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1.
GPS observations in the Western Bohemia/Vogtland earthquake swarm region revealed indications of horizontal displacements
of low amplitude, and no clear long-term trend in 1993–2007. On the other hand, in 1998–2001 there was relatively significant
active movement along NNE-SSW oriented line that we called the “Cheb-Kraslice GPS Boundary” (ChKB), identical with an important
limitation of earthquake activity. The most impressive were dextral (right-lateral) movements in the 1998–1999 period followed
by reverse sinistral (left-lateral) movements in 1999–2000 that correlate with prevailing motion defined by fault plane solutions
of the Autumn 2000 earthquake swarm. Before the February 2004 micro-swarm, two points located on opposite sides of the Mariánské
Lázně fault showed extension in the order of about 7 mm in the same NNE-SSW direction of ChKB. The new NOKO permanent GPS
station in Novy Kostel showed the peak-to-peak vertical changes up to 10 mm before and during the February 2007 micro-swarm.
Annual precise levelling campaigns in the local network around Novy Kostel revealed regular vertical displacements during
the 1994, 1997 and 2000 earthquake swarms. The points around the Novy Kostel seismological station showed uplift during the
active periods, including the micro-swarm February 2004. However, no such indication was observed on levelling points in the
period of the February 2007 swarm. Long-term vertical displacements depend on the same direction NNE-SSW (ChKB) as the GPS
displacements. Both geodetic techniques have revealed oscillating displacements, GPS horizontal, and levelling vertical, rather
than any long-term trends in the study period 1993–2007. The displacements exhibited significant spatial and temporal relation
to tectonic activity (earthquake swarms) including their coincidence with the seismologically determined sense of motion along
the fault plane during earthquakes. 相似文献
2.
Vladimir Schenk Zdeňka Schenkova Zuzana Jechumtálová 《Studia Geophysica et Geodaetica》2009,53(3):329-341
In West Bohemia in the period of 2003–2005 five permanent GPS stations were established to detect local movement trends. Their
mutual position changes were determined from time series of GPS observations and were associated with seismic, gravity, and
geo-scientific data related to the geodynamics of the West Bohemian region. Knowledge of local physical processes based on
spatial and time earthquake occurrences, focal mechanisms of main events, stress and strain fields set up a tool for recent
seismotectonic analyses. The permanent GPS measurements bring independent effective phenomenon, direct monitoring of site
movements. The movements detected by our GPS stations evidenced WSW-ENE extension with subsiding trends in the western part
of the Cheb Basin and the Smrčiny Mts. Besides, there were monitored dextral movements along the Mariánské Lázně tectonic
fault zone (MLF). A comparison of results with previous data formed a presumption that an antithetic stress pattern has to
exist inside the inner part of the MLF tectonic zone. This antithetic stress can explain the coexistence of dextral and sinistral
movements on individual tectonic elements in the West Bohemian area. 相似文献
3.
《Journal of Geodynamics》2003,35(1-2):5-32
The earthquake distribution pattern of Central Europe differs systematically from the neighbouring areas of NW and southern Europe regarding the fault plane kinematics. Within a belt between the French Massif Central and the northern part of the Bohemian Massif (1000 km) sinistral faulting along N-S zones dominates on the contrary to the Alps and their foreland with common bookshelf shears. One of the prominent N-S structures is the Regensburg-Leipzig-Rostock Zone (A) with several epicentral areas, where the main seismic center occurs in the northern Cheb Basin (NW Bohemia). The study demonstrates new structural results for the swarm-quake region in NW-Bohemia, especially for the Nový Kostel area in the Cheb Basin. There the N-S-trending newly found Počatky-Plesná zone (PPZ) is identical with the main earthquake line. The PPZ is connected with a mofette line between Hartušov and Bublák with evidence for CO2 degassing from the subcrustal mantle. The morphologically more prominent Mariánské Lázně fault (MLF) intersects the PPZ obliquely under an acuate angle. In the past the MLF was supposed to be the tectonic structure connected with the epicentral area of Nový Kostel. But evidence from the relocated hypocentres along the PPZ (at 7–12 kms depth) indicate that the MLF is seismically non-active. Asymmetric drainage patterns of the Cheb Basin are caused by fault related movement along Palaeozoic basement faults which initiate a deformation of the cover (Upper Pliocene to Holocene basin filling). The PPZ forms an escarpment in Pliocene and Pleistocene soft rock and is supposingly acting as an earthquake zone since late Pleistocene time. The uppermost Pleistocene of 0.12–0.01 Ma deposited only in front of the fault scarp dates the fault activity. The crossing faults envelope crustal wedges under different local stress conditions. Their intersection line forms a zone beginning at the surface near Nový Kostel, dipping south with increasing depth, probably down to about 12 km. The intersection zone represents a crustal anomaly. There fault movements can be blocked up and peculiar stress condition influence the behaviour of the adjacent crust. An ENE-WNW striking dextral wrench fault was detected which is to expect as kinematic counterpart to the ca. N-S striking sinistral shear zones. Nearly E-W striking fracture segments were formerly only known as remote sensing lineaments or as joint density zones. The ENE shear zone is characterized by a set of compressional m-scale folds and dm-scale faults scattered within a 20 m wide wrench zone. It is built up of different sets of cleavage-like clay plate pattern of microscopical scale. The associated shear planes fit into a Riedel shear system. One characteristic feature are tiny channels of micrometer scale. They have originated after shear plane bending and are the sites of CO2 mantle degassing. 相似文献
4.
Derived gravity field of the seismogenic upper crust of SE Germany and West Bohemia and its comparison with seismicity 总被引:2,自引:2,他引:0
The gravity field of the seismogenic upper crust was derived from the Bouguer gravity map by applying the Butterworth high-pass
filter in the wave-number domain. The cutoff wavelength of the filter was 110 km, to pass the gravity signals of structures
within the 18 km thick seismogenic layer. The derived residual gravity map reveals potential stress concentrating structures,
which may cause seismicity provided they lie within the existing zones of weakness. Furthermore we derived a shaded relief
map of the horizontal gravity gradient, which highlighted the tectonic lines accompanied by density contrast. The directional
analysis of this map shows three dominant strike directions. The most prominent one is “the Hercynian” NW-SE strike direction
represented by the Franconian Line, the Gera-Jáchymov Fault Zone and the Elbe Zone. The second dominant strike is the Rhenisch
NNE-SSW trending represented by the Upper Rhine Graben Zone, Rheinsberg-Heldburg Line and several Proterozoic volcanic belts
in the Teplá-Barrandien Unit. The third pronounced trending of the ENE-WSW direction is represented by the Erzgebirge and
Eger Graben gravity low. The N-S trending Rostock-Leipzig-Regensburg Zone (Pritzwalk-Naab Lineament) is not distinctly reflected
in the derived gravity maps, although many fault segments have a meridian direction.
The relative reactivation potential of some pre-existing fault systems identified in the gravity map was studied with respect
to the wide range of the recent stress configuration determined in the West Bohemia/Vogtland region. The resulting diagrams
show that the steep NNW-SSE to N-S faults (represented by some segments of the Mariánské Lázně Fault Zone) are oriented favourably
for reactivation. On the contrary, the orientation of the ENE-WSW faults limiting the Eger Graben (Litoměřice Fault, etc.)
is unfavourable for reactivation for all dip values. 相似文献
5.
Vratislav Blecha Tomáš Fischer Petr Tábořík Jan Vilhem Radek Klanica Jan Valenta Petra Štěpančíková 《Studia Geophysica et Geodaetica》2018,62(4):660-680
The western part of the Bohemian Massif hosts an intersection of two regional fault zones, the SW-NE trending Oh?e/Eger Graben and the NNW-SSE trending Mariánské Lázně Fault, which has been reactivated several times in the geological history and controlled the formation of the Tertiary Cheb Basin. The broader area of the Cheb Basin is also related to permanent seismic activity of ML 3+ earthquake swarms. The Eastern Marginal Fault of the Cheb Basin (northern segment of the Mariánské Lázně Fault) separates the basin sediments and underlying granites in the SW from the Kru?né Hory/Erzgebirge Mts. crystalline unit in the NE. We describe a detailed geophysical survey targeted to locating the Eastern Marginal Fault and determining its geometry in the depth. The survey was conducted at the Kopanina site near the Nový Kostel focal zone, which shows the strongest seismic activity of the whole Western Bohemia earthquake swarm region. Complex geophysical survey included gravimetry, electrical resistivity tomography, audiomagnetotellurics and seismic refraction. We found that the rocks within the Eastern Marginal Fault show low resistivity, low seismic velocity and density, which indicates their deep fracturing, weathering and higher water content. The dip of the fault in shallow depths is about 60° towards SW. At greater depths, the slope turns to subvertical with dip angle of about 80°. Results of geoelectrical methods show blocky fabric of the Cheb Basin and deep weathering of the granite bedrock, which is consistent with geologic models based on borehole surveys. 相似文献
6.
Vratislav Blecha Miroslav Štemprok Tomáš Fischer 《Studia Geophysica et Geodaetica》2009,53(3):295-314
We examined the shape of the Late Variscan Karlovy Vary granite massif located south of the Ohre/Eger graben in Northern Bohemia
by reinterpretation of existing gravity data on two perpendicular profiles. The granite body of about 360 km2 total outcrop size has the elongation ratio 0.35 with the major axis trending NE-SW. The SW part of the body was crossed
in the nineties by the seismic profile 9HR which localized the bottom of granites in a depth of about 10 km. We used this
value as a reference datum in our gravity profiles. We positioned one of our profiles along the seismic profile 9HR and the
other one perpendicularly, i.e. parallel with the elongation of the outcrop surface. We interpret the shape of the main granite
body in the vicinity of Karlovy Vary as a continuous desk whose floor is horizontal (or subhorizontal) and varies along its
whole extension about a depth of 10 km. This thickness is approximately identical with that of the Saxothuringian nappes imaged
by seismic reflection. The near surface upper contact of the granite body is mildly inclined, and outward dipping. It changes
to steep sides or inward inclined contacts in deeper levels. The Lesny-Lysina (Kynžvart) massif is a separate granite body
about 324 km thick, not continuously connected with the main Karlovy Vary massif. The gravity curve suggests that granites
often enclose in their endocontact large blocks of country metasediments or metabasites the existence of which is partly evidenced
by their outcrops outside the line of the profile. The granite body is found density-homogenous. Minor density differences
between granite varieties are caused mainly by more intense hydrothermal alterations in younger suite granites. We interpret
vertical conduits for the ascent of granitic magmas to be parallel to the Jáchymov-Gera and Ohře (Eger) lineaments or the
Mariánské Lázně fault zone as indicated by the elongation of some outcrops. However, they are not clearly imaged from the
gravity data. The effect of the depression of the Sokolov basin along the faults parallel with the Ohře (Eger) lineament is
shallow and it is not indicated by any change in the floor depth of the granite body. Comparison of the seismicity distribution
suggests that the hypocenters occur mostly outside of the granite bodies or near their contact with the country rock. 相似文献
7.
Continuous gas monitoring in the West Bohemian earthquake area,Czech Republic: First results 总被引:1,自引:1,他引:0
Eckhard Faber Josef Horálek Alena Boušková Manfred Teschner Ulrich Koch Jürgen Poggenburg 《Studia Geophysica et Geodaetica》2009,53(3):315-328
Two stations monitoring concentrations of carbon dioxide and radon in soil gas (Oldřišská and Novy Kostel) and one station
monitoring flow of carbon dioxide at a mofette (Soos) have been operated in the area of the West Bohemian earthquake swarms.
We present preliminary results obtained on the base of four-year observations. We found that data are not influenced considerably
by barometric pressure. Although the CO2 concentration varies greatly, the long-term trends at stations Oldřišská and Novy Kostel are similar, which indicates that
the CO2 flow is controlled by common geogenic processes. Also temporal trends of CO2 and Rn concentrations in soil gas at individual stations are analogous. We found diurnal variations of both CO2 concentration in soil gas and the CO2 flow at mofettes due to the earth tides. A response to tides of semi-diurnal period is insignificant in CO2 concentration and only weak in the CO2 flow. We also examined possible pre-seismic, co-seismic and post-seismic effects of the intensive 2008 earthquake swarm on
the CO2 concentration at Oldřišská and Novy Kostel, and on the CO2 flow at Soos. However, all potential indications were insignificant and there has not been proven any influence of the swarm
on the CO2 concentration as well as on the CO2 flow. Nevertheless, a gradual decrease of amplitudes of diurnal variations before the swarm and the lowest amplitudes during
the swarm is a noteworthy phenomenon, which might indicate the strain changes of the rock associated with earthquake swarm. 相似文献
8.
Shengzao Chen 《地震学报(英文版)》1992,5(4):749-758
Seismotectonic characteristics and its relationships with crustal structure have been analyzed in the lower Yangzi—South Yellow
Sea area. The finite element method is employed to evaluate the stress-strain status of the lithosphere, and the dynamic origin
of earthquakes is discussed. The moderate-weak earthquake division is tectonically controlled by three first-degree faults
in the Hangzhou bay—Qinling, Tancheng—Lujiang, and the Yangzi River mouth—Jizhou island. The earthquake frequency is higher
than 70% in the major hypocentral layer of the crust at a depth of 5 to 15 km of which the highest frequency particularly
emerges at a depth of 10 to 15 km, and generally, the depth ranges from 5 to 20 km in the predominant hypocentral layer. The
hypocentral layer is superimposed in the crustal magnetosphere with the mid-crustal low density layer. The results from the
finite element analysis show that the maximum horizontal displacements appear in the hypocentral layer of the crust, and that
the radial hypocentral zones on the flanks of the anomalous mantle, accompanied by the faults or fractured zones, correspond
to the gradient zones of the major principal stresses and strains varying within the lithosphere. Therefore, we could consider
the mechanism of the decoupling-drift of the lithosphere and the crustal sliding or detachment, from the continent to the
sea, as a main dynamogenesis of the earthquakes in the area studied.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 164–171, 1992.
This research was supported by the China National Post-Doctoral Research Foundation in part. Some contents on the aeromagnetic
anomalies and their mathematical processes are deleted in revision. 相似文献
9.
Summary Systematic observations of natural seismic activity in the West-Bohemian earthquake-swarm region began at two autonomous seismological
stations of the Geophysical Institute, the digital station Novy Kostel (NKC) and the analogue station Skalná (SKC), in May
1986 and December 1989, respectively. This paper presents the station data of NKC and SKC, the method of processing the records,
and the database structure. It also includes the interpretation of observations made at these stations in the period 1986–1993.
It was found that the seismic activity in the West Bohemian region, in the Vogtland (Saxony) and NE Bavaria was continuous.
Between two strong earthquake swarms, the energy in this area was released in the form of a large number of micro-earthquakes
of a markedly swarm-like nature, mostly concentrated in six focal regions. 相似文献
10.
《Journal of Geodynamics》2008,45(3-5):149-159
Locations of the Eger Rift, Cheb Basin, Quaternary volcanoes, crustal earthquake swarms and exhalation centers of CO2 and 3He of mantle origin correlate with the tectonic fabric of the mantle lithosphere modelled from seismic anisotropy. We suggest that positions of the seismic and volcanic phenomena, as well as of the Cenozoic sedimentary basins, correlate with a “triple junction” of three mantle lithospheres distinguished by different orientations of their tectonic fabric consistent within each unit. The three mantle domains most probably belong to the originally separated microcontinents – the Saxothuringian, Teplá-Barrandian and Moldanubian – assembled during the Variscan orogeny. Cenozoic extension reactivated the junction and locally thinned the crust and mantle lithosphere. The rigid part of the crust, characterized by the presence of earthquake foci, decoupled near the junction from the mantle probably during the Variscan. The boundaries (transitions) of three mantle domains provided open pathways for Quaternary volcanism and the ascent of 3He- and CO2-rich fluids released from the asthenosphere. The deepest earthquakes, interpreted as an upper limit of the brittle–ductile transition in the crust, are shallower above the junction of the mantle blocks (at about 12 km) than above the more stable Saxothuringian mantle lithosphere (at about 20 km), probably due to a higher heat flow and presence of fluids. 相似文献
11.
The vertical structure of the crustal block of the Songliao Basin can be divided into upper, middle and low Earth’s crust
according to density. There is an about 3-km-thick low density interval between the upper crust and the middle crust. This
interval may be a magma chamber accumulated in crust by “fluid phase” which is precipitated and separated from upper mantle
meltmass. The abiogenetic natural gas, other gaseous mass and hydrothermal fluids are provided to the Songliao rifted basin
through crustal faults and natural earthquakes. This is a basic condition to form an abiogenetic gas reservoir in the Songliao
Basin. On both flanks of the upper crust (or named basin basement) fault there are structural traps in and above the basement
and unconformity surface or lateral extended sand, which contains communicated pores, as migration pathway and natural gas
reservoir; up to gas reservoirs there is shale as enclosed cap rock, and the suitable arrangement of these conditions is the
basic features of abiogenetic gas reservoir.
Project supported by the National Natural Sc~ence Foundation of China. 相似文献
12.
Intraplate seismicity in the western Bohemian Massif (central Europe): A possible correlation with a paleoplate junction 总被引:5,自引:0,他引:5
Locations of the Eger Rift, Cheb Basin, Quaternary volcanoes, crustal earthquake swarms and exhalation centers of CO2 and 3He of mantle origin correlate with the tectonic fabric of the mantle lithosphere modelled from seismic anisotropy. We suggest that positions of the seismic and volcanic phenomena, as well as of the Cenozoic sedimentary basins, correlate with a “triple junction” of three mantle lithospheres distinguished by different orientations of their tectonic fabric consistent within each unit. The three mantle domains most probably belong to the originally separated microcontinents – the Saxothuringian, Teplá-Barrandian and Moldanubian – assembled during the Variscan orogeny. Cenozoic extension reactivated the junction and locally thinned the crust and mantle lithosphere. The rigid part of the crust, characterized by the presence of earthquake foci, decoupled near the junction from the mantle probably during the Variscan. The boundaries (transitions) of three mantle domains provided open pathways for Quaternary volcanism and the ascent of 3He- and CO2-rich fluids released from the asthenosphere. The deepest earthquakes, interpreted as an upper limit of the brittle–ductile transition in the crust, are shallower above the junction of the mantle blocks (at about 12 km) than above the more stable Saxothuringian mantle lithosphere (at about 20 km), probably due to a higher heat flow and presence of fluids. 相似文献
13.
Deep-seated materials from lithosphere are the ba- sic parameters and the foundation for geodynamic and continental dynamic studies. Division of lithosphere types and their deep-seated materials and structure can provide important evidence in interpreting the com- plex phenomena derived from the processes of forma- tion and evolution of continents, in evaluating the mineral resource potential, in predicting geological disasters and in the research of the continental dy- namic process. Huge lit… 相似文献
14.
The West Bohemia and adjacent Vogtland are well known for quasi-periodical earthquake swarms persisting for centuries. The seismogenic area near Nový Kostel involved about 90 % of overall earthquake activity clustered here in space and time. The latest major earthquake swarm took place in August–September 2011. In 1994 and 1997, two minor earthquake swarms appeared in another location, near Lazy. Recently, the depth-recursive tomography yielded a velocity image with an improved resolution along the CEL09 refraction profile passing between these swarm areas. The resolution, achieved in the velocity image and its agreement with the inverse gravity modeling along the collateral 9HR reflection profile, enabled us to reveal the key structural background of these West Bohemia earthquake swarms. The CEL09 velocity image detected two deeply rooted high-velocity bodies adjacent to the Nový Kostel and Lazy focal zones. They correspond to two Variscan mafic intrusions influenced by the SE inclined slab of Saxothuringian crust that subducted beneath the Teplá-Barrandian terrane in the Devonian era. In their uppermost SE inclined parts, they roof both focal zones. The high P-wave velocities of 6,100–6,200 m/s, detected in both roofing caps, indicate their relative compactness and impermeability. The focal domains themselves are located in the almost gradient-free zones with the swarm foci spread near the axial planes of profound velocity depressions. The lower velocities of 5,950–6,050 m/s, observed in the upper parts of focal zones, are indicative of less compact rock complexes corrugated and tectonically disturbed by the SE bordering magma ascents. The high-velocity/high-density caps obviously seal the swarm focal domains because almost no magmatic fluids of mantle origin occur in the Nový Kostel and Lazy seismogenic areas of the West Bohemia/Vogtland territory, otherwise rich in the mantle-derived fluids. This supports the hypothesis of the fluid triggering of earthquake swarms. The sealed focal domains retain ascending magmatic fluids until their critical pressure and volumes accumulated cause rock micro-fractures perceived as single earthquake bursts. During a swarm period, the focal depths of these sequential events become shallower while their magnitudes grow. We assume that coalescence of the induced micro-fractures forms temporary permeability zones in the final swarm phase and the accumulated fluids release into the overburden via the adjacent fault systems. The fluid release usually occurs after the shallowest events with the strongest magnitudes ML > 3. The seasonal summer declines of hydrostatic pressure in the Cheb Basin aquifer system seem to facilitate and trigger the fluid escape as happened for the 2000, 2008, and 2011 earthquake swarms. The temporary fluid release, known as the valve-fault action, influences the surface aquifer systems in various manners. In particular, we found three quantities, the strain, mantle-derived 3He content in CO2 surface sources and ground water levels, which display a 3–5 months decline before and then a similar restoration after each peak earthquake during the swarm activities. The revealed structure features are particularly important since the main Nový Kostel earthquake swarm area is proposed as a site for the ICDP project, ‘Eger Rift Drilling’. 相似文献
15.
The ratio of P- to S-wave velocities, VP/VS, is an important parameter characterizing rock composition and fluid saturation. We have studied properties of the ratio in the West-Bohemian seismically active region, using data from the earthquake swarm which occurred here in 2008. The earthquake swarm was well recorded by 23 seismic stations from epicentral distances less than 25 km. We selected a subset of 158 events with local magnitudes between 1.5 and 3.8. Applying the Wadati method to the measured arrival times of P and S waves, we arrived at an average value of VP/VS =1.68 ± 0.01. This differs a little from the value of VP/VS = 1.70, which is routinely used for earthquake locations in the region at present. Moreover, it was recognized that the points in the Wadati graphs for some stations were systematically deviated from the mean straight lines. In particular, the stations with the largest positive deviations (above the mean straight lines) are situated close to the Mariánské Lázně Fault and to some intensive mofettes. Further analyses revealed reduced P- and S-wave velocities along the seismic rays toward these anomalous stations. In our opinion, the seismic waves arriving at the anomalous stations probably propagated along a fault or another zone of weakness. In this way, our results support the hypothesis that the Mariánské Lázně Fault is a deep-seated fault continuing down to the seismically active zone of local earthquakes. From a general point of view, this study demonstrates that even some narrow structural anomalies in the crust, such as fault zones, can be recognized by the simple Wadati method if data from a dense seismic network are available. 相似文献
16.
3-D rheological structure is mainly the spatial distribution of lithospheric strength or viscos-ity, its strength and viscosity are indispensable parameters in quantitative study of the lithosphere deformation. Plate tectonics theory initially divided the… 相似文献
17.
18.
Suzanne Mahlburg Kay Beatriz Coira Gerhard Wörner Robert W. Kay Bradley S. Singer 《Bulletin of Volcanology》2011,73(10):1487-1511
The giant ignimbrites that erupted from the Cerro Galán caldera complex in the southern Puna of the high Andean plateau are
considered to be linked to crustal and mantle melting as a consequence of delamination of gravitationally unstable thickened
crust and mantle lithosphere over a steepening subduction zone. Major and trace element analyses of Cerro Galán ignimbrites
(68–71% SiO2) that include 75 new analyses can be interpreted as reflecting evolution at three crustal levels. AFC modeling and new fractionation
corrected δ18O values from quartz (+7.63–8.85‰) are consistent with the ignimbrite magmas being near 50:50 mixtures of enriched mantle
(87Sr/86Sr ~ 0.7055) and crustal melts (87Sr/86Sr near 0.715–0.735). Processes at lower crustal levels are predicated on steep heavy REE patterns (Sm/Yb = 4–7), high Sr
contents (>250 ppm) and very low Nb/Ta (9-5) ratios, which are attributed to amphibolite partial melts mixing with fractionating
mantle basalts to produce hybrid melts that rise leaving a gravitationally unstable garnet-bearing residue. Processes at mid
crustal levels create large negative Eu anomalies (Eu/Eu* = 0.45–0.70) and variable trace element enrichment in a crystallizing
mush zone with a temperature near 800–850°C. The mush zone is repeatedly recharged from depth and partially evacuated into
upper crustal magma chambers at times of regional contraction. Crystallinity differences in the ignimbrites are attributed
to biotite, zoned plagioclase and other antecrysts entering higher level chambers where variable amounts of near-eutectic
crystallization occurs at temperatures as low as 680°C just preceding eruption. 40Ar/39Ar single crystal sanidine weighted mean plateau and isochron ages combined with trace element patterns show that the Galán
ignimbrite erupted in more than one batch including a ~ 2.13 Ma intracaldera flow and outflows to the west and north at near
2.09 and 2.06 Ma. Episodic delamination of gravitationally unstable lower crust and mantle lithosphere and injection of basaltic
magmas, whose changing chemistry reflects their evolution over a steepening subduction zone, could trigger the eruptions of
the Cerro Galán ignimbrites. 相似文献
19.
This paper describes synthetically the seismic activity, deep and shallow structures and rock dynamic features in and near
Chaoyang—Yixian region. It is supposed that there is a low velocity layer in middle crust and the three-layered crustal velocities
are all lower than that in both sides of the region. There exists uplifts of upper mantle and asthenosphere-low resistance
layer. It is also studied the composition of matter of three-layered crust, low velocity layer, upper mantle and asthenosphere.
In the end the direct relations between the deep and shallow structure, composition and the seismic activity and new activities
of faults in this region are discussed.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 180–186, 1992. 相似文献
20.
Seismic tomography of the crust and upper mantle in the Bohai Bay Basin and its adjacent regions 总被引:1,自引:0,他引:1
In the Bohai Bay Basin and its adjacent regions(112°―124°E,34°―42°N),there exists abundant gas-petroleum while modern inter-plate seismic activity is robust.Although the tectonic structure of this region is very complicated,plenty of geological,geophysical and geochemical data and results are obtained through previous researches.On the basis of absorbing previous results,especially various kinds of geological and geophysical results,we collect and process the arrival time of P-wave phases of local events and tele-seismic events recorded by the station within this region from 1978 to 2004,build the responding initial model,and image the velocity structure of the crust and upper mantle of this region via tomography.The perturbation images of various depths and velocity profiles imply that the velocity structure of the crust and upper mantle in the Bohai Bay Basin and its adjacent regions is mainly influenced by the surface tectonic units,and is characterized by "Stripped along east-west,and zoned along south-north";some large-scaled faults penetrate Moho and lithosphere,and provide the channels for the basic lava or hot mass upwelling from the mantle. 相似文献