beyond doubt. It is
likely that it is the real source of the observed relations
between the sediments and nodules in the study areas in
the Clarion-Clipperton province as well as in the other
provinces with a high concentration of ferromanganese
nodules close to highly seismic zones considered in the
previous article.
ACKNOWLEDGMENTS
This work was supported by the Russian Foundation
for Basic Research, project no. 01-05-64263.
OCEANOLOGY Vol. 42 No. 5 2002
A POSSIBLE MECHANISM FOR THE FERROMANGANESE NODULES “FLOATING” 681
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... Some researchers also believe that the driving force for removing the sediment on the surface of such nodules may result from earthquakes. Millions of earthquakes occur on the ocean floor every year, and the combination of earthquakes and the action of bottom currents may also keep the nodules on the surface of the seabed [46,51]. Some researchers believe that different metallogenic environments make it difficult for buried nodules to be preserved, while nodules on the seabed surface are more suitable for preservation [52]. ...
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With the increase in demand for metal resources, research on deep-sea polymetallic nodule mining has been reinvigorated, but the problem of its environmental impact cannot be ignored. No matter what method is used for mining, it will disturb the surface sediments of the seabed, thereby increasing the concentration of suspended solid particles and metal ions in the water body, changing the properties of the near-bottom water body and sediments, and affecting biological activity and the living environment. Focusing on the ecological and environmental impacts of deep-sea polymetallic nodule mining, taking as our main subject of focus the dynamic changes in sediments, we investigated the environmental impacts of nodule mining and their relationships with each other. On this basis, certain understandings are summarized relating to the ecological and environmental impacts of deep-sea polymetallic nodule mining, based on changes in the engineering geological properties of sediment, and solutions for current research problems are proposed.
Conference Paper
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Micropaleontological investigations in two survey areas show that Tertiary outcrops of different ages are distributed on the bottom surface or under a thin layer of Quaternary sediments. The continuous sediment sequence from the Late Eocene to the Early Miocene (40-17 million years) and the regional hiatus between 17 and 1 million years were revealed. Age intervals of radiolarian complexes in nodules are Tertiary mainly Oligocene. Abundant manganese nodules occur on the bottom mainly on the surface of Quaternary sediments covering the Tertiary deposits of various ages. The statistical probability of the nodule formation age is mainly Oligocene. Consequently, the ages of the manganese nodules and sediments are different, usually older nodules occur on younger deposits. Most of the micropaleontologically characterized Quaternary sediments are 0.7-0.9 million years old. Micropaleontological investigations were carried out also in a block of the dense ancient miopelagic clay covered by the manganese crust. In contrast to nodules, the crust could be formed only after formation of an erosion surface, on which it accrued. The distribution of microfossil complexes in different samples taken from the block shows that the dense miopelagic clay is of the Late Oligocene age. Early and Middle Quaternary and Recent sediments penetrated it through cracks and burrows. Obviously, the manganese crust was formed in the Quaternary time. Micropaleontological complexes of Middle and Late Miocene, and Pliocene are present neither in the ancient clay, nor in the manganese crust, nor in Quaternary deposits containing mixed complexes of different ages. During that time the present erosion surface of the Late Oligocene clay was covered by younger deposits of the Late Oligocene, Miocene and Pliocene, which were eroded and washed away in the Quaternary. Probably the erosion begun about 0.9-0.7 million years ago at the beginning of “Glacial Pleistocene” when the ocean circulation, particularly near-bottom currents became more active. The assumption was stated (Barash, Kruglikova, 1999, 2000), that the erosion of Tertiary deposits by near-bottom currents could be intensified by an effect of strong earthquakes in tectonically active zones which can be affective within several thousands of kilometers. In watersaturated nonconsolidated medium of the ocean bottom the surface seismic Love and Rayleigh waves should be propagated which can cause a vibration effect. The seismic vibration effect on the surface sediment layer must disintegrate and stir up sediments, which are then carried away by the bottom current. Large-size components of the sediment including manganese nodules cannot be carried out by the current and form residual deposits. The same vibration effect causes ancient nodules to float up onto the surface of the Quaternary sediments. This assumption was considered from the point of view of geophysical mechanisms (Kuzin, Barash, 2001, 2002a, 2002b). We proposed the new approach, which is based on mechanical influence on sediments of Rayleigh waves, generating by strongest (М7.5) earthquakes within the nearest Central American seismic active region. The proposed approach is based on data concerning of oscillations, which were excited by Rayleigh waves of some catastrophic earthquakes (for example, Lisbon, 1775, Assam, 1950, and Alaskan, 1964). These oscillations are observed at epicentral distances from 2000-4000 to 8000 km. The considered mechanism is realistic and allows to use quantitative characteristics of Rayleigh wave amplitudes for the explanation of mechanical influence on sediments. The study of Rayleigh wave amplitudes was carried out with using of 200 records of earthquakes with M=6.0-8.2 at distances 560-9200 km for Petropavlovsk-Kamchatsky and North-Kurilsk seismic stations. For the analysis there were used data for various seismoactive regions of the Pacific Ocean. The close seismotectonic and seismic analogy between Kurile-Kamchatka and Central American segments of the Pacific belt allows us to apply the data recorded in the first region for study of same phenomena in the second one. Then for distances between investigated areas and the seismoactive Central American region of 3000-5400 km we have amplitudes of Rayleigh wave about 0.5 mm for single earthquake. The earthquakes with M = 7.5 – 8.5 can recure 20 times per 1000 years and capable to cause the “seismological erosion” of sediments up to 10 m/My but they are ineffective for manganese nodules movement, because of large dimensions (3-5 to 10 cm) of the nodules. For the explanation of nodules movement it was necessary to use another mechanism. For solution of this problem we have used for the first time the mechanism of near-bottom tsunami in open ocean, which are excited by the same way as Rayleigh wave by the strongest (M7.5) earthquakes of the Central American seismic zone. It is known from observations near the California and in the Alaskan Bay, that these tsunami are propagated in the near-bottom water layer (at 3000-5000 m ocean depths) with amplitudes of 0.8-3.0 cm and velocities up to 180 m/s (Filloux, 1982; Milburn, Bernard, 1990) (fig.2). Minerals of ocean. Int. Conf. 20-23 April. St.Petersburg. VNIIOkeangeologia. 2002. P.55-57. Mechanism of manganese nodules accumulation and their maintenance at the sediment surface (Clarion-Such perturbations of the near-bottom water layer are capable to cause both the erosion of sediments and the transference (rolling, overturning) of manganese nodules over the ocean bottom. As a result they can occur on the surface of sediment of various ages. That confirms our supposition about the mechanisms of “floating-up” of massive manganese nodules or their maintenance on the bottom surface. Thus, this assumption suggests one and the same reason for the peculiarities of the Clarion-Clipperton zone, that is, the regional stratigraphic hiatus, the formation of the residual nodule fields, and maintenance of ancient nodules at the surface of the Quaternary deposits. REFERENCES Barash, M.S., and S.B. Kruglikova. Age of radiolaria from ferromanganese nodules of the Clarion-Clipperton Province (the Pacific Ocean) and the problem of nodule unsinkability. Oceanology, 1995, V.34, N6, p.815-828. Barash, M.S., and S.B. Kruglikova. Age of manganese nodules of the Clarion-Clipperton Province and the problem of nodule maintenance at the sediment surface. PACON 99 Proceedings, Symp. on “Humanity and the World Ocean”, 2000, p. 220-230. Barash, M.S., S.B.Kruglikova, and V.V.Mukhina. Stratigraphic features of sediment formations of the Clarion-Clipperton Province (the east equatorial Pacific). Oceanology, 2000, V.40, N3, p.424-433. Filloux, J.H. Tsunami recorded on the open ocean floor. Geophys. Res. Lett. 1982. V.9. N.1. P. 25-28. Kuzin, I.P., and M.S. Barash. On new approach to solution of problem of “floating-up” of manganese nodules in near-equator part of the Pacific Ocean. 14th Int. School on Marine Geology, Abstracts, Moscow, Russian Ac. Sc., 2001, V.2, p. 286-287. Kuzin, I.P., and M.S. Barash. On influence of Rayleigh waves of strongest (М7.5) Central American earthquakes at sediment cover within the Clarion-Clipperton Province. Oceanology, 2002 (in press). Kuzin, I.P., and M.S. Barash. On possible mechanism of manganese nodules “floating-up” in the near-equatorial part of the Pacific Ocean. Oceanology, 2002 (in press). Milburn H.B., Bernard E.N. Deep ocean tsunami observations. Workshop on scientific uses of undersea cables. Jan.30-Febr.1, 1990. Honolulu. Hawaii.Washington, D.C. 1990. P.69-73.
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Tsunami generation eeciency is studied depending on the character of time evolution of the ocean bottom displacements occurring in a course of underwater earthquakes. In the frame of a general linear approach the amplitude and energy characteristics of axially symmetrical waves are compared for two t ypes of modeled bottom movements of nite duration diiering from each o t h e r b y the presence or absence of residual deformations after the underwater shock. It is shown that nonelastic bottom displacements are the most eecient tsunami generators. The set of such a tsunami generation regime is extended due to wave dispersion. Elastic bottom shifts become an essential factor in the case of large underwater earthquake duration, large ocean depth, and small radius of the tsunami source.
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Radiolaria were studied in 19 manganese nodules raised from the bottom. The nodules occurred mainly on the surface of thin Quaternary sediments covering the Tertiary deposits of various ages (Middle Eocene to Early Miocene). Radiolaria in nodule cores and in inner and surface layers were studied. We found 85 radiolaria species and groups of species. Usually 1-4 to 6-19 radiolaria species were detected in each of the samples. Species belonging to Middle Eocene, Late Miocene to Early Oligocene, and Oligocene to Early Miocene were found. Rare Neogene species were revealed only in fractured surface layers. The age of the nodules is mainly Oligocene. Seismic waves cause sediment vibration, loosening disintegration, and the removal of the suspension by bottom currents. The vibration effect causes ancient nodules to float up to the surface of the Quaternary sediment. This hypothesis suggests the reason for the characteristics of the Clarion-Clipperton zone: regional stratigraphic hiatus, accumulation of residual fields of nodules, and the “floating up” of nodules to the surface of the Quaternary sediment.
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The area studied is characterized by a regional stratigraphic gap from the early Miocene up to the Quaternary. Deposits from the late Eocene to the early Miocene were revealed at the bottom surface or under a thin sedimentary cover. Ferromanganese nodules, mostly of the Oligocene age, are deposited over the surface layers of the Tertiary or Quaternary sediments. A detailed micropaleontological study of a block of dense ancient clay coated with a ferromanganese crust was carried out. A study of the composition of the radiolarian and diatomaceous complexes found proved that the crust was formed in the Quaternary over an eroded surface of late Oligocene clay. In the Quaternary, the Neogene sediments were eroded and washed away by the near-bottom currents. It is likely that the erosion began 0.9-0.7 Ma at the beginning of the "Glacial Pleistocene." The erosion could be initiated by the loosening and resuspension of the surface sediments, resulting from the seismic action generated by strong earthquakes in the subduction zone of Central America. The same vibration maintained residual nodules at the seafloor surface. Thus, for the area studied, a common reason and a common Quaternary interval for the formation of the following features is supposed: the regional stratigraphic gap, the formation of the residual nodule fields, and the position of the ancient nodules over the surface of the Quaternary sediments.
Article
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During the expeditionary studies of the sedimentary cover at two test sites within the Clarion-Clipperton Province, an erosional cut of the Tertiary sediments was observed and paradoxical bedding of massive ancient manganese nodules over the sediment surface of different ages right up to the recent ones was recognized. The explanations available for the observed pattern are essentially qualitative and are not supported by sufficient argumentation. We proposed a new approach considering the mechanical impact of the Rayleigh waves generated by the strongest (M > 7.5) earthquakes within the nearest Central American seismic active region on the sediments. This approach is based on the data on the ground oscillations on land that were excited by the Rayleigh waves of selected catastrophic earthquakes (Lisbon, 1775; Assam, 1950; and Alaskan, 1964). These oscillations were observed at epicentral distances from 2000-4000 to 8000 km. The mechanism consideredis realistic and allows one to use quantitative characteristics of the Rayleigh wave oscillations for the explanation of their mechanical impact on the sediments. The study of the Rayleigh wave amplitudes was carried out using about 200 records of earthquakes with M = 6.0-8.2 at distances of 560-9200 km obtained at the Petropavlovsk-Kamchatskii and Severo-Kuril’sk seismic stations. For the analysis, we used the waves arriving from various seismically active regions of the Pacific Ocean. The close seismotectonic and seismic analogy between the Kuril-Kamchatka and Central American segments of the Pacific belt allows us to apply the data recorded in the former region for studies of the same phenomena in the latter area. Then, at distances between the test sites and the seismically active Central American region of 3000-5400 km, the amplitudes of the Rayleigh waves reach about 0.5 mm. These values are large enough to explain the “seismological erosion” of the sediments; however, they are insufficient for displacement of manganese nodules because of their large size (from 3-5 to 10 cm). For explanation of the nodule displacement, another mechanism is required.
Conference Paper
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The radiolarian complexes were investigated in sediments, in manganese nodules located on the bottom surface mainly on a thin layer of the Quaternary sediments, and in sediment covered by manganese crust. A continuous sequence of radiolarian biostratigraphic zones from the Late Eocene to the Early Miocene (40-17 million years) and a regional hiatus between 17 and 1 million years were revealed. Age intervals of radiolarian complexes in nodules are Tertiaiy mainly Oligocene. The age of the crust is Quaternary, it accrued on eroded surface of the Late Oligocene clay. Deposits of the end of the Late Oligocene as well as of Miocene and Pliocene were eroded and washed away in the Quaternary by near-bottom currents. Probably the erosion began about 0.9^0.7 million years ago at the beginning of «Glacial Pleistocene» when the ocean circulation became more active. The erosion of Tertiary deposits by near-bottom currents could be intensified by an effect of strong earthquakes in technically active zones of transform faults and subduction. The seismic vibration effect on the surface sediment layer must disintegrate and stir up sediments which are then carried away by the bottom current. Large-size components of the sediment including manganese nodules form residual deposits. The same vibration effect causes ancient nodules to float up onto the surface of the Quaternary sediments. Thus, this hypothesis suggests one and the same reason for the peculiarities of the Clarion-Clipperton zone, that is; the regional stratigraphic hiatus, the formation of the residual nodule fields, and floating up of ancient nodules to the surface of the Quaternary deposits.
Article
On March 14, 1979 a sizeable earth-quake (Ms-7.6 Richter scale) occurred on the continential shelf adjacent to S.W. Mexico, near Petatlan in the state of Guerrero. This earthquake generated a small tsunami that was recorded in deep water, 1000 km away, thus providing for the first time a glance at a tsunami traveling in the open ocean. The same sea floor pressure record displays conspicuous signals associated with vertical sea floor motions generated at the passage of the first Rayleight seismic wave, R1. Seismic and tsunami travel velocities are in agreement with our present understanding of the phenomena, and tsunami detectability in deep water is demonstrated to be well within present day state of the art in the design of sea floor pressure transducers. As calculations anticipate, the E.M. signals associated with the passage of the tsunami were too faint to be detected.
Katalog tsunami na vostochnom poberezh 'e Tikhogo okeana (Catalogue of the Tsuiiamis on the Eastern Coast of the Pacific Ocean
  • S L Solov 'ev
  • Ch N Go
Solov'ev, S.L. and Go, Ch.N., Katalog tsunami na vostochnom poberezh 'e Tikhogo okeana (Catalogue of the Tsuiiamis on the Eastern Coast of the Pacific Ocean), Moscow: Nauka, 1975.
On the Relation of the Tsunami Hazard from Underwater Earthquakes to the Conditions of Sed imentation on the Sea Floor, Problemy seismichnosti Dal'nego Vostoka (Problem of Seismicity of the Far East
  • V K Gusyakov
Gusyakov, V.K., On the Relation of the Tsunami Hazard from Underwater Earthquakes to the Conditions of Sed imentation on the Sea Floor, Problemy seismichnosti Dal'nego Vostoka (Problem of Seismicity of the Far East), Petropavlovsk-Kamchatski: 2000, pp. 46-64.