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Receiver Functions (receiver + function)

Distribution by Scientific Domains

Earth and Environmental Science	100%

Selected Abstracts

The Significance of Crust Structure and Continental Dynamics Inferred from Receiver Functions in West Yunnan

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2009
HE Chuansong
Abstract: In our study we collected the teleseismic record of 31 broadband stations and 9 PASSCAL stations in West Yunnan, as well as extracted more than a million receiver functions. Using the waveform model and stacking techniques, we calculated the earth crust thicknesses and Vp/Vs ratios below the stations and obtained 35 valid data points. At the same time, we evenly stacked the receiver functions at the same station and superimposed the two profiles' cross sections of the main tectonic units. The results show a clear difference between the crust thicknesses of different tectonic units. Because of the magma underplatting and delimanition of the lower crust in the role of deep process, the West Yunnan's crust can be divided two kinds,mafic-ultramafic and feldspathic crusts. The research also shows that the mafic-ultramafic crust corresponds to a good background of mineralization. The delamination of the lower crust is one of the leading causes for moderate to strong earthquake prone in central Yunnan. The thinner crust and high velocity ratio as well as the multimodal structure of Ps in the Tengchong volcanic area confirms existence of a deep process of the strong magma underplating. Due to the basic crust structure and nature, it is believed that the Honghe fault is a main suture of the Gondwana and Eurasia continents. [source]

Crustal structure of central and northern Iceland from analysis of teleseismic receiver functions

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2000
Fiona A. Darbyshire
We present results from a teleseismic receiver function study of central and northern Iceland, carried out during the period 1995,1998. Data from eight broad-band seismometers installed in the SIL network operated by the Icelandic Meteorological Office were used for analysis. Receiver functions for each station were generated from events for a wide range of backazimuths and a combination of inversion and forward modelling was used to infer the crustal structure below each station. The models generated show a considerable variation in the nature and thickness of the crust across Iceland. The thinnest crust (20,21 km) is found in the northern half of the Northern Volcanic Zone approximately 120 km north of the centre of the Iceland mantle plume. Thicker crust (24,30 km) is found elsewhere in northern and central Iceland and the thickest crust (37 km) is found close to the plume centre. Velocity,depth profiles show a distinct division of the crust into two main sections, an upper high-velocity-gradient section of thickness 2,8 km and a lower crustal section with small or zero overall velocity gradient. The thickness of the upper crust correlates with the tectonic structure of Iceland; the upper crust is thickest on the flanks of the northern and central volcanic rift zones and thinnest close to active or extinct central volcanoes. Below the Krafla central volcano in northeastern Iceland the receiver function models show a prominent low-velocity zone at 10,15 km depth with minimum shear wave velocities of 2.0,2.5 km s,1. We suggest that this feature results from the presence of partially molten sills in the lower crust. Less prominent low-velocity zones found in other regions of Iceland may arise from locally high temperatures in the crust or from acidic intrusive bodies at depth. A combination of the receiver function results and seismic refraction results constrains the crustal thickness across a large part of Iceland. Melting by passive decompression of the hot mantle below the rift zone in northern Iceland forms a crust of thickness ,20 km. In contrast, the larger crustal thickness below central Iceland probably arises from enhanced melt production due to active upwelling in the plume core. [source]

Array-conditioned deconvolution of multiple-component teleseismic recordings

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010
C.-W. Chen
SUMMARY We investigate the applicability of an array-conditioned deconvolution technique, developed for analysing borehole seismic exploration data, to teleseismic receiver functions and data pre-processing steps for scattered wavefield imaging. This multichannel deconvolution technique constructs an approximate inverse filter to the estimated source signature by solving an overdetermined set of deconvolution equations, using an array of receivers detecting a common source. We find that this technique improves the efficiency and automation of receiver function calculation and data pre-processing workflow. We apply this technique to synthetic experiments and to teleseismic data recorded in a dense array in northern Canada. Our results show that this optimal deconvolution automatically determines and subsequently attenuates the noise from data, enhancing P -to- S converted phases in seismograms with various noise levels. In this context, the array-conditioned deconvolution presents a new, effective and automatic means for processing large amounts of array data, as it does not require any ad-hoc regularization; the regularization is achieved naturally by using the noise present in the array itself. [source]

Improved imaging with phase-weighted common conversion point stacks of receiver functions

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010
A. Frassetto
SUMMARY Broad-band array studies frequently stack receiver functions to improve their signal-to-noise ratio while mapping structures in the crust and upper mantle. Noise may produce spurious secondary arrivals that obscure or mimic arrivals produced by P -to- S conversions at large contrasts in seismic impedance such as the Moho. We use a Hilbert transform to calculate phase-weights, which minimize the constructive stacking of erroneous signal in receiver function data sets. We outline this approach and demonstrate its application through synthetic data combined with different types of noise, a previously published example of signal-generated noise, and a large data set from the Sierra Nevada EarthScope Project. These examples show that phase-weighting reduces the presence of signal-generated noise in receiver functions and improves stacked data sets. [source]

Absolute S -velocity estimation from receiver functions

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007
L. Svenningsen
SUMMARY We present a novel method to recover absolute S velocities from receiver functions. For a homogeneous half-space the S velocity can be calculated from the horizontal slowness and the angle of surface particle motion for an incident P wave. Generally, the calculated S velocity is an apparent half-space value which depends on model inhomogeneity and P -waveform. We therefore, suggest to calculate such apparent half-space S velocities from low-pass filtered (smoothed) receiver functions using a suite of filter-parameters, T. The use of receiver functions neutralize the influence of the P -waveform, and the successive low-pass filterings emphasize the variation of S velocity with depth. We apply this VS,app.(T) technique to teleseismic data from three stations: FUR, BFO and SUM, situated on thick sediments, bedrock and the Greenland ice cap, respectively. The observed VS,app.(T) curves indicate the absolute S velocities from the near surface to the uppermost mantle beneath each station, clearly revealing the different geological environments. Application of linearized, iterative inversion quantify these observations into VS(z) models, practically independent of the S -velocity starting model. The obtained models show high consistency with independent geoscientific results. These cases provide also a general validation of the VS,app.(T) method. We propose the computation of VS,app.(T) curves for individual three-component broad-band stations, both for direct indication of the S velocities and for inverse modelling. [source]

Thickness of the lithosphere east of the Dead Sea Transform

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2006
Ayman Mohsen
SUMMARY We use the S receiver function method to study the lithosphere at the Dead Sea Transform (DST). A temporary network of 22 seismic broad-band stations was operated on both sides of the DST from 2000 to 2001 as part of the DESERT project. We also used data from six additional permanent broad-band seismic stations at the DST and in the surrounding area, that is, in Turkey, Saudi Arabia, Egypt and Cyprus. Clear S -to- P converted phases from the crust,mantle boundary (Moho) and a deeper discontinuity, which we interpret as lithosphere,asthenosphere boundary (LAB) have been observed. The Moho depth (30,38 km) obtained from S receiver functions agrees well with the results from P receiver functions and other geophysical data. We observe thinning of the lithosphere on the eastern side of the DST from 80 km in the north of the Dead Sea to about 65 km at the Gulf of Aqaba. On the western side of the DST, the few data indicate a thin LAB of about 65 km. For comparison, we found a 90-km-thick lithosphere in eastern Turkey and a 160-km-thick lithosphere under the Arabian shield, respectively. These observations support previous suggestions, based on xenolith data, heat flow observations, regional uplift history and geodynamic modelling, that the lithosphere around DST has been significantly thinned in the Late Cenozoic, likely following rifting and spreading of the Red Sea. [source]

Crustal structure deduced from receiver functions via single-scattering migration

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2002
E. Bertrand
Summary An investigation of the teleseismic P -wave coda is performed using the single-scattering approximation. The method allows one to image short-wavelength scale (,2 km) velocity and density heterogeneities and structures that are barely detected by traveltime tomography. Source effects are removed by using receiver functions for data interpretation, but the amplitude (especially the sign of the signal) is synthesized. Both broad-band seismological stations in the southwestern Alps (France) and Campanian plain (Italy) are used for the illustration of the proposed method. Because of the large aperture of our arrays, laterally small-scale heterogeneities are difficult to image and we must assume lateral continuity of the detectable structure. If so, we show that this depth migration based on a single-scattering approach can recover both the depth and the geometry of the main discontinuities below the studied areas. In the southwestern Alps, we underline a complex crustal structure and Moho dipping topography. The Moho depth increases from 20 to 30 km between the coastline and the Mercantour range. In the Campanian plain (surrounding Mount Vesuvius) we also find a southeastwards-dipping Moho. Furthermore, the three main discontinuities are imaged, showing a relatively shallow mantle,crust discontinuity and a deeper one near the coastline. [source]

Crustal structure of central and northern Iceland from analysis of teleseismic receiver functions

Upper mantle stratification by P and S receiver functions

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000
Véronique Farra
Summary Seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the Graefenberg array in southern Germany. The anisotropic P receiver function technique (Kosarev et al. 1984; Vinnik & Montagner 1996) is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the SV and T components of the Pds phases. The summary events provide better separation of the second azimuthal harmonic than the individual events. The parameters of the second harmonics of SV and T thus evaluated should be similar if they reflect the effects of azimuthal anisotropy. This can be used as a criterion to identify the anisotropy. To detect the Sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique, which can be termed the S receiver function technique It includes axis rotation to separate interfering P and S arrivals, determination of the principal (M) component of the S -wave motion, deconvolution of the P components of many recordings by their respective M components and stacking of the deconvolved P components with weights depending on the level of noise and the angle between the M direction and the backazimuth of the event. Both techniques yield consistent results for the Graefenberg array. As indicated by the P receiver functions, the upper layer of the mantle between the Moho and 80 km depth is anisotropic with dVs/Vs around 0.03 and the fast direction close to 20° clockwise from north. The fast direction of anisotropy below this layer is around 110°, The boundary between the upper and the lower anisotropic layers is manifested by the detectable Pds and Sdp converted phases. Shear wave splitting in SKS is strongly dominated by azimuthal anisotropy in the lower layer (asthenosphere). [source]