scholarly journals Structure of the mantle and tectonic zoning of the central Alpine-Himalayan belt

2018 ◽  
Vol 9 (4) ◽  
pp. 1127-1145 ◽  
Author(s):  
V. G. Trifonov ◽  
S. Yu. Sokolov
Keyword(s):  
Seismic Tomography ◽  
Upper Mantle ◽  
Tien Shan ◽  
P Wave ◽  
Rift System ◽  
Western Himalayas ◽  
East African Rift System ◽  
Low Velocity ◽  
P Waves ◽  
East European

The Alpine-Himalayan orogenic belt is characterized by longitudinal zoning and transverse segmentation. Using the 3D seismic tomography model, we compiled the sections showing the deviations of seismic P-wave velocities from the average values in the mantle, and analyzed the sections in comparison with the data on the crustal inhomogeneities expressed in geological structures. The sections go across of the central part of the belt from Adriatic to Western Tien Shan, Pamirs, Western Himalayas, and the adjacent territories of the East African rift system, the Arabian, Turanian and Scythian plates, and the East European platform. Our model based on the seismic tomography data is mainly targeted at studying the inhomogeneities in the upper mantle, considering the fact that the resolution of mantle differentiation in terms of P-waves is higher in the upper mantle than in the lower one. Based on the analysis of the sections, we determine the directions of seismically low-velocity upper-mantle flows spreading from the Ethiopian-Afar super-plume, which differ in intensity. The relationships are revealed between these flows and the high-velocity bodies that are subsided into the mantle due to subduction and collision of the plates. The deep-seated features that give evidence of transverse segmentation of the belt are detected.

scholarly journals Traces of the crustal units and the upper mantle structure in the southwestern part of the East European Craton

2014 ◽  
Vol 6 (1) ◽  
pp. 985-1021
Author(s):  
I. Janutyte ◽  
E. Kozlovskaya ◽  
M. Majdanski ◽  
P. H. Voss ◽  
M. Budraitis ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Velocity Model ◽  
P Wave ◽  
Seismic Velocities ◽  
P Waves ◽  
Teleseismic Tomography ◽  
East European ◽  
Seismic Experiment ◽  
Passive Seismic ◽  
Synthetic Datasets

Abstract. The presented study is a part of the passive seismic experiment PASSEQ 2006–2008 which took place around the Trans-European Suture Zone (TESZ) from May 2006 to June 2008. The dataset of 4195 manually picked arrivals of teleseismic P waves of 101 earthquakes (EQs) recorded in the PASSEQ seismic stations deployed to the east of the TESZ was inverted using the non-linear teleseismic tomography algorithm TELINV. Two 3-D crustal models were used to estimate the crustal travel time (TT) corrections. As a result, we obtained a model of P wave velocity variations in the upper mantle beneath the TESZ and the EEC. In the study area beneath the craton we observed 5 to 6.5% higher and beneath the TESZ about 4% lower seismic velocities compared to the IASP91 velocity model. We found the seismic lithosphere-asthenosphere boundary (LAB) beneath the TESZ at a depth of about 180 km, while we observed no seismic LAB beneath the EEC. The inversion results obtained with the real and the synthetic datasets indicated a ramp shape of the LAB in the northern TESZ where we observed values of seismic velocities close to those of the craton down to about 150 km. The lithosphere thickness in the EEC increases going from the TESZ to the NE from about 180 km beneath Poland to 300 km or more beneath Lithuania. Moreover, in western Lithuania we possibly found an upper mantle dome. In our results the crustal units are not well resolved. There are no clear indications of the features in the upper mantle which could be related with the crustal units in the study area. On the other hand, at a depth of 120–150 km we possibly found a trace of a boundary of proposed palaeosubduction zone between the East Lithuanian Domain (EL) and the West Lithuanian Granulite Domain (WLG). Also, in our results we may have identified two anorogenic granitoid plutons.

scholarly journals Traces of the crustal units and the upper-mantle structure in the southwestern part of the East European Craton

Solid Earth ◽  
2014 ◽  
Vol 5 (2) ◽  
pp. 821-836 ◽  
Author(s):  
I. Janutyte ◽  
E. Kozlovskaya ◽  
M. Majdanski ◽  
P. H. Voss ◽  
M. Budraitis ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Synthetic Data ◽  
Velocity Model ◽  
East European Craton ◽  
P Wave ◽  
Seismic Velocities ◽  
P Waves ◽  
Data Set ◽  
Teleseismic Tomography ◽  
East European

Abstract. The presented study is a part of the passive seismic experiment PASSEQ 2006–2008, which took place around the Trans-European Suture Zone (TESZ) from May 2006 to June 2008. The data set of 4195 manually picked arrivals of teleseismic P waves of 101 earthquakes (EQs) recorded in the seismic stations deployed to the east of the TESZ was inverted using the non-linear teleseismic tomography algorithm TELINV. Two 3-D crustal models were used to estimate the crustal travel time (TT) corrections. As a result, we obtain a model of P-wave velocity variations in the upper mantle beneath the TESZ and the East European Craton (EEC). In the study area beneath the craton, we observe up to 3% higher and beneath the TESZ about 2–3% lower seismic velocities compared to the IASP91 velocity model. We find the seismic lithosphere–asthenosphere boundary (LAB) beneath the TESZ at a depth of about 180 km, while we observe no seismic LAB beneath the EEC. The inversion results obtained with the real and the synthetic data sets indicate a ramp shape of the LAB in the northern TESZ, where we observe values of seismic velocities close to those of the craton down to about 150 km. The lithosphere thickness in the EEC increases going from the TESZ to the NE from about 180 km beneath Poland to 300 km or more beneath Lithuania. Moreover, in western Lithuania we find an indication of an upper-mantle dome. In our results, the crustal units are not well resolved. There are no clear indications of the features in the upper mantle which could be related to the crustal units in the study area. On the other hand, at a depth of 120–150 km we indicate a trace of a boundary of proposed palaeosubduction zone between the East Lithuanian Domain (EL) and the West Lithuanian Granulite Domain (WLG). Also, in our results, we may have identified two anorogenic granitoid plutons.

scholarly journals Studying the Depth Structure of the Kyrgyz Tien Shan by Using the Seismic Tomography and Magnetotelluric Sounding Methods

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 122
Author(s):  
Irina Medved ◽  
Elena Bataleva ◽  
Michael Buslov
Keyword(s):  
Seismic Tomography ◽  
High Velocity ◽  
Fault Zones ◽  
Magnetotelluric Sounding ◽  
Tien Shan ◽  
High Resistivity ◽  
Low Velocity ◽  
Low Resistivity ◽  
Velocity Models ◽  
Fluid Saturation

This paper presents new results of detailed seismic tomography (ST) on the deep structure beneath the Middle Tien Shan to a depth of 60 km. For a better understanding of the detected heterogeneities, the obtained velocity models were compared with the results of magnetotelluric sounding (MTS) along the Kekemeren and Naryn profiles, running parallel to the 74 and 76 meridians, respectively. We found that in the study region the velocity characteristics and geoelectric properties correlate with each other. The high-velocity high-resistivity anomalies correspond to the parts of the Tarim and Kazakhstan-Junggar plates submerged under the Tien Shan. We revealed that the structure of the Middle Tien Shan crust is conditioned by the presence of the Central Tien Shan microcontinent. It manifests itself as two anomalies lying one below the other: the lower low-velocity low-resistivity anomaly, and the upper high-velocity high-resistivity anomaly. The fault zones, limiting the Central Tien Shan microcontinent, appear as low-velocity low-resistivity anomalies. The obtained features indicate the fluid saturation of the fault zones. According to the revealed features of the Central Tien Shan geological structure, it is assumed that the lower-crustal low-velocity layer can play a significant role in the delamination of the mantle part of the submerged plates.

scholarly journals POLENET/LAPNET teleseismic <i>P</i> wave travel time tomography model of the upper mantle beneath northern Fennoscandia

Solid Earth ◽  
2016 ◽  
Vol 7 (2) ◽  
pp. 425-439 ◽  
Author(s):  
Hanna Silvennoinen ◽  
Elena Kozlovskaya ◽  
Eduard Kissling
Keyword(s):  
Upper Mantle ◽  
Fennoscandian Shield ◽  
P Wave ◽  
Significant Feature ◽  
Depth Range ◽  
Low Velocity ◽  
Lateral Velocity ◽  
International Polar Year ◽  
Northern Fennoscandia ◽  
Wave Tomography

Abstract. The POLENET/LAPNET (Polar Earth Observing Network) broadband seismic network was deployed in northern Fennoscandia (Finland, Sweden, Norway, and Russia) during the third International Polar Year 2007–2009. The array consisted of roughly 60 seismic stations. In our study, we estimate the 3-D architecture of the upper mantle beneath the northern Fennoscandian Shield using high-resolution teleseismic P wave tomography. The P wave tomography method can complement previous studies in the area by efficiently mapping lateral velocity variations in the mantle. For this purpose 111 clearly recorded teleseismic events were selected and the data from the stations hand-picked and analysed. Our study reveals a highly heterogeneous lithospheric mantle beneath the northern Fennoscandian Shield though without any large high P wave velocity area that may indicate the presence of thick depleted lithospheric “keel”. The most significant feature seen in the velocity model is a large elongated negative velocity anomaly (up to −3.5 %) in depth range 100–150 km in the central part of our study area that can be followed down to a depth of 200 km in some local areas. This low-velocity area separates three high-velocity regions corresponding to the cratonic units forming the area.

Different causes of the delamination on the example of Caucasus and Kyrgyz Tien Shan collision zones.

2020 ◽  
Author(s):  
Irina Medved ◽  
Ivan Koulakov ◽  
Mikhail Buslov
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
3D Models ◽  
Tien Shan ◽  
Gradual Transition ◽  
Mantle Lithosphere ◽  
Continental Lithosphere ◽  
Low Velocity ◽  
Mountain Areas ◽  
Velocity Anomalies

&lt;p&gt;The causes of delamination of the mantle lithosphere in collision zones is actively debated in the scientific community. The main discussions are focused on the initiation of sinking of the continental lithosphere into the asthenosphere to a depth. Most scientists believe that such kind of immersion is impossible. However, there are several articles showing that this process is nonetheless taking place. For example Kay and Kay, (1993), Faccenda, Minelli, Gerya, (2009), Ueda et. al., (2012) and others propose various mechanisms of delamination, for example: eclogitization of the mafic layer of the lower crust, the effect of convection in the upper mantle, or gradual transition of the oceanic subduction into continental collision. Does the mantle part of the lithosphere sink into the mantle or spread laterally, as described in [for example, Deep Geodynamics, 2001; Bird, 1991; Schmeling and Marquart, 1991]?&lt;/p&gt;&lt;p&gt;To answer these questions, we study deep structures beneath the Caucasus and Kyrgyz Tien Shan collision zones. The studies were carried out on the basis of multiscale seismic tomography methods: regional and global. This approach made it possible to study heterogeneities both in the crust and in the upper mantle. The obtained 3D models of seismic heteroheneities reveal similar features for the both collision regions. Beneath the mountain areas, in the uppermost mantle and lower crust, we observe prominent low-velocity anomalies that possibly indicate thickening of the crust and missing (or strongly thinned) mantle part of the lithosphere. At the edges of the collision zones, we reveal inclined high-velocity anomalies appearing as continuations of the continental plates sinking underneath the collision zones, which can be interpreted as delaminating mantle parts of the continental lithosphere. &amp;#160;Based on joint consideration of the tomography models with the existing models of tectonic evolution, we conclude that the mechanisms of delamination in the considered two regions are different. In Caucasus, the delamination could be gradually transformed from oceanic subduction that ended here approximately ~10-15 Ma. In the case of Tien Shan, the detachment of the mantle lithosphere could be triggered by the plume that existed beneath Central Tien Shan or by the eclogitization of the mafic layer of the lower crust.&lt;/p&gt;

Rapid map and inversion of P-SV waves

Geophysics ◽  
1991 ◽  
Vol 56 (6) ◽  
pp. 859-862 ◽  
Author(s):  
Robert R. Stewart
Keyword(s):  
Spatial Resolution ◽  
Seismic Data ◽  
P Wave ◽  
Rock Properties ◽  
Low Velocity ◽  
P Waves ◽  
Near Surface ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
And Inversion

Multicomponent seismic recordings are currently being analyzed in an attempt to improve conventional P‐wave sections and to find and use rock properties associated with shear waves (e.g. Dohr, 1985; Danbom and Dominico, 1986). Mode‐converted (P-SV) waves hold a special interest for several reasons: They are generated by conventional P‐wave sources and have only a one‐way travel path as a shear wave through the typically low velocity and attenuative near surface. For a given frequency, they will have a shorter wavelength than the original P wave, and thus offer higher spatial resolution; this has been observed in several vertical seismic profiling (VSP) cases (e.g., Geis et al., 1990). However, for surface seismic data, converted waves are often found to be of lower frequency than P-P waves (e.g., Eaton et al., 1991).

scholarly journals A new model of the upper mantle structure beneath the western rim of the East European Craton

2014 ◽  
Vol 6 (1) ◽  
pp. 559-598
Author(s):  
M. Dec ◽  
M. Malinowski ◽  
E. Perchuc
Keyword(s):  
Upper Mantle ◽  
Seismic Velocity ◽  
Seismic Station ◽  
Structural Features ◽  
East European Craton ◽  
P Wave ◽  
Mantle Structure ◽  
Reflected Waves ◽  
East European ◽  
Upper Mantle Structure

Abstract. In this article we present a new 1-D P wave seismic velocity model (called MP1-SUW) of the upper mantle structure beneath the western rim of the East European Craton (EEC) based on the analysis of the earthquakes recorded at the Suwałki (SUW) seismic station located in NE Poland which belongs to the Polish Seismological Network (PLSN). This analysis was carried out due to the fact that in the wavefield recorded at this station we observed a group of reflected waves after expected P410P at epicentral distances 2300–2800 km from SUW station. Although the existing global models represent the first arrivals, they do not represent the full wavefield with all reflected waves because they do not take into account the structural features occurring regionally such as 300 km discontinuity. We perform P wave traveltime analysis using 1-D forward ray-tracing modelling for the distances up to 3000 km. We analysed 249 natural seismic events that were divided into four azimuthal spans with epicentres in the western Mediterranean Sea region (WMSR), the Greece and Turkey region (GTR), the Caucasus region (CR) and the part of the North Atlantic Ridge near the January Mayen Island (JMR). Events from each group were sorted into four seismic sections respectively. The MP1-SUW model documents bottom of the asthenospheric low velocity zone (LVZ) at the depth of 220 km, 335 km discontinuity and the zone with the reduction of P wave velocity atop 410 km discontinuity which is depressed to 440 km depth. The nature of a regionally occurring 300 km boundary here we explained by tracing the ancient subduction regime related to the closure of the Iapetus Ocean, the Rheic Ocean and the Tornquist Sea.

scholarly journals The April 29, 1965, Puget Sound earthquake and the crustal and upper mantle structure of western Washington

1977 ◽  
Vol 67 (3) ◽  
pp. 693-711 ◽  
Author(s):  
Charles A. Langston ◽  
David E. Blum
Keyword(s):  
Upper Mantle ◽  
Source Parameters ◽  
Puget Sound ◽  
P Wave ◽  
Low Velocity ◽  
Crust And Upper Mantle ◽  
Low Velocity Zone ◽  
Crustal Model ◽  
Short Period ◽  
Velocity Zone

abstract Simultaneous modeling of source parameters and local layered earth structure for the April 29, 1965, Puget Sound earthquake was done using both ray and layer matrix formulations for point dislocations imbedded in layered media. The source parameters obtained are: dip 70° to the east, strike 344°, rake −75°, 63 km depth, average moment of 1.4 ± 0.6 × 1026 dyne-cm, and a triangular time function with a rise time of 0.5 sec and falloff of 2.5 sec. An upper mantle and crustal model for southern Puget Sound was determined from inferred reflections from interfaces above the source. The main features of the model include a distinct 15-km-thick low-velocity zone with a 2.5-km/sec P-wave-velocity contrast lower boundary situated at approximately 56-km depth. Ray calculations which allow for sources in dipping structure indicate that the inferred high contrast value can trade off significantly with interface dip provided the structure dips eastward. The effective crustal model is less than 15 km thick with a substantial sediment section near the surface. A stacking technique using the instantaneous amplitude of the analytic signal is developed for interpreting short-period teleseismic observations. The inferred reflection from the base of the low-velocity zone is recovered from short-period P and S waves. An apparent attenuation is also observed for pP from comparisons between the short- and long-period data sets. This correlates with the local surface structure of Puget Sound and yields an effective Q of approximately 65 for the crust and upper mantle.

scholarly journals A new model of the upper mantle structure beneath the western rim of the East European Craton

Solid Earth ◽  
2014 ◽  
Vol 5 (1) ◽  
pp. 523-535
Author(s):  
M. Dec ◽  
M. Malinowski ◽  
E. Perchuc
Keyword(s):  
Upper Mantle ◽  
Seismic Velocity ◽  
Seismic Station ◽  
Velocity Model ◽  
East European Craton ◽  
P Wave ◽  
Mantle Structure ◽  
Reflected Waves ◽  
East European ◽  
Upper Mantle Structure

Abstract. We present a new 1-D P wave seismic velocity model (called MP1-SUW) of the upper mantle structure beneath the western rim of the East European Craton (EEC) based on the analysis of the earthquakes recorded at the Suwałki (SUW) seismic station located in NE Poland which belongs to the Polish Seismological Network (PLSN). Motivation for this study arises from the observation of a group of reflected waves after expected P410P at epicentral distances 2300–2800 km from the SUW station. Although the existing global models represent the first-arrival traveltimes, they do not represent the full wavefield with all reflected waves because they do not take into account the structural features occurring regionally such as 300 km discontinuity. We perform P wave traveltime analysis using 1-D and 2-D forward ray-tracing modelling for the distances of up to 3000 km. We analysed 249 natural seismic events from four azimuthal spans with epicentres in the western Mediterranean Sea region (WMSR), the Greece and Turkey region (GTR), the Caucasus region (CR) and the part of the northern Mid-Atlantic Ridge near the Jan Mayen Island (JMR). For all chosen regions, except the JMR group for which 2-D modelling was performed, we estimate a 1-D average velocity model which will characterize the main seismic discontinuities. It appears that a single 1-D model (MP1-SUW model) explains well the observed traveltimes for the analysed groups of events. Differences resulting from the different azimuth range of earthquakes are close to the assumed picking uncertainty. The MP1-SUW model documents the bottom of the asthenospheric low-velocity zone (LVZ) at the depth of 220 km, 335 km discontinuity and the zone with the reduction of P wave velocity atop 410 km discontinuity which is depressed to 440 km depth. The nature of the regionally occurring 300 km boundary is explained here by tracing the ancient subduction regime related to the closure of the Iapetus Ocean, the Rheic Ocean and the Tornquist Sea.

Upper mantle structure along a profile from Oslo (NORESS) to Helsinki to Leningrad, based on explosion seismology

1990 ◽  
Vol 80 (6B) ◽  
pp. 2194-2213
Author(s):  
Vladislav Ryaboy
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Profile Analysis ◽  
Time Estimation ◽  
Seismic Profile ◽  
P Wave ◽  
Apparent Velocity ◽  
Low Velocity ◽  
Time Curve ◽  
Volcanic System

Abstract Waveforms from the NORESS array were analyzed for 147 industrial explosions during the 1985 to 1988 period, along a profile running east from Oslo (NORESS) to Helsinki to Leningrad (OHL profile). The events were 250 to 1300 km from NORESS and had local magnitude in the range 2.0 to 3.5. Event locations and origin times constrained by the University of Helsinki's regional seismic network provide a reliable basis for travel-time estimation at NORESS. We also used data recorded by NORSAR in 1979 for three shots on the FENNOLORA north-south, long-range seismic profile, which were near the OHL profile. Analysis of mantle P-wave signals from the explosions showed that first arrivals could be traced continuously to a distance of 750 to 800 km, where there is a cutoff and shift of approximately 2.0 to 2.5 sec in the travel-time curve and an increase in average apparent velocity. Interpretation of the observed travel times and waveforms for this profile suggests a low-velocity zone from approximately 105 to 135 km depth. Combined analysis of the seismic data with a Bouguer gravity map indicates the presence in the upper mantle of a high-velocity, high-density body of linear extent approximately from 200 to 300 to 500 to 600 km east of the NORESS array. It is postulated that this body may represent the root of an ancient volcanic system, in which lighter, silicic constituents were depleted from the upper mantle during the eruptive phase.

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