共查询到20条相似文献，搜索用时 625 毫秒
1.
《Journal of Geodynamics》2008,45(3-5):173-185
The island of Crete is located in the forearc of the Hellenic subduction zone, where the African lithospheric plate is subducting beneath the Eurasian one. The depth of the plate contact as well as the internal structure of the Aegean plate in the area of Crete have been a matter of debate. In this study, seismic constrains obtained by wide-angle seismic, receiver function and surface wave studies are discussed and compared to a 3D density model of the region.The interface between the Aegean continental lithosphere and the African one is located at a depth of about 50 km below Crete. According to seismic studies, the Aegean lithosphere in the area of Crete is characterised by strong lateral, arc–parallel heterogeneity. An about 30 km thick Aegean crust is found in central Crete with a density of about 2850 kg/m3 for the lower Aegean continental crust and a density of about 3300 kg/m3 for the mantle wedge between the Aegean crust and the African lithosphere. For the deeper crust in the area of western Crete two alternative models have been proposed by seismic studies. One with an about 35 km thick crust and another one with crustal velocities down to the plate contact. A grid search is performed to test the consistency of these models with gravimetric constraints. For western Crete a model with a thick lower Aegean crust and a density of about 2950 kg/m3 is favoured. The inferred density of the lower Aegean crust in the area of Crete correlates well with S-wave velocities obtained by surface wave studies.Based on the 3D density model, the weight of the Aegean lithosphere is estimated along an E–W oriented profile in the area of Crete. Low weights are found for the region of western Crete. 相似文献
2.
The island of Crete is located in the forearc of the Hellenic subduction zone, where the African lithospheric plate is subducting beneath the Eurasian one. The depth of the plate contact as well as the internal structure of the Aegean plate in the area of Crete have been a matter of debate. In this study, seismic constrains obtained by wide-angle seismic, receiver function and surface wave studies are discussed and compared to a 3D density model of the region.The interface between the Aegean continental lithosphere and the African one is located at a depth of about 50 km below Crete. According to seismic studies, the Aegean lithosphere in the area of Crete is characterised by strong lateral, arc–parallel heterogeneity. An about 30 km thick Aegean crust is found in central Crete with a density of about 2850 kg/m3 for the lower Aegean continental crust and a density of about 3300 kg/m3 for the mantle wedge between the Aegean crust and the African lithosphere. For the deeper crust in the area of western Crete two alternative models have been proposed by seismic studies. One with an about 35 km thick crust and another one with crustal velocities down to the plate contact. A grid search is performed to test the consistency of these models with gravimetric constraints. For western Crete a model with a thick lower Aegean crust and a density of about 2950 kg/m3 is favoured. The inferred density of the lower Aegean crust in the area of Crete correlates well with S-wave velocities obtained by surface wave studies.Based on the 3D density model, the weight of the Aegean lithosphere is estimated along an E–W oriented profile in the area of Crete. Low weights are found for the region of western Crete. 相似文献
3.
The distribution of the focal mechanisms of the shallow and intermediate depth (h>40 km) earthquakes of the Aegean and the surrounding area is discussed. The data consist of all events of the period 1963–1986 for the shallow, and 1961–1985 for the intermediate depth earthquakes, withM
s
5.5. For this purpose, all published fault plane solutions for each event have been collected, reproduced, carefully checked and if possible improved accordingly. The distribution of the focal mechanisms of the earthquakes in the Aegean declares the existence of thrust faulting following the coastline of southern Yugoslavia, Albania and western Greece extending up to the island of Cephalonia. This zone of compression is due to the collision between two continental lithospheres (Apulian-Eurasian). The subduction of the African lithosphere under the Aegean results in the occurrence of thrust faulting along the convex side of the Hellenic arc. These two zones of compression are connected via strike-slip faulting observed at the area of Cephalonia island. TheP axis along the convex side of the arc keeps approximately the same strike throughout the arc (210° NNE-SSW) and plunges with a mean angle of 24° to southwest. The broad mainland of Greece as well as western Turkey are dominated by normal faulting with theT axis striking almost NS (with a trend of 174° for Greece and 180° for western Turkey). The intermediate depth seismicity is distributed into two segments of the Benioff zone. In the shallower part of the Benioff zone, which is found directly beneath the inner slope of the sedimentary arc of the Hellenic arc, earthquakes with depths in the range 40–100 km are distributed. The dip angle of the Benioff zone in this area is found equal to 23°. This part of the Benioff zone is coupled with the seismic zone of shallow earthquakes along the arc and it is here that the greatest earthquakes have been observed (M
s
8.0). The deeper part (inner) of the Benioff zone, where the earthquakes with depths in the range 100–180 km are distributed, dips with a mean angle of 38° below the volcanic arc of southern Aegean. 相似文献
4.
An M8.3 earthquake struck the southwestern part of the Hellenic Arc, near the Island of Crete, in AD 365, generating a tsunami
that affected almost the entire eastern Mediterranean region. Taking into account that the time history of seismicity in this
region is fairly complete for such earthquakes in the historical catalog, which can be dated as back as the 5th century B.C.,
there is no indication that this segment of plate boundary has been fully ruptured again. The seismic hazard associated with
this part of the Hellenic Arc necessitates the evaluation of the rupture characteristics of this great event. The constraint
of the faulting geometry was initially achieved by using information from seismicity, and the focal mechanisms of earthquakes
that occurred during the instrumental period. A rupture model for this great earthquake is constructed by assuming an elastic
medium and calculating the theoretical surface displacements for various fault models that are matched with the observed surface
deformation gleaned from historical reports. The resulted fault model concerns thrust faulting with a rupture length of 160
km and a seismic moment of 5.7 × 1028 dyn·cm, an average slip of 8.9 m and a corresponding moment magnitude equal to 8.4, in excellent agreement with the macroseismic
estimation. The absence of such events recurrence is an indication of the lack of complete seismic coupling that is common
in subduction zones, which is in accordance with the back arc spreading of the Aegean microplate and with previous results
showing low coupling for extensional strain of the upper plate. 相似文献
5.
We investigate microseismic activity at the convergent plate boundary of the Hellenic subduction zone on- and offshore south-eastern
Crete with unprecedented precision using recordings from an amphibian seismic network. The network configuration consisted
of up to eight ocean bottom seismometers as well as five temporary short-period and six permanent broadband stations on Crete
and surrounding islands. More than 2,500 local and regional events with magnitudes up to M
L = 4.5 were recorded during the time period July 2003–June 2004. The magnitude of completeness varies between 1.5 on Crete
and adjacent areas and increases to 2.5 in the vicinity of the Strabo trench 100 km south of Crete. Tests with different localization
schemes and velocity models showed that the best results were obtained from a probabilistic earthquake localization using
a 1-D velocity model and corresponding station corrections obtained by simultaneous inversion. Most of the seismic activity
is located offshore of central and eastern Crete and interpreted to be associated with the intracrustal graben system (Ptolemy
and Pliny trenches). Furthermore, a significant portion of events represents interplate seismicity along the NNE-ward dipping
plate interface. The concentration of seismicity along the Ptolemy and Pliny trenches extends from shallow depths down to
the plate interface and indicates active movement. We propose that both trenches form transtensional structures within the
Aegean plate. The Aegean continental crust between these two trenches is interpreted as a forearc sliver as it exhibits only
low microseismic activity during the observation period and little or no internal deformation. Interplate seismicity between
the Aegean and African plates forms a 100-km wide zone along dip from the Strabo trench in the south to the southern shore-line
of Crete in the north. The seismicity at the plate contact is randomly distributed and no indications for locked zones were
observed. The plate contact below and north of Crete shows no microseismic activity and seems to be decoupled. The crustal
seismicity of the Aegean plate in this area is generally confined to the upper 20 km in agreement with the idea of a ductile
deformation of the lower crust caused by a rapid return flow of metamorphic rocks that spread out below the forearc. In the
region of the Messara half-graben at the south coast of central Crete, a southward dipping seismogenic structure is found
that coalesces with the seismicity of the Ptolemy trench at a depth of about 20 km. The accretionary prism south of Crete
indicated by the Mediterranean Ridge showed no seismic activity during the observation period and seems to be deforming aseismically. 相似文献
6.
The region of the Aegean Sea and the surrounding areas in the Eastern Mediterranean lies on the boundary zone between the Eurasian and the African plates. It is a zone of widespread extensive deformation and, therefore, reveals a high level of seismicity.Three-dimensional velocity structure, beneath the crust and upper mantle of the region between 33.0°N–43.0°N and 18.0°E–30.6°E, is determined.The data used are arrival times ofP-waves from 166 earthquakes, recorded at 62 seismological stations. In total, 3973 residual data are inverted.The resultant structure reveals a remarkable contrast of velocity. In the top crustal layer, low velocities are dominant in Western Turkey and on the Greek mainland, while a high velocity zone is dominant in the Ionian Sea and in the southern Aegean Sea.In the upper mantle, high velocity zones dominate along the Hellenic arc, corresponding to the subducting African plate and in the northern part of the region, corresponding to the subducting African plate and in the northern part of the region, corresponding to the margin of Eurasian plate.A low velocity zone is dominant in the Aegean Sea region, where large-scale extension and volcanic activity are predominant, associated with the subduction of the African plate. 相似文献
7.
Robert McCaffrey 《Pure and Applied Geophysics》1994,142(1):173-224
Deviations of slip vector azimuths of interplate thrust earthquakes from expected plate convergence directions at oblique subduction zones provide kinematic information about the deformation of forearcs and indirect evidence on the dynamics of the plate boundary. A global survey of slip vectors at major trenches of the world reveals a large variability in the kinematic response of forearcs to shear produced by oblique convergence. The variability in forearc deformation inferred from slip vector deflections is suggested to be caused by variations in forearc rheology rather than in the stresses acting on subduction zone thrust faults. Estimated apparent macroscopic rheologies range from elastic to perfectly plastic (or viscous). Forearc rheologies inferred from slip vectors do not correlate with age of the subducting lithosphere, but continental forearcs or old arcs appear to deform less than oceanic or young arcs. The inferred absence of forearc deformation at continental arcs from this study is counter to inferences drawn from compiled geologic information on forearc faults. Correlations of the apparent forearc rheology with backarc spreading, convergence rate, slab dip, arc curvature, and downdip length of the thrust contact are poor. However, great subduction zone earthquakes occur where forearcs are apparently more elastic (i.e., less deformed by oblique convergence), which suggests that the mechanical properties of forearcs rather than stress magnitude on thrust faults control both the kinematic behavior of forearcs and where great subduction zone earthquakes occur. 相似文献
8.
The island of Crete in the forearc of the Hellenic subduction zone has a rugged topography with local relief exceeding 2 km. Based on the elevation of marine shorelines, rates of rock uplift during the Late Holocene were previously estimated to range between 1 and 4 mm/a in different parts of the island. These rates may, however, not be representative for longer timescales, because subduction earthquakes with up to 9 m of vertical coseismic displacement have affected Crete in the Late Holocene. Here we use a well preserved sequence of marine terraces near Kato Zakros in eastern Crete to determine the rate of rock uplift over the last ∼600 ka. Field investigations and topographic profiles document a flight of more than 13 marine bedrock terraces that were carved into limestones of the Tripolitza unit. Preliminary age constraints for the terraces were obtained by 10Be exposure dating of rare quartz-bearing sandstone clasts, which are present on some terraces. The 10Be ages of these samples, which have been corrected for an inherited nuclide component, yielded exposure ages between ∼100 ka and zero. Combined with geomorphologic evidence the two oldest 10Be ages suggest that the terraces T4 and T5, with shoreline angles at an elevation of ∼68 and ∼76 m above sea level, respectively, formed during the marine isotope stage 5e about 120 ka ago. The correlation of the higher terraces (T6 to T13) with regional sea-level highstands indicates sustained rock uplift at a rate of ∼0.5 m/ka since at least ∼600 ka. As normal faulting has dominated the tectonics of Crete during the last several million years, upper crustal shortening can be ruled out as a cause for rock uplift. We argue that the sustained uplift of the island results from the continuous underplating of sediments, which are transferred from the subducting African plate to the base of the crust beneath Crete. 相似文献
9.
Ch. Kkallas C. B. Papazachos D. Boore Ch. Ventouzi B. N. Margaris 《Bulletin of Earthquake Engineering》2018,16(11):5121-5150
We model the macroseismic damage distribution of four important intermediate-depth earthquakes of the southern Aegean Sea subduction zone, namely the destructive 1926 M?=?7.7 Rhodes and 1935 M?=?6.9 Crete earthquakes, the unique 1956 M?=?6.9 Amorgos aftershock (recently proposed to be triggered by a shallow event), and the more recent 2002 M?=?5.9 Milos earthquake, which all exhibit spatially anomalous macroseismic patterns. Macroseismic data for these events are collected from published macroseismic databases and compared with the spatial distribution of seismic motions obtained from stochastic simulation, converted to macroseismic intensity (Modified Mercalli scale, IMM). For this conversion, we present an updated correlation between macroseismic intensities and peak measures of seismic motions (PGA and PGV) for the intermediate-depth earthquakes of the southern Aegean Sea. Input model parameters for the simulations, such as fault dimensions, stress parameters, and attenuation parameters (e.g. back-arc/along anelastic attenuation) are adopted from previous work performed in the area. Site-effects on the observed seismic motions are approximated using generic transfer functions proposed for the broader Aegean Sea area on the basis of VS30 values from topographic slope proxies. The results are in very good agreement with the observed anomalous damage patterns, for which the largest intensities are often observed at distances >?100 km from the earthquake epicenters. We also consider two additional “prediction” but realistic intermediate-depth earthquake scenarios, and model their macroseismic distributions, to assess their expected damage impact in the broader southern Aegean area. The results suggest that intermediate-depth events, especially north of central Crete, have a prominent effect on a wide area of the outer Hellenic arc, with a very important impact on modern urban centers along northern Crete coasts (e.g. city of Heraklion), in excellent agreement with the available historical information. 相似文献
10.
Anastasia A. Kiratzi 《Pure and Applied Geophysics》1993,140(3):391-402
Recent and historical seismicity as well as reliable fault plane solutions are used to study the active deformation caused by the occurrence of intermediate depth (60–170 km) earthquakes of the Vrancea region, Rumania. In this area, located in the southeastern part of the Carpathian arc, the westward subduction of the Carpathian trench has terminated, leaving continental lithosphere, at present, at the arc. The principalT axis of the intermediate depth events trends N159°E and has a plunge of 74°, which is the same as the dip of the subducted plate. TheP axis has a trend of 314° and a shallow plunge of 15°. The analysis of the moment tensor of six focal mechanisms showed that the dominant mode of deformation of the subducted lithosphere is a down-dip extension at a rate of about 2 cm/yr, based on seismicity data. 相似文献
11.
CHARACTERISTICS OF FOCAL MECHANISMS AND STRESS FIELD IN THE EASTERN BOUNDARY OF SICHUAN-YUNNAN BLOCK AND ITS ADJACENT AREA 
下载免费PDF全文
下载免费PDF全文 This study is devoted to a systematic analysis of the stress state of the eastern boundary area of Sichuan-Yunnan block based on focal mechanisms of 319 earthquakes with magnitudes between M3.0 and M6.9, occurring from January 2009 to May 2018. We firstly determined the mechanism solutions of 234 earthquakes by the CAP method, using the broadband waveforms recorded by Chinese regional permanent networks, and collected 85 centroid moment tensor solutions from the GCMT. Then we investigated the regional stress regime through a damp linear inversion. Our results show that:1)the focal mechanisms of moderate earthquakes are regionally specific with three principal types of focal mechanisms:the strike-slip faulting type, the thrust faulting type and the normal faulting type. The strike-slip faulting type is significant in the eastern boundary area of Sichuan-Yunnan block along the Xianshuihe-Xiaojiang Fault, the Daliangshan Fault, and the Zhaotong-Lianfeng Fault. The thrust faulting type and the combined thrust/strike-slip faulting type are significant along the Mabian-Yanjin Fault, Ebian-Yanfeng Fault and the eastern section of Lianfeng Fault; 2)The most robust feature of the regional stress regime is that, the azimuth of principal compressive stress axis rotates clockwise from NWW to NW along the eastern boundary of Sichuan-Yunnan Block, and the clockwise rotation angle is about 50 degrees. Meanwhile, the angels between the principal compressive axis and the trend of eastern boundary of Sichuan-Yunnan Block remain unchanged, which implies a stable coefficient of fault friction in the eastern boundary fault zone of Sichuan-Yunnan Block. The movement of the upper crust in the southeastern Tibetan plateau is a relatively rigid clockwise rotation. On the whole, the Xianshuihe-Xiaojiang Fault is a small arc on the earth, and its Euler pole axis is at(21°N, 88°E). The Daliangshan Fault is surrounded by the Anninghe-Zemuhe Fault, which formed a closed diamond shape. When the Sichuan-Yunnan block rotates clockwise, the Daliangshan Fault locates in the outer of the arc, while the Anninghe-Zemuhe Fault is in the inward of the arc, and from the mechanical point of view, left-lateral sliding movement is more likely to occur on the Daliangshan Fault. Our results can be the evidence for the study on the "cut-off" function of the Daliangshan Fault based on the stress field background; 3)The regional stress regime of the eastern boundary faults zone of the Sichuan-Yunnan Block is the same as the south section of the Dalianshan Fault, and the focal mechanism results also reveal that the Dalianshan Fault is keeping left-lateral strike-slip. There may be the same tectonic stress field that controls the earthquake activities in the southern section of Daliangshan Fault and Zhaotong-Lianfeng Fault. The regional stress regime of Zhaodong-Lianfeng Fault is also the same with the Sichuan-Yunnan Block, which implies that the control effect of the SE movement of the Sichuan-Yunnan block may extend to Weining. 相似文献
12.
D. D. Singh 《Pure and Applied Geophysics》1997,150(1):53-73
—Rayleigh and Love waves generated by sixteen earthquakes which occurred in the Indian Ocean and were recorded at 13 WWSSN stations of Asia, Africa and Australia are used to determine the moment tensor solution of these earthquakes. A combination of thrust and strike-slip faulting is obtained for earthquakes occurring in the Bay of Bengal. Thrust, strike slip or normal faulting (or either of the combination) is obtained for earthquakes occurring in the Arabian Sea and the Indian Ocean. The resultant compressive and tensional stress directions are estimated from more than 300 centroid moment tensor (CMT) solution of earthquakes occurring in different parts of the Indian Ocean. The resultant compressive stress directions are changing from north-south to east-west and the resultant tensional stress directions from east-west to north-south in different parts of the Indian Ocean. The results infer the counterclockwise movement of the region (0°–33°S and 64°E–94°E), stretching from the Rodriguez triple junction to the intense deformation zone of the central Indian Ocean and the formation of a new subduction zone (island arc) beneath the intense deformation zone of the central Indian Ocean and another at the southern part of the central Indian basin. The compressive stress direction is along the ridge axis and the extensional stress manifests across the ridge axis. The north-south to northeast-south west compression and east-west to northwest-southeast extension in the Indian Ocean suggest the northward underthrusting of the Indian plate beneath the Eurasian plate and the subduction beneath the Sunda arc region in the eastern part. The focal depth of earthquakes is estimated to be shallow, varying from 4 to 20 km and increasing gradually in the age of the oceanic lithosphere with the focal depth of earthquakes in the Indian Ocean. 相似文献
13.
The distribution of earthquakes from 1973 to 1982 in the South China Sea, Indochina and their vicinity was studied using the
data from I. S. C. It was found that the earthquakes are mainly concentrated along the boundaries of plates. Beside, some
of shallow eartqhuakes are distributed in west part of Burma and the boundary between Burma and China, a few of earthquakes
occurred in South China Sea. The features of Benioff zone along the boundaries between India plate, Philippine Sea plate and
Eurasia plate were studied. The plate do not coupled well under the Java trench and the Philippine trench. The subducted India
plate under Burmese range, Andaman—Nicobar arc moves NNE. The fault plane solutions of earthquakes were studied using the
first motions of P wave. The stress state on subduction zones and within the area were deduced from the fault plane solutions
and the fault movement. It was found that the direction of principal compression axis of stress is in the NNE in west part
of Burma, in S—N in south and middle part of Bruma and Thailand, and in NNE or S—N in the South China Sea. It was also found
that the stress state has close relation with the interaction of plates.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 129–137, 1991. 相似文献
14.
The focal mechanism solutions of 83 European earthquakes withM>6, selected from a total of 140, have been used to derive the directions of the principal axes of stress along the plate boundary between Eurasia and Africa from the Azores islands to the Caucasus mountains. Along most of the region, the horizontalP-axes are at an angle of 45° to 90° with the trend of the plate boundary. HorizontalT-axes are concentrated in central Italy and northern Greece in association with normal faulting. Large strike-slip motion of right-lateral character takes place at the center of the Azores-Gibraltar fault and the North Anatolian fault. From Gibraltar to the Caucasus the boundary is complicated by the presence of secondary blocks and zones of extended deformations with earthquakes spread over wide areas. Intermediate and deep earthquakes are present at four areas with arc-like structure, namely, Gibraltar, Sicily-Calabria, Hellenic arc and Carpathians. 相似文献
15.
Sujit Dasgupta Manoj Mukhopadhyay Auditeya Bhattacharya Tapan K. Jana 《Journal of Seismology》2003,7(2):155-174
The gross seismotectonic features for the Burmese-Andaman arc system which defines the northeast margin of the Indian plate are rather well known but variations in the subduction zone geometry along and across the arc and fault pattern within the subducting Indian plate have not been studied. Present workaims to study these by using seismicity data whose results are presented in the form of: (a) Lithospheric across-the-arc sections at about every 100–120 km (approximately one degree latitude apart) covering the 3500 km longBurmese-Andaman arc system, (b) a structure contour map showing the depth tothe top surface of the seismically active lithosphere and (c) interpretationof focal mechanism solutions for 148 Benioff zone earthquakes. Both penetrationdepth and the dip of the Benioff zone vary considerably along the arc in correspondence to the curvature of the fold-thrust belt which varies from concave to convex in different sectors of the arc. Several extensive `Hinge faults' that abut at high angles to the arc orientation, are inferred from aninterpretation of the structure contour map. Active nature of the hinge faultsis established in several areas by their association with earthquakes andcorroborated through fault plane solutions. At shallow level of the Benioffzone along these faults, focal mechanism solutions display left lateral strikeslip movement while at deeper levels reverse fault solutions are common. 相似文献
16.
V. O. Mikhailov T. Parsons R. W. Simpson E. P. Timoshkina C. Williams 《Izvestiya Physics of the Solid Earth》2007,43(1):75-90
Data on present-day heat flow, subsidence history, and paleotemperature for the Sacramento Delta region, California, have
been employed to constrain a numerical model of tectonic subsidence and thermal evolution of forearc basins. The model assumes
an oceanic basement with an initial thermal profile dependent on its age subjected to refrigeration caused by a subducting
slab. Subsidence in the Sacramento Delta region appears to be close to that expected for a forearc basin underlain by normal
oceanic lithosphere of age 150 Ma, demonstrating that effects from both the initial thermal profile and the subduction process
are necessary and sufficient. Subsidence at the eastern and northern borders of the Sacramento Valley is considerably less,
approximating subsidence expected from the dynamics of the subduction zone alone. These results, together with other geophysical
data, show that Sacramento Delta lithosphere, being thinner and having undergone deeper subsidence, must differ from lithosphere
of the transitional type under other parts of the Sacramento Valley. Thermal modeling allows evaluation of the rheological
properties of the lithosphere. Strength diagrams based on our thermal model show that, even under relatively slow deformation
(10−17 s−1), the upper part of the delta crystalline crust (down to 20–22 km) can fail in brittle fashion, which is in agreement with
deeper earthquake occurrence. Hypocentral depths of earthquakes under the Sacramento Delta region extend to nearly 20 km,
whereas, in the Coast Ranges to the west, depths are typically less than 12–15 km. The greater width of the seismogenic zone
in this area raises the possibility that, for fault segments of comparable length, earthquakes of somewhat greater magnitude
might occur than in the Coast Ranges to the west.
The text was submitted by the authors in English. 相似文献
17.
Giuseppe Pasquale Raffaella De Matteis Annalisa Romeo Rosalba Maresca 《Journal of Seismology》2009,13(1):107-124
The goal of this study was to estimate the stress field acting in the Irpinia Region, an area of southern Italy that has been
struck in the past by destructive earthquakes and that is now characterized by low to moderate seismicity. The dataset are
records of 2,352 aftershocks following the last strong event: the 23 November 1980 earthquake (M 6.9). The earthquakes were
recorded at seven seismic stations, on average, and have been located using a three-dimensional (3D) P-wave velocity model
and a probabilistic, non-linear, global search technique. The use of a 3D velocity model yielded a more stable estimation
of take-off angles, a crucial parameter for focal mechanism computation. The earthquake focal mechanisms were computed from
the P-wave first-motion polarity data using the FPFIT algorithm. Fault plane solutions show mostly normal component faulting
(pure normal fault and normal fault with a strike-slip component). Only some fault plane solutions show strike-slip and reverse
faulting. The stress field is estimated using the method proposed by Michael (J Geophys Res 92:357–368, 1987a) by inverting selected focal mechanisms, and the results show that the Irpinia Region is subjected to a NE–SW extension with
horizontal σ
3 (plunge 0°, trend 230°) and subvertical σ
1 (plunge 80°, trend 320°), in agreement with the results derived from other stress indicators. 相似文献
18.
Seismic Sources on the Iberia-African Plate Boundary and their Tectonic Implications 总被引：1，自引：0，他引：1
—The plate boundary between Iberia and Africa has been studied using data on seismicity and focal mechanisms. The region has been divided into three areas: A; the Gulf of Cadiz; B, the Betics, Alboran Sea and northern Morocco; and C, Algeria. Seismicity shows a complex behavior, large shallow earthquakes (h < 30 km) occur in areas A and C and moderate shocks in area B; intermediate-depth activity (30 < h < 150 km) is located in area B; the depth earthquakes (h
650 km) are located to the south of Granada. Moment rate, slip velocity and b values have been estimated for shallow shocks, and show similar characteristics for the Gulf of Cadiz and Algeria, and quite different ones for the central region. Focal mechanisms of 80 selected shallow earthquakes (8 mb 4) show thrust faulting in the Gulf of Cadiz and Algeria with horizontal NNW-SSE compression, and normal faulting in the Alboran Sea with E-W extension. Focal mechanisms of 26 intermediate-depth earthquakes in the Alboran Sea display vertical motions, with a predominant plane trending E-W. Solutions for very deep shocks correspond to vertical dip-slip along N-S trends. Frohlich diagrams and seismic moment tensors show different behavior in the Gulf of Cadiz, Betic-Alboran Sea and northern Morocco, and northern Algeria for shallow events. The stress pattern of intermediate-depth and very deep earthquakes has different directions: vertical extension in the NW-SE direction for intermediate depth earthquakes, and tension and pressure axes dipping about 45 ° for very deep earthquakes. Regional stress pattern may result from the collision between the African plate and Iberia, with extension and subduction of lithospheric material in the Alboran Sea at intermediate depth. The very deep seismicity may be correlated with older subduction processes. 相似文献
19.
20.
Mediterranean island arcs and origin of high potash volcanoes 总被引：1，自引：0，他引：1
Active volcanoes of the Mediterranean Sea are distributed along two arc structures: the Hellenic arc in the Aegean Sea and the Calabrian arc in the Tyrrhenian Sea. The active volcanoes in both arcs lie above earthquakes with focal depth greater than 100 km. The depth of these earthquakes increases generally northward reaching a maximum depth of about 200 km in the Aegean Sea and more than 300 km in the Tyrrhenian Sea. 相似文献