scholarly journals Lateral variation of upper mantle structure beneath New Caledonia determined from P-wave receiver function: evidence for a fossil subduction zone

1988 ◽  
Vol 95 (3) ◽  
pp. 561-577 ◽  
Author(s):  
M. Regnier
Keyword(s):  
Subduction Zone ◽  
Upper Mantle ◽  
New Caledonia ◽  
Receiver Function ◽  
P Wave ◽  
Mantle Structure ◽  
Lateral Variation ◽  
Upper Mantle Structure

P-wave travel times from shallow earthquakes recorded in India and inferred upper mantle structure

1968 ◽  
Vol 58 (6) ◽  
pp. 1879-1897
Author(s):  
K. L. Kaila ◽  
P. R. Reddy ◽  
Hari Narain
Keyword(s):  
Upper Mantle ◽  
P Wave ◽  
Mantle Structure ◽  
Travel Times ◽  
The North ◽  
Shallow Earthquakes ◽  
Upper Mantle Structure ◽  
Wave Travel ◽  
Excess Value ◽  
Velocity Changes

ABSTRACT P-wave travel times of 39 shallow earthquakes and three nuclear explosions with epicenters in the North in Himalayas, Tibet, China and USSR as recorded in Indian observatories have been analyzed statistically by the method of weighting observations. The travel times from Δ = 2° to 50° can be represented by four straight line segments indicating abrupt velocity changes around 19°, 22° and 33° respectively. The P-wave velocity at the top of the mantle has been found to be 8.31 ± 0.02 km/sec. Inferred upper mantle structure reveals three velocity discontinuities in the upper mantle at depths (below the crust) of 380 ± 20, 580 ± 50 and 1000 ± 120 km with velocities below the discontinuities as 9.47 ± 0.06, 10.15 ± 0.07 and 11.40 ± 0.08 km/sec respectively. The J-B residuals up to Δ = 19° are mostly negative varying from 1 to 10 seconds with a dependence on Δ values indicating a different upper mantle velocity in the Himalayan region as compared to that used by Jeffreys-Bullen in their tables (1940). Between 19° to 33° there is a reasonably good agreement between the J-B curve and the observation points. From Δ = 33° to 50° the J-B residuals are mostly positive with an average excess value of about 4 sec.

P-wave amplitudes and magnitudes between 10° and 35°

1974 ◽  
Vol 64 (6) ◽  
pp. 1887-1899
Author(s):  
George A. McMechan ◽  
Warren G. Workman
Keyword(s):  
Upper Mantle ◽  
Epicentral Distance ◽  
Maximum Amplitude ◽  
Body Waves ◽  
P Wave ◽  
Ray Theory ◽  
Mantle Structure ◽  
Upper Mantle Structure ◽  
Wave Trains ◽  
Theory Technique

abstract The observed behavior of P-wave relative amplitudes, as a function of epicentral distance, between 10° and 35°, is controlled primarily by the velocity-depth structure of the upper mantle. P-wave synthetic seismograms calculated by the new quantized ray theory technique are used to determine theoretical log (A/T) versus log Δ curves from a number of upper mantle models. Maximum amplitude arrivals show less model dependence than the first arrivals in the same wave trains, and hence are more consistent magnitude indicators for regions where the upper mantle structure is poorly known. Log (A/T) versus log Δ curves vary considerably, but predictably, from model to model. This model-dependent variation can account for a major part of the large standard deviations usually associated with the calculation of magnitudes from body waves.

Upper mantle structure of the northern Cascadia subduction zone

1995 ◽  
Vol 32 (1) ◽  
pp. 1-12 ◽  
Author(s):  
M. G. Bostock ◽  
J. C. Vandecar
Keyword(s):  
British Columbia ◽  
Subduction Zone ◽  
Upper Mantle ◽  
Puget Sound ◽  
Cascadia Subduction Zone ◽  
Mantle Structure ◽  
Data Set ◽  
Juan De Fuca Plate ◽  
Upper Mantle Structure ◽  
Juan De Fuca

Previous knowledge of the structure of the Cascadia subduction zone north of the Canada–United States border has been derived from a variety of geophysical studies that accurately delineated the downgoing Juan de Fuca plate from the offshore deformation front to depths of ~50–60 km beneath south-central Vancouver Island and the Georgia Strait. Little is known, however, of the structure of the Cascadia subduction zone farther westward and to greater depths in the upper mantle. We have assembled a set of some 1100 teleseismic traveltimes from events recorded on the Western Canadian Telemetered Network to augment a previously existing data set recorded on the Washington Regional Seismograph Network. The composite data set is inverted for upper mantle structure below Washington, Oregon, and southwestern British Columbia. We analyze the new northern portion of the model between 48.5–50°N and 118–127°W, which provides the first images of the deep slab structure in this region. The model is parameterized using splines under tension over a dense grid of knots. The nonlinearity of the inverse problem is treated by iteratively performing three-dimensional ray tracing and linear inversion. Resolution tests performed with a synthetic slab model indicate that the deep structure is resolved by the data north to at least 50°N. The inversions are characterized by a quasi-planar, high-velocity body inferred to represent the thermal and compositional anomaly of the subducted Juan de Fuca plate. This body exhibits velocity deviations of up to 3% from the background reference model and extends to depths of at least 400–500 km. The depth contours of the slab in the upper mantle mimic those of the shallow slab by changing strike, in the latitude range 48.0–48.5°N, from north–south in Washington to northwest–southeast in southern British Columbia. This forces the development of two arch-type structures: a main arch observed in previous studies trending east–west over Puget Sound and a possible second arch extending northeasterly from the Georgia Strait into the British Columbia interior. A steepening of the deep slab dip from British Columbia south towards Puget Sound and complexity in the evolution of the arches in depth may be the result of a change in plate motions at 3.5 Ma associated with the detachment of the Explorer plate.

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 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.

scholarly journals Upper mantle structure around the Trans-European Suture Zone obtained by teleseismic tomography

2014 ◽  
Vol 6 (2) ◽  
pp. 1723-1763 ◽  
Author(s):  
I. Janutyte ◽  
M. Majdanski ◽  
P. H. Voss ◽  
E. Kozlovskaya ◽  
PASSEQ Working Group
Keyword(s):  
Upper Mantle ◽  
Western Europe ◽  
Velocity Model ◽  
Suture Zone ◽  
P Wave ◽  
Mantle Structure ◽  
The West ◽  
Lower Velocity ◽  
Teleseismic Tomography ◽  
Upper Mantle Structure

Abstract. The presented study aims to resolve the upper mantle structure around the Trans-European Suture Zone (TESZ) which is the major tectonic boundary in Europe. The data of 183 temporary and permanent seismic stations operated during the period of the PASsive Seismic Experiment PASSEQ 2006–2008 within the study area from Germany to Lithuania was used to compile the dataset of manually picked 6008 top quality arrivals of P waves from teleseismic earthquakes. We used the non-linear teleseismic tomography algorithm TELINV to perform the inversions. As a result, we obtain a model of P wave velocity variations up to about ±3% compared to the IASP91 velocity model in the upper mantle around the TESZ. The higher velocities to the east of the TESZ correspond to the older East European Craton (EEC), while the lower velocities to the west of the TESZ correspond to younger Western Europe. We find that the seismic lithosphere-asthenosphere boundary (LAB) is more distinct beneath the Phanerozoic part of Europe than beneath the Precambrian part. To the west of the TESZ beneath the eastern part of the Bohemian Massif, the Sudetes Mountains and the Eger Rift the negative anomalies are observed from the depth of at least 70 km, while under the Variscides the average depth of the seismic LAB is about 100 km. We do not observe the seismic LAB beneath the EEC, but beneath Lithuania we find the thickest lithosphere of about 300 km or more. Beneath the TESZ the asthenosphere is at a depth of 150–180 km, which is an intermediate value between that of the EEC and Western Europe. The results imply that the seismic LAB in the northern part of the TESZ is of a shape of a ramp dipping to the NE direction. In the southern part of the TESZ the LAB is shallower, most probably due to younger tectonic settings. In the northern part of the TESZ we do not recognize any clear contact between Phanerozoic and Proterozoic Europe, but further to the south we may refer to a sharp and steep contact on the eastern edge of the TESZ. Moreover, beneath Lithuania at the depth of 120–150 km we observe the lower velocity area following the boundary of the proposed palaeosubduction zone.

Upper Mantle Structure in Southern Saskatchewan and Western Manitoba from Project Edzoe

1975 ◽  
Vol 12 (12) ◽  
pp. 2134-2144 ◽  
Author(s):  
Allan Bates ◽  
D. H. Hall
Keyword(s):  
Upper Mantle ◽  
Linear Increase ◽  
P Wave ◽  
Mantle Structure ◽  
Low Velocity ◽  
Wave Velocities ◽  
P Wave Velocity ◽  
Upper Mantle Structure ◽  
Chemical Explosions ◽  
Velocity Zone

A line of eight recording sites in southern Saskatchewan and Manitoba, with ranges from 793 to 1284 km, recorded a series of chemical explosions in Greenbush Lake, British Columbia, as part of Project Edzoe in 1969.It is found that travel-times fall into two branches. The first branch is interpreted as representing the effect of a linear increase of P wave velocity, increasing from 8.10 km/s at the top of the mantle, with a gradient of 0.0017 s−1. The second branch indicates a rapid increase of gradient occurring somewhere between depths of 120 km and 150 km. Amplitude studies suggest, in the absence of complete triplication, a zone of low velocity gradient beneath the rapid increase. The presence or absence of a low velocity zone was not indicated in the data.Previous long-range refraction surveys indicate that a similar gradient in velocity also occurs beneath the Superior province of the Canadian shield, and that P-wave velocities are lowest at its center, reaching higher values at its edges.

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