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1.
A. A. Stepashko 《Russian Journal of Pacific Geology》2010,4(3):228-241
It is shown that the deep structure of the lithosphere played a decisive role in the recent deformations and seismicity in
the Far East. The regional variations in the composition of the mantle xenoliths and Neogene-Quaternary basalts provided grounds
for mapping the NE-extending wedge-shaped block of the Fe-rich mantle at the base of Sikhote Alin. Its boundaries continue
the Yilan-Yiton and Fushun-Mishan strike-slip faults of the Tan-Lu zone, along which this mantle block was displaced along
the continental margin in the Jurassic-Cretaceous. The localization of strong (M ≥ 5.0) earthquake epicenters in the Amur
region shows that such a mantle structure determines the key features of the regional deformations and seismotectonics. Under
the dominant western compression due to the Amur Plate’s motion, the mantle wedge is extruded in the northeastern direction
to provide an additional stress at the Okhotsk Plate boundary. This process resulted in the formation of the Sakhalin high-seismicity
zone at the front of the mantle block. In its characteristics, the zone is similar to the convergence area between the Indian
and Eurasian plates. In both cases, the main deformation and seismicity features were caused by the horizontal pressure of
the tectonic block, the frontal part of which is marked by regularly alternating compression and extension zones. In Sakhalin,
strong earthquakes with M ≥ 6.0 are confined to the seismic suture 50 km wide with concentrated compression. This structure
is discordant relative to the main faults of the island, being parallel to the front of the mantle wedge. The two migration
cycles established for the Sakhalin earthquakes with M ≥ 6.0 correspond to periods of 1907–1971 and 1995–2007. During both
cycles, the first shocks occurred in the north and subsequently migrated in the southeastern direction simultaneously decreasing
in the depths of the earthquake foci. The systematic migration implies that asymmetrical compression is responsible for both
the extrusion of the mantle wedge and its southeastward clockwise rotation. The latter plays the decisive role in the initiation
of strong earthquakes on Sakhalin. 相似文献
2.
A. N. Ovsyuchenko S. V. Trofimenko S. S. Novikov A. N. Didenko V. S. Imaev 《Russian Journal of Pacific Geology》2018,12(2):135-150
The studied region is located at the junction between the Pacific and Central Asian seismoactive belts. Macroseismic data on earthquakes of this region are available for the last 150 years, while instrumental seismological observations began in the mid-20th century; however, the recurrence interval of strong earthquakes can be up to several centuries and even thousands of years. In this respect, many areas of the Amur region had been believed to be nearly aseismic until earthquakes occurred there. Paleoseismogeological studies of recent years have allowed the character of Holocene displacements to be estimated for some of the main regional structures. As a result, the main tendencies of the Late Quaternary geological evolution of the region remain uncertain and the potential seismogenerating structures are not completely known. Therefore the problem of revealing new zones and periods of seismic activity is topical for the entire Amur region. The importance of this problem is related to the weak degree of study of the region by contemporary methods of active tectonics, the intensive development of engineering infrastructure, which is vulnerable to seismic impacts, and the necessity of long-term seismic forecasting. The present work provides the results of paleoseismogeological studies of the active faults in the Amur region. On the basis of new data on the magnitude potential of seismogenerating structures based on the magnitudes of historical earthquakes and instrumentally recorded ones, we have estimated the seismic effects from strong deep-focus earthquakes and the attenuation coefficients and calculated radii of the first three isoseismals for crustal earthquakes. By using the methods of statistical modeling, we distinguish the periods when seismic effects increased from earthquakes with 2 ≤ M ≤ 6. It is shown that seismic hazard assessment should take into account the dynamics of the seismic regime, caused by the change of the earthquake source depth. It is found that the epicenters of earthquakes with 5 ≤ M ≤ 6 form non-crossing seismic zones in different phases of changes in the Earth’s annual rotation. 相似文献
3.
Characteristics of the seismicity in depth ranges 0–33 and 34–70 km before ten large and great (M
w
= 7.0−9.0) earthquakes of 2000–2008 in the Sumatra region are studied, as are those in the seismic gap zones where no large
earthquakes have occurred since at least 1935. Ring seismicity structures are revealed in both depth ranges. It is shown that
the epicenters of the main seismic events lie, as a rule, close to regions of overlap or in close proximity to “shallow” and
“deep” rings. Correlation dependences of ring sizes and threshold earthquakes magnitudes on energy of the main seismic event
in the ring seismicity regions are obtained. Identification of ring structures in the seismic gap zones (in the regions of
Central and South Sumatra) suggests active processes of large earthquake preparation proceed in the region. The probable magnitudes
of imminent seismic events are estimated from the data on the seismicity ring sizes. 相似文献
4.
《Russian Geology and Geophysics》2007,48(5):442-455
The study addresses the space distribution of lithospheric density contrasts in 3D and 2D surface (spherical) sources of gravity anomalies to depths of 120 km below the geoid surface and their relationship with shallow deformation and Archean, Early Paleozoic, and Late Mesozoic geodynamic environments. The lithospheric section in northeastern Transbaikalia and the Upper Amur region includes two layers of low-density gradients attendant with low seismic velocities and low electrical resistivity. The lower layer at depths of 80–120 km is attributed to an asthenospheric upwarp that extends beneath the North Asian craton from the Emuershan volcanic belt and the Songliao basin. The concentric pattern of density contrasts in the middle and lower crust beneath the Upper Amur region may be produced by the activity of the Aldan-Zeya plume, which spatially correlates with the geometry of the asthenospheric upwarp as well as with the regional seismicity field, magnetic and heat flow anomalies, and stresses caused by large earthquakes and recent vertical crustal movements. The relationship between shallow and deep structures in the crust and upper mantle bears signature of horizontal displacement (subduction) of the lower crust of the Baikal-Vitim and Amur superterranes beneath the North Asian craton. 相似文献
5.
The Bureya orogen is a special object among the geodynamic factors determining the high seismicity of the Lower Amur region. Its location and deep structure are studied on the basis of comprehensive geophysical and tectonic data. This orogen is a low-density lithospheric domain expressed by an intensive negative gravity anomaly and Moho sunken down to 40 km depth. Within the limits of this lithospheric structure, contemporary uplifting takes place to form a meridional dome peaking at more than 2000 m altitude. The position of the orogen in the regional structure gives us grounds to think that the Bureya orogen formed in the Paleogene, at the finishing stage of tectonic block movement along the Pacific margin represented by the NE-trending strike-slip faults of the Tang Lu Fault Zone. Compression was concentrated at the triple junction between the Central Asian, Mongolian–Okhotian, and Sikhote Alin tectonic belts. The meridional orientation of the Bureya orogen is associated with the parallel elongated Cenozoic depressions in the region. The united morphotectonic system may have formed resulting from lithospheric folding under horizontal shortening in the Paleocene–Eocene. The wavelength of the Lower Amurian fold system is 250 km, which is consistent with the theoretical estimates and examples of lithospheric folds in other regions. The contemporary activation of the Bureya orogen began in the Miocene, under the effect of the Amurian Plate front moving in the northeastern direction. As a result of shortening, the meridional cluster of weak (M ≥ 2.0) earthquakes formed along the western boundary of the orogenic dome. The most intensive deformations caused another type of seismicity associated with the activation-related uplift of the mentioned orogen. As a result, the so-called Bureya seismic zone formed above the apex of the dome, and it is here that the strongest regional earthquakes (M ≥ 4.5) occur. 相似文献
6.
O. P. Pandey K. Chandrakala P. R. Reddy G. Koti Reddy 《Journal of the Geological Society of India》2009,73(4):457-468
Recent surge in intraplate seismicity has led to detailed geological and geophysical investigations, covering different continental
segments of India including seismogenic region of Latur. A synthesis of such data sets to understand the prevailing tectonic
and thermal state of the Lithosphere beneath Latur region, that witnessed a large scale human loss due to 1993 seismic activity,
has revealed shallow surfacing of denser deeper crustal segments which may have resulted due to ongoing active subsurface
tectonic activity like uplift and erosion since geological past. Below this region, Moho temperature exceeds 500°C, heat flow
input from the mantle is quite high (29–35 mW/m2) and the asthenosphere is shallow (∼100±10 km). It is suggested that stress generated by ongoing upliftment and related subcrustal
thermal anomaly is concentrating in this denser and stronger mafic crust within which earthquakes tend to nucleate. In all
likelihood, the seismic activity witnessed in the region may stem from the deep crustal/lithospheric dynamics rather than
the role of fluids at the hypocentral depth. 相似文献
7.
The volcanic complexes from the Eolian islands to the Campania/Roman regions and Tuscany further north, rest on lithospheric sectors which overlie the Adriatic continental lithosphere sinking along the Apennine-Maghrebian orogenic belt. Evidence for this stems from the melting, at mantle depth, of upper crustal materials as indicated by the widespread interaction of S-type and K-alkaline melts. The genesis of atypical magmas of the Roman Province (central-southern Italy) appears to be the result of an important block faulting and deep lithospheric rifting of the Apennine continental margin lying parallel to and above relic sinking slabs. Intermediate and deep-focus earthquakes indicate that the lithospheric slab is still seismically active under the Eolian-Calabrian area and, sporadically, at the southern end of Campania. On the other hand, in the Roman/Tuscan region, it seems to be almost inactive, few earthquakes having been located with hypocentral depths not exceeding 150 km. The analysis of the spectral content of seismic sources supports the existence of two distinct zones of lithospheric shortening in correspondence of Tuscany and South Tyrrhenian sea, which are separated by a tensional region, which extends from Latium to Calabria. The existence of distinct lithospheric slabs along the Tyrrhenian rim is supported by surface wave dispersion and scattering measurements as well as P-wave residuals, and is confirmed by the trend of long-wavelength gravity anomalies. Bidimensional gravity models along transects in the Tyrrhenian sea and italian peninsula interpreted within the geometrical constraints imposed by the results of the interpretation of aeromagnetic, seismic and seismological data have been used to delimit the spatial distribution of the density contrasts in the upper mantle which might be due to the existence of the above-mentioned lithospheric slabs. 相似文献
8.
Variations of seismic mode in the region of the Avachinsky Gulf (Kamchatka, Russia) are considered. Observed anomalies (seismic quiescence, the ring seismicity, reduction of the slope of the earthquake recurrence diagram) provide a basis to consider this region as a place of strong earthquake preparation. The Kamchatka regional catalogues of earthquakes between 1962–1995 were used in the analysis. A reduced seismicity rate is observed during 10 years in an area of 150 km × 60 km in size. During the last five years, in the vicinity of the area considered, earthquakes with M > 5 occurred three times more often than the average over thirty years. It is interpreted as ring seismicity. The block of 220 km × 220~km in size, including the quiescence zone, is characterized by a continuous decrease of the recurrence diagram slope, which has reached a minimum value for the last 33 years in this region. 相似文献
9.
Sujit Dasgupta Basab Mukhopadhyay Manoj Mukhopadhyay 《Journal of the Geological Society of India》2012,80(3):393-402
The Burmese Arc seismic activity is not uniform for its ∼ 1100 km length; only the Northern Burmese Arc (NBA) is intensely active. Six large earthquakes in the magnitude range 6.1–7.4 have originated from the NBA Benioff zone between 1954–2011, within an area of 200 × 300 km2 where the Indian plate subducts eastward to depths beyond 200 km below the Burma plate. An analysis on seismogenesis of this interplate region suggests that while the subducting lithosphere is characterized by profuse seismicity, seismicity in the overriding plate is rather few. Large earthquakes occurring in the overriding plate are associated with the backarc Shan-Sagaing Fault (SSF) further east. The forecasting performance of the Benioff zone earthquakes in NBA as forerunner is analysed here by: (i) spatial earthquake clustering, (ii) seismic cycles and their temporal quiescence and (iii) the characteristic temporal b-value changes. Three such clusters (C1–C3) are identified from NBA Benioff Zones I & II that are capable of generating earthquakes in the magnitude ranges of 7.38 to 7.93. Seismic cycles evidenced for the Zone I displayed distinct quiescence (Q1, Q2 and Q3) prior to the 6th August 1988 (M 6.6) earthquake. Similar cycles were used to forecast an earthquake (Dasgupta et al. 2010) to come from the Zone I (cluster C1); which, actually struck on 4 February 2011 (M 6.3). The preparatory activity for an event has already been set in the Zone II and we speculate its occurrence as a large event (M > 6.0) possibly within the year 2012, somewhere close to cluster C3. Temporal analysis of b-value indicates a rise before an ensuing large earthquake. 相似文献
10.
We present the first seismic image of the upper mantle beneath the active intraplate Changbai volcano in Northeast Asia determined by teleseismic travel time tomography. The data are measured at a new seismic network consisting of 19 portable stations and 3 permanent stations. Our results show a columnar low-velocity anomaly extending to 400-km depth with a P-wave velocity reduction of up to 3%. High velocity anomalies are visible in the mantle transition zone, and deep-focus earthquakes occur at depths of 500–600 km under the region, suggesting that the subducting Pacific slab is stagnant in the transition zone, as imaged clearly by global tomography. These results suggest that the intraplate Changbai volcano is not a hotspot like Hawaii but a kind of back-arc volcano related to the deep subduction and stagnancy of the Pacific slab under Northeast Asia. 相似文献
11.
A. T. Sorokina A. P. Sorokin M. A. Serov A. A. Popov 《Russian Journal of Pacific Geology》2011,5(1):13-25
The results of long-term studies of the neotectonic processes and related phenomena such as the Earth’s interior degassing,
the fluid discharge, and the high seismicity in the zone of interaction between the Amur and Okhotsk lithospheric plates at
the transition between the Verkhnii and Srednii Amur regions were used for defining the separate structural blocks with different
geodynamics and analyzing their relations with the seismic events during the periods of high seismic activity and quiescence.
The heliometric and atmochemical studies in the Zeya-Bureya basin revealed zones of high permeability. Long-term observations
of the fluid dynamics at the Konstantinovka mineral water deposit demonstrate a correlation between the variations in the
water-soluble helium contents and the changes in the stress-deformed state of the blocks located up to 200 km away from regime
observation sites. 相似文献
12.
Abstract: 3–D velocity images of the crust beneath the northern margin of the North China Plate have been constructed using P-wave travel time residuals of the latest earthquakes, with the data supplied by Chinese seismic networks.
The seismic image results indicate that there is a lateral heterogeneity in the crust beneath the northern part of the North China block. The velocity images of the upper crust show features closely related to the tectonic features on the surface. It can be seen from these velocity images of the vertical sections, and from the horizontal slice images at depths of 11 and 16 km that there exist East-West and North-East structures. The images indicate that the juncture zone of basin–and–range terrain is between the blue-colored high–velocity block corresponding to the Yanshan mountain range that developed during the Yanshan period in northwest Beijing and the green low-velocity area corresponding to the North China basin in southeast Beijing (Fig. 5). The juncture zone between high-velocity and low–velocity, and EW and NE fault zones have significant ore-control effects. From the chart of epicenters in the northern region of North China, we find that the epicenters of earthquakes are almost entirely distributed within the NE strip. Almost all major earthquakes took place in the transition strip between the high and low-velocity zones in the crust. The distribution of epicenters also reflects the strikes of known NE–faults. From the image sections along the latitude, we find that in the area between 114.0 E –118.0 E , there is a blue high-velocity block standing upright from the Moho to the upper crust (Fig. 6), from which can be deduced that some materials such as magma moved upward from the upper mantle during the history of its geological development. 相似文献
The seismic image results indicate that there is a lateral heterogeneity in the crust beneath the northern part of the North China block. The velocity images of the upper crust show features closely related to the tectonic features on the surface. It can be seen from these velocity images of the vertical sections, and from the horizontal slice images at depths of 11 and 16 km that there exist East-West and North-East structures. The images indicate that the juncture zone of basin–and–range terrain is between the blue-colored high–velocity block corresponding to the Yanshan mountain range that developed during the Yanshan period in northwest Beijing and the green low-velocity area corresponding to the North China basin in southeast Beijing (Fig. 5). The juncture zone between high-velocity and low–velocity, and EW and NE fault zones have significant ore-control effects. From the chart of epicenters in the northern region of North China, we find that the epicenters of earthquakes are almost entirely distributed within the NE strip. Almost all major earthquakes took place in the transition strip between the high and low-velocity zones in the crust. The distribution of epicenters also reflects the strikes of known NE–faults. From the image sections along the latitude, we find that in the area between 114.0 E –118.0 E , there is a blue high-velocity block standing upright from the Moho to the upper crust (Fig. 6), from which can be deduced that some materials such as magma moved upward from the upper mantle during the history of its geological development. 相似文献
13.
R. B. S. Yadav J. N. Tripathi D. Shanker B. K. Rastogi M. C. Das Vikas Kumar 《Natural Hazards》2011,56(1):145-167
The return periods and occurrence probabilities related to medium and large earthquakes (M
w
4.0–7.0) in four seismic zones in northeast India and adjoining region (20°–32°N and 87°–100°E) have been estimated with
the help of well-known extreme value theory using three methods given by Gumbel (1958), Knopoff and Kagan (1977) and Bury (1999). In the present analysis, the return periods, the most probable maximum magnitude in a specified time period and probabilities
of occurrences of earthquakes of magnitude M ≥ 4.0 have been computed using a homogeneous and complete earthquake catalogue prepared for the period between 1897 and 2007.
The analysis indicates that the most probable largest annual earthquakes are close to 4.6, 5.1, 5.2, 5.5 and 5.8 in the four
seismic zones, namely, the Shillong Plateau Zone, the Eastern Syntaxis Zone, the Himalayan Thrusts Zone, the Arakan-Yoma subduction
zone and the whole region, respectively. The most probable largest earthquakes that may occur within different time periods
have been also estimated and reported. The study reveals that the estimated mean return periods for the earthquake of magnitude
M
w
6.5 are about 6–7 years, 9–10 years, 59–78 years, 72–115 years and 88–127 years in the whole region, the Arakan-Yoma subduction
zone, the Himalayan Thrusts Zone, the Shillong Plateau Zone and the Eastern Syntaxis Zone, respectively. The study indicates
that Arakan-Yoma subduction zone has the lowest mean return periods and high occurrence probability for the same earthquake
magnitude in comparison to the other zones. The differences in the hazard parameters from zone to zone reveal the high crustal
heterogeneity and seismotectonics complexity in northeast India and adjoining regions. 相似文献
14.
The characteristics of seismicity prior to the series of eight very strong earthquakes (M
w
= 7.0–9.0) in Northeast Japan are discussed. Ring seismicity structures that appeared prior to all eight events in two depth
ranges of 0–33 and 34–70 km are identified. The epicenters of the main shocks were located near areas of crossing or touching
of shallow and deep rings. It was shown that the sizes of shallow rings and threshold magnitudes corresponding to seismicity
rings grow with the energy of the main shocks. It was noted that the prognosis with respect to the place and magnitude of
the catastrophic earthquake on March 11, 2011, had been made before it based on the data obtained prior to July 1, 2009. Use
of the new data obtained prior to March 10, 2011, enabled us to specify this prognosis significantly. We obtained correlation
dependences of threshold magnitudes on the energy of the main shocks (with a high correlation coefficients). It was shown
that the duration of the period for seismicity rings to emerge in the considered region nearly did not depend on magnitude.
The nature of annular structures and the possibility of application of their parameters for prognosis of strong earthquakes
were discussed. 相似文献
15.
What triggers Koyna region earthquakes? Preliminary results from seismic tomography digital array 总被引:1,自引:0,他引:1
S. S. Rai Sunil K. Singh P. V. S. S. Rajagopal Sarma D. Srinagesh K. N. S. Reddy K. S. Prakasam Y. Satyanarayana 《Journal of Earth System Science》1999,108(1):1-14
The cause for prolific seismicity in the Koyna region is a geological enigma. Attempts have been made to link occurrence of
these earthquakes with tectonic strain as well as the nearby reservoirs. With a view to providing reliable seismological database
for studying the earth structure and the earthquake process in the Koyna region, a state of the art digital seismic network
was deployed for twenty months during 1996–97. We present preliminary results from this experiment covering an area of 60
× 80 km2 with twenty seismic stations. Hypocentral locations of more than 400 earthquakes confined to 11×25 km2 reveal fragmentation in the seismicity pattern — a NE — SW segment has a dip towards NW at approximately 45°, whilst the
other two segments show a near vertical trend. These seismic segments have a close linkage with the Western Ghat escarpment
and the Warna fault. Ninety per cent of the seismicity is confined within the depth range of 3–10 km. The depth distribution
of earthquakes delimits the seismogenic zone with its base at 10 km indicating a transition from an unstable to stable frictional
sliding regime. The lack of shallow seismicity between 0 and 3 km indicates a mature fault system with well-developed gouge
zones, which inhibit shallow earthquake nucleation. Local earthquake travel time inversion for P- and S-waves show ≈ 2% higher
velocity in the seismogenic crust (0–10 km) beneath the epicentral tract relative to a lower velocity (2–3%) in the adjoining
region. The high P- and S-wave velocity in the seismogenic crust argues against the presence of high pressure fluid zones
and suggests its possible linkage with denser lithology. The zone of high velocity has been traced to deeper depths (≈ 70
km) through teleseismic tomography. The results reveal segmented and matured seismogenic fault systems in the Koyna region
where seismicity is possibly controlled by strain build up due to competent lithology in the seismic zone with a deep crustal
root. 相似文献
16.
Possible long-term seismic behaviour of the Northern strand of the North Anatolian Fault Zone, between western extreme of
the 1999 İzmit rupture and the Aegean Sea, after 400 AD is studied by examining the historical seismicity, the submarine fault
mapping and the paleoseismological studies of the recent scientific efforts. The long-term seismic behaviour is discussed
through two possible seismicity models devised from M
S ≥ 7.0 historical earthquakes. The estimated return period of years of the fault segments for M1 and M2 seismic models along
with their standard deviations are as follows: F4 segment 255 ± 60 and 258 ± 12; F5 segment 258 ± 60 and 258 ± 53; F6 segment
258 ± 60 and 258 ± 53; F7 segment 286 ± 103 and 286 ± 90; F8 segment 286 ± 90 and 286 ± 36. As the latest ruptures on the
submarine segments have been reported to be during the 1754–1766 earthquake sequence, and the 1912 mainshock rupture has been
evidenced to extend almost all over the western part of the Sea of Marmara, our results imply imminent seismic hazard and,
considering the mean recurrence time, a large earthquake to strike the eastern part of the Sea of Marmara in the next two
decades. 相似文献
17.
Cenozoic Magmatism of the North-Eastern Eurasian Margin: The Role of Lithosphere Versus Asthenosphere 总被引:6,自引:1,他引:6
Sikhote-Alin and Sakhalin are located in the Russian Far Eastflank of the northernmost part of the Sea of Japan. Magmatismin this region preceded, was concurrent with, and continuedafter the extension and sea-floor spreading (2518 Ma)that formed the Sea of Japan. Among the Sikhote-Alin and Sakhalinvolcanic suites, EoceneOligocene (5524 Ma) lavasare characterized by greater large ion lithophile element andrare earth element enrichments compared with EarlyMid-Miocene(2315 Ma) tholeiites, and also show a depletion in highfield strength elements (HFSE). The geochemical characteristicsof the EoceneOligocene and EarlyMid-Miocene basaltsare consistent with migration of the locus of magma generationbeneath the Sikhote-Alin and Sakhalin areas from subduction-modifiedlithospheric mantle into mid-ocean ridge basalt (MORB)-sourceasthenosphere as spreading in the Sea of Japan progressed. Mid-MiocenePliocene(145 Ma) lavas, erupted following the opening of theSea of Japan, include alkaline and sub-alkaline basalts withwide ranges in trace-element abundances, varying between twodistinct end-members: (1) volumetrically minor alkaline basaltswith ZrNb and SrNbPb isotope compositionssimilar to asthenosphere-derived, intra-platehotspotbasalts from eastern China; (2) more abundant, lithosphere-derived,low-alkali tholeiites depleted in HFSE. The similarity of isotopicsignatures coupled with systematically different rare earthelement (REE) abundances in the Mid-MiocenePliocene andChinese basalts are best modeled by similar extents of meltingof spinel lherzolite and garnet lherzolite, respectively. TheMid-MiocenePliocene alkali basalts were generated bysmall degrees of partial melting of hot asthenosphere beneatha thin lithospheric lid; the thin lithospheric mantle beneaththe Sikhote-Alin and Sakhalin region resulted from heating andextension associated with the opening of the Sea of Japan. KEY WORDS: north-eastern Eurasian margin; Sikhote-AlinSakhalin; Japan Sea opening; subcontinental lithosphere; asthenosphere 相似文献
18.
S. V. Trofimenko 《Russian Journal of Pacific Geology》2016,10(6):427-434
The spatial distribution of the epicenters and hypocenters is analyzed for earthquakes of 2 ≤ M < 6 that occurred in the northeastern segment of the Amur Plate in two phases of changes in the angular speed of the Earth’s rotation. Groups of seismic events in the magnitude interval of 5 ≤ M < 6 are distinguished in the form of NE-trending seismic clusters regularly alternating along the plane of latitude. The seismic clusters are up to 1500 km long and 180–240 km wide and cover the seismic zones with different geodynamic and seismotectonic conditions of seismicity origination. In terms of the epicentral distributions for earthquakes with 2 ≤ M < 4, seismic activity zones are distinguished; these zones are seen as seimolineaments coupling the Tan Lu seismic zones and the eastern flanks of the latitudinal seismic zones. A scheme of distinguishing the compression and extension zones from the spatial clusters of earthquakes with 5 ≤ M < 6 in two phases of changes in the angular speed of the Earth’s rotation is proposed. This scheme satisfactorily agrees with the model of seismotectonic reconstructions of the compression–extension fields and axes. 相似文献
19.
Seiichi Miura Narumi Takahashi Ayako Nakanishi Tetsuro Tsuru Shuichi Kodaira Yoshiyuki Kaneda 《Tectonophysics》2005,407(3-4):165-188
The Japan Trench subduction zone, located east of NE Japan, has regional variation in seismicity. Many large earthquakes occurred in the northern part of Japan Trench, but few in the southern part. Off Miyagi region is in the middle of the Japan Trench, where the large earthquakes (M > 7) with thrust mechanisms have occurred at an interval of about 40 years in two parts: inner trench slope and near land. A seismic experiment using 36 ocean bottom seismographs (OBS) and a 12,000 cu. in. airgun array was conducted to determine a detailed, 2D velocity structure in the forearc region off Miyagi. The depth to the Moho is 21 km, at 115 km from the trench axis, and becomes progressively deeper landward. The P-wave velocity of the mantle wedge is 7.9–8.1 km/s, which is typical velocity for uppermost mantle without large serpentinization. The dip angle of oceanic crust is increased from 5–6° near the trench axis to 23° 150 km landward from the trench axis. The P-wave velocity of the oceanic uppermost mantle is as small as 7.7 km/s. This low-velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process. By comparison with the seismicity off Miyagi, the subduction zone can be divided into four parts: 1) Seaward of the trench axis, the seismicity is low and normal fault-type earthquakes occur associated with the destruction of oceanic lithosphere. 2) Beneath the deformed zone landward of the trench axis, the plate boundary is characterized as a stable sliding fault plain. In case of earthquakes, this zone may be tsunamigenic. 3) Below forearc crust where P-wave velocity is almost 6 km/s and larger: this zone is the seismogenic zone below inner trench slope, which is a plate boundary between the forearc and oceanic crusts. 4) Below mantle wedge: the rupture zones of thrust large earthquakes near land (e.g. 1978 off Miyagi earthquake) are located beneath the mantle wedge. The depth of the rupture zones is 30–50 km below sea level. From the comparison, the rupture zones of large earthquakes off Miyagi are limited in two parts: plate boundary between the forearc and oceanic crusts and below mantle wedge. This limitation is a rare case for subduction zone. Although the seismogenic process beneath the mantle wedge is not fully clarified, our observation suggests the two possibilities: earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab. 相似文献
20.
长白山火山的起源和太平洋俯冲板块之间的关系 总被引:6,自引:0,他引:6
近年来,尽管不同学科通过不同手段对长白山火山进行过广泛研究,然而,目前人们对它的起源仍不清楚。利用全球地震层析成像和区域层析成像结果,综合分析了长白山火山的起源。结果表明,它的起源既不同于夏威夷等板内热点火山,也不同于日本等岛弧火山,而是一种与太平洋俯冲板块在地幔转换带内的滞留和深部脱水等过程密切相
关的弧后板内火山。 相似文献